No, not on 7812, just across the collector to base pins on its pads underneath the PCB, of the relay driving NPN BJT (the lower one near the 300//300 or 600//600R positions). The 2 mysterious relay chatter incidents occured due to oscillation of that transistor. The reason is still obscure. Several NPN types were checked to no avail. So it can still be a 546 or 550. Both types giving no problem at all with 3 relay types on the mega majority of builds. Unfortunate individual relay or 7812 are two scenarios to scrutinise further. But the remedy is a 150nF mylar film or ceramic cap, tried and tested on those two incidents with complete and measured success on Kannan's hand held Fluke with miniscope display.
Picture shows the Film cap - ceramic cap wprks as well - solder it only if needed
kannan
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Onething strange about this problem that I noticed was that it did not oscillate but the transistor was repeatedly switching low and high with unequal period - something looked like unable to drive the inductive load rather than 7812 oscillating. I will test this with decoupling cap on 7812 - say 100nF and report. Right now I am working on something else - kept this aside, probably try this test in couple of days
Kannan
What might be the dimensions of each board ? I back tracked 20 or so pages but did'nt see them mentioned.
Thanks salas,crt and others for your efforts in getting this wonderful project up and running.
These look interesting.Any thoughts on them?.http://cgi.ebay.ca/VALAB-Audio-23-S...in_0?hash=item439a73905f&_trksid=p3911.c0.m14Is there any el cheapo stepped 20-25k on epay with fake Dale pre assembled for you to try?
Thanks salas,crt and others for your efforts in getting this wonderful project up and running.
I have been following this topic from day one, and must say that I am amazed with the tenacity and genius of the main players (not to mention the sneakiness of one who shall not be mentioned from the first incarnation!).
I look forward to building this amazing result, and have entered my order in the spreadsheet.
Once again, thank you all and congrats.
mac1963
I look forward to building this amazing result, and have entered my order in the spreadsheet.
Once again, thank you all and congrats.
mac1963
I will try to keep the boards at that. I think a re-tool is needed for the new silk screen. That wont drive up costs too much, maybe 50 cents each.
I will probably have to scale the shipping a bit higher, when more than 2 boards are ordered. There are quite a few who want more than 5 boards. With tear-proof bubble envelopes included the costs can get overrun even domestically after some early deliveries. Please don't complain, as it is, the DIYaudio donation per order is very small.
The boards have not been ordered yet. Still waiting for the numbers to settle a bit, and give proto-builders some more time to get any parts changes warranted to BOM to get figured out. I also expect real orders may be lower than what's on the spreadsheet.....When it comes time to pay up.
Yes, I received them 2 days ago. Thank you.
BTW the design uses a single bridge so a 2 x 12 transformer can be used again. This was not possible with the double bridge that Ferds used. Less heat, less loss, less money.
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Last night I turned the pot around and cobbled together a heat sink out of an old Pentium 2 heatsink. In this application, overkill is an understatement for that sink. I would rather too much sinking than not enough, and that is what I have. I left things running for a little over an hour last night, and the DC offset was still sitting about 6 mV on the left channel. Tonight my plan is to swap around the matched fets and see if I can get things in to spec. I will post some pictures later.
Maybe just set the price slightly higher, just to make sure you are fully covered
If theres any money left, donate them to forum
A more tricky option could be to order some more boards, and sell whats left to forum donation
There always seem to be some who "missed the boat"
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All right, I am now up and running. I got the DC offset to be less than 3.5mV on both channels by swapping around the jfets. 4th combo and position was the key. Persistence paid off. I let things warm up and run in a bit and then sat down to listen. I have pried myself away after about 2 albums to write this. This thing is incredible. I am listening to a pair of axon home theater speakers (zalytron design) through chip amp and this B1. I have had the speakers up and running for about 2 months and thought them to be OK. A bit veiled, missing detail and definition, but ideal for home theater with plenty of bass kick and treble extension. Well, remove the Harmon Kardon preamp and drop in the B1 and I have to change my initial evaluation of the speakers. Of course that means that the B1/Gainclone combo is a big step up from what I was hearing before. This thing is passing huge amounts of micro dynamics and detail. The top end is just what you feed it and the bass is all there with impact and the mids are all there with all the emotion. I was listening to Marc Cohen's Walking in Memphis and it made the hair on my neck stand up. That hasn't happened with that album in some time.
Dave is a happy boy. I will review the BOM tomorrow, but for now, I have to say that this GB is good to go.
Dave is a happy boy. I will review the BOM tomorrow, but for now, I have to say that this GB is good to go.