[vmiguel]

I need some help, please, with tubes for a TA-26.
Reading this thread, I've already bought a RCA JAN-6AS7G as a replacement to the 6N5P.

Now, as a replacement for the 6N8P I'm looking at 6SN7 types. Am I correct?
Any advice on specific models? My budget can extend up to 60€.
TIA

 

[roderickvd]

After 60 hours of so burn-in with the Philips Heerlen E80CC's, I just swapped in my Sylvania 6189W's again. I think the E80CC's had a tad too much bloom when paired with my Amiron Home cans. Those already have quite a bit of mid-bass and together it might be a bit too much?

This is hard to A/B test of course, so let's see how it goes.

 

[hmscott]

After 60 hours of so burn-in with the Philips Heerlen E80CC's, I just swapped in my Sylvania 6189W's again. I think the E80CC's had a tad too much bloom when paired with my Amiron Home cans. Those already have quite a bit of mid-bass and together it might be a bit too much?

This is hard to A/B test of course, so let's see how it goes.

Yup, the tough part is waiting an hour+ for the swapped pair to warm up to start critiquing...

Plus it might take more hours than 60, like 200 for those "huge" cathode/grid/plates to seat/burn-off - if I didn't get "pre-burned-in" E80CC's and E180CC's along with the new pairs, I might still not have heard the "best" sound. My "new" E180CC's were in for weeks before the edge completely came off.

That is why it was so nice to have a backup amp - 2nd (A90), 3rd (FiiO M15), 4th (TA-26) options (5th/6th if I include my BTR5/BTR3k's) to enjoy while running in tubes on the TA-20 side by side in the background. It can get grating and make the ears overly sensitive or worse - desensitized - if I listen to the tubes with harsh edges all the while they are breaking in.

I had the Amiron Wireless Copper running on wired for many hours, those sounded awesome - until I had to return them due to increasingly flakey Bluetooth connections - it was sad, as I haven't been able to find another set since.

Maybe get a nice inexpensive alternative stack, and even a nice compact BTR5 original/2001 or BTR3k (PS4 compatible), might be nice to have a side system to allow running in tubes for longer periods without needing to check up on them? Or, is that what you already do? What is your "backup" system?

Do you have the product/sale link for those particular Philips Heelen E80CC's? If after 200 hours they are still too much you might need to look for other makes/production years.

For example, on the TA-26 all of my NOS 6SN7 variants are pleasant to listen to in all of my headphones/IEM's so far, except for the Russian Melz 6N8S's, they extend far too far into the treble range and with the right (wrong?) headphones/IEM's those Melz as they are now are far too "detailed" to bear - but they are breaking in too, so who knows if they also might trim their sharp edges over time.

It also varys from person to person...you might look into a solution to attenuate or filter out frequencies over a certain range of comfort for you. I've not had to look into that yet - except maybe the Melz? - so I don't have an immediate suggestion - except look for software filters / equalizer to try to cut the edge so you can enjoy your new edgy tubes while breaking in?

I need some help, please, with tubes for a TA-26.
Reading this thread, I've already bought a RCA JAN-6AS7G as a replacement to the 6N5P.

Now, as a replacement for the 6N8P I'm looking at 6SN7 types. Am I correct?
Any advice on specific models? My budget can extend up to 60€.
TIA

If you read back in this thread there are lots of comments on tubes tried in various Xduoo Amps, that should help to start...here's a couple with a 1st post with variant listings and additional info:

The Reference 6SN7 Thread
https://www.head-fi.org/threads/the-reference-6sn7-thread.117677/post-1380036

For 6AS7G tube rollers here .....
https://www.head-fi.org/threads/for-6as7g-tube-rollers-here.410326/post-5441008

There are others, but tackling those first posts + reading through those threads - and catching up on current discussions will help too.

I've made a few posts here and there about what I am using in my TA-26, you could search for my posts with TA-26 in them.

 

[roderickvd]

I had the Amiron Wireless Copper running on wired for many hours, those sounded awesome - until I had to return them due to increasingly flakey Bluetooth connections - it was sad, as I haven't been able to find another set since.

