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

[baronbeehive]

Does anyone on here do mods for others? Let me know what you do and what you charge.

No, there's not enough people here to do that. Best thing would be if you could find a friendly electronics engineer and ask him if he could do it. I have had a TV repair man do some circuit testing for me in the past on my initial build.

 

[CopperFox]

Where did you order from? China or US? The LD site in US, littledous.com, has told me that they place great value on customer relations and test each amp thoroughly before sending out, and their warranty looks good. Whereas the China site have been undergoing changes recently.

It was littledotus who did not respond to my question about the black color resuming production. Ordered from Shenzenaudio.

 

[talan7]

It was littledotus who did not respond to my question about the black color resuming production. Ordered from Shenzenaudio.

How long did it take before Shenzhenaudio shipped out your amp? I ordered a MKVI from them almost 2 weeks ago. I received an email from them the day after I placed my order asking what color I wanted. I said silver, and that was that.

 

[baronbeehive]

I hope you guys do alright with Shenzenaudio. Sorry to say from what I've heard on the other LD forum that people have experienced problems which is why I contacted littledotus.com to see what was happening because littledot.net couldn't be contacted, but they have now got their website back up. The US site were very friendly and helpful and said that they had upgraded their testing prior to shipping, and their warranty seemed to be good. I hope this is the case, because if not I fear many will give up on Little Dot which is a shame as the amp itself is good, and I never used to hear of problems unlike what seems to be happening now.

 

[CopperFox]

How long did it take before Shenzhenaudio shipped out your amp? I ordered a MKVI from them almost 2 weeks ago. I received an email from them the day after I placed my order asking what color I wanted. I said silver, and that was that.

Three weeks.

 

[talan7]

Three weeks.

Oh ok thanks. I feel much better

 

[baronbeehive]

Three weeks.

Glad to hear it arrived safely!

 

[Maxx134]

The slow shipping is probably because of the weight.
I remember when I ordered just one replacement transformer and it took about 4weeks...

I feel that the most interesting area of upgrade to go in now would be to do the same as has been done for the 6SL7 tube but for the 6SN7

So the issue with the different tube is not the optimal bias point, but the fact that it has a different output level to the output stage.
The gain switch may be needed to switch to get an optimal gain for the next stage (output tubes) but the question is, how much gain or output would be optimal for which output tube type?
The stock setup has basically such a low driver output to not matter, but not so with these moded setups.

So my point is that you should consider which output tubes your settling on, and also the gain switch setting, before settling on a driver tube choice.

My amp is not the mark6 , so I would rather let others chime in with optimal combos for that unit..


Ideally, we would want least global feedback, which would mean the higher gain switched.
Then a driver tube that outputs it's level in the sweet spot to drive the output tubes.


For me, I first tested and settled on an output tube type, then I rolled tubes untill I found my fav driver tube to compliment the output tube.
For instance, my choice of output tubes were none of the recommended types, and they required more input gain, so the higher "MU" type 6SL7 was preferred, for my setup.
I am assuming the LD mark6 output tubes, would be better off with a lower gain 6SN7 type.


The variability of the mark6 to use more output tube types than the Mark8, makes it a bit more effort in rolling to find what you like.

While both the tube and cap upgrades basically overlap, help & compliment each other, in general:
The tubes basically are the sonic image, depth and richness, while the cap characteristics are basically the clarity, style & finesse..

Just mentioning these points, from a designer's perspective, because at this stage, we stopped modding long ago.
Basically this thread has actually been redesigning.

 

[CopperFox]

Feels great to have the amp running again... in the black chassis. I put the new PCB and vu meters there .

Now with the 8* parallel 330uf 100v Nichicon KZ caps as cathode bypass. They will need to burn in along with the rest of the caps.

 

[baronbeehive]

Feels great to have the amp running again... in the black chassis. I put the new PCB and vu meters there .

Now with the 8* parallel 330uf 100v Nichicon KZ caps as cathode bypass. They will need to burn in along with the rest of the caps.

Haha.. it's getting mighty crowded in there! The amp looks great, glad it's all up and running again. You took the PCB out of the new silver amp and put it in the black amp? Good work .

Check in again when you have an idea of what the cathode bypasses sound like.

 

[baronbeehive]

So the issue with the different tube is not the optimal bias point, but the fact that it has a different output level to the output stage.
The gain switch may be needed to switch to get an optimal gain for the next stage (output tubes) but the question is, how much gain or output would be optimal for which output tube type?
The stock setup has basically such a low driver output to not matter, but not so with these moded setups.

So my point is that you should consider which output tubes your settling on, and also the gain switch setting, before settling on a driver tube choice.

Hey Maxx, great to hear from you again, I've been trying to hold the fort while you've been away .

Yes I'm going to look again at my graphs showing load lines and optimal bias points for 6SN7 and 6SL7 to see if I might have missed something. The issue is that it would be impossible to draw the load line for 6SN7's with their optimal bias point on the graph for 6SL7's which had also been optimised, I will check back in when I have re-examined this. On the stock amp both tube types worked with no problem because neither were at their optimal point which was obviously a compromise by LD to enable tube rolling.

Just mentioning these points, from a designer's perspective, because at this stage, we stopped modding long ago.
Basically this thread has actually been redesigning.

