Well, I've been having a little play with my amp.
Here is a list of modifications so far....
- Removed preamp stage and wired 100K pot as a variable shunt series attenuator as per instructions on page 4 of this thread (forum default).
- Replaced all electrolytics in the amp stages with 100V Nichicon FG series (Fine Gold) caps.
- Replaced C213 and C238 with silver mica caps of same value.
- Replaced C214 and C239 with polystyrene caps of same value.
- Replaced all other ceramic caps to class1 NP0 (or C0G) rated ceramic capacitors.
- Replaced all polyester capacitors to same of better quality.
- Replaced R209 and R257 with 1K trimpots and adjusted to read 55mV across R213 and R210, and R260 and R258. This is to set Vbias, and help eliminate crossover distortion. (The point at which the transistors turn on and off as the waveform crosses 0V, I think...)
- Replaced R230 and R253 with 1.8K resistors. This lowers the gain of the amp from 48 to 27.1. I might replace these with 5K or so trimpots, for variable gain control.
Mods still to do:
-Build a stepped attenuator, probably a 23 step ladder type.
-Build a new faceplate (CNC/laser milled and etched)
-Possible modification to the SOAR circuitry.
-Replace non-polarised electrolytics (C205, C212, C233, C240) with polypropylene caps of same value.
The setup was run from my computer with one amp on the left channel and the other on the right. This allowed me to pan left and right to compare the two amps. (Not quite double blind, but it did the job...)
All I can say is wow. I didn't think that the modifications would make such a difference. The bass is more powerful and defined, the highs are clear but not overpowering and the mids are smooth but not muddy. The original amp just sounds cheap by comparison. The bass is weak, highs indistinct and overall the music sounds 'compressed', like a badly recorded mp3.
I do recommend 'fixing' this amp!
Oh, and thanks to Greg Erskine, for his help on a number of these mods (resistor mods mainly).
Here is a list of modifications so far....
- Removed preamp stage and wired 100K pot as a variable shunt series attenuator as per instructions on page 4 of this thread (forum default).
- Replaced all electrolytics in the amp stages with 100V Nichicon FG series (Fine Gold) caps.
- Replaced C213 and C238 with silver mica caps of same value.
- Replaced C214 and C239 with polystyrene caps of same value.
- Replaced all other ceramic caps to class1 NP0 (or C0G) rated ceramic capacitors.
- Replaced all polyester capacitors to same of better quality.
- Replaced R209 and R257 with 1K trimpots and adjusted to read 55mV across R213 and R210, and R260 and R258. This is to set Vbias, and help eliminate crossover distortion. (The point at which the transistors turn on and off as the waveform crosses 0V, I think...)
- Replaced R230 and R253 with 1.8K resistors. This lowers the gain of the amp from 48 to 27.1. I might replace these with 5K or so trimpots, for variable gain control.
Mods still to do:
-Build a stepped attenuator, probably a 23 step ladder type.
-Build a new faceplate (CNC/laser milled and etched)
-Possible modification to the SOAR circuitry.
-Replace non-polarised electrolytics (C205, C212, C233, C240) with polypropylene caps of same value.
The setup was run from my computer with one amp on the left channel and the other on the right. This allowed me to pan left and right to compare the two amps. (Not quite double blind, but it did the job...)
All I can say is wow. I didn't think that the modifications would make such a difference. The bass is more powerful and defined, the highs are clear but not overpowering and the mids are smooth but not muddy. The original amp just sounds cheap by comparison. The bass is weak, highs indistinct and overall the music sounds 'compressed', like a badly recorded mp3.
I do recommend 'fixing' this amp!
Oh, and thanks to Greg Erskine, for his help on a number of these mods (resistor mods mainly).
mods
Cool, Xephon.
Regardind power transistors, in the Rod Elliot somebody mentioned fake 2sa1943/2sc5200,
http://sound.westhost.com/fake/counterfeit-p2.htm#1943
Sadly, no images nor measurements or additional tips-with exception of something very important: fakes are a failure per se, and don´t work for a long time . There is a nice description of what a genuine looks like: in the real thing is very difficult to read the markings. You need very good light, and maybe some optical aid. More so, the plastic encasing is of black dull colour.
The fakes, instead, have the markings printed against a shiny surface, and the lettering is easy to read.
A time ago I checked mine, and the difficult to read the markings was readily apparent. Apparently, the ones in the Greg photos are identical to the iones I have. I believe that they`re OK.
Hope yours too.
Enjoy, and cheers.
Cool, Xephon.
Regardind power transistors, in the Rod Elliot somebody mentioned fake 2sa1943/2sc5200,
http://sound.westhost.com/fake/counterfeit-p2.htm#1943
Sadly, no images nor measurements or additional tips-with exception of something very important: fakes are a failure per se, and don´t work for a long time . There is a nice description of what a genuine looks like: in the real thing is very difficult to read the markings. You need very good light, and maybe some optical aid. More so, the plastic encasing is of black dull colour.
The fakes, instead, have the markings printed against a shiny surface, and the lettering is easy to read.
A time ago I checked mine, and the difficult to read the markings was readily apparent. Apparently, the ones in the Greg photos are identical to the iones I have. I believe that they`re OK.
Hope yours too.
Enjoy, and cheers.
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