Little DOT MK III Mods?? - Page 2

These are input capacitors on the MK IV, output capacitors are the large ones in the middle of the PCB with per channel having one large electrolyte with large Wima and smaller Vishay bypass forming the output capacitor.

That would be the Bullplug mod made by ethebull, right?

A nice option if your source is a PC or a MP3 player.
I guess the γ1 DAC requires very little power (300mA), but does the internal powersupply deliver sufficient current to drive both the amp and the DAC without affecting the performance of the amp?

I modified mine but I hesitate to provide what I did as the chassis the MK III is shoehorned into is a major PITA to pull the pcb out of and then get it all back in again.

You need the patience of a Saint IMO to work on this amp.

As Always YMMV.

Peete.

Now that we're warned, could you please disclose your modifications for us? I've had the pcb out on my MKIV - a lot of screws had to be removed, but with a little patience it worked OK.
I mean, this whole thread is about modifying a LD amp which in most cases would imply modifications on the pcb. If I want to mess with my amp it's at my own risk (hopefully I know what I'm doing or at least I can reverse the process).

Sure OK.....as always the moment anyone pulls a tube amp board or opens one up the following warning applies... High Voltage is present and it is extremely dangerous so make sure your large caps are drained of voltage and current. You also void your warranty, obviously

I bypassed all the large value caps directly with .033uf 500V NOS K42Y0-2 Russian PIOs, changed the 68 ohm 2W grid resistor on the 2 power tubes to 121 ohm 3W Kiwame (for the 6H30Pi tube mod). I added 4 x Panasonic 1 ohm 3 W resistors to all four tube sockets at the filament V pins (to drop the V to as close to 6.3V as I could get it) as the V to these is unregulated and running higher than spec (my line V is 127V) which means additional heat and premature tube failure.

I bypassed the WIMA 3.3uf 50V MKP output coupling caps with a pair of NOS T-3 Russian 0.1uf 600V Teflon caps that had to be slung underneath the chassis because of their size (big caps). That meant changing the feet on the MK III chassis to large brass cones (Audioselection I think....)

I already use the king of power tubes with it, a costly pair of 6H30Pi-DR's from the 1980's with either Sylvania round getter black plates (6AK5WB mil spec) or Tung Sol 403B drivers. Other great tubes to use are Telefunken CV4010 Diamond bottom, Amperex PQ E95F (rare but outstanding), Mullard CV4015 large shield logo mil spec, Raytheon USN - Jan 6AK5 among others.

Here a few pics of the mods......(sorry about the crappy quality, I had a really old cam at that time). The pics do not show the 1 ohm 3W resistors I added a few weeks later nor all of the .033uf 500V K42Y-2 PIOs (5 in total). The MK III review thread has details of another member pointing out the filament V mod that alerted me to the unregulated V being fed to the heaters. If your mains V is at 115 or 120V then you don't need to add those parts but my line V is always at 127V which put the heater V at around 6.9 or 7.0V which is a little too high. The addition of the 4 x 1 ohm 3W resistors dropped the line V about .5V or so getting it much closer to spec which dropped chassis temps and should make all the tubes last a normal period of time (closer to their MTBF spec).








All of these mods had a positive impact on the SQ of the MK III. Well worth the effort. Some future mods worth doing are subbing the 3.3uf 50V WIMA output coupling caps for a pair of Auricap 3.3uf or if you can find them a pair of PLIO K75-10 NOS Russian caps (2.2uf 400V). Of course you keep the T3 0.1uf 600V using them to bypass the K75-10's.

Changing out the I/O wiring for some silver plated copper wiring or Mundorf silver/gold 23 awg hookup wire. Swap out the cheap brass/gold plated RCA jacks for CMC copper billet/gold plated types and finally change out the pair of 220uf 200V caps for Nichicon FG/KG or if you really want to spend some money Black Gates. The mains filtering caps could also be subbed for some higher quality units (computer rated CDE or Aerovox BHC). The 3 resistors of the PSU section could be subbed for high quality Mills types (5W max but 3W would be ideal). IRC makes terrific resistors for this application (the Mil spec stuff is very good and fairly cheap compared to Mills or Reiken). The generic metal film resistors could be subbed with Vishay/Dale (matched pairs would be a good idea for the signal pathways).

Lots of things to consider.

The MK IV could definitely benefit from the swap of the 2.2uf Solens for some better quality caps like the K75-10 PLIO/T3 Teflon combo or Mundorf Silver/Gold PIOs or any other high quality type. I'd also pull the WIMA box caps and replace those with same value types of your fav brand (size is a limiting factor obviously) but I've never found the WIMA sound to be anything special other than the Black Box WIMAs that cost a fair pile of dough (but would be ideal in this spot). Anyway just a few thoughts on this amp as I don't own one but have sent parts to another MK IV owner to try these suggestions out. (the K75-10 PLIO/T3 Teflon combo and some K42Y-2 .033uf 500V PIOs as bypass caps for the 5 large electrolytic caps ) That member is no longer active at HF so I have no idea how this mod turned out but it should be similar to the MK III in SQ.

