Pars

A question on paralleled output sections such as that used in the multi-amp: If the gains of each of the 4 complementary pairs are matched closely, as well as between the pairs, is the goal to have equal currents thru each of the 8 legs (4 + and 4-), or equal voltage drops across the emitter resistors? I know that if everything was perfectly matched, those would be one and the same. Of course, nothing is perfect I guess in a nutshell what I am asking is that if I notice one pair having a higher drop across the emitter resistors, would I want to slightly increase the resistance to achieve the same current, or lower the resistance to get the same voltage drop? Anal question, I know

That is an interesting article on Thorsten. I've always enjoyed reading his posts on various forums.

^ Uhhh, yeah At any rate, just reporting what I found. It makes perfect sense from a board layout perspective to have swapped the devices used for each of the complementary pairs as they are on the proper side of the chip to be the closest to the output side they are handling. BTW, what layout software are you kids using?

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