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Little Dot MK8SE / MK6 Super Mods (All verified mods are on first page)

post #1 of 2321
Thread Starter 

If you're a beginner in electronics or, better yet, don't know sh*t about it, stay at the first page where all verified mods are explained in a newbie friendly fashion.

If you read the thread backwards things can get very confusing.

 

 

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PREAMBLE - SAFETY PRECAUTIONS

 

Before opening your amp and start modding it, you are supposed to be aware of all the safety rules that go with this activity. Voltages and currents may be harmful, and even life-threatening...even when switched off, even when unplugged.

 

- Always unplug your amp before opening it.

- Wait for some minutes after switching-off before moving the amp and opening it (discharge of the remaining energy in the "discharge resistors") 

- Always check the voltage of your power rails.

 

 

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We've been talking about this mods thread since too long, so here it is.

 

Maxx134 and I will be feeding it in the next few weeks, filling the "reserved" posts and editing them as we progress in our writing. 

 

Some pictures for appetizers, we will do better ones if needed. They were taken from my amp, but we will had Maxx/Coin/others as their layouts/components may differ from mine.

 

 

 

Introduction / Context

 

Little Dot has done a fine job with those amps and we fully understand that the "price tag" leads to some compromises ...

 

Since I was little, I always dreamed that one day I would mod an MK8 ... bla bla bla

 

 

What we want to do in this thread

 

It was (and still is) an adventure and we wanted to share what we have found and done.

We don't claim we have found any "final truth" or our mods are the best. But everything has been tested and is operational in our amps.

 

 

What we DO NOT want to do in this thread

 

We will not feed the trolls, obviously.

We will not answer to rude/impolite comments. 

 

 

Table of Contents:


1 - Coupling Caps
2 - Decoupling Caps

3 - Around the Power Cathode

     3.1 - Cathode Bypass Caps

     3.2 - 5998 / WE421A Bias switch mod for the MK6 (by SonicTrance)

4 - PSU "Last stage" Caps
5 - Resistances
     5.1 - Power resistors
     5.2 - Grid resistors
6 - Internal Cabling/Fuses/Pwr Cord/Heat/Rectfier Diode
7 - Tubes

8 - Background stuff / Documentation

9 - Around the Amps (Headphones, DACs, Power Supply, cables, ... )

10 - The next mods

     10.1 The "WCF" Coupling cap (Tested/Verified on Maxx/Redge)

 

 

Overview of the "cap mods" done in the Power Stage (ie "The Quadfecta")

 


Edited by Redge78 - 5/19/16 at 11:41am
post #2 of 2321
Thread Starter 

1 - Coupling Caps

 

The Coupling caps (or Interstage caps) mod is one of the most important mod we will present.

The Coupling cap is in the main signal path, between the Driver stage and the Power Stage. Its main role is to remove any DC voltage from the signal. 

 

Basically, the impact of this cap on the sound will always be negative. All this mod is about, is to make it the least negative as possible. This cap will have the greatest impact on the sonic signature of the amp.

Ideally, the best coupling cap would be NO coupling cap (a straight wire),
Second best would be a interstage transformer. But we would need four of them, and good quality ones are even more expensive than the caps. (And the circuit needs to be finely tuned ... too complex/risky in a mod perspective.)


Values :

 

Capacity :

(MK8se) we have increased two steps (0,22µF > 0,33µF > 0,47µF) the capacity of the replacement caps, in order to lower the cut frequency of the "high pass" filter.
As there is many "high pass" filters in the amp, the addition of them may have an impact on the lowest usable frequencies.

The "original" capacity should be fine nevertheless, but we are going for improvements.

(MK6) From "original" value up to 1µF (CoinM will confirm)

Voltage :

The lowest limit should always be the Voltage of the cap you're replacing, unless you really understand what you are doing.

The SCR cap is interesting because the rated Voltage ("630V") is way higher than what's the PSU is providing (around 200V for the MK8). A "derating" (ratio between "Cap Rated" and "Max Real" voltages) of 3x has been applied when choosing these caps and actually this derating of "3x" on caps is good practice.

Can we go higher than "630Vdc" ? Yes indeed. The "Mundorf S/G/O" that are part of an official LD upgrade are 1000Vdc.

Can we go lower than "630Vdc" ? Yes. I have been using "500V" coupling caps on my amp for months. But the more you will want to lower the rated voltage, the more you'll have to be sure of what is the "Max Real" DC voltage.

Temperature :

Temp is THE cap-killer. If you have to choose between two caps of same quality, always choose the one with the highest Max Temp. I wouldn't buy a cap with a Max Operating Temp of 70° ... 80/85° seems the reasonnable minimum.

