I think an adjustment of P3 will have far more effect than the choice of mosfet in this preamp. Have you tried it?
I am not sure the mosfet choice will be as pronounced as on a power amp. current and bias levels are low, the mosfets are not doing much.
I have tried Fairchilds, IRF and Toshiba in the F5 power amp. My favorite are the Toshiba mosfets.
I am not sure the mosfet choice will be as pronounced as on a power amp. current and bias levels are low, the mosfets are not doing much.
I have tried Fairchilds, IRF and Toshiba in the F5 power amp. My favorite are the Toshiba mosfets.
P3 effects DC offset. Just a warning since you have no output cap. And adjusting P3 has a pretty dramatic effect. I think adjusting for dominant 2nd harmonic will satisfy you.
Are you sure the offset is stable? That has not been my experience at all. I see 100mv fluctuations with temp.
Kind of off topic but I've communicated with someone who has changed the feedback arrangement on the BA-3 to one like the Vfet 2 front end. It's very interesting and it makes the offset stable (no need for a cap). All one needs is a few resistors to try it. I haven't tried it but it's worth a shot.
Are you sure the offset is stable? That has not been my experience at all. I see 100mv fluctuations with temp.
Kind of off topic but I've communicated with someone who has changed the feedback arrangement on the BA-3 to one like the Vfet 2 front end. It's very interesting and it makes the offset stable (no need for a cap). All one needs is a few resistors to try it. I haven't tried it but it's worth a shot.
I wonder if this "brightness" is down to a reduced phase margin of this "amplifier"?
Have you checked how well it copes with fast signals?
Kind of off topic but I've communicated with someone who has changed the feedback arrangement on the BA-3 to one like the Vfet 2 front end. It's very interesting and it makes the offset stable (no need for a cap). All one needs is a few resistors to try it. I haven't tried it but it's worth a shot.[/QUOTE]
You can find more on this in the BA3 balanced thread. Generg has experimented with it and has also posted some simulations. I wonder how it changes the sound?
You can find more on this in the BA3 balanced thread. Generg has experimented with it and has also posted some simulations. I wonder how it changes the sound?
I'll recheck the DC offset again tonight, but it has been pretty stable. I was previously using the B1 buffer with this setup and I found it to not be on the bright side at all. I just needed more gain. I am using the preamp for 2 turntables, CD player and Burson DAC. I am using a Blue ALPS 20k pot shunted with a 47k resistor. I've also use a 50k before and had the same results. I'm sorry for the scattered responses to the questions.
One thing I did change from the norm is R13. I decreased it's value to 150 and 170 because there was too much gain there is a channel imbalance.
One thing I did change from the norm is R13. I decreased it's value to 150 and 170 because there was too much gain there is a channel imbalance.
I would check the offset. I am not sure if your Aleph is cap coupled on input or not but I fear for your speakers.
I'm going to throw in some output caps and adjust P3 tonight. Does anyone have any suggestions on how to do this without a way to measure for 2nd and 3rd harmonic? Is there a program I can download to measure, so I can make a more accurate adjustment? Or should I just do this based on my ears?
Some sort of FFT analyzer software (a lot of freeware available on the net) and a USB audio interface will work. Or a oscilloscope, of course.
Feed the amp a 1V or 2V sine wave (1Kz) and look at the harmonics. Adjust to where the 2nd harmonic is above the 3rd harmonic and consistent channel to channel.
You can use your ears but it's not precise and the channels will be uneven. You can try, say 5 turns one way on the pots and relisten.
I believe the boards are mirrored so check that the pots work the same way channel to channel. I am not sure.
Feed the amp a 1V or 2V sine wave (1Kz) and look at the harmonics. Adjust to where the 2nd harmonic is above the 3rd harmonic and consistent channel to channel.
You can use your ears but it's not precise and the channels will be uneven. You can try, say 5 turns one way on the pots and relisten.
I believe the boards are mirrored so check that the pots work the same way channel to channel. I am not sure.
I added some output capacitors and adjusted P3 using an FFT analyzer. The first side went well. I was able to get the 2nd above the 3rd, however I'm maxed out with the adjustment. The other side did not turn out as well. Having P3 maxed out, the 3rd is still slightly higher than the 2nd. I'm thinking I have some poorly matched components? What is a reasonable difference in 2nd and 3rd harmonics to shoot for with my adjustments?
Also, after getting the unit's DC reset, I turned it off and let it sit a while. When I restarted it up, there was quite a bit of DC on the outputs. I'll be leaving the output caps in place. Thanks for the advice and warning.
As far as the sound goes, it made a noticeable difference. Certainly more of what I am looking for.
Also, after getting the unit's DC reset, I turned it off and let it sit a while. When I restarted it up, there was quite a bit of DC on the outputs. I'll be leaving the output caps in place. Thanks for the advice and warning.
As far as the sound goes, it made a noticeable difference. Certainly more of what I am looking for.
madskaman,
Are you turning the pots in the same direction or opposite direction to each other? second harmonic will increase turning in either direction but it's in phase in one direction and out of phase in the other. The point where second is nulled is not in the center of the trim pot, at least thats my experience. Just remember the two channels are mirror imaged on the board so turn the pots in the opposite direction in relation to each other.
Are you turning the pots in the same direction or opposite direction to each other? second harmonic will increase turning in either direction but it's in phase in one direction and out of phase in the other. The point where second is nulled is not in the center of the trim pot, at least thats my experience. Just remember the two channels are mirror imaged on the board so turn the pots in the opposite direction in relation to each other.
It's not a one way, 2nd harmonic goes up adjustment. It may go up or down for a while and then go the other way. I'd try turning the pot the other way.
Also, well matched components leads to a REDUCTION in even order harmonics.
I seem to be one of the few around here who prefers 3rd dominant...
Honestly, the best thing to do do with would be to test at the output of your aleph. This way you actually know the harmonic distribution going to your speakers.
Also, well matched components leads to a REDUCTION in even order harmonics.
I seem to be one of the few around here who prefers 3rd dominant...
Honestly, the best thing to do do with would be to test at the output of your aleph. This way you actually know the harmonic distribution going to your speakers.