[Maxx134]

The gain switch is part of the NFB loop. Nothing good will come of removing it.

Sorry I did not mean to change the circuit, just solder a position of either low or high gain...
I do not like or trust these switches,
and believe they may cause volume imbalance if one of them lessen contact.
I personally don't need it.

 

[Maxx134]

Since we are talking hundreds of kilohms involved with the switch,
switching in resistors..
I could see how the tiny dip switches themselves may become a factor if the switch is defective or tarnished..

 

[Benny-x]

I've been keeping one eye on this thread and the other out for a MK6+. I'm talking to a seller right now of one that says it's his 2nd and that both have exhibited some external transformer hum and some noise through the 1/4", SE headphone jack.

Now the noise through the SE headphone jack I've read a lot about, and I just plan on using this balanced anyway. But the external transformer hum is something I don't recall reading about and I'm wondering if all you guys in here also have this issue with your Mk6s and Mk8s?

 

[baronbeehive]

I've been keeping one eye on this thread and the other out for a MK6+. I'm talking to a seller right now of one that says it's his 2nd and that both have exhibited some external transformer hum and some noise through the 1/4", SE headphone jack.

Now the noise through the SE headphone jack I've read a lot about, and I just plan on using this balanced anyway. But the external transformer hum is something I don't recall reading about and I'm wondering if all you guys in here also have this issue with your Mk6s and Mk8s?

 
No, and I haven't heard of this before. I doubt the others have experienced it either or I would have known about it. Maybe you could get a new one under warranty? It can't be much more expensive.
 
I just remembered that when I sold my mkivse the person that bought it insisted there was a hum and sent it back and when I tried it there was no hum so it's possible this is peculiar to one's system maybe.

 

[Benny-x]

No, and I haven't heard of this before. I doubt the others have experienced it either or I would have known about it. Maybe you could get a new one under warranty? It can't be much more expensive.

Hmm, maybe he just has a ground loop and that's causing transformer hum?

Anyway, holy shiit am I were glad you said I should just check out a new amp, as the cost shouldn't be too different! I forgot that the exchange rate had changed vs. the Chinese Yuan. Now I can get a new Mk6+ for about $660USD, shipped to my door... I never realised that at all, so no more worries about trying to snag a deal on some classifieds, I can just buy from LD or an authorized dealer! Haha

Thanks for the heads up! Now if only I could find a matched quad of Tung-sol JAN CTL 5998s or WE 421a for some ridiculously low price~

 

[baronbeehive]

Hmm, maybe he just has a ground loop and that's causing transformer hum?

Anyway, holy shiit am I were glad you said I should just check out a new amp, as the cost shouldn't be too different! I forgot that the exchange rate had changed vs. the Chinese Yuan. Now I can get a new Mk6+ for about $660USD, shipped to my door... I never realised that at all, so no more worries about trying to snag a deal on some classifieds, I can just buy from LD or an authorized dealer! Haha

Thanks for the heads up! Now if only I could find a matched quad of Tung-sol JAN CTL 5998s or WE 421a for some ridiculously low price~

 
Yes you beat me to it re: the ground loop hum - see my last post!
 
But l assume you're joking about the cheap TS's/WE's, if not let me know!
 
Of course if you do get a new mkvi you might be thinking of voiding the warranty

.

 

[Maxx134]

If I bought an MK6,
The tube type is actually an ideal choice for me,
and I definitely would have spent more money to get those great tubes.

I bought the MK8 instead since I had an HD800.
I almost never heard a better tube amp for the hd800.
Using 6h30dr Supertubes was not cheaper either.

Yet now I settled on rolling tubes to a 6n6p (at higher bias) which is quite inexpensive which save me a ton money,
and actually more holographic than the expensive Supertubes I still have.

Since the MK8 is set for higher impedance cans, I needed to lower it for my choice of planar cans.
The output impedance switch mod testing solved that Problem.
Since I didn't install the switch yet,
I currently have the amp I one setting to match a 20ohm can, since my best headphone is the HEKV2.

So, my point is, I went for the more expensive amp, which turns out using cheaper tubes than MK6..

Yet if I knew what I know now, I would have choosen the MK6,
Both for my power needs with planar heaphones,
And for the magic of the output tube choice (WE tubs).

I am guessing my MK8, in its current tube choice,
is less tube sounding and definitely less powerful than MK6,
but enough juice for my HEKV2.

Yet for either MK6 & MK8 amp, I am strongly convinced on using same driver tubes.

The 6C8G tubes with adapters. ( a 6sL7 equivalent type).