 

 

The "Original" part :

A small black "SCR PB" cap. Funnily, it was a 0,22µF/630V in the early MK8se (Redge's), and was upped to 0,33µF/630V latter on (Maxx's)

Those "SCR PA/PB" caps are really the very bottom of the entry-level of the MKP caps, but they will do a better job than any Lytics cap anyway. They are cheap, easily available and used in a very large number of amps (including some pretty expensive ones). Virtually any other MKP/PIO/Teflon cap will do better than those SCR PB, inclusing some beauties up in the SCR line.

 

 

The "boutique" caps (High quality / high price)

 

Jupiter "Copper Foil in Wax" : Clear upgrade from the Mundorf S/G/O - Wonderfull overall organic sound & holography - Quite expensive
Duelund Cast Cu : Best only if you can afford them

Mundorf Silver/Gold/Oil : Little Dot is offering them as an official upgrade - Best value for overall performance, with a brighter sweet tonality

Other options exist : V-cap, Audio-Note, Jensen that can offer a very high quality with different flavors.

 

 

The "russian" caps (Good quality / very low price)

 

K75-10 : (Hybrid tech) They are big, green things. Wonderful mid-range, quite enough bass, slightly recessed treble. A good companion of the HD800. Cost virtually nothing

K73-16 : (polyethylene-terephthalate PEPT) Dynamic, lots of details, less bass than the K75-10 but more treble. A good companion of the HD650. Cost virtually nothing too.

The "Teflon" family : can be used as "bypass" of the caps above or as main caps. FT-1/2/3, K72N-6 depending on the value you want. As bypasses, they are said to help the treble/detail area. Bypass value between 1/10 and 1/100 of the main cap, depending on the effects you want.

We were going to test those, but as we have now Jupiters and Duelung in our amps, there is not much point trying to bypass those beauties with "Teflon caps".

K40Y-9 : ("Paper In Oil" (PIO)) Not tested but highly regarded as main caps

The "Silver/Mica" family : Can be used as Bypass too. Or bypass of bypass ...

 

 

 

Some Pics

 

Before (SCR PB 0,22µF/630V) :

 

 

 

After (the replacement pack - tested or to be tested)) :

 


Edited by Redge78 - 10/2/15 at 9:09am
post #3 of 2321
Thread Starter 

2 - Decoupling Caps

 

 

This addition to the original design is used for creating a reservoir of "fast delivery" power for the tubes to use, the supply of the power will be more independant of the PSU, hence the name "DE-coupling"...

 

 

 

The PSU has "large output caps" and is working on "constant load" mode. This is one design that is very musical and  effective. It brings/improves silences, air, dynamic, clarity ...

 

To improve this PSU, we have decided to add to the original design a "decoupling" cap near each power tube. The current feeding the headphones will be provided by the PSU and/or the decoupling cap, depending on the respective impedence at this time.

 

The impedence will be both resistive (ESR) and inductive (ESL) and will depend on the technology of the cap, its value and the frequency of the signal. And the higher the impedance, the more difficulty the PSU will have to provide the current, resulting in ... well ... less air, less dynamic, less clarity ...

 

Electrolytics caps can have huge values in a compact package, the average ones have high (bad) ESR and ESL. Their impedance rise significantly from the 10Khz onwards, even for the rather small value ones used in Tube amps. 

Of course, there are better Lytics ... FRS type (Philips BC 56-57 series), TFRS type (Philips BC 154-155 series) or low impedance ones (Philips BC 135-136 series) but they are hard to find and mostly offered in packs of 1000, which makes the few we need a bit costly.

 

Good film caps (MKP or PIO) on the contrary have virtually no ESR ( +/- 1milliOhm) and can have a significantly lower impedance on a large frequency band (few thousands Hz and above). Therefore, they will provide most of the "fast" energy/current in this FB. And this will improve significantly the sound.

 

Good Decoupling caps :

- (stellar) Foiled/Metalized polypropylene (FKP/MKP) for pulse circuit or with huge current capacity ( +/- 100 Irms). See what Coinmaster has stuffed his extrabox with ...

- All other FKP/MKP caps

- The "Paper In Oil" (PIO) will do well 

The value/capacity will be the prime factor here, no need to go "boutique" here, WIMA DC-LINK, Mundorf EVO or SCR/Solen will do fine.

For those "on a budget", the motor-run MKP caps used in DC electrical motor are cheap and can be found in high values. And they are very good (and very large) 

 

Where to put those Decoupling caps ?

Each centimeter/inch of wire will bring an extra impedance that will have an impact on the speed of the current needed.

So those caps need to be put as close to their associated tube as possible.

Ideally, they will be soldered directly on the leads of the Anode resistor (+200V side)  and the Cathode resistor (Ground side). 

Don't underestimate the difficulties that this constraint will bring, having to stick large caps in a small space is not that easy. The extra-box option will seem more appealing then. If you really don't want the extraBox, talk to Maxx, he's been through this and survived ... mostly.

