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I'll leave it to you to ohm it out with a DMM when you open it up.

They are electrets, thus only four pins on the connector. Only the TOTL ECR 800 or 880 or whatever was a full blown electrostatic, which seems not to have passed the test of time as well as the ECR 500s.

I looked at Gary's pics again (well, a thumbnail since the imageshack servers stopped hosting them), and it seems the way to open them is not through the baffle side, but the outer side. I used my fingers to pry open the metal backside, which was glued onto the plastic housing in two places. You have to be careful not to damage anything when doing so (plastic from the 1970s is not so good), and I have not yet thought of a good way to put the metal backside on without making it permanent. Maybe it doesn't really need anything other than friction.

Soldered in the CCS adjustment yesterday and fired up the boards for the first time. Initial offsets very minimal, could have worked fine without any trimpot adjustments. I have also stuffed the digital attenuator boards but have not tried them out yet. Next up is to build and test the ubal to bal boards next weekend, now that I have all the parts.

I'm trying to recable my ECR 500 with a Lambda Sig cable but it's not immediately obvious how to disassemble the headphone to replace the cable. Taking it apart has clearly been done before, given Gary's and other peoples' pics floating around the internet. Help? Edit: I can obviously open it up from the driver side by unscrewing the baffle. Then the driver is held into the frame and the long driver tabs go across to the other side.

http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/FJPF2145TU/?qs=%2fha2pyFadui9BXYxjh0%252blwo7N7LskIUoGMKoPSrDrpk%3d FJPF2145 is in TO220F package which has insulated tab It might be nice to have space for small gate stopper resistors on the 2sk216s?

Cool! Where's the volume control? Did you reduce your rails to +-450V? Would love a shot of the internal PCBs if you have one.

Thanks! I might hit Justin up for a few if he still has some for sale, that seems like an easier option. Need to buy some Stax jacks from him anyway.

Just curious, where did you get your 2sa1486s?

I would simply buy and test some 91V zeners to replace the 100V ones.

Check the zener diode string and swap as necessary so that they add up to the right amount. Can use dy294 to test the zeners if you have one

Input JFETs just came in the mail. Most of them look real, there are a couple 2sk170s that have funky looking printing on them that I'm not sure about. Will measure IDSS later. Finally the project can move forward! Actually, I still need to get a few more things. Just ordered the amp and PS cases yesterday, and am about to put in a final mouser order for some other parts. I'm going to be out of town this weekend but should have the attenuator boards and Multi Amp up and running fairly soon, and breadboarding the ubal to bal and phono boards will shortly follow.

5V what? Peak to peak, peak, or RMS?

Yeah I'm sure it does very little as the OP07/OP27 max offset is already 1.5mV and the thermal stability of trimpots aren't very good. I should have followed the datasheet with a 20k pot but got 100k instead. For anyone that has these older version boards and want to put in the trimpot, you're going to also need to jumper the NC pin to the offset pin if using the OP07/OP27 since the pinout of the OP07/OP27 are slightly different from the OPA445. The servo caps I put in are 2.2uF MLCC, will use 255 ohms bias resistors and will add in the LED bias adjustment after all since you said so. The bias resistor slots are actually marked 510 ohms on the silkscreen. I have followed the values in the schematic over the silkscreen for the other resistors as well. So I should also follow the schematic and not the board for the ubal to bal as well? The CCS resistor value is 100 versus 180, there's 50 ohms in series on the output, and again I believe the front end to be cascoded with the extra BJT and the voltage divider from the rails to gnd connected to the bases but could be wrong. Going to make this as KG approved as possible eventually since it's the KGITSOCH, I will build scaled down Dynahi power supplies for this thing. It will have three transformers with pass FETs connected to offboarded heatsinks to give the feel of the DIY T2 supply. I will also put in the MM stage you posted somewhere that you designed in the '70s unless you have a newer design.

Thanks! Yes, my boards are missing the CCS adjustment but they have the trimpot for offset on the servos. I saw the Dynalo SS schematic previously but didn't see the ubal to bal one. I noticed the input diff pairs aren't cascoded in your schematic but seem to be on the board? Also, would you recommend putting in a CCS adjustment for the ubal to bal CCSes?

I did some board stuffing while I think of what to do about the j74s. I read that the Linear parts are different enough from the Toshibas that they are not direct drop-ins so I can't do complementary pairs from different manufacturers. Decided not to bother with offboarding the CCS offset adjustment so I'm going to just put in the 20k resistors. Need to put in another mouser order and populate the attenuator boards, so I can actually start programming the damn thing. Preliminary testing is good with the uC, it connected to my phone through the cloud just fine with the wifi antenna I bought. It's a small planar antenna with an adhesive backing so should be easy to mount to an enclosure. Just want to make sure I have the ubal to bal boards traced correctly so I don't build it wrong (not sure if a schematic has been posted). It's a cascoded diff pair with source degeneration and a CCS tail into a wilson current mirror driving output BJTs? Are the LEDs across what I think is the mirror used for Vbe temp tracking or some other purpose?

Thanks anyway Marc. I have 2SK170s but don't have any p channels.

The OP07 datasheet specifies a maximum of +-18V supply voltage so I personally wouldn't go above if using that opamp. I am going to run mine at +-16V (mainly based on the 15VAC transformers I have on hand).

AKG K340s with Jensen caps and unregulated power supplies to improve power supply rejection of the amplifier Definitely don't get Stax, they don't have colour and are grainy sounding

That's not a good sign. If the package doesn't show up tomorrow I'll contact headinclouds about what to do.

This thread reminds me I still haven't received boards. Has anyone in the US gotten boards yet?

Thanks, will do!

It's set by the voltage divider between r6 and r5+r29 compared to the 10V reference in the discrete error amplifier. These are for the positive rail, are you just replacing the parts from the positive rail thinking it's going to change the negative rail? Tbh I think the best solution is to get someone else to build you a working power supply from scratch. You could seriously injure yourself at this rate.

Okay well I'll just get a set of eight and the closest four of the eight will be the ones I use. Audio stuff is making my wallet take too massive of a beating. Probably gonna have to order the THAT340 for the Multi Amp boards unless the other four are relatively close.