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Happy Birthday Jim! I hope you have a great one!

Happy Birthday!!

Happy Birthday John!

16.98V is about what you would get if you had R7 and R8 swapped. Check the positions on the board.

RIP to your friend Jimmy, Brent.

Happy Birthday!

I would think cfp2hmt as the latest one.

Just started watching this last night (s1e1). Enjoyed it, and will continue.

Interesting. Where is a good source for forming taps?

Happy Birthday and miss you Matt! RIP

The standard audio grade from Toroidy is the same transformer; just not encapsulated. It is screened, etc. just like the supreme, and at least for mine, was half the cost. Mine only took about 4 weeks from order to delivery. I might consider the 100Vac transformer. You might need to deal with some extra heat, and ensure that component ratings are sufficient for that.

I would check with Toroidy in Poland. I had a pair of 6 secondary 100VA transformers done and they were pretty reasonable. Dual primary, 4x24V and 2x8V for either 57 EUR for their standard audio grade or 107 EUR for the audio supreme grade (I went with the audio supreme). They could do your 90Vac and 8Vac with no problems. Shipping was a bit high as is to be expected, but they came in about the same delivered as SumR, who I wouldn't use now.

I would guess that those are for turning on the opto coupler ( CPC1117NTR), same as the normal GRHV's have, for delay purposes. Haven't looked at the schematic for the 100, but for the normal GRHV, you have to apply a voltage to turn it on. You can leave the CPC1117 out if you don't need this feature. I probably wouldn't use mica insulators for something like this (aluminum oxide instead), but I know mica has been used throughout the years for HV applications.

What?!!! No more BD?

I do recall on the one CFP3 I worked on, half the LEDs were different, so I changed them all out for the correct ones. Later, the builder said he ran out of the normal ones and used what he had. Not the right move.

https://www.mouser.com/ProductDetail/CK/7203SD9AQE?qs=G14F9ppgKfS26PW35gemkA%3D%3D

Measure across 1 resistor only. Then across the other one. Yes the voltage will change as the amp warms up. Ideally, you would do this with the amp cased and having warmed up an hour or so. Some might go as far as having the top on (or partially on) when doing this as well. When I build one, it will run at 30V. I believe Dukei's do as well (at least the one I worked on was running 30V supplies).

Isn't 20V kind of low for a CFA3? I thought most were running at 30V? For bias, measure across each of the 1 ohm resistors. Hopefully they are about the same. I don't recall what the target output current is for a CFA3. EDIT: it appears that most have gone for 120-150mA, but some run at 200mA. Unclear whether the ones going higher were using lower voltage or not. The only CFP3 I have listened to was at +/-30V.

The first thing to do is power each of the GRLVs up (not connected to anything) and verify that the output voltages are correct. Once that is done you can start connecting one of the CFP3 boards at a time to the GRLV, and begin testing. You will want to remove the servo opamp, and measure: DC offset voltage from output + and - to gnd Measure the bias across the 1 ohm resistors and calculate the bias current from that These measurements should be done with the inputs shorted to ground. If you have a volume pot connected, turned down all the way works fine. I believe the 5K trimpots (RV1 and RV2 on the schematic) are for the bias, and the 10K trimpot (RV1) is for the offset. All of this is from memory though, so I could be wrong. I would strongly suggest using Kevin's protector board with this amp as it is capable of easily toasting a set of phones.

Happy Birthday Todd! Hope you have a great one!

Happy Birthday!

Haha... my birthday was back in mid-May and most of you had already wished me a Happy Birthday then, but thanks again!

Happy Birthday Antonio!!!

Hadn't heard or read any of this. Very sad...

One additional pic showing one of my favorite aspects: I used TE Conn. D5200 Dynamic connectors for the AC on the voltage select/momentary switch board (Mark Johnson's ACPRSS from diyaudio, modified layout for connectors). These are rated at 600V, are 5.00/5.08mm spacing and don't take up much more room than the screw down phoenix connectors. These are very nice, and IMHO would be a really good choice for the stat stuff (Carbon, GRHV, etc.). There are 2 alignment pins on the footprint, so not a drop-in replacement (these do pull out, so you might be able to get away with that).