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Aiyima TPA3251 Modification Build Thread !
Aiyima TPA3251 Modification Build Thread !
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Old 22nd November 2020, 08:40 AM   #141
ClaudeG is offline ClaudeG
diyAudio Member
 
Join Date: Jan 2015
So we kept going on our experiments, bypassing the last caps we had to in hope to improve further the signal. We thought in particular of the +12V analogue feed to the TI chip, as that is likely to impact sound (first internal amplification stage amongst other things).

The last caps we had to try were the three 470uF caps, note already bypassed with 2.2uF X7R. Would an additional 0.1uF C0G bring something?

We tried each cap one by one and TBH the sonic differences were nil or near 0. None of these caps responded really to this additional bypass.

So our remaining bypass caps went in the end back were they last brought some sonic benefits, at the legs of the big PS caps.

Another bit that brought no change was to add up solder at the terminals to make a more direct connection, were the tiny wires stand. Yes, it doesn't look great the way it is done at factory, yes, it seems it made a difference at least in Rich's case and I have no reason to doubt him. But on our amps, perhaps because the production process was better or we were just lucky, it made no difference. Of course it is still worthwhile checking, your amp might be different, and perhaps desoldering everything, possibly swapping the tiny cable, and resoldering everything properly might improve something. Perhaps... we leave that to others :-)

As of us, we feel we did all what we could resonably do during the lockdown, avoiding desoldering and dremeling, so merely adding things. We came to the point were difference are too subtle to our ears, kind of diminishing returns in our POV, so unless someone comes with a brillant idea we are done in that area. Xell, nearly, there are still these Wimas I would like to try as OPA PS bypass when I have the units on hand again.

The tweaks amps sound really great, and we are yet not done with the heavy mods!

Enjoy music

Claude... and Gilles
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Old 22nd November 2020, 08:50 AM   #142
ClaudeG is offline ClaudeG
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Join Date: Jan 2015
So, what are the heavy mods requiring my tools (mostly) and my skills (unlikely now given Gilles skill development with this fun project)?

Well, I have on my TODO list:
1- Remove the existing volume pot
2- Replace the signal output filter, that is 4 output coils and 4 output caps with dedicated ones
3- Replace the PS caps with better ones for Class D, same capacity value
4- Try increasing the PS caps capacity by adding some external caps
5- Try an additional Wima bypass on the OPA PS

I will also keep an eye on Mark's 6A SMPS filter to come... this should be better than the one I designed.

So... when are we permitted to meet again to do all that?

Enjoy music

Claude
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Old 22nd November 2020, 09:07 AM   #143
ClaudeG is offline ClaudeG
diyAudio Member
 
Join Date: Jan 2015
Following what we did, for those not confident with the soldering iron, not wanting to desolder anything, just playing with thin add-ons easy to do and undo, and keeping the casing, safety, functions etc.

These are the amp mods one could do...Total mod material cost is at Mouser's 19E WITH TAX... Meaning the cost of a modded Aiyima with its PS is less than 85E!

The bypass caps used are all tiny Murata that all fit underboard and can be soldered either way (no polarity), either 10uF/25V or 2.2uF/50V "X7R type", or Murata 0.1uF/50V "C0G type". Links at Mouser below:

https://www.mouser.fr/ProductDetail/Murata-Electronics/RCER71E106K3A2H03B?qs=Zt%252BKPUOg4ofsQVPTPVDJLw%3 D%3D

RCE5C1H823J2A2H03B Murata Electronics | Mouser France

RCER71H225K2A2H03B Murata Electronics | Mouser France

The recommended Op amp to fit is TI's excellent dual OPA1656:
https://www.mouser.fr/ProductDetail/...52BbIcnQ%3D%3D

For the OPA PS bypass we also used Elna Silmic II
https://www.mouser.fr/ProductDetail/...BgiKy0fOOcuQ==

Last but not least, you could for similar cost also use Wima MKP10 for the PS OPA bypasses instead of the recommended C0G caps.

