Hi,
This thread is about 04 and not 07, so can't comment on 07 really.
Regarding 04, you may want to read all the pages of this thread as the sound part of the schematic has been discussed (initial version and then what Aiyima changed) and all proposed mods have even better than that: location of the parts to tweak with pix to make sure you don't get it wrong.
This thread also includes several mods that are each rated re sonic value vs price and later even classified in 2 packs so to speak, proposing on one side all the heavy mods we did, on the other a lighter version with what we considered the main mods, so you get most of the benefits without build hassle /risk and of course the best value. On my side I did 2 amps with the full mods, and one with the light pack, but numerous others did also or whatever variations.
Last but not least, in Gilles case, 2 of these amps with 2 dedicated SMPS plus filters have all been built into a old big amp case with all appropriate connections and wires, outboard volme control, making one big bi-amp amplifier with proper external connections and vintage look. OK, the O4 small cases have been retained in that case, not a must but very convenient, and TBH I see little point in changing that as bigger heatsink etc. are not likely to be that profitable, but then who knows...
Don't ask me what posts to look for, you really have to go through this thread (perhaps use my name in the advanced search funtion to be more efficient), but if you own a 07 then there are other threads dedicated to that amp - there are some similarities with 04 but also some majour differences between these units apparently.
Have fun
Claude
This thread is about 04 and not 07, so can't comment on 07 really.
Regarding 04, you may want to read all the pages of this thread as the sound part of the schematic has been discussed (initial version and then what Aiyima changed) and all proposed mods have even better than that: location of the parts to tweak with pix to make sure you don't get it wrong.
This thread also includes several mods that are each rated re sonic value vs price and later even classified in 2 packs so to speak, proposing on one side all the heavy mods we did, on the other a lighter version with what we considered the main mods, so you get most of the benefits without build hassle /risk and of course the best value. On my side I did 2 amps with the full mods, and one with the light pack, but numerous others did also or whatever variations.
Last but not least, in Gilles case, 2 of these amps with 2 dedicated SMPS plus filters have all been built into a old big amp case with all appropriate connections and wires, outboard volme control, making one big bi-amp amplifier with proper external connections and vintage look. OK, the O4 small cases have been retained in that case, not a must but very convenient, and TBH I see little point in changing that as bigger heatsink etc. are not likely to be that profitable, but then who knows...
Don't ask me what posts to look for, you really have to go through this thread (perhaps use my name in the advanced search funtion to be more efficient), but if you own a 07 then there are other threads dedicated to that amp - there are some similarities with 04 but also some majour differences between these units apparently.
Have fun
Claude
To Claude,
In keeping with the main topic, Aiyima themselves re-released the A04 a month or two ago.
At its heart is still the TPA3251 but it seems the surrounding circuitry has been revamped significantly.
From what I've heard, improvements have been made to op-amps' power supply section (there're 4 op-amps now), and as usual the amp lends itself well to op-amp upgrades (OPA1612 and OPA1656). Prices aren't too bad either (around 40$-ish from AliExpress), 32V PSU included.
I'm curious if you want to take a look at this updated A04, assuming you still have any interest in Class D amps.
Have a great day,
K.
In keeping with the main topic, Aiyima themselves re-released the A04 a month or two ago.
At its heart is still the TPA3251 but it seems the surrounding circuitry has been revamped significantly.
From what I've heard, improvements have been made to op-amps' power supply section (there're 4 op-amps now), and as usual the amp lends itself well to op-amp upgrades (OPA1612 and OPA1656). Prices aren't too bad either (around 40$-ish from AliExpress), 32V PSU included.
I'm curious if you want to take a look at this updated A04, assuming you still have any interest in Class D amps.
Have a great day,
K.
TBH, I have never been "in ClassD", only did this to have a look at it, for a friend mainly.
Didn't regret though. I am yet not completely done as I have a crazy project re op amp rolling, but that will have to wait and I will post in due time.
Following your post it would be indeed interesting to have schematics or pix of the latest 04 then. BUT TBH I can see tone controls on the front, so probably a very different animal and that could also explain the extra op amps. Perhaps a less puristic approach also?
Whatever, it would be nice if someone could tell if the new 04, as it comes, sounds as good as the old 04... that got this thread started, a good VFM amp, a lucky draw into a big chinese field.
Enjoy music
Claude
Didn't regret though. I am yet not completely done as I have a crazy project re op amp rolling, but that will have to wait and I will post in due time.
Following your post it would be indeed interesting to have schematics or pix of the latest 04 then. BUT TBH I can see tone controls on the front, so probably a very different animal and that could also explain the extra op amps. Perhaps a less puristic approach also?
Whatever, it would be nice if someone could tell if the new 04, as it comes, sounds as good as the old 04... that got this thread started, a good VFM amp, a lucky draw into a big chinese field.