Since the 6C8G have more gain (mu), I get close to the fabled ECC35 type I also have.

The 6sn7 types weren't as lively in comparison,
since they played better with higher bias.
Yet the best one was the Silvania 6sn7W.

Since the driver stage for the MK8 is almost identical, I am convinced this applies to both, regardless of the powerube stage.

On the MK8, I tried literally every 9pin driver tube possible, regardless of spec.

The best were the tall e80cc pinch, yet for all the 9pin tubes,
Literally No 9pin, not even one, could beat the best 8pin tubes.
Most probably because of this the amp design.

It was actually a great thing for me to be able to try all types of 8pin types, and I rolled so many different types.

Then one day I put in a different type with a bad adapter.
I fell asleep before I could test and left the amp on...

Long story short,
I end up waiting a dam long time over a month for a replacement Transformer,
as my driver tube "heater winding" was burned.

That put a halt to my modding ,
And left me pretty sore about Little Dot customer service.

I lost my motivation after that.
I recently got my motivation back with the tiny cute tube amp I use for headphone break in.
It all tubes:


http://www.head-fi.org/t/780178/any-opinions-reviews-on-gemtune-appj-pa1502a/260_20#post_13145720



This tiny amp is a jewel in that it is running class a triode mode,
And has Japan output transformers, and implement a modern PSU design to the tubes with Constant Current, and DC heaters.

 

[baronbeehive]

..............

Then one day I put in a different type with a bad adapter.
I fell asleep before I could test and left the amp on...

Long story short,
I end up waiting a dam long month for a replacement Transformer,
as my driver tube "heater winding" was burned.

That put a halt to my modding ,
And left me pretty sore about Little Dot customer service.

I lost my motivation after that.
I recently got my motivation back with the tiny cute tube amp I use for headphone break in.
It all tubes:


http://www.head-fi.org/t/780178/any-opinions-reviews-on-gemtune-appj-pa1502a/260_20#post_13145720

 
Hey, don't worry about falling asleep on the job, we all have our off days

.
 
I too have been kept going by my little amp and continue to be amazed by it. I first heard about it through Steve Guttenberg and it's kept me going ever since I got it when my mkvi has been offline!
 
I'm also looking forward to trying those WE's, I've got 3 atm so looking for a cheap one to complete the set. They're not matched so it's a bit or a gamble. I have yet to try my ecc35's as well.
 
It's a pity about the LD customer service. Their good reputation was a big reason I got my LD in the first place.

 

[SonicTrance]

 
Hey, don't worry about falling asleep on the job, we all have our off days

.
 
I too have been kept going by my little amp and continue to be amazed by it. I first heard about it through Steve Guttenberg and it's kept me going ever since I got it when my mkvi has been offline!
 
I'm also looking forward to trying those WE's, I've got 3 atm so looking for a cheap one to complete the set. They're not matched so it's a bit or a gamble. I have yet to try my ecc35's as well.
 
It's a pity about the LD customer service. Their good reputation was a big reason I got my LD in the first place.

http://www.ebay.com/itm/Western-Electric-421A-Tube-NOS-Dated-11-21-67-/142263860185?hash=item211f963bd9:g:1BYAAOSw44BYkNyM
 
Cheap but untested^^
 
Might be worth a shot.

 

 

[baronbeehive]

  http://www.ebay.com/itm/Western-Electric-421A-Tube-NOS-Dated-11-21-67-/142263860185?hash=item211f963bd9:g:1BYAAOSw44BYkNyM
 
Cheap but untested^^
 
Might be worth a shot.

 

 
Thanks. I'll follow it just in case.......

 

[Maxx134]

Hey guys,
I was reading about the virtual sea of caps out there , and found out a few points good to know,
So this just an update about caps.
Specifically, our cathode Electrolytic caps..

There are instances where using bipolar caps are superior to polarized.

If the amp has split supplies , bipolar
since there is no voltage to bias the cap.


varying amounts of bias distortion can change on a polarized electrolytic, causing bias distortion for polarized Electrolytic.
So it can be twice or more than the distortion of the bipolar electrolytic capacitor.

To qoute Batemen's summary:

" In every case, the bipolar capacitor produced much lower levels of distortion than measured on similar value and voltage polar capacitors."


So the bottom line is a better sounding lyctics in general using bipolar,
So better to use in areas of signal , and my choice of mundorf have also been noted better sounding than popular Elma silmic.

This was a decision taken by the original designer which, puzzled me at the time.
I did not know the reason why, at the time that the choice of a bipolar cap for cathode caps,
was a choice made for a better sounding cap.