The Amiron Wireless is closed back, right? I have never heard those. My wired Amiron Home cans are open back. Should sound quite different, I image, although probably both tuned for smooth listening.

Maybe get a nice inexpensive alternative stack, and even a nice compact BTR5 original/2001 or BTR3k (PS4 compatible), might be nice to have a side system to allow running in tubes for longer periods without needing to check up on them? Or, is that what you already do? What is your "backup" system?

No, I don't have another tube system yet.

Do you have the product/sale link for those particular Philips Heelen E80CC's? If after 200 hours they are still too much you might need to look for other makes/production years.

I bought them from here. They were a single pair. Most of the letters fell off but from what there is, the photos are really good:
https://www.marktplaats.nl/v/audio-...1813963766-e80cc-philips-heerlen-matched-pair

It also varys from person to person...you might look into a solution to attenuate or filter out frequencies over a certain range of comfort for you. I've not had to look into that yet - except maybe the Melz? - so I don't have an immediate suggestion - except look for software filters / equalizer to try to cut the edge so you can enjoy your new edgy tubes while breaking in?

I guess it will just take some more time to find out whether it's burn-in or just my personal preference.

At this moment I'm really enjoying these Sylvanias! And indeed it just might be personal preference (plus that already warm tuning of the Amiron Home). Remember I have long listened to pretty high-quality solid state. So my listening neurons are all wired for transparency and speed. Not for a dry, analytical sound, though -- can't stand that. So these tubes may just be a mix of what I know with a bit of added tube softness that SS can miss.

Relevant too may be the source in the chain. Mine has long been R2R, first Soekris and now this Denafrips Ares II. Both with NOS filters (not real NOS, I know, for both of them). Such a DACs sound much warmer and liquid to my ears than the delta-sigma likes of (particularly) ESS and AKM.

I might open up the TA-20 sometime soon to measure up the caps and see if I can get into cap rolling.

 

[roderickvd]

I opened up my TA-20 today and I was surprised both ways.

First, for any of you who are thinking of doing the same, a quick how to. This unit is built *compactly* and so not the easiest to disassemble. That said, it's also not the hardest, but it requires a bit of fiddling.

First, unscrew the bottom plate and everything on the back plate. Now take the bottom plate off and unscrew everything, *except* the four screws that hold the socket raiser and the two screws that hold a strengthening mechanism on the XLR output. Finally, take out the connector between the board and the display.

When you are done, it should look like this:



You may now slightly lift the board near the volume/input knob, then wiggle a little to slide it out to the front. *Take care* to this slowly and gently, you will notice that you cannot take it out entirely because there are connectors from the top of the board (not pictured) going to the power supply section. These function like a leash and at this point you can only angle the board or you will sever those connections and have a lot of repairs on your hands.

If you want to take the board out completely, then you will need to desolder these top connections. Like I said, this unit is not made for tinkering.

Now starting with the bad news, I was dismayed to see a lot of oxidation on the bottom as well as a lot of smears. Obviously this is very poor QC and workmanship from whoever soldered the through-hole components together and forgot to remove the solder flux remains. I don't know if xDuoo will say my warranty is void for opening this unit, but they should thank me for it! The oxidation was pretty severe already and would have caused a short at some point.

Here are some pictures of this very poor performance. I used flux remover on it and it went away immediately.

Note not only the smears in the center but also the white abrasion around the joints on the right:



Abrasion again as well as some thick smears:



See the abrasion in the center? That one almost shorted the two joints!



For anyone reading this from QC, here is the board serial number:



Now for the good news. Without reverse engineering the schematic or claiming to be an expert in amplifier design, it does seem quite a bit of attention has gone into the design of this unit. Here are Nichicon FW caps, judged by their capacitance and voltage rating, used as power supply caps for the solid state section on the secondary side:

\

The FW range is "standard audio grade". We can only hope that these are genuine. Many parts sourced from China are fake. But regardless whether they are genuine or not, these caps are pretty good but there are better ones to be had. Space is limited, though. They are now 16 mm in diameter and 25 mm high. There is a little room to grow, but not much.

