Bryston amps are legendary, and many people here have toyed with the idea of building one. Well, I've started a 4B ST clone. So far the PCB's have been designed, manufactured and I have most of the components for the main amp boards installed. I've been pondering how exactly to set the bias on the amplifier though. I've not had any luck finding a service manual or other document with this information. Any ideas?
(will post pics soon)
(will post pics soon)
Photos of the amp boards
Here are the amp boards, I have all the passives installed minus some jumpers and output inductors. The output transistors in the one image are just to show spacing and that these will go through the heatsink and solder directly into the pcb. The boards will also mount directly onto the heatsink. Signal paths are short and compact. Metal film 1% 3/4W resistors for the most part, audio critical caps are poly film, boards are double sided gold plated. Schematics can be found on the Bryston website. Next is to clean these up, mount them on heatsinks and get a power supply running to start testing. Wish me luck!
Here are the amp boards, I have all the passives installed minus some jumpers and output inductors. The output transistors in the one image are just to show spacing and that these will go through the heatsink and solder directly into the pcb. The boards will also mount directly onto the heatsink. Signal paths are short and compact. Metal film 1% 3/4W resistors for the most part, audio critical caps are poly film, boards are double sided gold plated. Schematics can be found on the Bryston website. Next is to clean these up, mount them on heatsinks and get a power supply running to start testing. Wish me luck!
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I will be very curious to see how these come out. The 4B for some reason really has good bass control. I couldn't believe the difference, it was like adding another entire octave to the bottom end of my speakers simply by swapping in an old 4B, but the top end was too harsh for my liking. But that was an old 4B I was playing with too. not the ST version.
Zc
Zc
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Joined 2009
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So, is this just "show and tell", or are you going to divulge your PCB layouts and plans for the project? Will others be able to build this based on the work you're doing? What's your plan?
What chassis are you designing this for? The cutouts in the PCB have an obvious purpose, but I can't guess what that might be.
..Todd
What chassis are you designing this for? The cutouts in the PCB have an obvious purpose, but I can't guess what that might be.
..Todd
Not entirely sure yet. Just wanted to get some feedback on how to set the bias on this properly. Depends on how much interest there is and how well it works out. I'll document as I go and put together a build-through pdf,
I'll be building the chassis from scratch (that's the current plan plan anyway)
I'll be building the chassis from scratch (that's the current plan plan anyway)
The boards are designed in mount against a heatsink that is a little wider than the board itself. The T0-3's will be sitting in a channel that runs down the centre of that heatsink. the slots are for all of the T0-220 pack transistors to mount directly onto the heatink as well. The schematics can be found here:
http://bryston.com/BrystonSite05/pdfs/LegacyPowerAmplifiers/3B-8Bst_Schematics.pdf
http://bryston.com/BrystonSite05/pdfs/LegacyPowerAmplifiers/3B-8Bst_Schematics.pdf
I'm using OnSemi (motorola) MJ15003/MJ15004. The BR6521/6522 transistors I believe, are just MJ's that had specific measurements. I did a lot of reading a few years ago when I started contemplating this project, and don't remember where I found this information. (may even have been through discussions on this forum)
If it were my project, I'd use MJ21193/94 or 95/96 assuming you will be using the original rail voltage and are using it for PA/DJ purposes, for home audio it wouldn't need the robustness. If I remember other discussions correctly, that output topology requires that you match the output devices fairly carefully.
..Todd
..Todd
Yup, I am using the original rail voltages. The power supply has been modified considerably, using a much simpler soft-start circuit, designed around a single 1kVA transformer, etc.
Todd, what specific reasons do you have for suggesting the MJ21193/94 95/96 transistors?
I'm aware of the matching issue, and will be attempting to follow this recommendation closely.
Todd, what specific reasons do you have for suggesting the MJ21193/94 95/96 transistors?
I'm aware of the matching issue, and will be attempting to follow this recommendation closely.
All the spec's are somewhat improved, but of primary concern with an amp this powerful is the SOA profile. The MJ21193/4 family will be more indestructible. Bryston switched to these when they became available. See the 4BSST schematic.
Bryston spec'd things a little close to the edge for my comfort -- especially their heatsinks, they run HOT when used for pro audio. It doesn't hurt to beef things up and run it less stressed. After all, you are not (I assume) trying to pinch pennies for a large manufacturing run.
FYI: I noticed Plitron had some suitable power toroids available in their surplus bin on their website. 100VCT 580VA. Use 1 per channel.
..Todd
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