I bet those stock blue caps were specifically chosen for the job.

 

[baronbeehive]

Hey guys,
I was reading about the virtual sea of caps out there , and found out a few points good to know,
So this just an update about caps.
Specifically, our cathode Electrolytic caps..

There are instances where using bipolar caps are superior to polarized.

If the amp has split supplies , bipolar
since there is no voltage to bias the cap.


varying amounts of bias distortion can change on a polarized electrolytic, causing bias distortion for polarized Electrolytic.
So it can be twice or more than the distortion of the bipolar electrolytic capacitor.

To qoute Batemen's summary:

" In every case, the bipolar capacitor produced much lower levels of distortion than measured on similar value and voltage polar capacitors."


So the bottom line is a better sounding lyctics in general using bipolar,
So better to use in areas of signal , and my choice of mundorf have also been noted better sounding than popular Elma silmic.

This was a decision taken by the original designer which, puzzled me at the time.
I did not know the reason why, at the time that the choice of a bipolar cap for cathode caps,
was a choice made for a better sounding cap.

I bet those stock blue caps were specifically chosen for the job.

 
Very interesting.............ever get the feeling that you're getting into the heads of  the designers?
 
Glad I didn't go for the Elna Silmics, the Mundorfs are dirt cheap as well!

 

[Maxx134]

Actually the general consensus I read Elna Silmic2 as very good sounding.

The topic of how they sound was one point,
And the distortion aspects was another.

There is also the "Audio Note" KAISEI Electrolytic Capacitors that supposed to be superior sounding and from the makers of famous "blackgate" caps.

Anyways, in our amp, that is not too critical as we added the smaller .1uf "paper in oil" paralleled caps to help out the Electrolytic.

 

[MrCurwen]

I find parallel caps create "crossover distortion". I use this effect in guitar amp builds; parallel two caps of different types and create a different sound.

I personally never use parallel caps if I can avoid it. Or electrolytics. Then again, if your design calls for a cathode bypass cap, you've got to use something.

 

[Maxx134]

I find parallel caps create "crossover distortion". I use this effect in guitar amp builds; parallel two caps of different types and create a different sound.

I personally never use parallel caps if I can avoid it. Or electrolytics. Then again, if your design calls for a cathode bypass cap, you've got to use something.

Agreed, this design takes advantage of using an electrolytic for cathode bypass in powertubes section. Pretty standard.

Distortion lowering is most probably why the original designer used a bipolar cap per cathode.

Also, fortunately the distortion scenario you describe, is not happening here,
AS I also would not recommend to parallel COUPLING CAPS, unless they are exactly the same type/brand/amount.
Even then it not a good idea, (for coupling).

Yet for most other purposes, especially across an electrolytic,
They are actually improving the Electrolytic performance with an added cap.


For this amp scenario, the cathode cap selection was briefly explained first page, and also a known practice to do for the Electrolytic.

Also, the selection of bypass using the specific PIO choice made at the specific value of.1uf for bypass on the cathode Electrolytic was not guess work.
It was a researched decision from Ridge78 with help of an old authority and author of tubes.

Also, another type of cap usage we know that helps is the decoupling cap methods,
by bypassing caps with paralleled ones at a higher order/ multiplier, not in similar range like what MrCurwen noted can happen.

There was a link which was deleted which covered this multiplier at another site.
In essence, We benifit from the smaller cap's higher set impedance curves,
so we still have the capacitive part of smaller caps its impedance curve where the larger cap would not be as effective as it get close to Inductive.
So at higher 100khz plus range it would help with any possible intermodulation distortion that could arise from this amp, being that it use NFB.

Anyways, testing this and other ideas was put on hold.

Another curious note about caps,
is that they can have same voltage and capacitance spec, yet still sound different and why we have the links to caps in first page.

I must agree that even though caps technology has gained ground with better Electrolytics like "Audio Note KAISEI" , and better "film caps" like copper foils,
In general Caps still are to be avoided in signal path if possible and why you see some expensive tube amplifiers using interstage Transformers instead of coupling caps.
Quality Transformers are fairly expensive though,
And why such advantage to use hybrids designs.

I bet MrCurwen is familiar with such designs/solutions.

There are still those that choose the old fashioned tried and true pure "less is more" way.
I really appreciate both.


As I can also appreciate the implementation of solid state to solve issues in my mini tube amp, for example.

My tiny tube amp uses SS very effectively to eliminate the PSU Transformer for a switching one.
It is a huge cost savings.

I still playing around with it to see if I can optimize the somewhat limited PSU.


It is a great conversation piece because it is so dam small a full tube amp: