I am trying to bias mine now.
It's taking a lot of turns of p1 and p2….I've gone about half way on the pot and still no voltage on R10/11. Or R9.
I am using 1K pots and the fairchild mosfets. Mosfets are cold, Jfets are getting warm. I've verified the BA-3 board is seeing voltage from the PSU.
Is this normal?
It's taking a lot of turns of p1 and p2….I've gone about half way on the pot and still no voltage on R10/11. Or R9.
I am using 1K pots and the fairchild mosfets. Mosfets are cold, Jfets are getting warm. I've verified the BA-3 board is seeing voltage from the PSU.
Is this normal?
Success!!! After shorting the inputs biased up to 1V and about a couple mv of offset.
My new rule is always let 6L6 do it first. Special thanks to him for really helping out on this project.
Now I just need to sort out the source selector, volume pot and extension shafts and put in the output caps.
My new rule is always let 6L6 do it first. Special thanks to him for really helping out on this project.
Now I just need to sort out the source selector, volume pot and extension shafts and put in the output caps.
In your Pumpkin Cookbook you recommended using XLR connectors and balanced POTS (two 2-channel, or 1 4-channel), and solder 1 and 3 pins in cable jack for input/output connection.
Blue Jeans Cables has a good tech article on balanced vs. unbalanced. The also recommend not mixing (problems with hum, ground loops) but suggest using a balun transformer if you cannot avoid:
A Question of Balance -- Blue Jeans Cable
Maybe after many winters of DIY, one would have a balanced DAC, balanced F-4 monoblocks, replaced CD with balanced version, built a balanced phono amp, rewired TT. Maybe, probably not.
More likely, one may consider a balanced amp (F-4) and use unbalanced sources. Do you think it would make sense to build a balanced pre-amp for that scenario?
pretty much matter of one's taste
SE ( so , non- balanced) generally will yield more even harmonics in THD spectra , while balanced will yield more odd harmonics in THD spectra
it is really most prominent to have entire signal & amplification chain either balanced or SE , and - when mixed - having appropriate and of best quality gadget for conversion
is great tool for these conversions , same as BA3 Bal FE , used as preamp stage
SE ( so , non- balanced) generally will yield more even harmonics in THD spectra , while balanced will yield more odd harmonics in THD spectra
it is really most prominent to have entire signal & amplification chain either balanced or SE , and - when mixed - having appropriate and of best quality gadget for conversion
is great tool for these conversions , same as BA3 Bal FE , used as preamp stage
Did any of you consider to put the volume control at the output of the pre ?
... Like the stepped attenuator on the Aleph 1.7.
A 5K log attenuator would only have around 500 ohm output impedance in the midle setting I think. It would lower any noise there would be in the preamp by less than full power.
I have just build a mega C-R-C PSU and ordered PCB and transistors. And parallel I am going to build a transformer coupled tube pre. Both will be test devices on a piece of wood.
... Like the stepped attenuator on the Aleph 1.7.
A 5K log attenuator would only have around 500 ohm output impedance in the midle setting I think. It would lower any noise there would be in the preamp by less than full power.
I have just build a mega C-R-C PSU and ordered PCB and transistors. And parallel I am going to build a transformer coupled tube pre. Both will be test devices on a piece of wood.
The maximum output impedance of any resistive attenuator is ¼{Rs+Track resistance}
if Rs = 200ohm and the pot is 5K then the maximum output impedance is 1300ohms, not 500ohms.
This occurs when the attenuator is set to half voltage (i.e. middle setting ~= -6dB)
K guys I am in a pickle....I wanted to feed my Aikido 12VAC into my BA3-FE to get more gain. All I end up with is distortion even at very low levels. Here is what I have done to troubleshoot with no avail:
1. replace Aikido 12vac with B1
2. replace ALL jfets with new ones
3. turned down the voltage
4. swapped interconnects
5. re-biased BA3-FE to 1V
So yes I know it has to do with my BA3-FE, but this is the same one I pulled out my F4 and I know its good, so what gives? The only true delta is my ac-dc regulator which is pushing out a 25V DC.
1. replace Aikido 12vac with B1
2. replace ALL jfets with new ones
3. turned down the voltage
4. swapped interconnects
5. re-biased BA3-FE to 1V
So yes I know it has to do with my BA3-FE, but this is the same one I pulled out my F4 and I know its good, so what gives? The only true delta is my ac-dc regulator which is pushing out a 25V DC.
I originally had the BA3 in my F4 amp, got pretty hot inside it and once I had the Aikido built, I decided to move the BA3 into its own chassis. I had tested the B1, DCB1 and Aikido with the BA3 when the BA3 was in the F4 chassis. So I built a dc regulator, had to tweak some parts so I get 24V per rail. Put the regulator in the chassis, used the light bulb and verified it had no issues. Placed my BA3 into the chassis, wired it up and re-biased to 1V.
One thing that caught my attention and I thought it had to do with the heat of the F4 (because I first saw this when coupled inside F4) is that the DC offset is really hard to keep at 0, its always drifting....thought this was common to heat? Anyways once I get it close to 1V and 0 offset I connected my preamp (Aikido, or B1 or DCb1) and slowly turning up the volume I hear music but then it starts distorting in both channels. Distortion begins soon as I start turning volume.
I have rechecked my wiring. I know my other preamps are good and they have been used with this BA3 before, they also work just fine going into my F4, with very little sound/gain
I dont believe it has anything to do with any of my preamps (B1 and DCB1 1 x gain and Aikido 8 x gain) because they function as they supposed to with my F4 and I had used them before with this very BA3.
One thing that caught my attention and I thought it had to do with the heat of the F4 (because I first saw this when coupled inside F4) is that the DC offset is really hard to keep at 0, its always drifting....thought this was common to heat? Anyways once I get it close to 1V and 0 offset I connected my preamp (Aikido, or B1 or DCb1) and slowly turning up the volume I hear music but then it starts distorting in both channels. Distortion begins soon as I start turning volume.
I have rechecked my wiring. I know my other preamps are good and they have been used with this BA3 before, they also work just fine going into my F4, with very little sound/gain
I dont believe it has anything to do with any of my preamps (B1 and DCB1 1 x gain and Aikido 8 x gain) because they function as they supposed to with my F4 and I had used them before with this very BA3.
As 6L6 suggests above your post it sounds as though you are overloading the power-amp - especially so with the Aikido.
What are your expectations in adding the BA3 in the chain?
Have you tried, again, the F4 - but WITHOUT the BA3 in any position in the chain? And the results? IF OK, then leave the BA3 out of the chain.
What are your expectations in adding the BA3 in the chain?
Have you tried, again, the F4 - but WITHOUT the BA3 in any position in the chain? And the results? IF OK, then leave the BA3 out of the chain.
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