The easy mods are the following:

1) Resolder properly the output wiring to LS terminals
=> Cost 0, gain probably 0, depends on your unit

2) Replace the 2 removable OP amps with 2 x OPA1656 (these have to be soldered on adapters by you or any decent student)
=> Op amp cost 5.5E, gain +5

3) Big PS caps bypass, with each 2x 2,2uF and 1x 0.1uF (so 6 in total)
=> Cost 4E, gain +2.8

4) Bypass all 9 electrolytic caps around the op amps with 0.1uF
=> Cost 3.8E, gain +2
NOTE: bypassing the middle one only gives already +1

5) Bypass the three 470uF caps with each one 2.2uF cap, and the 100uF and 22uF ones with each one 0.1uF cap
=> Cost 3.4E, gain +1... you to decide if worth doing "while at it"...

6) Op amp PS, bypass each of the 2 op amp PS with 10uF Elna Silmic II + 10uF X7R + 0.1uF
=> 3.6E, gain +4

You then end up with a sonic upgrade that is 3 times the step the widely acclaimed and massively perceived sonic step OPA1656 represents => Say a modded unit that works significantly better for 19E material cost.

I hope this is of interest

Claude
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Old 22nd November 2020, 09:14 AM   #144
ClaudeG is offline ClaudeG
diyAudio Member
 
Join Date: Jan 2015
Some of you asked us "what are the most cost efficient easy to do mods"?

Based on the above post, for the "very leazy, very greedy, ungifted with a soldering iron starving student", the mods you could consider are:

1) Resolder properly the output wiring to LS terminals
=> Cost 0, gain probably 0 - depends on your unit but worth checking it is OK

2) Replace the 2 removable OP amps with 2 x OPA1656 (these have to be soldered on adapters by you or any decent student)
=> Op amp cost 5.5E, gain +5

3) Big PS caps bypass, with each 2x 2,2uF and 1x 0.1uF (so 6 in total)
=> Cost 4E, gain +2.8

4) Bypass the electrolytic caps "in the middle of the row of 5 under the the op amps" with 0.1uF
=> Cost 0.3E, gain +1

5) Op amp PS, bypass each of the 2 op amp PS with 10uF Elna Silmic II + 10uF X7R + 0.1uF
=> 3.6E, gain +4

This is the bare minimum, no reason not to give it a try... and a few hours and Euros later you have a significantly better amp.

Enjoy music

Claude
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Old 22nd November 2020, 09:37 AM   #145
ClaudeG is offline ClaudeG
diyAudio Member
 
Join Date: Jan 2015
Last one for the road, as we are unlikely to post soon again here.

This is mainly for our host Rob, as he has been very kind letting us posting so widely here...

We have not carried out the following mod, as we don't need to: we went for an external volume pot to control in one go both amps. However, should I want a cheap mod to replace the existing (presumably very avreage) volume pot, I would consider the following:

DACT Type SMD Steeped Attenuateur 21 etape Controle du volume10/20/50/100/250K | eBay

For less than 10$ you are likely to end up with a pot that is very small and possibly as good as an Alps Blue. Not the best performer, doing though a reasonably good job, but again space is an issue and quite good VFM... Cost is low to give it a try, I would chose the 20k value. Note it is a stepped attenuator, so only 21 volume positions, not continuous. If you want continuous, look at the small Alps series, likely to fit straight on the pot board.

Will this stepped attenuator fit? You to decide! Gilles went the trouble to measure everything so you can make you own mind.

IMHO it will require fiddling to get the damned volume board out and then some more fiddling to make this pot fit. You are likely to need to drill to offset the shaft hole upwards, and you may want to purchase a bigger volume knob to mask the offset estheticaly.

My guess is you would need to fit the pot in such a way that the connectors are upside, right or left, so it fits in. Not an issue: makes soldering even easier and don't forget once the volume knob is in place you can fit it such a way no one can see the rotation you went for.

Anyway, this is what we can give you to get started: guys let us know how you do it!

Claude... and Gilles
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Last edited by ClaudeG; 22nd November 2020 at 09:47 AM.
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Old 28th November 2020, 09:33 AM   #146
daniboun is offline daniboun  France
diyAudio Member
 
Join Date: Nov 2019
Location: Lyon (France)
Another good candidate for mod :
TPA325A with SMPS PSU

Click the image to open in full size.
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