JoaMat

I managed to get this working in Proteus. Headphone protector. A combination of Kevin’s comparator based protector and Stax delay circuit. Delay time set by C1/R8. LED D1 is blinking when relay is disengaged and steady when engaged. The screenshot shows U1 detecting an error – relay disengaged and LED is blinking…

Thanks for info, Kevin. Now changed driver voltage from +/-15 V to +/-35 V and op amp to OPA445 (from OP27). So far I’m happy with the outcome.

Merry Christmas!

Completed a second channel of a Raal amplifier. Current through output boards are 2.5 A giving heat sink (Modushop 300 x 40 x 80 mm) temperature of 85 degree Celsius (185 dergee Fahrenheit). Driver boards powered by +/- 15V. Original it’s +/-35V. I might try the higher voltage but my idea is to use mostly smd parts in driver boards and then you probably have to reduce voltage to something like +/- 15V. There is no bass filter at the moment on the boards but Roon is taking care of that. Rear plate is to short. But that was what I had at hand – shouldn’t affect the sound?

Here on ”test bench” or floor. Output board on heat sink powered by the box to the right containing two Mean Wells 2*24V/15A. Driver board is powered by AMB dual sigma set at 15V. Upper DMM shows 0.166V cross one of the 0.47 ohm power resistor. 65.5 on the other meter is temperature in Celsius, prob has a special hole in the heat sink. I’ve run this at higher current… 95 degree Celsius - not got good for wooden floor. Sound quality – interesting. Try a balanced version. Two output boards on one (bigger) heat sink…

So far only been connected to power supplies. Have had a couple of long nights in kitchen.

Here is an attempt to make a “smd raal uberamp driver”. I followed Kevin’s schematic. The big resistor is for feedback/gain, I guess 1.5 – 2 W is required and a few components on “solder” side. The real challenge will be the power sections. 3A x * +/-24V * 8 * balanced - might be a bit extreme for headphone amplifier…

Lately the left channel humming has increased to become even more bloody annoying. But… today I cured it (pure luck - trial and error approach). I have two umbilicals between psu and amplifier. Both carrying 580V bias and then joining at the stax connector. So, I removed left 580V bias wire in amplifier and the hum disappeared. To my ears the amplifier is now dead silent.

Aerial picture of opamp driver and psu. I had some disturbing noise from the Mean Wells. After putting them their own enclosure the noise reduced considerable but there still is audible noise. With AMB’s Sigma22 supply +/-29V the amplifier was noise free. I only tried sigma22 for a few minutes since it hasn’t the current capability as the Mean Well, but it sounded OK. As for sound I find it enjoyable to listen to but I also think it has some sonically drawbacks (maybe) due to the switching mode power supplies. Bottom line is that I agree with the designer

Milled a second board today and after some struggling I eventually have a stereo opamp driver. Now I listen to this and this… Grüner Veltliner for my father-in-law... he was born in Austria.

I might. Give me a ping.

Here is a (my) version of Kevin’s opamp RAAL driver. Board is kitchen made. Some parts are smd but schematic is same as original. Only one channel working and it’s powered by lab power supply max 3A. Occasional when playing, not very load , leds indicating max current hit are flickering. But I've two 340W Mean Well supplies at hand. Mouser don't sell them supplies to ordinary consumers in Europe so my wife bought them for me. Lucky me.

Did this tonight

LES SIÈCLES, FRANÇOIS-XAVIER ROTH Sur instruments d’époque / On period instruments

Anyone out there have built the raal opamp driver besides justin? I’m interesting and I guess other people are as well in the outcome and thoughts about the driver.

look - terminal blocks...

B - (((R8+R9+R10)/R7)-1)*Vref

To me it sounds that you built yourself a nice amplifier. Enjoy.

At the power supply schematic – shouldn’t D12 anode be connected to the cathode of D1?

If you remove C2 (0.1uF cap) I guess it will possible to set BIAS to 230V with help of the 1M trimmer.

Thanks. Who made them - Mueller-r.. something?