These are just suggestions and my own opinions so others results might vary depending on what parts used, soldering skill,execution of the mods, wire selected etc etc...

Peete.

Great!

Hey Pricklely Peete,

Thanks for the great MOD write up! I have one question, since I want to do one mod at a time... The 6H30Pi tube mod, ( I am new to this lol ) can I use the Kiwame 5W/120 ohms resistor? I might be mistaken, but doesn't a 120 ohm resistor be capable of 110 ohms to 130 ohms, giving a -/+ 10 lee way? The ones I have an option of getting are only 2W and 5W, so I am assuming the 5W would be o.k., since 3W is required? Thanks for your time, and once again, great job...

Hey thanks, Peete. Nicely done mods, now we're getting somewhere!

Execellent photos. Of course the chassis always puts a limit to the mods you can make, but Peete you seem to have found a (daring) solution I see now what you mean about fitting it all back into the chassis. You've got a lot of wires there.

Did you do the mods step by step in order to hear what each mod sounded like, or did you do it all at once since the pcb was out of the box anyway? And could you comment a little more on how the mods has changed the sound (overall and in particular)?

I don't want to get too off topic here (since there's already a 128 pages thread dedicated to LD tube rolling), but with my Unison Research amp the EL34 power tubes makes a HUGE difference. From the dull JJs (Tesla) to the brilliant Svetlana and the rich sounding Electro Harmonix.

Also, is it not right that if you short-circuit the power cable, you automatically drain the amp of voltage and current?
Just a tip in stead of having to wait 30+ minutes for the power to run out.

Thanks also for sharing your thoughts on upgrades for the MKIV model.
The MKIV already comes with CMC gold plated RCA jacks though

SebastianL

I believe the originals are 2W...I used 3W to give me some headroom in the parts spec. I'd stay at 120 or 121 ohm. Email David though since I think the newer MK III's may already be 6H30Pi ready.

Peete.

Thanks !

I did the mods in two stages. First I changed out the grid resistors for the 6H30Pi mod and listened to that for a few months then pulled the amp apart again to add the mods I talked about.

The SQ improvements were 3 fold in nature. better bass response and extension. Much quieter SNR due to extra smoothing of the mains filtering caps (lowering ESR as well) while the output coupling cap bypass added some much needed details to the signal output. Overall I'd say the SQ gained resolution and refinement without upsetting the tube magic in the mids. A decent quality mains cable and decent quality RCA cables were the final touches.

I don't think shorting the mains leads (L + N) is a good idea...you need a bleeder network installed on the mains filter caps or use a device that does the same thing mounted on a stick or plastic wand. You parallel a 150K 1W resistor across the +- terminals of each large cap and then measure them with a DMM to make sure all the voltage has been bled safely off the caps. I'm not 100% sure of the resistor value but you can google it and find out for certain.

I believe the Mk IV CMC are one step below the ones I suggested. Here's a link to the ones I'm talking about

Charming Music Conductor-CMC-805-2.5CU,,cmc-audio,Tube Socket,cmcaudio,banana,spades,binding posts,rca jacks,rca plugs

Peete.

I believe you're right, but I'm fully satisfied with the 'standard' CMC rca's in my MKIV amp. They are very tight with my Neutrik jacks. To upgrade these would be a waste of money. LD has done an excellent job there.

It sounds good to me. With a minimal "E" config (coaxial SPDIF to analog only) I measured it on an HP E3610A lab power supply at 12mA when at 5.00 volts. The 5 volt regulator on board is rated to 1A, so unless it is already at or above 98.8% capacity I doubt there should ever be any trouble.

Just had a thorough look inside my MKIV just to be very disappointed discovering that the caps are not of the brands mentioned by Little Dot.
The 'Solens' 3.3µF are marked 'Phenix HiFi'. They look a lot like Solen but with a different (although similar) logo. I've done a search and couldn't find them anywhere. They could be produced by Solen though.
Neither are there any Rubicon or Nichicon caps. Only Nippon Chemicons.

I'm now investigating the components I'm considering as substitutes, and SIZE DOES MATTER! Now I see why you chose the untraditional positioning of the caps outside (underneath) the box. Mundorf 3.3µF caps are much too large to fit in anywhere. Also I think the Mundorfs are much too expensive (€95 each) compared to the pricerange of the Little Dot amp. For that kind of money I'd rather buy another amp to begin with.

One last thing: any suggestions on a power cable upgrade?

Please Help!

Hello everyone,

I have a newbie question, Regarding the 6H30Pi Mod, from looking at the PCB pictures I cannot find which resistor to change! There are many! If anyone can specify where this resistor is, and how many of them, since I only has six of these resistors... Thanks for your time! Cheers,

-Mike.