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Old 24th January 2013, 09:41 PM   #21
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Location: Paris, Ontario
Originally Posted by Struth View Post
MJ15024/25 are what the original Bryston output devices were based on. These have twice the Ft of the MJ15003/4.

Possibly of more importance is the voltage rating: 250V for the 24/25 vs 140V for the 3/4. The outputs can see the full width of the supply, which is 180V in newer versions, maybe 160V in older.
The 3B operates on 55V rails. If it were a 4B I would have used the MJ15024 / MJ15025 due the the higher 80V rails in the bigger model. I felt comfortable coming to within 30V of the device Vceo because the design incorporates 'catching' diodes to clamp potential reactive excursions beyond the rails.

Neither device has spectacular Ft but I figured likely high enough. The plan as it sits is to order the correct outputs from Bryston once all my reconditioning is complete. At $15/per device I want to be sure the thing proves itself.

I'm impressed so far, sounds nice.
---Jason Kuetemann---
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Old 2nd February 2013, 12:34 AM   #22
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So, carrying on with my little exercise on this vintage 3B, I'm curious to know what the sonic differences are compared to the 4B. So far I'm very pleased, but curious too.

The circuits are very similar, yet I have seen many comments on the superiority of the 4B from the sonics point of view. In looking at the differences (attached schematic, hope this is OK, see below) they should be quite similar in sound. The diagram has been stripped of all component values and device types, excepting the 3B / 4B differences as noted on the schematic. I addition the schematic is freely available from Bryston here:

Aside from differences (A) (C) (D) (G) (H) which seem to be specific to the higher rails and greater power capability, the most likely sonic differences would originate from differences (B) (E) (F) which appear to be the amplifier's compensations. Any thoughts on this?

So then the next logical question is can one make the 3B sound more like the 4B by compensating the 3B the same as the 4B, assuming there is no issue with stability?
Attached Images
File Type: png 3B-4B.png (236.5 KB, 75 views)
---Jason Kuetemann---
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