Enjoy music
Claude
Hello all ! I have an old CD player. It has a linear output of about 2 volts. In the topic I found message No. 637 on page 32. It talks about the input of amplifier A04 and four resistors limiting the input voltage. The board of my A04 is an old modification. I would like to add these resistors for the >2V input. It would also help me with my speakers since they are designed for 15-20 watts (4om) and the real power that the A04 has is simply excessive for them. Does anyone know the meaning of these resistors and their size.....? That would be very cool 
. (sorry for my English - google translate)
. (sorry for my English - google translate)If you feel the power is excessive why don't you simply turn the volume down on the 04?
The volume pot is an attenuator at amp entry and simply reduces the (maximum BTW) 2V from your CD player. The volume pot is a variable resistor (well, "network", but lets keep it simple) already... Nothing to be done here IMHO...
Good luck either way
Claude
The volume pot is an attenuator at amp entry and simply reduces the (maximum BTW) 2V from your CD player. The volume pot is a variable resistor (well, "network", but lets keep it simple) already... Nothing to be done here IMHO...
Good luck either way
Claude
Yes you are right. But I wanted to go the “difficult” way
.Two problems:
1.I think that some songs from the CD player have too strong a signal, and distortion appears in the A04.
2.Now the volume control limit is small. (from minimum to maximum). I usually listen at low volume.
Amplifier power supply 24 volts.
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Stick a dual gang potentiometer in the RCA cable between the CD player and the A04. Output of the CD player to one end and the other of the pot, input to the A04 to the wiper and whichever end is the shield of the RCA cable. Set it and forget it, adjust your desired max volume and leave it alone after that.Hello all ! I have an old CD player. It has a linear output of about 2 volts. In the topic I found message No. 637 on page 32. It talks about the input of amplifier A04 and four resistors limiting the input voltage. The board of my A04 is an old modification. I would like to add these resistors for the >2V input. It would also help me with my speakers since they are designed for 15-20 watts (4om) and the real power that the A04 has is simply excessive for them. Does anyone know the meaning of these resistors and their size.....? That would be very cool
to: jeff5may
Yes, first I made a simple attenuator with two resistors per channel. And the distortion ended, but the “magic” in the sound disappeared. The attenuator was connected from the A04 side. I remembered about this forum....read it....and decided to reduce the input sensitivity as in the “new” version of A04. Unfortunately, I don’t have the A04 circuit......maybe these resistors (which are in the new version) are the same attenuator.
Yes, first I made a simple attenuator with two resistors per channel. And the distortion ended, but the “magic” in the sound disappeared. The attenuator was connected from the A04 side. I remembered about this forum....read it....and decided to reduce the input sensitivity as in the “new” version of A04. Unfortunately, I don’t have the A04 circuit......maybe these resistors (which are in the new version) are the same attenuator
.
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The 04 amps have a very basic pot
It might sound OKish at higher volumes to novice ears and it dees indeed a reasonable job.... there.
As all cheap pots it does a more miserable job at high attenuation / low volules settings, for various design reasons. Read below 9 O'Clock usualy.
IF, and that's a big IF, the maggic disapears at low pot positions, then MAYBE another pot could bring some benefits. Or rather another way to attenuate without loss and distorsions. Tons of materials on this, starting with step attenuators ages ago.
PERHAPS (???) and please note the big question marks, that could resolve your issue. Resolving it playing blindly with resistor networks / attenuators in line with the existing pots and guessing resulting impedances mismatches, or trying to alter the gain structure whereas it is not the real problem (but indeed somewhere contributes to it) is IMHO, and that's just me please!, a waste of time.
I mean that assuming the gain structure isn't completely off, and with 2V to start with and an usual power amp with 2 relativelay low gain summed stages it isn't likely to be a majour problem unless something else is off - or you have 100db/m/W high end horn LS but then that amp isn't for you anyway LOL.
All Just IMHO
Claude (last line of mine on this as not realy general tweaking related and rather very specific, so who am I to comment someone elese's perception and system... )
It might sound OKish at higher volumes to novice ears and it dees indeed a reasonable job.... there.
As all cheap pots it does a more miserable job at high attenuation / low volules settings, for various design reasons. Read below 9 O'Clock usualy.
IF, and that's a big IF, the maggic disapears at low pot positions, then MAYBE another pot could bring some benefits. Or rather another way to attenuate without loss and distorsions. Tons of materials on this, starting with step attenuators ages ago.
PERHAPS (???) and please note the big question marks, that could resolve your issue. Resolving it playing blindly with resistor networks / attenuators in line with the existing pots and guessing resulting impedances mismatches, or trying to alter the gain structure whereas it is not the real problem (but indeed somewhere contributes to it) is IMHO, and that's just me please!, a waste of time.
I mean that assuming the gain structure isn't completely off, and with 2V to start with and an usual power amp with 2 relativelay low gain summed stages it isn't likely to be a majour problem unless something else is off - or you have 100db/m/W high end horn LS but then that amp isn't for you anyway LOL.
