johnwmclean

Ultravox - Vienna

Nick Cave and the Bad Seeds - The Boatman's Call

The Birthday Party - Prayers on Fire

Joan Baez - (Vol 1)

Public Image - First Issue

Bauhaus - Mask

Bauhaus - In the Flat Field

Dead Kennedys - Fresh Fruit For Rotting Vegetables

x 2 If you can do it balanced can do no harm and has better potential.

Alela Diane - Alela & Wild Divine

Joe Jackson - Body and Soul

That makes sense then. Thanks Birgir.

^ Nice one eggil An observation after changing the output current to 8.8mA. Whilst the balance remains stable, offset drifts around considerably. I can achieve zero offset on both channels no problem, but it will drift ~5V or so over time. Is ambient temperature a factor? I know 5V is nothing, but should I be worried about stability?

Sorry to hear about you experience, I’ve dealt with Cam-Expert for years and the one thing I will never do with them is hand them CAD files. They exclusively use FPE software, so they’ll take your CAD file and maually input the data back into FPE which is open to all sorts of interpetations. I can’t tell you the amount of mistakes and fuck-ups I’ve had but it was considerable, my EHHA top plate was wrong twice, at least 3 out of 7 panels for my DCB1 were screwed just off the top of my head. Cam-Expert always replaced free of charge and shipped back out to Australia.

It’s the only piece of audio kit that I can tell any difference with a cable. My take is there must be something fundamentally floored with the stock cable.

Yes SumR.

Thanks Victor, There’s not really much to see, however here is what I did. Either side of the LED in R8 and R9 positions the default 180ohm resistor is still in place I simply paralleled a 300ohm resistor over the top. This changes the value to 112.5ohm. The calculation mA is derived; 1.7v - vbe junction (.7) /112.5 ohms == 8.8mA (see Kevin’s post #1893 for detail) Thanks Kevin and Birgir for all your help with this.

Thanks! The transformer is a beefier 150VA model, it uses a screen and the 420 V windings are now capable of continuous current @ 250mA. The psu is standard 450V, for the amp boards I changed R8 and 9 from 180ohm to 113ohm, simply by parallelling 300ohm over the existing 180ohm resistors which saved lifting the amp boards of the heat sinks. I was going to dabble with the third stage, but chose to leave it, I was concerned about not being able to get the boards to balance. As it is I can get both boards under 1 V, but cannot get down to the ~ 0 V where I was before, not that is matters, just worth mentioning. As for heat, there’s not much difference, runs slightly warmer overall. Listening I found higher frequencies have opened up, sounded really good to my ears and definitely worth the effort.

I now have my HV running 8.88 mA.

Good luck matching, you could get lucky, I've had batches of 200pcs with very poor yield.

The Neutrik RCA’s data sheet will have panel mount drawing measurements that already take into account fit tolerances. Unless you’re making a concession for something unexpected... I’ve used these measurements many times using Cam-Expert and FPE with no problems. Try and mount the JT relay module/s on the back panel as close to the I/O’s as possible. Keep the relay driver board with 30VA transformers furtherest away from sensitive audio lines at the other side of the layout.

Always leave a small margin of tolerance when manually measuring. For example if a hole measures 40mm x 20mm, I’d CAD it at ~40.3mm x 20.3mm. If you can find data sheets for component panel measurements, then I CAD them exactly to these measurements, and manually measure the actual component for a double check, don’t blindly go straight from the data sheets without checking. Make a dummy cardboard panel, cut the holes out with a scalpel and mount your components on this for a triple check, screws and all.

Thanks Kevin.

Bump for post #2022 Kevin or Birgir I would appreciate some guidance with this, my understanding of the circuit is dreadful at best, your knowledge would be most appreciated. Regards, John

Kevin, what value did you have in mind when you said “You can bump up the 3rd stage a bit”? ... in my case I have Modushop 3U 400mm sinking with the output current stage targeted for 10mA with A1968’s parts. If you have a formula for the 3 stage source resistors that would be helpful.