The black capacitors in the background must be the coupling caps. They are branded xDuoo and must be standard MKP types. They measure a little over 20x30 mm - quite small actually.. Earlier in this thread someone managed to fit standard Mundorf Map Classic's in there, that are 22x33. That really is about as far as you can go.

That the coupling caps are so close together may be pleasing to the eye but is not best for performance. The closer they are, the greater the capacitive coupling will be, and the greater the stereo crosstalk. Alas, there is no space in the unit to do something about that.

On the other end of a little transformer there are Nippon / Chemi-Con KXG's. From their specifications I assume that these are the tube section on the primary side, although the placement on the board might make you think otherwise. Again not bad:



They are specified to be 12.5 mm in diameter and 20 mm high.

Then I noticed two TDK ZJY-2P01's here. They are common mode distortion filters. Nice to see attention is paid to that:



Finally, the solid state section on the bottom consist of unbranded D882M and B772M NPN/PNP pairs. They actually look like they are MOSFETs instead of plain resistors, good stuff. They read "RZAA" and "FSAA" respectively but there's very little to be found on that. The one and only trail I could find on Google leads to the Hong Kong based MAKOSEMI, which I have never heard of before.

There are four little potentiometers above them that silently scream "do not touch" as they have probably been biased at the factory.



So in conclusion, when we temporarily forget the very poor QC and just focus on the engineering, it does look like xDuoo did not try to build this as cheap as possible, but in fact put some pretty decent components in here and there.

I will try and come up with some ideas for cap rolling. But like I said, space is tight! Any ideas?

 

[Ufanco]

I opened up my TA-20 today and I was surprised both ways.

First, for any of you who are thinking of doing the same, a quick how to. This unit is built *compactly* and so not the easiest to disassemble. That said, it's also not the hardest, but it requires a bit of fiddling.

First, unscrew the bottom plate and everything on the back plate. Now take the bottom plate off and unscrew everything, *except* the four screws that hold the socket raiser and the two screws that hold a strengthening mechanism on the XLR output. Finally, take out the connector between the board and the display.

When you are done, it should look like this:



You may now slightly lift the board near the volume/input knob, then wiggle a little to slide it out to the front. *Take care* to this slowly and gently, you will notice that you cannot take it out entirely because there are connectors from the top of the board (not pictured) going to the power supply section. These function like a leash and at this point you can only angle the board or you will sever those connections and have a lot of repairs on your hands.

If you want to take the board out completely, then you will need to desolder these top connections. Like I said, this unit is not made for tinkering.

Now starting with the bad news, I was dismayed to see a lot of oxidation on the bottom as well as a lot of smears. Obviously this is very poor QC and workmanship from whoever soldered the through-hole components together and forgot to remove the solder flux remains. I don't know if xDuoo will say my warranty is void for opening this unit, but they should thank me for it! The oxidation was pretty severe already and would have caused a short at some point.

Here are some pictures of this very poor performance. I used flux remover on it and it went away immediately.

Note not only the smears in the center but also the white abrasion around the joints on the right:



Abrasion again as well as some thick smears:



See the abrasion in the center? That one almost shorted the two joints!



For anyone reading this from QC, here is the board serial number:



Now for the good news. Without reverse engineering the schematic or claiming to be an expert in amplifier design, it does seem quite a bit of attention has gone into the design of this unit. Here are Nichicon FW caps, judged by their capacitance and voltage rating, used as power supply caps for the solid state section:

\

The FW range is "standard audio grade". We can only hope that these are genuine. Many parts sourced from China are fake. But regardless whether they are genuine or not, these caps are pretty good but there are better ones to be had. Space is limited, though. They are now 16 mm in diameter and 25 mm high. There is a little room to grow, but not much.

The black capacitors in the background must be the coupling caps. They are branded xDuoo and must be standard MKP types. They measure a little over 20x30 mm - quite small actually.. Earlier in this thread someone managed to fit standard Mundorf Map Classic's in there, that are 22x33. That really is about as far as you can go.

That the coupling caps are so close together may be pleasing to the eye but is not best for performance. The closer they are, the greater the capacitive coupling will be, and the greater the stereo crosstalk. Alas, there is no space in the unit to do something about that.

