Hi
I have put together a BGT kit were I tried to address the problems with weak bass...
It's basically a LM3875 BGT kit with an extra parallel power supply with larger caps...
The enclosure is almost the same as my previous 4 Hypex amps, byt with heat sinks instead of venting holes...
Here is the layout for the standard kit...
Transformers are 2*24 V 165VA...
in parallel with the standard kit I made an extra power supply consisting of double rectifiers, 1 Ohm resistors, 15000µF BHC Aerovox caps, Rifa 4 µF metalized polyprop going to fuses (one for + and one for -, gives me the possibility to "disconnect" the extra power supply for different tests) and via diodes on to the BGT PCB...
The purpose of the diodes is to create a voltage drop compared to the standard PSU so that the big caps will only "kick in" when needed (transient music signal, a lot of bass etc.)
They also make it impossible for the standard BGT rectifier to charge the big caps... The resistors in the extra PSU will dampen any spikes in the rectifier, maybe making it a little slow, something I can afford since I have the fast BGT PSU intact...
-it really seems to work
The bass is much better articulated compared to the standard setup and I have not noticed any sonic degradation of the mids and highs...
/Stefan
I have put together a BGT kit were I tried to address the problems with weak bass...
It's basically a LM3875 BGT kit with an extra parallel power supply with larger caps...
The enclosure is almost the same as my previous 4 Hypex amps, byt with heat sinks instead of venting holes...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Here is the layout for the standard kit...
An externally hosted image should be here but it was not working when we last tested it.
Transformers are 2*24 V 165VA...
in parallel with the standard kit I made an extra power supply consisting of double rectifiers, 1 Ohm resistors, 15000µF BHC Aerovox caps, Rifa 4 µF metalized polyprop going to fuses (one for + and one for -, gives me the possibility to "disconnect" the extra power supply for different tests) and via diodes on to the BGT PCB...
The purpose of the diodes is to create a voltage drop compared to the standard PSU so that the big caps will only "kick in" when needed (transient music signal, a lot of bass etc.)
They also make it impossible for the standard BGT rectifier to charge the big caps... The resistors in the extra PSU will dampen any spikes in the rectifier, maybe making it a little slow, something I can afford since I have the fast BGT PSU intact...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
-it really seems to work
The bass is much better articulated compared to the standard setup and I have not noticed any sonic degradation of the mids and highs...
/Stefan
Mr Evil said:Those are quite possibly the nicest cases I have ever seen an amp in
OA51 said:Any size suggestions for bleeder resistors?
I believe the idle current of the chips is around 35ma each, which seems like a good amount to bleed. With 24V rails that's roughly equivalent to 330 ohms across each rail. Use minimum 10W resistors to have a healthy derating.
Stefan, just an idea, have you thought about to have a conventional FAT PSU and loose those diodes?
BTW: Can you explain how you have done? It seems that you charge the big caps but you can't discharge them, only one diode?
I have serious doubts in having small smoothing caps but that's me only.
BTW: Can you explain how you have done? It seems that you charge the big caps but you can't discharge them, only one diode?
I have serious doubts in having small smoothing caps but that's me only.
Peranders
The basic idea is something like this...
Electronics CAD-program MS-Word
Stefan
The basic idea is something like this...
An externally hosted image should be here but it was not working when we last tested it.
Electronics CAD-program MS-Word
Stefan
OA51 said:
The basic idea is something like this...
Can you describe role of some elements in your shematic like that 1 and 400 ohms resistors and 4uF cap.
Tnx
p.s.
Has anyone else tried this psu?
peranders said:I have serious doubts in having small smoothing caps but that's me only.
.....
i ve built a small amp with opa 549 and one can i tell... one needs serious psu / capacitance to listen to music through those chips realistically... actually the result with 1000uf x2 was unbearable at high levels... much better was the result with 20000uF elna for audio per channel or even nippon chemicon @ 44000uF per channel... off course all these with some 470u starget on the chip... in my humble opinion, the difference is not only the huge improvement in bass, but in much more... airness in highs and mids, ambience sense and dynamics...
I am very interested in your psu design. I just compared regulated and unregulated psu for 3875 and it was something that make you think. That lm3875 is soo special!
I can't experiment any more! I must put things in a box because it seems that i will never do that. So i like your idea and i want to hear some listening impresions but it seems that nobody tried it.
I can't experiment any more! I must put things in a box because it seems that i will never do that. So i like your idea and i want to hear some listening impresions but it seems that nobody tried it.
OA51 said:
What where your impressions from the comparison between regulated and unregulated psu for 3875?
Well, if i must choose one word to describe this difference i would say: unrecognizable. Yes, bass is more defined but all other become so... average?
I don't have high qual speakers for some detailed analisys. That's why i want to hear other peple expirence.
I am making this amp, with shorter and longer breaks, for couple months, always trying something new and always back at the begining. I will try your psu and if i don't like it i will choose that snuberize version.
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