JoaMat

You seem to have a very fruitful collaboration, ang728 and jeohpj. Congratulation to really nice amplifiers.

Wow, very nice!

Interesting topic this inlet AC controlling. Found this board in my closet. Small power supply with a PIC 10F202. Input IR and toggle momentary switch. Out to SS relay and two color LED for on/off indication. This board has served in a T2 power supply. For some reason it didn’t work when I used it for BH and Megatron. Those amplifiers draw more current than the T2 and the control powered up just to fall back to off within a second. So I took it out. I’ve a similar board with SS relay onboard in a KGSShv power supply and that works OK. Mean Well has small power modules that might be used to power the control unit. Like this. Correction: not toggle switch - it is a momentary switch.

Nice! Is there a trimmer on the vertical board? Looks so to me.

Went back and looked at this again; a lot to like here! Agree. I like the small boards close to power inlet. @sorenb I guess the power switch on front panel is a toggle type? Is the switch just an elegant black one or is there light in it?

Thanks everyone for all the kind words and encouragement along the building of the Carbon. I think it turned out very well. In previous post I said it sounded all right – that’s an understatement, it sounds fantastic. But of course everything you just built is the best sounding ever built never trust a DIYer. George, I wish you hadn’t asked me about the 500 V. Yep, I run it at 500 V. I’ve read the datasheets but I haven’t told the amplifier.

Today I’ve shorten in the front and back panels. Makes the three layer Carbon looking neater. Dual power connectors on the back. Using the T2 power supply, too lazy to build a new one. Still more work to. But it works as it is and it sound all right.

I’ve used the method described by Soren for a quite a while. Found it reliable and easy to use and it’s an advantage not to do the measurements on a live amplifier. While I did this on my latest board I got some funny readings on one current source. Increasing the voltage (I use lab power supplies) the current increased to a much higher value then expected. It turned out that when increasing voltage above some 15 volts the other current source start to provide current. At about 70 V it provided full current. Didn’t understand how this could happen unless I did something wrong. Checked my board layout for more errors, changing components etc.etc., but I didn’t found anything explaining this issue. Finally, after two days of investigations, I decided to just power it up and hoping for the best. OK flipped feedbacks. When corrected the board worked all right.

I’ve a bad habit. I want my boards to be symmetrical. Take the first board turn it 180 degrees and flip it. Next I’ve to tidy it up to get it working. This time I missed a couple of things. Kevin once told me this method – maybe there was something I didn’t understood.

A picture from my kitchen. My dear is away for a few days and will be back on Friday evening so I have time to fix this mess. Anyhow, a second board of three layer Carbon is done. This one’s offset is as good as the first board after fixing an error. Mixed up the feed backs so first offset was +440V and -440V. First board was free from errors but this one have some serious errors. Glad I didn’t sent it to a board house for manufacturing.

The 33pF and 220pF need to be at a higher voltage? I use 1000 V Cornell Dubilier micas.

Pripps blå – caused me a lot of problem as a youngster.

so now Ryder Blue Hawaii Bipolar Race begins

Sure your amplifier is well within specifications. I should be more careful with the words. Trying to fix something that isn’t a problem could very well cause real problems. I’ve five boards with opto servo and they all have offsets close to 0. But that could very well be a lucky coincidence. Next five might change the statistic.

So, with no signal at inputs and balance at zero you have an offset of 1.5 -1.6 V?

All right. I guess your amplifier works properly. Set the meter to VDC with one decimal (or switch it off) and enjoy the music. Be proud over an successful first built of an electrostatic amplifier.

I have used the opto servo in one T2 and one grounded grid for quite a while and that servo works very well. The offset is mostly in mV range. I can’t tell if it effects the sound negatively. Offset within 30 or 20 volts is not much to worry about with an electrostatic amplifier with only trimmer/resistor. 1.5V is very good. If your amplifier has an opto servo then 30 or 20 volts offset is abnormal, even 1.5 V tells you that the amplifier is’t working properly. No, the numbers are not great. For an opto servo they are normal. Well done!

An amplifier with the opto servo engaged can’t have an offset other than approximate zero volt.

I believe you should have some negative potential at leg 6 when servo is working.

If you turn up the trimmer with the amplifier on - what happen to the offset?

One thing at the time. My idea s to find out if the servo makes any difference at all. Leg 3 is grounded?

Those values are all as they should. Also 0 V on leg 2 and -1 V on leg 6 seems reasonable. If you turn up the trimmer to max resistance - what happens to the offset?

This seems interesting. Do you dare to remove the 120 ohms - or whatever you have there - which is in series with the trimmer and see what happens? Than offset is set by pzta06 entirely. That's the way my grounded grid and Carbon work. Haven't had any smoke so far. Knock on wood.

Agreed, very much true!

I’ve one grounded grid and the three layer Carbon (one channel only), all boards with opto servo and no trimmers with associated resistors. All of them are within 50 mV. If unbalance then the average is within same mV range. Your first board seems to behave as mine. For the other – are you sure the trimmer not is set at a (slightly) to low value? The trimmer must be set to an offset above zero volt without the servo engaged. Turn the trimmer and see what happens…. you have probably already done that?