 

From the top :

 

 

A closer view, look for the red vertical wires soldered to the blue ("original" cathode) cap and to the black ("original" anode) resistors.

The resistors may not be black in yours tho. 

 

 

 

Values :

 

Capacity :

It's not worth putting anything lower than 10µF, the impedence at high freq. will be too high.

The higher the value, the better. Between 47µF and 100µF should be fine.

From what I remember from Maxx experience, 47µF is the largest he was able to put in an amp without extra-box. 

Voltage (*) :

Basically, we have the same requirements than for the Coupling caps.

Min : 250Vdc 

Good : 600Vdc

Stellar : The sky's the limit

Temperature :

Same as above. MKP caps should be given for Max T° : 85°, it may be less for PIOs. So you have to be careful and adapt the choices you make with the Max Temp° in your amp. 

 

(*) we have been said that choosing a cap with a higher "rated voltage" could be beneficial to the "max. pulse rise time" (V/msec), giving faster current to the system. WIMA is documenting this in its datasheets, but only for pulses equal to the rated voltage. 

As there is no negative impact in increasing this "Rated Voltage", we tend to always choose the highest ones, if size, price, avaibility ... are similar.   

 

 

 

Before (none, this is an addition to the design) :

 

 

After :

 

A quad of "Clarity Caps SA 33µF/630V" ... and a secret ingredient

 

 

 

Or the compact version (white Mundorf Mcap 47µF) :

 

LL

 

Or some industrial "over the top / because I'm worth it" AVX FFVI 100µF/1100V monsters ! The 4 in a row.

More to come in the "how to connect those beauties" chapter...

 

LL

 

Or the very inspiring Decoupling caps of a Belgium MK2 ... a pair of white Mundorf Evo 82µF

 

 

 

 

About soldering points for the Driver Stage decoupling caps :

 

You can take the board out : the easiest is to remove the small round cap and the red rectangular WIMA near it (both are connected together in parallel) and put/solder the decoupling one there

 

The 'round cap', one at each side of the amp.

 

 

Same location, from the other side of the board :

 

LL

 

 

 

You can't take the board out : it's more tricky, you'll have to solder at the Driver's Anode/Cathode ends (you leave the round caps alone). This is what I did, I'll put some pics in the 1st page post.

 

Anode : From Maxx's pic, it's the (+) at the top, from the other side of the board, it's the leads of the 215K/220K 2W resistors (the side the 2 leads have "0" Ohm resistance). Easy to find, easy to solder. The "decoupling" wire is the yellow twisted one, obviously !

 

 

 

Cathode : the tricky part ! From the group of 3 resistors you have both ways near the pot, the CathoDe are the caps nearer the pot (the 2 other ones are Grid resistors for each triode of one tube).

In the pic below, they are the soldering points (on the left) just above the "Dot" writing and (on the right) just above the " sword_yang" 

 


Edited by Redge78 - 10/18/15 at 4:54am
post #4 of 2321
Thread Starter 

3.1 - Cathode Bypass Caps

 

 

We are here in the Power stage. Each 6H30 tube is made of 2 triodes, those 2 triodes are used together in a "White Cathode Follower" (WCF) design.

So, one cathode for a 6H30 tube, composed of a resistor setiing the polarisation voltage and a bypass cap.

 

This bypass cap is important as a significant part(*) of the modulated (AC) current that will feed the headphones will go through the cathode (and the "Regulating Triode"). This AC Current will preferably go through the caps (rather than through the resistor).

(*) half the current around the "Push-Pull" functionning point.

 

In a WCF, the "cathode bypass cap" also plays a role in increasing the gain and lowering the output impedance, all of which are pretty good for us.

 

The difficulty here is to find a upgrade of at least the same "rather high" value than the "original" cap (220µF).

This 220µF value starts to be a significant value if you want to switch technology to some MKP or PIO caps. It's even worse if when you want to push the values two steps up (470µF). Those huge MKP/PIO caps would weight pounds (or even kilogrammes) each. It's feasable, it would be expensive, hard to manage ... but it could be better than even the best Lytics.

 

 

"Main" Lytics caps : 

The reasonnable alternative is to find the best Lytic caps possible.

There are several Lytic caps that have been developped with audio in mind and we'll stick with those, we can't try every single brand/product ...

BlackGate, Elna Silmic, Nichicon Muse, Mundorf, Panasonic FC ... 

- BlackGate : probably the best, but they are out of production and hard to find (and bloody expensive). Also, burning-time is in hundreds of hours before they stabilise.

- Elna Silmic 2 : our second best, cheap and available everywhere. Probably as good as the BlackGate above when properly bypassed. 

- Mundorf : our other second best, if you want to spend more

CAREFUL : The Lytics are polarized caps, they have a (+) and a (-) and you need to solder them the correct way.

