I am new to builds but have begun the Poindexter 6v6 Musical Machine. Very basic question: How does one connect the Power supply to 2 audio channels?? The schematics show power supply connections to only one channel. Thanks so much for any help.
Attachments
Points A, B, C and heaters are common for both channels, points D (bias) are individual (one for the left channel and one for the right)
Not that is exactly relevant to your question, but these aren’t the latest revision of this amp. The final version has a CCS for the LTP and other driver tubes.
You might want to look them up. They float around this board I think. Otherwise ask me.
You might want to look them up. They float around this board I think. Otherwise ask me.
Thanks so much for your help - another question. I have finished the build and am quite happy with the sound except I am getting only 1.8V across 8 ohm output (approx 2W power). Any thoughts on how I can increase that power output. I am using Klipsch 96db speakers, which are not quite loud enough. Thanks
Adjust the "idle" current of each PP pair downward (a larger negative potential on the grids). That moves the operating conditions set away from Class "A" towards Class "B".
Poinz envisioned an amp that rarely cuts the O/P tubes off. Call it "shallow" Class "A". To get a larger max. power value, those tubes need to cut off somewhat more frequently. As always, compromises reign.
Remember, max. theoretical efficiency for Class "A" is 1/2 and Π/4 for Class "B". Obviously, Class "AB" lies between those numbers.
This amp, built correctly and to the specs, should provide 5-6W (even in the class A it should be around 4W). So either something is wrong with the assembly or your source doesn't put up enough signal voltage.
Thanks for the replies. Absolutely, there could be something wrong with build. As a matter of fact, surprised if there wasn’t. That said, the sound quality is great, just not enough of it. Thanks again. I will probably try another build, any suggestions??
That's true for that operating point (intended for AB, 300V/30mA, 9W dissipation) while keeping in class A. Obviously the amp intended to work solely in class A should be biased much hotter.
My suggestion would be fixing the existing amp first.
As TG said it is a good idea to try to fix this issue first if you are happy with the sound.
Anyway it's not possible to extract substantial power from a simple 6V6 PP triode connected. It may be interesting to go to grid current territory but that's not possible with this circuit.
Did you check all voltages? enough input gain?
Anyway it's not possible to extract substantial power from a simple 6V6 PP triode connected. It may be interesting to go to grid current territory but that's not possible with this circuit.
Did you check all voltages? enough input gain?
No, I do not know how to do that. I calculated power by measuring voltage across speaker outputs using white noise and P = (VxV)/R
That's not the calculated power, that's some random number.
If you don't have dedicated signal generator, but do have standard component CD player, find or generate 1kHz sine wave (0dB peak or -3dB RMS, which is the same), burn it onto CD blank and use it as the test signal.
If you have line-level preamp of some sort, you can probably get away with the computer or even smartphone as a signal source.
Having the 8 Ohm dummy load (20W+ wirewound resistor) and an oscilloscope (to check for actual output distortion/clipping) would also help immensely.
If you don't have dedicated signal generator, but do have standard component CD player, find or generate 1kHz sine wave (0dB peak or -3dB RMS, which is the same), burn it onto CD blank and use it as the test signal.
If you have line-level preamp of some sort, you can probably get away with the computer or even smartphone as a signal source.
Having the 8 Ohm dummy load (20W+ wirewound resistor) and an oscilloscope (to check for actual output distortion/clipping) would also help immensely.
Thanks to all. I increased the idle voltage slightly with little to no effect. I changed the 6v6 from triode to pentode but got a very loud hum so changed them back. Guess I will live with the reduced volume.
When I go from triode to pentode - I used take-off from B+ voltage, before OPT - is that correct or should I use another voltage source?
Thanks
Thanks