Split PREamp / Poweramp PSU for the Leach Amp - diyAudio
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Old 31st January 2003, 10:39 AM   #1
stigla is offline stigla  Norway
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Default Split PREamp / Poweramp PSU for the Leach Amp

Hello there!

I buildt myself a version 4.3 Leach amp 2 years ago with great success! But, as always, one start to think of ways of upgrading. Since I really don't want to mess with the actuall circuit, the PSU caught my attention.
I was thinking about making a totally stand-alone-PSU for the Preamp section only. Sort of from R32 /R33 and out, maybe even from the MJE15031/...030. Leaving the Output transistors alone with the main capacitor bank.
Made som measurments yesterday, and got around 13,2mA running through the R32/33 resistors. This is not awfully lot and making a new PSU with a separate Transformer to supply this part would be quite easy. Maybe even making a regulated PSU is tempting. Or, maybe a large stack of 12 volts batteries??? TOTAL silence!!! heh...

I think this idea will give me some fine sonic results, since the class AB output stage draws quite large amount of current under dynamic situations, this must have some effect on the input circuit.
I can even use higher voltage on the input circuit maybe, if this would be benefical...
The only thing struggling my mind is the Q12 (VBE multiplier) interaction with the Output transistors may be different when they use different PSU's.


So, my question is therefore, firstly; Have anyone tried this, on a Leach amp or any other amp? Is there any sonic advantages to be gained from such a setup? I know it is common to do this in High End Tubeamps.

My current PSU is a 500VA used by both channels, but with separate rectifiers and capacitor bank, so I sort of considder the same for the PRE-amp PSU, One transformer wich splitts into to channels.

So i'd appreciate some suggestions, impressions and thoughts from you guys! Thanks in advance!

Stigla
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Old 31st January 2003, 01:39 PM   #2
stigla is offline stigla  Norway
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Oh, yeah, forgot to give up a link to the schematic.

Here'ya go;

http://users.ece.gatech.edu/~mleach/...aphics/ckt.pdf


regards
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Old 31st January 2003, 05:54 PM   #3
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Regulation for the input/voltage amp stages is already achieved to some degree by two stages of decoupling and zener regulation.

I'd considered this route myself, but I think the preferred approach is to supply a slightly higher (5 - 10%) voltage, meaning that a separate power transformer is usually needed, or quite
a stack of batteries.
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Old 31st January 2003, 08:35 PM   #4
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Quote:
Originally posted by Damon Hill
Regulation for the input/voltage amp stages is already achieved to some degree by two stages of decoupling and zener regulation.

I'd considered this route myself, but I think the preferred approach is to supply a slightly higher (5 - 10%) voltage, meaning that a separate power transformer is usually needed, or quite
a stack of batteries.
...Or you can use a doubler, as I proposed on another thread.

If current is low, and it should be for those stages, you will have no problems.

Then you can regulate, as Nelson Pass did on the A75 supply. Have a look at the supply articles for that amp at the the Pass DIY site.


Carlos
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Old 3rd February 2003, 09:19 AM   #5
stigla is offline stigla  Norway
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Thanks for the posts guys!

Quote:
I'd considered this route myself, but I think the preferred approach is to supply a slightly higher (5 - 10%) voltage, meaning that a separate power transformer is usually needed, or quite
So you mean that, if i have 59V on the output, I should / can use 62-65V in the input PSU? This is just great! I have a 34-0-34 volts tranny that I can use with a voltage doubler or something...

I took a look at the Pass DIY site and found the Active Regulaors. Great suff, just what I was looking for! I think this one would suite me good

http://www.passdiy.com/projects/zenv3-5.htm (figure 6.)

Any one got some sonic impressions on this regulator?

Will there be any troubles with the Q7's (VBE multiplier) interaction with controlling the bias of the output transistors you think?

regards,

stigla
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