On the other end of a little transformer there are Nippon / Chemi-Con KXG's. From their specifications I assume that these are for the tube section, although the placement on the board might make you think otherwise. Again not bad:



They are specified to be 12.5 mm in diameter and 20 mm high.

Then I noticed two TDK ZJY-2P01's here. They are common mode distortion filters. Nice to see attention is paid to that:



Finally, the solid state section on the bottom consist of unbranded D882M and B772M NPN/PNP pairs. They actually look like they are MOSFETs instead of plain resistors, good stuff. They read "RZAA" and "FSAA" respectively but there's very little to be found on that. The one and only trail I could find on Google leads to the Hong Kong based MAKOSEMI, which I have never heard of before.

There are four little potentiometers above them that silently scream "do not touch" as they have probably been biased at the factory.



So in conclusion, when we temporarily forget the very poor QC and just focus on the engineering, it does look like xDuoo did not try to build this as cheap as possible, but in fact put some pretty decent components in here and there.

I will try and come up with some ideas for cap rolling. But like I said, space is tight! Any ideas?

It‘s a shame thats you need to unsolder it to gain access to clean off the solder flux remains. Going just hope the QC was better with mine. Still it was interesting to see inside the TA20 thanks for the pictures along with the detailed description.

 

[roderickvd]

Not sure if I got that across correctly: you can open it and remove most of the flux without desoldering. It’s just that when you want to get the board out completely, say to get on a workbench, then you need to desolder. Otherwise you can but the enclosure upright with the board angled out. Just be sure the enclosure doesn’t tip over because that would surely break something.

 

[hmscott]

Althought "messy" / "crunchy" flux seems like something to clean up, it actually doesn't do anything "bad" sitting there.

When I did electronics assembly/rework over a period of 8 years, I went from "must clean up", to "heck it don't matter", and various places in between as the customer requirements varied.

There are some specifications that require completely clean boards/connections - we used to have "baths" to hose down the boards after rework with 1-1-1 Methyl-Ethyl-Ketone, but that is usually reserved for conformal coating - the board solder side is coated, and in some situations the whole board is "dipped". Adherance of the material to the board and components requires the cleaning, flux instability would destabilize the coatings. There are other situations where a clean board is required for post inspection QA, during QA they often want to see the rework flagged / tagged - whether to clean before/after is up to their request.

Another consideration is "weight" on builds you want to remove all of the extraneous materials from the build that you can. Short wires, tight lead clipping without solder encrochment, and removing unnecessary debris - like thick flux and by-products.

I'd leave the flux on unless the solder connection integrity was in question.

Early on when I was deciding on what to purchase, I found a couple of video's on youtube where the guy was intent on finding upgrade components in all of his equipment, and a TA-20 or similar was discected and capacitors were selected to fit - and he found some nice ones - but after they were replaced he didn't find any difference in the audio, which I thought was a bit odd given the quality and quantity of parts replaced. He never came back with another video, and now I cannot find them on youtube. But, there is a lot of "Audio capacitor" discussion and speculations.

BTW, a well known "fix" when hearing noise in the TA-20 is tightening up the green yellow stripe ground wire - that thick green wire you can see connected under the bottom plate. A few have mentioned improving noise by tightening the ground connection.

If you do find replacement capacitors or other components that improve the sound I'd love to hear about them. So far everyone I've heard from on this subject thinks there isn't enough room in the case of the TA-20, and outboard caps could be a solution... perhaps building a new larger capacity case would be needed to get the best capacitors sized for the task?

You've probably already found these, but here are some mentions of capacitor for the TA-20 / TA-26
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16727359 - values mentioned
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16524266 - mention of outboard caps for TA-26
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16524655 - response showing TA-26 internals photo's and the tight fit for upgrades

I don't see too many mentions here, I had to look elsewhere to find mentions of TA-20 component upgrades, and I haven't really looked for TA-26 component upgrades.

@PetFju - how have your component upgrades gone? Have you had any additional changes? How has the sound changed as the caps aged?
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16735640
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16735863

How about you @Wiljen and @AudioCats - did you do any upgrades to components in/outboard of your TA-26's?
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16524655

 

[roderickvd]

Althought "messy" / "crunchy" flux seems like something to clean up, it actually doesn't do anything "bad" sitting there.

