Pars

Congrats to Peter, Jim! Awesome story! Yeah, that Chicago crew is a dirty bunch

Avnet still has the MPSW56. Good price too. That's where I got mine from for the multi-amp. http://avnetexpress.avnet.com/store/em/EMController/GP-BJT/ON-Semiconductor/MPSW56RLRAG-BKN/_/R-8954392/A-8954392/An-0?action=part&catalogId=500201&langId=-1&storeId=500201&listIndex=-1&page=1&rank=0

Testing board #1 and all looks good. I think for the time being I will use 301R for R38/R39. This is giving me around 360mV drop across the emitter resistors, so 18mA of current. Others I have tried: no resistor: not recommended 370 ohm: 520mV across the emitter resistors, so around 26mA 316 ohm: 410mV across emitter resistors, 20.5mA I may end up using the 316 ohm, but it is still kind of cold in my basement and I would want to see how these did cased up. Still not sure about the pots. RV3 seems to do little or nothing. RV1 and RV2 seem to need to be balanced for best offset + or - to gnd. Once these are dialed in, the + to - offset seems to more or less take care of itself. With no servos in, the + or - to gnd offset seems to float around about 2-3 mV. These servos seem to be more aggressive than what I recall from the original dynalo. Using TL071 opamps, offset is held below 1mV, and gets there quickly, even in earlier testing before I had things adjusted better.

If you have 4 wires, ohm out the tip of the plug. That wire is L+. RIng would be R+. Then measure that color wire (L+ and R+) on the portion of the cable going to the phone to the two ground wires. The one that shows some conductivity is the - for that channel (L- or R-). As Mister X mentioned, if you only have 3 wires, time to rewire the phones. I like the Mogami 2893 mini-quad myself. If you need an adapter cable to use the phones with a unbalanced amp, keep the old plug and the chunk of cable and put a 4-pin female inline XLR on it.

^ No comments on the above, eh? Almost had an oopsies testing board #1. Fired it up while watching offset (+ and - to ground). Hmmm, 1.x volts, doesn't look good. Caught a trace of smoke and shut it down. After verifying that it was the only sets of emitter resistors I had put in (1 pair per side) giving off a bit of smoke, I was looking things over and realized I had forgotten to put the 255 ohm R38/R39 in, and was running 7.x volts across the emitter resistors. After putting 255 ohm in for starters, things looked much better. No adjustment, there is ~40mV offset +/- to ground. I think I'll replace the emitter resistors that are present anyhow. Currently only dropping about 200mV across the 20 ohm emitter resistors, so only 10mA. I'll play around with R38/R39. I had bought a bunch of the Xicon 271 series 0.25W resistors for the emitter resistors so I could match them. I also have some Dale CCF-55 which are 0.25 / 0.5 W rated that I had forgotten about. Any preference as to which YOU would use?

Happy Birthday Al!

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