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Marking the jpg up that GrindingThud posted, I arrived at this. It appears that the board has Q1/Q3 and Q2/Q4 of the THAT340 swapped compared to the schematic. The + amp section is on the left side of the board, - amp section on the right.

I have a variac you are welcome to borrow. Just pay shipping. My brother lives in the Twin Cities and can retrieve, so just one way on the shipping.

Happy Birthday!

Helps as I can mark that up. I was looking for something that had Q1, etc. (the part IDs) labeled.

Does anyone have a top board view with the part designations (not the values) per the schematic? If not, I'll figure it out. Thanks!

What layout software do you use?

Sorry NE guys... has to suck balls.

Agreed. Very nicely done. I like the faceplate treatment around the volume knob as well.

You can order the LSK170s from diyaudio at ~$18 for a set of 8. Not sure how these typically match up; I know Spritzer said the LSJ74s were all over the place for Idss.

Anyone have a transformer recommendation for a multi-amp? The sigma22 I had built up has a Triad FD7-36 56VA 2x18V secondary on it currently, which might be enough. The original Dynalo (headamp) used an Amveco 35VA transformer in it. I think Kevin mentioned that each board draws ~300mA, so 30V * 600mA (2 boards) would be ~18VA?

Had a great time seeing Jim, John, Bryan and Mike at Analogue, home of the biscuit boy meltdown. Sorry I wasn't quite there at that moment... And, I never got to try the biscuits!

This version should incorporate all of Kevin's corrections from my previous version. One further question: I know on Ti Kan's protection circuit, the relay drive requirements were pulling the + rail down, though he was using a virtual ground scheme on his. A user was the one who suggested the use of the 2N7000 and a 24V rather than a 12V relay, so that both rails were involved in supplying the relay drive. I notice here the you are using a 12V relay and driving it with V+ / GND. In actual use, does this present any problems? Gilmore_protect3_schematic.png.pdf

Thanks Kevin. Yes, that is much easier to see than what the gerber viewer was showing me

I was going thru the schematic and the gerbers for this to do a layout including a muting switch and Molex KK connectors, which I like better than the terminal blocks. From what I am seeing in the gerbers, I had a couple of questions: It appears that the LM339s are powered by V+/V- rather than V+/GND? The LM339 has 4 comparators in it. It appears that 2 are being paralleled for each input signal? The input protection diodes run from V+/V-? There are a couple of 1uf capacitors (the yellow ones on GrindingThud's board above) that I am not sure where these go? I attached a pdf of the Eagle schematic I have worked up so far. Gilmore_protect3_schematic.png.pdf

Happy Birthday Fitz!

vt4c has some pretty nice ones... Also look at THL Audio

Ain't that the truth. You would expect 50% of the cases to turn worse...

Here I go quoting myself again From Kevin's post: if you go with fets you can multiply both Rf and Ri by 10 to increase the input impedance. 1) Is there a reason I would want to increase the input impedance even more by going 50K for Ri and 250K for Rf? I wasn't sure whether your statement really does not matter for this applied to the ubal to bal, or to the multi amp.

Thanks. I just looked at the gerbers and the 4.7uf are indeed bypass caps. With 100uf electros on the board, any reason to choose 4.7uf as a bypass? I'm not really up on the latest thoughts regarding bypassing and whether it is well thought of or not. I have in the past seen some pretty good reasons not to do it.

Good point Marc. I hadn't thought of that, though I am not sure it is an issue. From what I gather, using the FET input instead of bipolar already increases the input impedance considerably just by itself? Looking at the original Dynalo schematic, with the SJ109/SK389 input, there is no series resistance; my stuff has no issue with driving that.

If I am using FET inputs instead of the THAT340, is there a reason I would want to increase the input impedance even more by going 50K for Ri and 250K for Rf? I wasn't sure whether your statement really does not matter for this applied to the ubal to bal, or to the multi amp. Also, a couple of part questions (trying to do this with what I have around): 1) The 1uf integrator caps... any reason to get ceramic X7Rs if I have some polyester film laying around? 2) The 4.7uf film caps... I presume these are rail bypass caps? So value isn't particularly important? 3) If I do raise the impedance, does the compensation 5pf cap need to be changed? Thanks!

You should see if he can use Royal Mail or something that would hook up with USPS. Not likely, but with UPS you could get hit with customs. Of course, I could be wrong

Finally got around to measuring 200 transistors: MPSW-06 NPNs from Mouser and MPSW-56 PNPs from Avnet. FIrst off, these seem to be tighter in spec than the Toshibas from the original Dynalo. The NPNs overall were a bit higher than PNPs. I used a base resistance of 221K ohms with power at 16V for these. I had a DMM in the base and collector legs set for uA and mA, respectively. Ic ranged from 15mA to 22mA or so; most fell within 19-21mA. I waited until the DMM measuring Ib hit a particular value and then recorded the Ic. Subjective, but it seemed like a good way to do it. I already had a home etched board with SIP sockets and posts on it for test leads, resistor, etc. I put resistor leads in the DUT SIP socket and tested the devices while still on the tape; didn't seem to affect the result. Should be enough close matches for a multiamp I think.

campagnolo... campagnolo... you know you want it Sorry, I've been a Campy-phile since the '70s. It hasn't always been the best choice over the years (I feel like the fonze trying to say sorry), but it always has worked for me. Of course I am stuck back in friction mode, but I did like the Ergos on my brother's Bianchi. The shit just doesn't break. Decades.

Looks very nice Jose! What is the knob to the left of the volume knob for? And, how does it sound?