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Happy belated Birthday!

Happy Birthday!

That was pretty much my understanding as well; the cable shield is part of the chassis ground, which may or may not be the same as signal ground. I also recall ground loop interupters, such is what is used on my headamp Gilmore refererence board. Basically a low value resistor (4.7 ohms?) and a cap, tieing board ground to chassis. I don't see this done much anymore, unless I haven't been paying attention. GND LOOP CAPACITOR 1 DIGIKEY EF4104 GND LOOP RESISTOR 1 MOUSER 280-CR5-4.7 EDIT: probably shouldn't have made the topic so cryptic

Yeah, those. From the Neutrik description: Wired according to IEC 268-12: Pin 2: signal Pin 1 and 3: connected to ground

Does the Hosa RCA/XLR adapter short the L/R - signals to ground? On a differential input, those need to be grounded when going SE. I know Kevin recommended the Neutrik adapters for the multiamp, which do this.

Mine might even be the prior gen.; refurb from Apple store. No issues in 2 years?

the older one isn't?

Yet Another XLR Question... Building my first balanced amp, some connection questions: What do you do with the shield? Reading the RANE app notes seems not appropriate for parts of this, since I am using 4-pin XLR, and the 3-pin standard has pin 1 as ground. I am reworking the previous 4-conductore rewiring my phones right now, and chopped the previously wired 1/4" plug cable part way to wire in a 4-pin female/4-pin male (the male will be the main phone connector into a 4-pin female on the amp), turning this cable portion into an adapter for when I want to use the phones from an SE amp. The main cable terminates at the phones in a 4-pin mini XLR, in which the shield is not terminated. I assume use the telescoping shield philosophy and terminate the shield to the connector body on both std. 4-pin XLRs at the mid point? For 3-pin XLR balanced amp inputs, just follow the RANE notes? Describe how YOU did things Also, on the balanced Dynahi SS thread, I see one amp using a male 4 pin XLR for the jack? Seems like a bad idea, and that the standard is (or should be), Male for inputs, Female for outputs?

Happy Birthday Doug!

Some people claim they can hear servos. I'm not one of them. Since they normally operate well below 1Hz, and having the servo can protect you from bad things happening, I see no downside to using it, even if the circuit is stable without it.

Happy Birthday Doug!

The LSK389 is an N-channel device while the SJ devices are P-channel. Here is a thread on diyaudio discussing at least the 2SK147 compared to the 2SK389 / 2SK170, etc. http://www.diyaudio.com/forums/solid-state/23954-2sk170bl-2sk369-mc-stage.html

I think most people are using the ON Semi parts. They released an EOL notice last fall that apparently their Korean packaging subcontractor would no longer do TO92s . Mouser still has some in stock, so I'd buy what you think you will need now.

Probable stupid question time: I was playing around with board #1 and ran a test signal into it using a Discman (SE, I- tied to gnd). On the outputs, I was seeing 2 signals (O+ and O-) that were each around 2.5Vpp, 180 degrees out of phase. The input signal was from the line out. With a gain of 6 in SE mode, I would have expected the output signals to be larger? Or do I need a load resistor across the outputs (O+ to O-)? Or is this potential loading of the input impedance? Gain resistors are the stock 5K and 25K. This is the first time for me playing around with balanced signals also.

I played around with RV3 today, and it worked as described. The other 2 pots should be close to center, so I left them alone. These seem to take small adjustments, whereas RV3 takes a considerable amount of adjustment, which is probably why I didn't think it was doing anything previously. At first I messed around using RV3 to try to provide equal base voltage on Q6 and Q9, measured at R21/R25. Offset looked terrible. Then I tried the same thing, only with the collectors of Q6 / Q9 (measured at R1/R2 and R23/R4... whats up with that numbering anyhow ). Offset again looked terrible. I centered RV3, then monitored offset on both the + and - to gnd, and started turning RV3. It got the adjustment quite close; close enough that I didn't bother with the other 2 pots. Without servo, it was drifting ~4 or 5 mV total, most of the time more like 2-3mV. With servos, easily within +/- 1mV. I let it run for about an hour. At 365mV 18mA, the board barely gets warm. I even put a box over it to see if it would heat up more, and it didn't. I still think I could crank the current up higher, at least to the 25mA range. At that point I would probably replace the output emitter resistors with something bigger than the CCF55s I have in now.

^ They show backordered... wonder if they'll get them Temporarily out of stock - back order for despatch 24/03/2015

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?