 

 

Bypass : in order to help the Lytic cap in the areas it is weakest (treble, microdynamics, ...), we add in parallel an another cap of a different techno, smaller and faster.

After having tested various caps (Teflon, Polypro, PIO, Styroflex, ...) the best "musical" match was with some (multilayer metallized paper) PME271 used as "electromagnetic interference suppressor". 

 

 

Values :

 

Capacity : 

From 220µF up to 470µF (that would set the cut-off frequency from 5Hz to 2,5Hz). Around 0,1µF for the PME271 bypass.

Voltage : 

Not much voltage here, the "original" 50V is more than enough. The PME271 is given for 275V

Temp : 

Same as always, higher is better. But we should not have much problem here : the Elna are given for 85°, the PME271 for 110°

 

 

Before ("Blue" Philips BC 220µF/50V) 

 

 

 

 

 

 

After (Elna Silmic 2 470µF/50v // RIFA PME 0,1µF/250V)

 

 

And installed (with the huge green K75-10 Coupling Caps behind) :

 

 

 

 

 

3.2 - 5998 / WE421A Bias switch mod for the MK6 (by SonicTrance)

 

This mod is only for MK6 users and is a mod that optimizes the MK6 to use the 5998's and WE421A's power tubes. Sure, you can use those tubes without doing this mod and it'll sound good. But when your done and the mod is complete you wont regret doing it. That's a promise! 

 

The sonic gain is incredible. Especially the low end gets improved with much more weight and slam. Also overall dynamics and clarity improves. I rate this mod as one of the big ones for the MK6, if you’re using these tubes that is. 

 

You may have noticed, if you’re using 5998’s or 421A’s as power tubes in your MK6, that the amp runs much cooler and bias meters only reads about 30mA, while the 6080/6AS7G’s gives you 60mA on the meters and amp runs hot? That’s because the 5998/421A’s bias differently and doesn't get enough current in a 6080/6AS7G circuit.

 

 

What are we doing here?

 

The goal with this mod is to cut the stock cathode resistor value in half, which in turn will double the amount of current to the tubes. The MK6 has 330 ohm cathode resistors, so 165 ohms is what we're looking for here.

 

To do this you could either just swap the stock cathode resistors for some 165 ohm ones. But then you can’t use any 6080/6AS7G’s. So we implement a bias switch. That way we can use all our favorite power tubes.

 

Basically what we do is get a 4 pole switch (one pole/tube) and 4 additional 330 ohm cathode resistors. Then connect the new resistors in parallel to existing resistors through the switch.

As the stock cathode resistors are on top side of the board it’s easier to connect the new ones on component side in parallel to the cathode bypass caps. When the switch is on the cathode resistor value will be 165 ohms which is the new 5998/421A setting. And when switch is off the cathode resistor value will be stock 330 ohms for the 6080/6AS7G’s.

 

These are the cathode bypass caps

 

 

Here's pics of the finished mod

 

 

 

 

 

 

How do we do this?

You can see from above pics that I've soldered the resistors on one end of the cathode bypass caps, and a wire from the other end. Then run the wires to the switch which makes them parallel to the stock cathode resistors. It is that simple. 

 

I chose to have my bias switch through the bottom cover as the case is 10mm thick and it was hard to find a switch that would fit. Plus it was handy to be able to take the bottom cover off and drill the hole for the switch and not worry about getting metal residues inside the amp.

 

 

What parts do we need?

 

- 4 x 330 ohm resistors, Mills MRA5

 

- A 4 pole switch, the higher the voltage rating the better. Be sure to measure size first as well. A lot of switches are huge and wont fit depending on where you're planning to put it. 

 

- Wire. I used 22awg silver plated copper with PTFE insulation. Decent size and easy to work with.

 

 

It’s only recommended to switch while amp is off. If you have to switch while amp is on then be sure to unplug your headphones first!

 

 

Big thanks to user and amp builder @2359glenn for help and information about this mod!


Edited by Redge78 - 4/30/16 at 2:26pm
post #5 of 2321
Thread Starter 
4 - Power Supply Units (PSU)


We didn't feel the need to change much on that part, the PSU is already quite "beasty" with a C-R-C Pi filter with 1000µF before the "regulators".
It's excessive, unusual but effective. The 330µF output caps that are providing the modulated currents are constantly feeded by the regulators (MJ15020/MJ15021) and that's a very "musical" design.

The only main change done here are those Electrolytic (AKA "Lytics") 330µF output caps, replaced by much faster ones ("MKP" Film caps) that will better feed the Decoupling caps down the line. 
Maxx wanted to keep everything into the "original" box, so the "MKP caps" solution was not possible (those caps are too big), we chose the best Lytics caps that fitted (Mundorf M-Lytics 1500µF).