All Just IMHO
Claude (last line of mine on this as not realy general tweaking related and rather very specific, so who am I to comment someone elese's perception and system... )
Hi,
IME the std inductors are a pain to remove while moving up to top parts yeld only a very little sonic benefit.
Maybe it can get greater if you do use a lot of power and get more saturation from the std part, who knows...
Really not the priority IMHO on that unit, enjoy it with other tweaks
Claude
IME the std inductors are a pain to remove while moving up to top parts yeld only a very little sonic benefit.
Maybe it can get greater if you do use a lot of power and get more saturation from the std part, who knows...
Really not the priority IMHO on that unit, enjoy it with other tweaks
Claude
I didn't read all previous pages, but I think no one mentioned a really crucial point with the 04. The opamps are originally fed with an 78M12 voltage stab IC, where the supply voltage (12V) is then halved by a divider, so the IC is actually fed with +/- 6V DC supply voltage.
Most opamps perform miserably with such low voltages, so I hooked an LM317LZ at the input of the M12 to feed the Opamps with a somewhat higher voltage. In my case it is set to 22V (incoming supply voltage for the amp is 28 V) This way the Opamps "see" a +/- 11V supply voltage.
Be aware that the TPA 3251 must be fed with 12V (not higher!) at pin 1, 2, and 22, so preserve the PCB rail from the output os 78M12 to the 3251, but cut the foil leading to the Opamps supply pins and the divider, and hook it up to the output of the 317LZ so the Opamps recieve the elevated voltage. Big improvement, instantly audible increase in dynamics and lower distortion. The Vref filter cap (for the divider) must also be replaced with a higher voltage type.
Most opamps perform miserably with such low voltages, so I hooked an LM317LZ at the input of the M12 to feed the Opamps with a somewhat higher voltage. In my case it is set to 22V (incoming supply voltage for the amp is 28 V) This way the Opamps "see" a +/- 11V supply voltage.
Be aware that the TPA 3251 must be fed with 12V (not higher!) at pin 1, 2, and 22, so preserve the PCB rail from the output os 78M12 to the 3251, but cut the foil leading to the Opamps supply pins and the divider, and hook it up to the output of the 317LZ so the Opamps recieve the elevated voltage. Big improvement, instantly audible increase in dynamics and lower distortion. The Vref filter cap (for the divider) must also be replaced with a higher voltage type.
Thanks for your input
Well, as you said, "you didn't read all the pages", and the OPA PS "with VMID " or "a floating 6V"... has been already mentioned... a couple of years back.
And "OPA PS" addressed in another way.
But then all paths lead to Rome and yours is a worthwhile addition I guess - I haven't tried it. So thanks for posting as that is a new path not tried yet, although perhaps not as easy for beginners. I do understand fully what you are doing, but based on past experience some might not - and as I don't even own such a unit anymore so I suggest you post schematic and full details of your mods so people willing to follow you can proceed easily.
Please note that actually some op amps do perform better re distorsions with a somewhat lower rail voltage, but that's an entirely different topic altogether... and I am anyway entirely with you that in that specific 04 case the voltage is indeed rather on the low side and the rail supply with VMID NOT what I would have designed for my own units indeed LOL.
Once the numerous additional PS caps are in place I felt we got the PS much better and a satisfying end result altogether.. but then I haven't indeed tried your mod so who I am to tell.? And there is improvement margin in the bass altogether for the entire final unit, but then this is just a Chinese 70E beast LOL
Please post all your mods and pix so someone can evaluate if worthwhile going for it on top of the usual mods we tried already. It is IMHO a matter of an "all"
There is more in this unit then this single PS point, but for that I am afraid you might have to read the entire thread if you haven't LOL
Claude
Well, as you said, "you didn't read all the pages", and the OPA PS "with VMID " or "a floating 6V"... has been already mentioned... a couple of years back.
And "OPA PS" addressed in another way.
But then all paths lead to Rome and yours is a worthwhile addition I guess - I haven't tried it. So thanks for posting as that is a new path not tried yet, although perhaps not as easy for beginners. I do understand fully what you are doing, but based on past experience some might not - and as I don't even own such a unit anymore so I suggest you post schematic and full details of your mods so people willing to follow you can proceed easily.
Please note that actually some op amps do perform better re distorsions with a somewhat lower rail voltage, but that's an entirely different topic altogether... and I am anyway entirely with you that in that specific 04 case the voltage is indeed rather on the low side and the rail supply with VMID NOT what I would have designed for my own units indeed LOL.
Once the numerous additional PS caps are in place I felt we got the PS much better and a satisfying end result altogether.. but then I haven't indeed tried your mod so who I am to tell.? And there is improvement margin in the bass altogether for the entire final unit, but then this is just a Chinese 70E beast LOL
Please post all your mods and pix so someone can evaluate if worthwhile going for it on top of the usual mods we tried already. It is IMHO a matter of an "all"
There is more in this unit then this single PS point, but for that I am afraid you might have to read the entire thread if you haven't LOL
Claude
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