When I did electronics assembly/rework over a period of 8 years, I went from "must clean up", to "heck it don't matter", and various places in between as the customer requirements varied.

There are some specifications that require completely clean boards/connections - we used to have "baths" to hose down the boards after rework with 1-1-1 Methyl-Ethyl-Ketone, but that is usually reserved for conformal coating - the board solder side is coated, and in some situations the whole board is "dipped". Adherance of the material to the board and components requires the cleaning, flux instability would destabilize the coatings. There are other situations where a clean board is required for post inspection QA, during QA they often want to see the rework flagged / tagged - whether to clean before/after is up to their request.

Another consideration is "weight" on builds you want to remove all of the extraneous materials from the build that you can. Short wires, tight lead clipping without solder encrochment, and removing unnecessary debris - like thick flux and by-products.

I'd leave the flux on unless the solder connection integrity was in question.

Nice to hear that you've actually been in this industry. I'm not directly, but now one or two things -- probably not as much as you.

It wasn't just the crunchy, salty bits on the PCB. I'm not sure if you could make it out on video but there was even one "bath" (now solidified) or excess flux.

Now I know that not all flux is bad, particularly nowadays with that RoHS flux that is supposedly "no clean". But those "no clean" properties depend entirely on the right application - in the right amount with the right temperature. That doesn't have seem to happened here.

Even the RoHS "no clean" flux is acidic and hygroscopic in nature. Meaning that over time, it can act as either an insulator but also as a conductor, depending on humidity.

All in all not something I want to see on my boards in these gobs!

Early on when I was deciding on what to purchase, I found a couple of video's on youtube where the guy was intent on finding upgrade components in all of his equipment, and a TA-20 or similar was discected and capacitors were selected to fit - and he found some nice ones - but after they were replaced he didn't find any difference in the audio, which I thought was a bit odd given the quality and quantity of parts replaced. He never came back with another video, and now I cannot find them on youtube. But, there is a lot of "Audio capacitor" discussion and speculations.

I can imagine. To have an audible improvement you would want to replace the parts with ones of much higher quality. But such parts are also much larger. So, within the confines of what you have, you can only step up a notch. For example, from the Nichon FW you could upgrade to the KW series in the same form factor. It'll be a bit better but don't expect miracles. And certainly subject to many hours of burn-in at which point your brain has tilted expectancy too...

BTW, a well known "fix" when hearing noise in the TA-20 is tightening up the green yellow stripe ground wire - that thick green wire you can see connected under the bottom plate. A few have mentioned improving noise by tightening the ground connection.

I have zero noise issues. Never had with any piece of kit by the way, except the surrounds of my Harman Kardon Citation system. And those are ungrounded so probably just have a really cheap PSU and poor wiring layout.

The ground wire in my TA-20 was already nicely tucked in to the very far end of the case, as to minimise any interference with PCB paths and components.

I should add that I run my setup fully balanced, so grounding problems are not to be expected. But all my previous single-ended gear I also have had zero grounding issues.

If you do find replacement capacitors or other components that improve the sound I'd love to hear about them. So far everyone I've heard from on this subject thinks there isn't enough room in the case of the TA-20, and outboard caps could be a solution... perhaps building a new larger capacity case would be needed to get the best capacitors sized for the task?

I smile at outboard caps because not only do I usually find that pretty ugly, also there is physics at work. The area between the leads of the capacitor acts as an inductive field. The further away the caps, the longer the leads, and the greater the inductivity -- all of which hampering sound quality instead of improving it. So I will definitely stay within the dimensions of the unit.

@PetFju - how have your component upgrades gone? Have you had any additional changes? How has the sound changed as the caps aged?
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16735640
https://www.head-fi.org/threads/xduoo-amplifiers.682282/post-16735863

Thanks for summing those up. I would expect @PetFju's cap change to not be groundbreaking. Probably the xDuoo branded MKP's that are in there are in more or less the same league as the basic Mundorf MCap Classics. It really is a pity that there isn't more room to work with here, because other coupling capacitors would probably be the greatest return on investment.