Installed:







Schematics of the PSU feeding the Power stage :



Edited by Redge78 - 10/2/15 at 9:12am
post #6 of 2321
Thread Starter 

5 - Resistances

 

5.1 - Power Stage resistors

 

MK8 - 150ohm (Mills MR5)
MK6 - 330ohm (Mills MR5)

Mills MR5 are best choice in this location, being a compact non-inductive wirewound of superior performance.

The anode resistors are the most important ones here, they are the "sense resistors" : their voltage will trigger the "WCF" regulating triodes (the bottom ones in the schematics). So the less distortion there is in the resistor the less it is amplified. 

The Mills MRA resistors exceed MIL-R-26E specs and are 1% tolerance.
The MRA-5 is a 5 watt resistor which will handle overloads 5X its power rating (25 watts) for 5 seconds with operating voltages up to 500V.
TCR:
10+Ω: ±20ppm/°C;
1-10Ω: ±50ppm/°C;
<1Ω: ±90ppm/°C

 

5.2 - Grid/"Driver stage" resistors

 

VALUES:


Driver Stage:

4X 220K Ohm (Anode resistors) - TKD CM2 Series 2 Watt - 1% Metal Film Resistors - High quality (Japanese) Audio grade resistor.
4 X 10k ohm ("Grid stopper" resistors)
2 X 1.5k ohm ("Common" Cathode esistors)

Power Tube Grids:
MK8: 8 X 300ohm
MK6: 4 X 300ohm

 

"Power rating" recommendation : always take the highest power handling you can (reasonnably) find, it generates less noise and the cooling is better.  


Resistor Brand choice:
1 - Vishay zfoils (tested)
2 - Shinkoh "Tantalum" (tested)
3 - Takman "REY" (not verified)


The choice of resistor here is based on sound quality. So only resistors with history of audiofile preference is recommended.

 

 

MK8 overview

 

 

Red = grid resistors
Yellow = WCF grid resistors
Purple = driver stage resistors
Purple = WCF Coupling caps..

 

 

MK6 Overview :

 

 

 

Red = grid resistors
Yellow = WCF grid resistors
Purple = driver stage resistors (anode/Cathode)
Pink = WCF Coupling Caps


Edited by Redge78 - 1/19/16 at 10:30am
post #7 of 2321
Thread Starter 

6 - Internal Cabling / Fuses / Power Cord / "Heat management" / Diode Bridge


Internal Cabling :

This is a noticable upgrade potential area. You will hear a difference.
For some reason, the stock wiring is not really up to par, and was initially an optional upgrade, for a time at LD.

The LD designer himself recomended the upgrade be a silver plated teflon coated wire.
Maxx134 also chose supplement silverplated with "OCC copper" for the outputs of board to jacks.

The internal chasis of this amp uses four runs of 2-foot long cables, that are 3-conductor each.

Regarding the recabling, advice :
Cooper with silver platting, section 0,3 à 0,5 mm² (you'll work out the awg equiv. [22 to 20...]), light teflon coating, twisted pairs
normalised : UL1213 (industrialà and/or MIL-DTL-16878/4 (Type E) (mil) for high temp.

Links :
http://fr.rs-online.com/web/p/fil-de-cablage-electrique/1771113/​
http://www.mouser.com/Alpha-Wire/Wire-Cable/Hook-up-Wire/_/N-5ggs?P=1z0zo8oZ1yzs67rZ1yzoop6

Also can find similar teflon coated, silver plated, 3conductors (twisted & shielded).
You can find also on ebay:


BUT:
If you are like Redge78 & coinmaster, who are not confined to internal dimensions of the amp or stock heat issues, then you can choose many many more cable options.


Fuses

 

Why not ... won't break the bank, anyway and you'll have a new way to sound crazy at the office.

 

There is 3 fuses in the amp.

One on the power plug at the back and two inside the amp, each side of the middle relay (one inch above the pot).

Obviously, you need to replace the old fuses by an audiophile ones of same values.

 

You can go for some "inexpensive" PADIS (kind of rebranded "Furutech" fuses), some "HiFi-Tuning", or for the rich kids some "Synergistic Research RED Quantum"

 


Power Cord :

 

Same as above.

Redge is using a massive Zavfino "THE MAJESTIC"  (PC-OCC Single Crystal 6N Copper Conductor - 12AWG/Core )

 

 


"Heat management" :


Diode Bridge : (Optional)

IXYS FRED Rectifier Bridge FBE22-06N1 ( High performance 600v/22amp rectifier bridge with fast recovery diodes). Sonic improvements were not verified at time of installation.
http://www.mouser.com/ds/2/205/FBE22-06N1-6885.pdf


Edited by Redge78 - 10/18/15 at 5:24am
post #8 of 2321
Thread Starter 

7 - The Tubes

 

 

7.1 The Power Tubes

 

MK6

 

MK8se (6H30PI - Electro Harmonic "Gold pins")

 

 

 

7.2 The Driver Tubes

 

MK6

 

MK8se (12AT7)


Edited by Redge78 - 10/18/15 at 5:04am
post #9 of 2321
Thread Starter 
reserved
Edited by Redge78 - 10/2/15 at 9:16am
post #10 of 2321
Thread Starter 

8 - Background stuff / Documentation

 

 

Balanced vs Unbalanced

 

- Wikipedia : "Balanced audio"

https://en.wikipedia.org/wiki/Balanced_audio

 

 

"White Cathode Follower" (the "Power Stage" circuit design)

 

- John Broskie's Guide to Tube Circuit Analysis & Design :  A good introduction to the WCF 

http://www.tubecad.com/2014/05/blog0292.htm

 

 

 

"... Mr. Eric White, the British inventor who worked for EMI, patented his famous White cathode follower in 1940 in England (GB564250), which was also patented in the USA in 1944 (US 2,358,428). His circuit is a unity-gain, push-pull buffer that accepts an unbalanced input signal and presents an unbalanced output.

This feat of magic is performed by the top triode's plate resistor that functions current-sense resistor that experiences a variation in voltage drop corresponding to the variation in current conduction by the top triode. This variation in voltage drop becomes the input signal for the bottom triode, which responds in an anti-current phase fashion, creating a complementary, balanced push-pull operation by the two triodes. As the top triode conducts more, the bottom triode conducts equally less; as the top triode conducts less, the bottom triode conducts equally more.

 

The result is class-A, push-pull operation that yields an output impedance half of what it would be with the same tube in a cathode follower and lower distortion. Moreover, the White cathode follower can deliver a peak output current swing into the load twice that of its idle current. The load is all important and its impedance must be factored into the calculation of the sense resistor’s value. Without the external load, the two triodes could not differ in current conduction, so no push-pull operation would be possible. Without the load, the sense resistor would not create the needed drive signal for the bottom triode..."

 

(See in "New mods" : White Cathode Follower - Balanced Push-pull)

 

 

- A paper from Alex Cavalli from Cavalliaudio : "...The White Cathode Follower as An OTL Power Stage for Headphones..."

A good introduction and a lot of number crunching. You'll learn here how to calculate the Zout of your amp !

https://www.cavalliaudio.com/diy/docs/WCFOptimization.pdf [EDIT : dead link, have to find an another one]

 

 

Capacitor reviews

 

- Humble Homemade Hifi - Capacitor Test

Large selection of boutique caps, can be useful for our "Coupling caps" 

http://www.humblehomemadehifi.com/Cap.html

- Capacitor Musing

Large selection of various caps, including Russian ones. Bypasses are discussed as well.

http://www.enjoythemusic.com/diy/0708/capacitor1.htm

 

 

Film capacitors Vs. Electrolytic capacitors (From "ClarityCap" documentation)

 

"... The ESR (Equivalent Series Resistance) of a film cap is up to several orders of magnitude lower than an electrolytic capacitor. This enables the capacitor to remain charged at all times and to quickly deliver higher peak power when required. ESL (Equivalent Series Inductance) is also many times lower than an electrolytic. This reduces distortion and phase shift and ensures that there are no delays or ringing in response to step changes in demand on the capacitor. The dry construction of a film capacitor extends lifetime relative to an electrolytic cap. In an electrolytic capacitor, the gradual evaporation of electrolyte reduces capacitance and increases ESR, leading to degraded performance and eventual failure. Film cap is non-polarized, ensuring simplified assembly [...] The higher voltage ratings eliminate any need in circuit design for complex series/parallel connections and balancing resistor networks.

 

When selecting a film capacitor to replace an electrolytic, consider that due to the minimal heat loss and faster transient response of the film cap, a relatively low-capacitance film cap may typically be provisioned. OEMs that have implemented the technology have successfully used TC to replace electrolytics in ratios of capacitance from 1:2 to 1:10..."

 

 

... much more...


Edited by Redge78 - 3/19/16 at 4:00am
post #11 of 2321
Thread Starter 

Around the Amps (Headphones, DACs, Power Supply, cables, ... )

 

 

Design (because uglyness is not a fatality)

This is where Maxx will demonstrate that the more the amp shines, the better the sound is ! Voodoo magic !

 


Edited by Redge78 - 9/27/15 at 11:08pm
post #12 of 2321
Thread Starter 

The new mods

 

because we always think of new ways to torture the amp

because you guys help us

...

 

White Cathode Follower - Balanced Push-pull

 

" ...The load is all important and its impedance must be factored into the calculation of the sense (Anode) resistor’s value. Without the external load, the two triodes could not differ in current conduction, so no push-pull operation would be possible. Without the load, the sense resistor would not create the needed drive signal for the bottom triode..."

 

=> if the "load resistance calculation" seems not very important for the MK8 - the load will always be high between 300/600 Ohms - what about the MK6 with its alleged 32Ohms to 300Ohms allowed Loads? What about the push-pull operation when a 32 Ohms load is plugged ? Is it still balanced or do we have one triode working more than the other one ? And therefore is it possible to adjust the "sense (anode) resistor" to bring back balance between the 2 triodes and maximise the power output ?

 

Cavalli formula : Ra = 1/Gm*[1+2*"Load resistance"/"Plate resistance")   Gm = Transconductance of the triode

 

 

 

 

10.1 The "WCF" Coupling cap (Tested/Verified on Maxx/Redge) [EDIT Oct. 08th, 2015]

 

The functionning of the "White Cathode Follower" has been explained above (chapt 8).

When analysing it, what struck us is the regulating triode (T2) is driven by a capacitor and resistor in series to the T2 grid. We can consider this cap as a coupling cap for the T2.

So, even if this cap is less important that the "Coupling cap" fed by the Driver Stage that impact the whole Power Stage, it will have a direct sonic impact on half the power triodes. Which is more than enough to have a closer look at them in our books.

 

 

 

The bad news are that the caps put originally by LD are pretty lame (for the MK8se at least), some WIMA MKS4 0,22µF/250V that they also use on other areas for antiparasitic purposes. 

We were not very happy with the original "SCR PB" coupling caps put by LD, but at least those were "Polypropylene" MKP with half-decent dissipation factors. Those "polyester" WIMA MKS4 are bloody garbage and need to be replaced ASAP.

 

 

Values :

 

Capacitance :

No need to push it here, the associated Cut-off frequency is already low enough. So 0,22µF should be quite sufficient. But we tested 0,33µF and 0,47µF (because those were the best "audio" caps we had available) without any problem.

 

Voltage :

Same as "original" 250V or higher

 

Temperature :

As always, higher max temp is better. 

 

Recommended caps :

- Same as for "Coupling caps", they will perform the same task

- As we don't want to be sued, we also recommend to try some WIMA FKP1 (Foiled "polypropylene" caps, the best line of product WIMA do in that kind of capacitance). They should be way much better than the original crap and are very affordable. And they are square ... and red ... and large ...

- As the capacitance is quite low, why not trying some FT3 russian teflon ? 

 

 

Appreciation / subjectives results

 

The impact on sound was not minimal or trivial.

Basically, there is an increase in sonic quality overall which is like the missing third piece to the trifecta of coupling, cathode, & now this "WCF" C.cap
All three play an intimate role of the sonic signature...
But...
Since this cap was the weakest link of the three,
It will make a MORE NOTICABLE sonic improvement than the Cathode cap (maxx134 observation)

The main sonic aspects of this cap are:

Increased Clarity
Increased depth
Increased holography
Increased dynamics
In that order..

As a result, PowerTube swapping is easily noticable, even in MK8.

The sound turns much more intense and real.
And remember, the sonic qualities of this cap will pervade into the signature of the amp,
So get a cap of your sonic preference..

 

 

"How to .."

 

The caps can be nicely unsoldered if you move the board. That's the elegant way.

Or ... you can crush /cut the garbage caps ("medieval style") and only keep the leads intact on the board. 

 

The caps don't have to be positionned near the board, you can use some inches of wires for easier fit.

 

 

Pictures :

 

Precise locations (MK8se)

 

 

Precise locations (MK6)

 

 

 

 

 

The Garbage cap was just below the circle of pins, where it is written "0.22µ/250V".

Two "Silver coated ultra high purity cooper teflon insulated" wires are soldered to the remaining leads ...

 

 

 

The new "WCF" caps have been artistically positionned above the Jup'

 

 

 

And finally in the box, with all the other caps ...

 


Edited by Redge78 - 4/30/16 at 2:31pm
post #13 of 2321
COMPACT VERSION

This is a current picture of the Compact version internals...


Udated with new WCF Coupling caps:

smily_headphones1.gif

Still a "work in progress",
As it will be implementing a few last Ridge78 (secret) mods that will be tested...
wink.gif


Coupling caps:
As you can see, .47uf jupter caps are implemented.
They are a bit thinner and a bit longer than the Mundorf .47uf..
The Jupiter cap is rather new to gaining top status,
and I feel is tuley at the very top with few others.

Since we are aiming for "supermod" level, I can only recommend this cap.
Although, my second place choice for now, would still be Mundorf.

For MK6, a .67uf size is recommended, while coinmaster went a bit far to the suggested limit of 1uf..


Decoupling caps:
The red and white "Decoupling" caps were chosen as largest possible within original confines of the amp.

The 25uf red WIMA Decoupling caps feed the driver tubes,
While the white 47uf Mundorf decoupling caps feed the power tubes..

Although these caps are not as large as Redge78 or Coinmaster caps,
they are within values to be an effective solution,
As well as having advantage of both proximity,
And being directly soldered onto board..

