MASantos

Refurbishing my old Pete Millett hibrid. The electrolitcs are over 15 years old, Should I replace them all or might they still be good? Building a new wood and aluminum case.

Don't forget that a transformer shouldn't work near max output current. Most recommendations for Class A amplifier are to use something with at least double the output current capability.

That's quite a compact build, what is the size of that case? Looks good! What VA is that transformer? It looks quite big.

I replaced the opamp and now it reads as the other 3. The offset still drifts around below 10mV. All other amplifiers I built (cfa, ckk3) with dc servos were very steady once the servos were installed. Is this drifting normal in the dynalo mini? I can't seem to find any solder bridges, it is as if the servos are not doing their job at all. Sound is now centered and similar in both SE and BAL ouputs, it is just the drifting that is puzzling me.

So I found a dead resistor in the R+ channel and replaced it. The L+ channel is the one acting up. I removed the servo jumpers and dialed the offset to less than 5mV on each channel. All fine. When I reinstalled the jumpers the L+ dc offset jumped to around 350mV while all the other channels remain below 2-3mV (but still wondering between 0 and 2-3mV, not ultra stable). The servo opamp for the L+ channel is getting power as it should. Might the IC be damaged and causing this? On further inspection, the 100k resistor next to the opamp measures 28K when soldered (I removed it and

Those are dc offset mV indeed. long day yesterday... I'll take readings on the resistors and check the biasing circuits to start!

My dynalo mini started acting up. Balanced output works fine, but SE output had low volume and distortion. I did another thorough clean up with alcool, double checked everywhere for solder bridges and it started working again, probably some bridge of flux I didn't spot before. It now has almost even level between channels, but just a bit lower level on the left channel. It could almost be due to a potentiometer inbalance but it is perfect in balanced output. Dc is 0.1-0.2 on the right channel and 2.4-2.6 on the left. When starting up the bias goes down quickly on the right chan

Done! Neutrik 4 pin xlr mounted from behind with blind taps. all in all went well considering it was done all with a hand drill. No drill press around 😔 The on/off indicator led was mounted underneath the case, makes for a nice effect. Quite happy with the result! Now the quest for a better streamer starts!

Thanks! I've listened to the CFA and dynalo mini for about 2 hours this afternoon trying to compare them. I liked the cfa better I believe but will keep listening. They are both great amplifiers but I can only keep one.

What is the SS/ZF thing?

I have about 160mA bias atm and the heatsink is about 34 Celsius. Transistors are about 10 C higher. I'll push it a bit closer to 180-200 once it is all done to see if it makes any difference.

The case is alright. Not top notch but also not a bad price considering it has most of the drilling done. The whole for the switch is 13mm wide with a little bevel on the front. The cap on the pushbutton didn't fit right so I made that cosmetic upgrade. I am considering painting the front panel mate black.

It's alive! Finished wiring today, only thing missing is drilling the front panel for the 4 pin XLR, waiting on a drill bit. Probably the best amplifier I had for the HD650. Absolutely dead silent, great sound! I'll need to make a better comparison with the dynalo mini, but at first glance it sure seems like a winner. Thanks for all the help I got during the build!

So when I got my case I got pretty upset with the looks of the power switch: So I search around the house for what could be used to improve this and found and unused aluminum kitchen drawer handle. Nice looks, hollow and easy to cut. A couple of minutes later:

That's reassuring! Mouser forgot my opamps. They're in transit as we speak. Regarding biasing, I have about 190mV across the 1ohm output resistors, heatsink is around 40 C . What is the target for biasing?