As for the other caps, I still think its fun to spend some time and money at. I'm evaluating options that might fit including the popular ones from Nichicon and Panasonic.

One thing I wonder is why xDuoo chose to put Nichicon audio caps in there. Those are caps made for in the signal path. Would it in a power supply section be more appropriate to use ones intended for that purpose, like the Panasonic F-series?

 

[Ufanco]

Spent the weekend tube rolling and for my setup the 12BH7a are right up there with the 13D5a and possible better it’s kinda a tossup and both out perform the other 12UA7 and even the Amperex ECC82 I have.
The only thing with using 12BH7a is the higher heat so using a 40mm computer fan to bring the heat level down.
I have a pair of CBS 12BH7a coming today there suppose to be nos so going have to let them burn in. Thinking of selling some of the 12ua7 and buying another pair of the sylvania 12BH7a curved black plate. Other thoughts are the rca 12BH7.

 

[roderickvd]

Some more TA-20 teardown.

I forgot to mention two posts ago, but when you look carefully in the picture with the Nichicon's, you can see a Zener diode in the top right. There are two of them there, probably used as voltage reference. I believe that depending on the diode used, this can garner quite a stable voltage. Having two diodes does seem to me that the regulation is non-tracking, i.e. the positive and negative rail each have their own voltage reference. This is usually the case I believe. The only design I know of that does rail tracking is the AMB σ22 DIY PSU. Principally it should not matter if voltages differ a bit, but what you want ideally is that any variances are mirrored. With two Zeners, you don't have that mirroring, and so the rails are not guaranteed to work in unison.

The markings on the two opamps in the center are hard to read but are 2604's. I'm not sure which brand. The full marking reads "BB OPA 2604AU B58JC". Any of those B's could be 8's or vice versa. There seem to be two more opamps at the top in the middle, but those markings are almost completely vanished.



Couple of more capacitors here. These seem to be four 10µF 35V Elna SILMIC II's. These are input caps I guess to block any DC? These Elna's are quite good but I know of even better ones: no input caps at all! I have no sources with DC offset nor have I had ever. I'm new to tubes -- is there anything particular about tube amps that require this capacitance? If not, my experience has shown that removing input caps really improves sound stage.



This picture from the top of the Nichicon's show there is a teeny bit of room to grow. The current ones are 16 mm in diameter. I suspect the outer circle is 18 mm.
You can also see the tiniest bit of space left around the MKP output caps, which I more accurately measured as 22x32 mm.



The Nippon Chemi-Cons really have no space for something larger in diameter:



Again note the two Zeners in that picture, in the corner of the two lower caps.

Now for the room you have in between the PCB and the enclosure, that's just about 39 mm.



Note that this is for the back part of the unit. The front is shorter in height, about 29 mm. It's hard to say exactly where this drop in height starts. From what I could see, the Nichicon's are about where the higher ceiling starts.



So there you have it. I tried opening the transformer where I am pretty sure a switching mode power supply resides. But for that I would have to remove the array of RCA inputs which are hot-glued to the top, and now cover two screws to gain access. I didn't feel like undoing that glue so that's where I stopped.

By the way, if it indeed is a SMPS powering this unit as I believe it is, then again there are better caps specifically for SMPS applications than the Nichicons, which are intended for in the signal path.

So brewing on the list:
- replacing the Nichicons for ones on SMPS duty
- bypassing the input caps (any reason not to specific to tube amps?)

And maybe have a look at the Chemi-Cons. Not much wrong with them probably, but who knows.

 

[roderickvd]

Sorry for keeping posting my train of thought.

I've narrowed down the cap choices to this:

Nichicon FW -> Panasonic FR. Low ESR (0,080 -> 0,056) and almost double the higher ripple current (1950 -> 3820). That should work well for SMPS usage. All this in the same 16x25 mm package! My only worry is that the SMPS may become unstable with too low of an ESR, if it was engineered for a specific higher ESR and without proper phase compensation.

Chemi-Con KXG -> Panasonic EE. Only slightly higher (12.5x20 -> 12.5x25) but again with much higher ripple current (390 -> 1290) and lower ESR (0,08 -> 0,06). This one may need a bit of looking around, as it seems to be sold out on the major outlets.

