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Little DOT MK III Mods?? - Page 9

post #121 of 149

The little dot mk III  comes with a 100kohm Alps 16mm diameter Pot.  From new I had some issues with this pot, sometimes when turning + or - the volume knob it was some noise (bad contact scratching inside the pot) and so I decided to change it.

 

At first I checked if  a bigger pot would fit in the Little dot little mkIII chassis and enclosure, and the conclusion is that the maximun body diameter allowed to fit is 21mm diameter.

 

I found on ebay a DACT stepped pot 100K with 21 mm diameter from China ($12) and same kind of shaft.  I'm posting the picture here.  Very fine and good pot.

 

I will strongly suggest to change the original pot to an stepped pot 100K 21mm diameter, all the noise when moving the knob disappeared and the sound is more accurate and tigth.  

The cables in the LD are very thin and you have to desolder and solder carefully because the length also is constrained (can't cut to shorten the cable).  Of course you can make an entire new and strong cable, but this was not my goal.

There is only one grounding cable and you have to insert a little copper "bridge" between L and R ground on the new pot before soldering the cable.   After soldering use a silicon hot glue gun to fill the place, this will add mechanical strength and galvanic isolation.

 

 

 


Edited by jdamico - 8/4/13 at 11:15am
post #122 of 149

After +250 hours can share the results of my mods (strictly IMHO).

 

Input cap: WIMA MKP10 3.3 uF  bypassed with Obbligato Gold 0.047 uF

 

Bypass for the output electrolytic stock cap:  Obbligato gold 0.68 uF  (didn't changed the output electrolytic stock cap because there is not enough space to do it without changing the whole Little Dot external aspect).
 
Alps pot changed to DACT stepped 21mm body 100k pot.
 
Output tubes:  stock russian (the best)
 
Input (drive) tubes:  Tung Sol Jan 6AJ5 dated 1945
 
 
The first 40hrs hours of listening are some how unpleasant:  The new caps sounded brigth (not bad but unreal), so is mandatory to give them some time to burn in.
 
After 50+ hours things become better and better.  Input caps:  you get the best of both worlds:  Wimas tigth bass and obbligato's liquid, clear and beautiful highs.

 

Pictures:  didn't remember to take pcb pics with the LD wide opened when doing the last mods, so they are taken only from the front

without the aluminium front cover.

 


Edited by jdamico - 8/4/13 at 8:49am
post #123 of 149
Quote:
Originally Posted by jdamico View Post

The little dot mk III  comes with a 100kohm Alps 16mm diameter Pot.  From new I had some issues with this pot, sometimes when turning + or - the volume knob it was some noise (bad contact scratching inside the pot) and so I decided to change it.

 

At first I checked if  a bigger pot will fit in the Little dot little mkIII chassis and enclosure, and the conclusion is that the maximun body diameter allowed to fit is 21mm diameter.

 

I found on ebay a DACT stepped pot 100K with 21 mm diameter from China ($12) and same kind of shaft.  I'm posting the picture here.  Very fine and good pot.

 

I will strongly suggest to change the original pot to an stepped pot 100K 21mm diameter, all the noise when moving the knob disappeared and the sound is more accurate and tigth.  

The cables in the LD are very thin and you have to desolder and solder carefully because the length also is constrained (can't cut to shorten the cable).  Of course you can make an entire new and strong cable, but this was not my goal.

There is only one grounding cable and you have to insert a little copper "bridge" between L and R ground on the new pot before soldering the cable.   After soldering use a silicon hot glue gun to fill the place, this will add mechanical strength and galvanic isolation.

 

 

 

 

 

Thanks for this. I will have to change the cables on mine as well, because I already made them shorter...and now they're a pain to solder. They're also horrible quality. VERY thin, but at the same time, they dont bend, the isolation feels like plastic rather than rubber. I'll have to get a thicker wire. 

