BGW Performance Series 2 Schematics needed

[nevetslab]

I have the last of the four BGW Amps on the bench....this one is a Performance Series 2, though not the stock production version. Doesn't have the normal front panel Display/Volume Control Pot PCB, doesn't have the adhesive-backed escutcheon in place to identify what model it is. After brushing out all of the dust bunnies sucked in from the fan in the front power supply compartment, I connected it to the power analyzer/variac, and began turning up the AC Mains, having first removed the heat sink assembly to check for shorted power xstrs on the heatsink.

I didn't find any shorted devices there, but with the amp module back into place, and monitoring the power output busses for DC level, I began turning up the variac. I didn't see any sudden high current draw, but I did find the DC level on Ch 1 had climbed up to 22V before I stopped, with Ch 2's DC level also going north, but not to that level.

I don't have the schematics for these. I thought I had loaned them to Duke for his documentation project, but found in my list of what I gave him, the Performance and Millennium Series amps weren't among them. I was sure I had kept documentation on everything they produced...may still be in other boxes in storage...where, ???

So, I'm in need of either a Performance Series 1 or 2, or a Millennium Series 1 or 2 schematics. Even Performance Series 3 or Millennium Series 3 would tell me enough. I brought in my blank PS 3 PCB I had designed the layout for back in the early 90's. Andy Hefley had done the circuit design of the Performance Series amps. I found his contact info at diyAudio, and sent him a PM, though see he hadn't been active there since 2014.

[nosaj]

Any chance this is what you want?
nosaj

[nevetslab]

Any chance this is what you want?
nosaj

Yes....this was it. I had to sign up with audiokarma.org, and while that was going on, the owner of the BGW Amps found all of his schematic files, and started transferring hundreds of MB of files and came close to crashing my laptop. So, now, I'm swimming in files, and trying to download a copy of 7-Zip for Win XP so I can move files out of the zip file folders he sent and then purge all those email files. I had no idea he was going to pull that. Now, I just hope I can reclaim my webmail system.

At least now I have the files needed to go digging into what's died. I see my name on drawings of these files, and so many more that I've just downloaded.

Thanks,

steven

[Enzo]

MY huge collection of BGW files consists of: 750B and 7000A. Suspecting those are not too helpful now.

[vintagekiki]

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[nevetslab]

MY huge collection of BGW files consists of: 750B and 7000A. Suspecting those are not too helpful now.

The 750B is more useful than the 7000. The 7000 was one of the first experiments using the newly installed sheet metal shop, and we had stamped out and folded up aluminum heat sinks from 3/16" aluminum. Had surface area, though now where near that of the Wakefield or Ahem multifin + mass extrusions we used on the 750B....still using metal can TO-3's at that time.

[nevetslab]

Now armed with the schematics for the PS2, I see what was built that I have on the bench is prototype that was made for Monster Cable, used in evaluating cable samples they were sending us. I don't recall that project. I do see from the schematics, this built as a PS1, only having 2 pairs of output xstrs, though it does have a PS2 power xfmr. So, +/- 78V supplies instead of +/- 68V supplies as used in the PS1 amp (both built in the same chassis).

Jeff had indicated he had this amp running for at least five years before it stopped working. No screws in the top cover. Sure lots of dust bunnies inside. Looks like the amp was at the bottom of pile of stuff, perhaps on the floor, so sure worked ok as a vacuum cleaner sucking up all available dust in front of it!

As I had found the output buss DC level began rising from 0VDC as I brought up the variac, watching the power analyzer for fault current, I shut it down when Ch A it got a bit over 20VDC. Ch B was also changing some, but not to that extent.

I turned to connecting a small dual tracking DC supply to run the op amp stages from +/- 15VDC, just under the zener voltage on the zener supplies fed from the output stage supplies. There, I found the output from Pin 1 was just a little shy of the +15V supply level, while the DC level of Pin 1 on Ch B's op amp was up a bit....0.85VDC. So, I have at least one MC33078 needing to be replaced.





The Front Panel PCB doesn't have any pots installed. The Front Panel Display assembly was mounted to a spring-steel mounting bracket, end tabs of both ends of the PCB fitting into the slots, so the board/bracket wasn't supported by the pot terminals. The assembly WAS still mounted to the front panel/chassis using the pot bushing hardware. I'll have to look at the schematics for the PS4, as that amp had two power xfmrs up front, with the same heat sink extrusion turned into a tunnel, fan at each end, with the amp PCB's running from the middle to the two sides of the chassis. We had to resort to using a VCA from THAT Corp for the volume controls (front panel pots was DC control voltage to the VCA). I think that PCB shown above was also used for that. Been enough years since the project that I don't recall without documentation.

Here's the schematics for the PS2:

ps 2 signal and control rev.g.pdf

ps2 ch a amp schematic rev.g.pdf

ps2 mains ac.pdf

Enough time had passed since being inside this amp, that finding a relay PCB below the amplifier PCB surprised me. It's shown in the block diagram which I had drawn, so I knew it was part of the product design. I can't recall if we had put DC sense circuits in place to disconnect the speakers from a fault in the output stage. I'll have to see if that module/schematic came over yesterday with all the documentation Jeff sent over to me, having found the files. More to come over....I had to get him to halt sending files, as I nearly crashed the webmail program with too much data. Got the files moved out of the inbox, so back to normal for the time being.

I did find in the test procedure I just found in the documents I received from Jeff there IS DC Fault Condition sensing on that output relay module. I couldn't imagine it not having that....just couldn't remember.

Now onward to see what I can find out after swapping out the two MC33078 Dual Op Amps.

[nevetslab]

I had looked yesterday at the amp using an external bipolar 15V supply to power the front end stages of the amp. It was after looking at the schematic I had downloaded that i saw the problem in doing that, as the stage I was looking at didn't have a closed feedback loop around that op amp stage with the power amp supply turned off. So, today it did latch up to the positive supply on both Ch A and Ch B, after I had replaced those two op amps for Ch A and Ch B power amp stages (still powering externally from bipolar 15V supplies) . I next put the power amp module back into the chassis, reattaching all of the wiring, and with DMM's attached to monitor the power amp output buss, I tried powering up the amp off of AC Mains. This time, I didn't get any DC level shift while raising the AC Mains, nor any fault current. I was able to raise the Mains to 120VAC, finding nominal idle current of 750mA/563W @ 120VAC. Amp turned on and off just fine, relays pulling in. Bias was in the nominal 10mA range per output pairs of power xstrs. Drives output just fine now.

I will have to advise Jeff (owner) of the absence of the other pair of output xstrs that were used on this prototype. Looks like a PS1 amp module was installed in a modified PS2 chassis for the task. With 8 ohm loads, not much danger, but with higher supply voltages and only two pairs of outputs, not recommended for 4 ohm loads.