Bryston 4B SST clone

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#863
Hello

I have order that Bryston 4B SST clone

I have only have a power transformer to give +50 v -50 v DC

So, that clone amp will not have a supply of +85 v -85 v , but only +50 v -50 v DC

I do not mind to have less output power, I know that the bias will be lower, but is there others change to do in some parts values ?

Thank

Bye

Gaetan
 
#864
chalky said:
bobina if you look back to post #369 you'll see I detail all of the changes I made to the parts you mentioned. I made the changes because the PN100A/PN200A are obsolete. I know, so are the BC560C but I have a large stash of them, as do many other people. If you want current production devices then use the KSC1845/KSA992 pair ( with a bit of lead dressing ). I changed the resistor values so that the quiescent current of the VAS transistors Q5/Q6 was cut from 12mA to 6mA. At the original current Q5/Q6 were dissipating 400mW and ran pretty hot - now they run cool. To cut the loading on Q5/Q6 now that the standing current was reduced I used output devices with potentially 4x the hfe of the MJE172/MJE182. I've redrawn the schematic with my revised parts values and attached it to this post.
Click to expand...
Hello chalky

Looking at your BrystonSmallInp.pdf schematic.

You did replaced the cfp vas by a standard vas and the Vbe multiplier by D3 D4 R14 for the bias.

Wy did you take out the cfp vas and the Vbe multiplier ?

Is it because cfp are less stable ?

Any others reasons for those changes ?

Thank you

Bye

Gaetan
 
Last edited:
#865
Hello chalky

I forgot to say that my Bryston 4B SST clone do have cfp vas, I found out that there is other version of this clone with no cfp vas but with a standard vas.

Thank

Bye

Gaetan
 

Attachments

  • push pull vas amp.gif
    push pull vas amp.gif
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#866
I think you're talking at cross purposes here. My modifications were to the input board, not the power amplifier board. The schematic you've shown is for a simple push pull vas, not a complementary feedback pair push pull vas, in the power amplifier board. If the latter were true then both the upper and lower vas would be comprised of two, rather than one, transistors.
On a different topic I notice that some of the more recent dual input boards have servos to null out the output offset voltage. This is only necessary because the non-optimal choice of input and feedback resistors leads to an output offset voltage. The output offset voltage of the (older) input boards which adhered more closely to the original Bryston design is negligible and doesn't require an output offset servo.
 
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