 

[hmscott]

The markings on the two opamps in the center are hard to read but are 2604's. I'm not sure which brand. The full marking reads "BB OPA 2604AU B58JC". Any of those B's could be 8's or vice versa. There seem to be two more opamps at the top in the middle, but those markings are almost completely vanished.

Xduoo's responses to my questions about swapping opamps in the Xduoo TA-20:
https://www.head-fi.org/threads/the-opamp-thread.432749/post-16699436

I've narrowed down the cap choices to this:

Nichicon FW -> Panasonic FR. Low ESR (0,080 -> 0,056) and almost double the higher ripple current (1950 -> 3820). That should work well for SMPS usage. All this in the same 16x25 mm package! My only worry is that the SMPS may become unstable with too low of an ESR, if it was engineered for a specific higher ESR and without proper phase compensation.

Chemi-Con KXG -> Panasonic EE. Only slightly higher (12.5x20 -> 12.5x25) but again with much higher ripple current (390 -> 1290) and lower ESR (0,08 -> 0,06). This one may need a bit of looking around, as it seems to be sold out on the major outlets.

The question is, of course, is what would be the effect of changing those power supply caps on the sound of the audio?

As far as removing coupling caps on tubes, it has been done in the design stage, IDT it would be successful only removing the caps - there are other considerations and I recalled reading this thread a while back on DIYaudio when searching for tube info - a great site:

A Tube amp without coupling capacitors? Possible?
https://www.diyaudio.com/community/threads/a-tube-amp-without-coupling-capacitors-possible.341298/

I wish I had the equipment together to participate in a build myself - like a couple of extra TA-20's to experiment on so I could still listen with a functional TA-20 while the other two are pulled apart, but perhaps some other time.

Have fun

 

[roderickvd]

The question is, of course, is what would be the effect of changing those power supply caps on the sound of the audio?

Little, probably. On the primary side in particular. On the secondary side though, there is a chance of a small improvement. Those Nichicons are not made to be driven by an SMPS and I’m this case have a 64% higher resistance than the Panasonics. Guess we’ll only know by trying

As far as removing coupling caps on tubes, it has been done in the design stage, IDT it would be successful only removing the caps - there are other considerations and I recalled reading this thread a while back on DIYaudio when searching for tube info - a great site:

A Tube amp without coupling capacitors? Possible?
https://www.diyaudio.com/community/threads/a-tube-amp-without-coupling-capacitors-possible.341298/

I know that thread and basically it very much depends on the amp design, whether there is negative feedback or not, also the discussion is a mix of discussion on output, input and interstage coupling caps.

Principally most OEMs put input caps as an absolute precautionary measure, protecting speakers and cans from damage when DC would be on the input. In my experience this is rarely if ever the case and so it’s a protection that can be removed. Hypex for example had input caps on their UcD models (and bypassing them was a popular mod) but did away with them on the NCores.

It’s an easy mod to try and should really up the sound quality if the amp is OK with it, or would otherwise lead to very bad distortion or worst case arcing in the tubes. So I’ll try with the stock tubes and a cheap pair of earbuds

I also ordered some Vishay MKP1837’s 0.01uF to bypass the output caps with. Pretty sure I’ll be able to squeeze them in, and should be a worthwhile upgrade!

 

[roderickvd]

An input bypass mod for the TA-20 is born!



Warning: this mod makes the amp DC coupled. Be sure that you do not have DC on the inputs. That usually is the case. But if, just if, there is DC on the inputs now or ever during an output failure of the source, then you can damage your headphones permanently. Obviously this mod is completely at your own risk.

In the picture above I just soldered four jumper leads on the bottom of the board, where the small, gold-and-black colored Elna capacitors are soldered through. On the top of the board these are marked as C122, C123, C124 and C125. You could also cut those capacitors and tie their leads together. That might be easier, but obviously irreversible. Soldering jumpers is a bit more fiddly but allows you to undo the mod when you want. It also has the advantage that you don’t need to remove the board from the chassis, just remove the bottom plate.

To my ears, this mod gives an immediate and significant improvement in clarity, lower end and three dimensionality. Loving this!