Haha, yes you might have stopped modding ages ago, I just finished mine recently by putting in those Neotech OCC silver output wires to try to sharpen up things as much as possible, first time I've been inside for ages.. and the last time lol.

Edit: Redge was back on the Oblivion thread recently!!

 

[baronbeehive]

@Maxx134 I've looked again at the graphs for 6SN7's, below, and 6SL7's, bottom. I've included my comments at the time.

To summarize:

I've drawn 2 load lines, line 1 and line 2, on the 6SN7 graph which could be used to try different bias points. The lines show tube output current - l, anode resistor - Ra, and cathode resistor - Rk. Ra and Rk are the values to be tried experimentally.


The max rating of 20mA on the datasheet is well above the values that could be experimented with, and the typical operating value is 10mA so values on either line 1 or line 2 would be OK to try as the highest output is 7mA on point 3, line 1.

Out of interest I have included on the graph the ideal bias point I found for the 6SL7 tube, (in green). You can see why the amp is better for 6SL7's, at least with the stock bias point. Another factor is that the 6SL7 has an amplification factor of 70 whereas the 6SN7 is 20.

@CopperFox I would ignore the points on line 1 and just go for the points on line 2 or points on an intermediate line given by an anode of around 22k as I said previously. The reason is that the max rating for the 6SN7 is 20mA with a typical operation of 10mA.

Where I might have slipped up is in including the 6SL7 ideal bias point on the 6SN7 graph and visa versa the 6SN7 ideal bias point on the 6SL7 graph because that doesn't work.

So ignore the green point above and the blue points below, and what I commented about them. They were just there to indicate where they were in relation to the other tube type if that makes sense.

...and the 2 blue bias points correspond to points 1 and 2 on line 2 on the previous post, which showed the graph for 6SN7's, just out of interest.

I hope that's clear, maybe not!



So it appears that both the stock amp and the amp optimised for 6SL7's will work with 6SL7 and 6SN7 tubes. But the amp optimised for 6SN7's will not run on 6SL7 tubes so that should be born in mind. That's obviously why LD chose their tube parameters.

So my conclusion about optimised points for 6SL7 and 6SN7 not working without a switch was wrong, clearly you can't superimpose a bias point for one tube type on another tube type's grid curves because the electrical characteristics are different, silly of me ! No one spotted my deliberate mistake lol. You are right that it is the outputs that might need to be switched, but only to adjust the gain appropriately.

The output from 6SL7 has gone up from about 0.5mA - stock, to around 1.5mA - ideal point.

The output from 6SN7 has gone up from about 0.5mA - stock, to around 7mA - ideal point, well within operating parameters.

I hope that's cleared that up .

 

[Maxx134]

I read years ago, where the designer was explaining about testing load lines, and how, across the linear portion of the bias point, you can still have a preferred point..
A point that may not be exactly in the middle of the linear portion, but as long as the + & - amplitude of the signal lies inside that area, you won't have signal compression distortion.

So the point is, that's your preferred bias point, ideally, should be tested and listened to.

In my own experience, I have noted slight differences or both liveliness and image distance, with different bias points within usable range.
At the non-linear range, I did notice some dynamics compression.

That's why I feel it is sometimes an art, to design tube amps, and that, for instance, I view the stock driver tube bias points, an intentional design choice, rather than a compromise. A choice for wider tube rolling.
They could have increased the voltage supply for better bias points, but chose to retain a lower voltage.
Another reason why I lowered those last PSU resistors (to increase plate voltage) on the sides of the board, that are in series just before the tube anodes & "Decoupling caps"..

 

[baronbeehive]

So the point is, that's your preferred bias point, ideally, should be tested and listened to.

Yes, exactly! A point that looks good on paper might not be that good and visa versa. You only know after you have tested it. There could be many points that sound better than the ones we've tried yet!

They could have increased the voltage supply for better bias points, but chose to retain a lower voltage.
Another reason why I lowered those last PSU resistors (to increase plate voltage) on the sides of the board, that are in series just before the tube anodes & "Decoupling caps"..

Yes, that definitely helped with an extra 20 volts or so.

I think the reason that the stock point works is that there is very little voltage swing in that position so that the swing either side of zero signal is linear because it doesn't swing far enough to reach non linear areas.. clever of LD !

The whole area of bias points is a compromise between output current, voltage swing, linearity.. and chance as well! For example when I was testing this I didn't test the differences in voltage swing at all, so that might also have yielded interesting results.

I think this area of experimentation is the only interesting one left after the other mods have been done, that's why I've been going over it with @CopperFox .There could be interesting results if some of the different points are tried. I certainly felt, as you did, that liveliness and transparency were affected so it's well worth pursuing this.

 

[baronbeehive]

@Maxx134 I'm very happy with the amp as it is now and that's my mods finished lol!

I tested it on some high res music such as this:

and this one by Dire Straits:

The thing about these speaker demos, you get the sound as it is coming out of the top end speakers which sounds sensational both through my HE-800's and my Monitor Audio Silver speakers! I really can't imagine anything better than this, the clarity is simply stunning which I think might be partly due to the CCS. And.. there is scope for further improvements in this aspect with a Neotech headphone cable which you have I believe. I haven't bothered with one up to now because there is not really any need.

Also the fact that the little APPJ is right up there too is quite amazing, so I will never get rid of them.. ever .