 

In fact, I'm sorry to say this, the entire MKIII amp is of poor quality.  Not the aluminium case which looks good, but the inside is very badly put together. Very poor soldering,  wires are thin and brittle, half the solder joints are brown and rusty looking, etc. Not a nice sight when opening the amp.  It obvious why some amps cost more than others...and its not just their performance that matters. For example Nuforce HDP or Musical Fidelity V-CAN are so perfect looking on the inside, everything is precise and clean, like a swiss watch, while MKIII looks like it was built during a coffe break by someone who didn't really care much for it. Not to mention its impossible to get the components out without desoldering certain wires, which is totally ridiculous and makes any repair much more time consuming than it has to be.

post #124 of 149
Quote:
In fact, I'm sorry to say this, the entire MKIII amp is of poor quality.  Not the aluminium case which looks good, but the inside is very badly put together. Very poor soldering,  wires are thin and brittle, half the solder joints are brown and rusty looking, etc. Not a nice sight when opening the amp.  It obvious why some amps cost more than others...and its not just their performance that matters. For example Nuforce HDP or Musical Fidelity V-CAN are so perfect looking on the inside, everything is precise and clean, like a swiss watch, while MKIII looks like it was built during a coffe break by someone who didn't really care much for it. Not to mention its impossible to get the components out without desoldering certain wires, which is totally ridiculous and makes any repair much more time consuming than it has to be.

 

 

 

Yes, all you said is truth.  But for the price is one of the best performing headphone (and line) amps out there.  And if you have some soldering skills and love mods and tube rolling, can be a very satisfying thing.  The bad is the little enclosure with almost no additional space.

Mine came with cheap chinese film capacitors (not even wima or another well known brand) and so decided to change them all.

Electrolytics are a reasonably good standard for tube amps (long life, high temperature ones).

In mine the solder joints are not bad but miserly stingy. The good is that this make more easy to desolder things.

Good luck.

post #125 of 149

I have another question related to volume pot.  I decided I'll go with the classical Alps 16 100k pot, as stock inside the MKIII. But my problem now is, there seem to be many variations of alps 16 pot.  I found two types of 100k pot,  the 50W and 100W ones. I assume W means watts, but which one should I take?  Does it even matter? Prices are the same.

Also, what kind of wire should I use to connect the PCB and the volume pot? Does it matter even? Can I use just any copper, insulated piece of wire or does it have to be special?

post #126 of 149

Never saw something like 50W or 100W  in audio pots.    All audio pots of this kind are max 1/4 watt; typical 1/8 watt or less for sure.  Sorry, can't help you with this.

Alps pot used in LD mk III is, as far as I know,  old stock not in production now, but there is a huge inventory in China.

Most important things to select the pot are:  100Kohm, Type "A" (for audio),  stereo (X2),  max 21 mm body diameter,  shaft diameter 1/4"  (stepped pots with individual resistors for each step are the best for audio and lasts almost forever).

IMHO any good insulated copper cable will do the work, but avoid more than 22 AWG gauge and more than 300V insulation if you don't want to figth to solder and to bend them inside the enclosure. Length of cables should be the shorter as possible but don't worry too much about it as with the quality of the potentiometer.

post #127 of 149
Quote:
Originally Posted by jdamico View Post

Never saw something like 50W or 100W  in audio pots.    All audio pots of this kind are max 1/4 watt; typical 1/8 watt or less for sure.  Sorry, can't help you with this.

Alps pot used in LD mk III is, as far as I know,  old stock not in production now, but there is a huge inventory in China.

Most important things to select the pot are:  100Kohm, Type "A" (for audio),  stereo (X2),  max 21 mm body diameter,  shaft diameter 1/4"  (stepped pots with individual resistors for each step are the best for audio and lasts almost forever).

IMHO any good insulated copper cable will do the work, but avoid more than 22 AWG gauge and more than 300V insulation if you don't want to figth to solder and to bend them inside the enclosure. Length of cables should be the shorter as possible but don't worry too much about it as with the quality of the potentiometer.

 

 

Sorry I meant 50 mW and 100 mW, not watts.  I'll try to find an acceptable wire in one of my old broken speaker amps. I bet there are wires inside that I could use.

post #128 of 149

For LD mk III you can search on ebay for: DACT Type 21 Stepped Attenuator Potentiometer 100K 2A3 (let me clarify I don't have any relation with this seller and is not my intention to promote him).

