Thanks for the photos Tim.
Do you get the DC offset to zero by setting exactly 1V across R10 and R11?
Chris
Not exactly. Once I had 1V across each, I measured the offset voltage and tweaked either P1 or P2 to minimize offset.
I don't know: I got them at a surplus store for 20c each. They were originally a different shape (you can see how I mangled them) so they probably are performing slightly better than spec (more stretched out than originally).
They get up to about 34 degrees C with the cover off in my overheated workspace - probably no more than 10 degrees over ambient.
tim
BA-3 wierdnesses
I've noticed a couple of slightly strange things with my BA-3:
tim
I've noticed a couple of slightly strange things with my BA-3:
- It takes a while for the right channel to develop gain. When I first turn it on, there's normal gain in the left channel, but the right channel is quieter. It comes up to normal over a period of several minutes.
- The -ve rail seems to draw more current than the +ve rail, which leads to slightly different supply voltages for each. Not a big difference, and probably due to transistor variation, I'd guess?
tim
Could be. I need to take it out of the system and see if I can find changing voltages during warm-up. I guess it could also be a heat-sensitive component.
Ha, ha! I am not alone....
I had the difference in the negative supply voltage too!
But only with a supply like Nelson used in X0 with an 7815, the voltage got down to 5 (!) V on the negative rail.
This did not happen with shunties and the aleph P supply...
The x0 supply works fine with all other pres Aleph P, pumpkin...
I do not know why......
Timbarnes do you have a gain of 30 or about 8 like Botte and me?
I could not get less distortion with the higher bias, but I did not check the sound.
Hi all,
I found out about the diyAudio Universal Mounting Specification from this thread about the BA-3. Rather than distract from the main thread of conversation here, I started a separate thread to discuss it here: http://www.diyaudio.com/forums/construction-tips/198695-universal-mounting-specification.html
I hope folks who are considering using the standard will contribute.
I found out about the diyAudio Universal Mounting Specification from this thread about the BA-3. Rather than distract from the main thread of conversation here, I started a separate thread to discuss it here: http://www.diyaudio.com/forums/construction-tips/198695-universal-mounting-specification.html
I hope folks who are considering using the standard will contribute.
Ha, ha! I am not alone....
I had the difference in the negative supply voltage too!
But only with a supply like Nelson used in X0 with an 7815, the voltage got down to 5 (!) V on the negative rail.
This did not happen with shunties and the aleph P supply...
The x0 supply works fine with all other pres Aleph P, pumpkin...
I had a big power supply sag when I had a couple of 30V zeners in the power supply (with series resistors, of course). I thought I'd calculated them to allow enough current, but the power supply sagged to 9V. The amp worked fine, but it didn't seem like the right thing, so I took out the zeners and resistors, and put a power resistor in the AC line after the fuse to bring down the line voltage a bit.
My transformer is 24+24V, which gives 37V no-load.
So with a simple CRC filtered supply it's all working OK, even though 32V is a big higher than ideal.
tim
I don't know what the gain is: I'm running a CD player and a turntable into my F4 and getting plenty of volume, so I expect the gain is towards the higher end.
I suppose I could play a sine wave CD and measure the output voltage vs input voltage?
I will shortly be in the same situation
Any suggestions for a decent piece of equipment that does not cost thousands of $. Please PM. Sorry, for being OT - won't happen again!
Cheers,
Nic
I will shortly be in the same situation
Any suggestions for a decent piece of equipment that does not cost thousands of $. Please PM. Sorry, for being OT - won't happen again!
Cheers,
Nic
I think this setting the required amount of harmonics is part of the heart of the BA-3.
I once saw a series of block 'waves', a specific pattern, described in an article, that was supposed to show a drift off 0 volt, when 2nd harmonics was present in the amplifier. I must admit this article was from the early eighties, probably in l'Audiophile,
I hope mentioning this triggers someone else.
At least I can look out for it
.So then the pattern can be distributed as a WAV file and you would not need a sophisticated measurement.
albert
Tim,
Is your power supply then just CRC filtered with no voltage reg?
Recent experiences with the BiB shunt reg where I thought the current was seven times lower than it actually was. With a lesser load I could set the voltage happily at the required 12V but in actual use under the bigger load it wouldn't shift above 9V until I increased the current to the mosfet. I just wonder whether one of the mosfets here is being starved somehow. Layman's point of view this.
Chris
Just CRC - 15 ohm because that's what I had lying around.
Because the BA-3 is able to be set up as part of a power amp, I simply created a smaller version of a typical Pass power supply. I could also have just run power from the F4, I guess, but I liked the idea of a separate power supply for greater flexibility.
tim