The method used, to secure the large .47uf mundorf caps on board,
Was to Insert one end into the hole designated for the resistor...
Then just wrap the resistor lead on the newly inserted cap lead..


The gold .33uf RIFA "bypass" caps are also connected in inparallel to them..

I was going to place these .33uf Rifa,
on other side of board, like member "coinmaster":

This is good for an MK6,
As most the heater feed runs in between tubes(red wires)...

But take note, the blue "Output wire" is too thin(!)
As are ALL the output wires,
Leading from the board to the XLR jacks..
And so they all need upgrading...(!)

For the MK8, there was some space restrictions for placing the .33uf RIFAs on top like the pic above,
because the wiring is on the side those caps would be..


The smart move is to do this bypass cap installation at same time as replacing the super thin output wires, (from board to sockets).
That way, you only pull out the board ONCE...

My wire upgrade (from board to sockets), was done with OCC copper there(doubled,twisted& taped),
Which is extremely difficult to keep in place without hotglue..
tongue.gif



Cathode Bypass caps:
These are Mundorf 220uf 63V Bipolar caps..
Why bipolar?
The layout.
Also,if you look at data sheet you will read it's advantages for music signals:

http://www.soniccraft.com/datasheets/Mundorf_ECap_RAW-data.jpg

http://www.hificollective.co.uk/catalog/ecap63030-220uf-63vdc-mundorf-ecap-electrolytic-p-4010.html

They are preferred for this Compact version,
as they can be "stacked" one on top of the other to conserve space:



...with the accompanying RIFA .1uf "bypass" caps on other side of board:

With Mills MR5 wirewound power resistors moved over the vent holes..


There are also "Optional" mods in place which are currently unverified for sonic gains:

1- Larger (black gate) caps for PSU control circuit stage.

2- Implementation of "IXYS FRED Rectifier Bridge" in place of original bridge..

3-Black damping material on all the elecrrolytics...

OPTIONAL MODS remain only as an option.
They are separate from the main posted mods above.

WE will focus first on the mods which were sonically verified to give performance gains.
tongue.gif

Heat/ventilation
This is important modification for this compact veraion..
The wiring (stock or replaced) suggestion is to raised up,
for better air circulation around to top of board..(done in picture)
The existing stock wire placement prevents air flow on sides to top.

This is where a hotglue gun comes handy to hold all in place,
and yes I like to use alot wherever needed.
smily_headphones1.gif

So, the combination of all these upgrades,
provides for an extremely fast, responsive, detailed, dynamic and musical design(!).

It is now one of best amp for the HD800, presenting a powerfull experience rarely heard anywhere else.(!)

More is being added daily so keep checking first page!

HEAT MANAGEMENT :

For the compact version,
We most definitely need to upgrade fans..

Go with this post by:
Sound Engineer:
http://www.head-fi.org/t/522099/little-dot-mk-vi-little-dot-mk-viii-se-owners-unite/1860_20#post_11586342

There you will see to open larger hole and place largest fan possible,

Instead of smaller noisy fans. .

And also a fan speed controller which I use and highly recommend.
Edited by Maxx134 - 5/31/16 at 2:16pm
post #14 of 2321
CAN ANYONE DO THIS?..

Quote, MisterX:
"...No shame in letting someone else do the job though..."

I have been asked this question from members not feeling confident to do the mods...

I have proposed one possible solution..

Post a "electronics or amplifier job" in your local college..
There are many "starving students" in electronics field who would take on this job, quite enthusiastically, for a nominal fee, and can also use it for their own benifits for project requirements in college.

This way, you wont get ripped off going to some "Joe Shmo" tube repair shop where the guy will take forever and complain it goes against his training..

College Students are a ripe source for young, sharp, enthusiastic minds open to new things...

Just make sure you can trust the person to be responsible to carry it out...
smily_headphones1.gif





COSMETIC MODS:

SonicTrance MK6 transformer mod:
http://www.head-fi.org/t/782183/little-dot-mk8se-mk6-super-mods/80_20#post_11966905



Visual mods are separate from sound quality of super mods,
But can inquire in thread.
smily_headphones1.gif

SonicTrance
Mk6 visuals:






smily_headphones1.gif



smily_headphones1.gif





smily_headphones1.gif



smily_headphones1.gif




Extra pics for visuals to compliment mods:

MK8:


smily_headphones1.gif


smily_headphones1.gif


smily_headphones1.gif

smily_headphones1.gif

smily_headphones1.gif

smily_headphones1.gif

smily_headphones1.gif

smily_headphones1.gif



smily_headphones1.gif


Edited by Maxx134 - 6/10/16 at 3:26pm
post #15 of 2321

Nice guys! Been looking forward to this. I still can't believe the huge improvement I got from only changing coupling caps and power resistors:)

 

@Maxx134 Dude, your amp looks crazy now! In a good way:)

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