Not only will fit perfectly mechanical and electrical, but is a clear upgrade over the stock pot.  I'm using it, very happy with the results, and is my best advice.

For short cables handling small currents I have a recycle trick: if you have an old and damaged computer case standard power supply, you will find that is plenty of 18 AWG 300 Volts cables of different colors.  You can cut and use them, they are very flexible and better than LD stock.

post #129 of 149
Nice job jdamico. Swapping or bypassing the caps really made a huge difference in my LD MKIV SE. One piece of advice though: be careful with the hot glue as it tends to melt once the amp gets hot. Especially close to the tubes. I glued my Jantzen caps to the pcb at first, but they all came off after a while.
post #130 of 149
Quote:
Originally Posted by jdamico View Post

For LD mk III you can search on ebay for: DACT Type 21 Stepped Attenuator Potentiometer 100K 2A3 (let me clarify I don't have any relation with this seller and is not my intention to promote him).

Not only will fit perfectly mechanical and electrical, but is a clear upgrade over the stock pot.  I'm using it, very happy with the results, and is my best advice.

For short cables handling small currents I have a recycle trick: if you have an old and damaged computer case standard power supply, you will find that is plenty of 18 AWG 300 Volts cables of different colors.  You can cut and use them, they are very flexible and better than LD stock.

 

 

Ahhh, yea, I have loads of power supplys at home. I'll take them apart and have a look. Thanks a lot, i totally forgot about that.

post #131 of 149

Is it normal that when I start the amp, for the next 10-15 minutes there's slight ticking audible from the headphones? Its not loud, barely audible, it sounds like metal hitting glass, very gentle sound. Does that mean tubes might be ready for replacement? 

post #132 of 149
Quote:
Is it normal that when I start the amp, for the next 10-15 minutes there's slight ticking audible from the headphones? Its not loud, barely audible, it sounds like metal hitting glass, very gentle sound. Does that mean tubes might be ready for replacement? 

 

Sparkling inside tubes?

Tubes should have near 2000 hrs of life (standard tubes, military made tubes will last even more). Make your own calculations based on your average listening sessions.

Check the heater wires (6.3V from the transformer), maybe they have poor soldering and the tubes have a cold start.

Also you can write to LD in their forum to have an answer direct from factory.

post #133 of 149
Quote:
Originally Posted by jdamico View Post

 

Sparkling inside tubes?

Tubes should have near 2000 hrs of life (standard tubes, military made tubes will last even more). Make your own calculations based on your average listening sessions.

Check the heater wires (6.3V from the transformer), maybe they have poor soldering and the tubes have a cold start.

Also you can write to LD in their forum to have an answer direct from factory.

 

No sparkling on the tubes at all, I was checking that very carefully. The clicking noises disappear after about 10-15 minutes.

post #134 of 149

It could be the tubes heating up if the room temperature is rather cold. I've heard sounds like this as well both from my LD and from my all tube speaker amp. If you hit the tubes gently with a fingernail while the amp is powered up, you are likely to hear a similar sound due to some microphony in the tubes.

Tube rings might help.

post #135 of 149

SebastianL wrote:
Nice job jdamico. Swapping or bypassing the caps really made a huge difference in my LD MKIV SE. One piece of advice though: be careful with the hot glue as it tends to melt once the amp gets hot. Especially close to the tubes. I glued my Jantzen caps to the pcb at first, but they all came off after a while.

 

Thankyou, At first I was afraid because heard lot of comments about sound smearing when bypassing caps, but the results are very pleasant and satisfactory, and of course the amp sounds better than the original stock amp.

The hot glue or another insulation is horrible but necessary because the Obbligatos gold comes with external metal shield  and have to avoid the accidental touch between them and pcb solder joints and/or  component leads, but my LD never gets hot enough inside to melt the silicon.  I measured max. 60 celsius after hours at 75% volume knob.

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