Solved. Thank you very much.
To adjust the bias, should it wait 1/2 hour for the temperature to stabilize?
Yes.. Also air flow -even breathing- can fluctuate readings..
So don't breathe while biasing 😉
I could not believe this when I first read it, so I tried on mine when I was setting them up. Its true.
Still cannot decide what pre to put with which amp. Just have to build another amp so I can use all three on an Aleph amp.
B1,B1.2 and B3.
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True. 😱
I have another problem. With the same input signal (1KHz sinusoidal, 100mV) One channel outputs 500mV and the other output 600mV. The transistors are paired (diyaudio kit) the resistors are 0.1% and the power stable. Bias adjusted to 800mV and in C3 there are between 5-8mV in both channels. Any ideas?
Do you have a load resistance on the outputs?
I was panicked when I had high voltage readings at
the outputs, then discovered that when I plugged into
an amp the voltage out of the caps was as it should be.
Just a thought.
I think the hard portion is over...I have no favor to drill and machine metals. I always thought I could do that stuff well, but I like more so... to solder and such. To machine metal at home is getting harder. I am getting older and I struggle to see well. I have magnifying glasses and a fancy monocle and I wear eye glasses.
I think I made some progress?
Many potentiometers to adjust?
I tried...yes?
I think I made some progress?
Many potentiometers to adjust?
I tried...yes?
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No Sound yet. I have the curse of 'Six Pots'.
If you go way back to Little House on the Prairie in the 70's
You too can find many pots to be adjusted.
Looks like this is a tweaker circuit. NP set it up for much adjustment. I must establish a base operation and then adjust further? Apparently I can go off on a tangent to 'measure' distortion to my like. I expect to comment on the sound of this circuit when your children get to university or jail.
I need at least a few weeks yes?
Jah.
If you go way back to Little House on the Prairie in the 70's
You too can find many pots to be adjusted.
Looks like this is a tweaker circuit. NP set it up for much adjustment. I must establish a base operation and then adjust further? Apparently I can go off on a tangent to 'measure' distortion to my like. I expect to comment on the sound of this circuit when your children get to university or jail.
I need at least a few weeks yes?
Jah.
Not that hard to bias and set DC offset when you understand why and what you are doing. Use many multimeters makes it easier. Jim's (6L6) build guide explains the procedure well. Center P3 and leave alone during setup. P3 is there for those that like to play and no need to touch for setup. P1 and P2 are the ones used in tandem and in small steps for bias and achieving low DC offset in front of C3.
Attach a voltmeter across R10 and another across R11 and another in front of C3 and start turning P1 and P2 in small steps watching the meters across P1 and P2 until you have 1V across each one. Then tweek P1 and P2 until the 3rd meter at the front of C3 has less than 50mv of dc with R10 and R11 showing close to 1V across each resistor. Then do the other channel. Many NP designs use same setup. I just this week stuffed another BA-3 board and set it up for a friend. Took only 30 minutes or less to set up both channels but then I used 6 meters. Great looking build.
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Using IRF9610/610, P1 & P2 = 1k I have:
+/_ 28VDC supply
0.6VDC measured across R10 & R11
5mVDC offset at C3
This is the highest voltage drop I can get across R10 & R11 while maintaining low DC offset with short aluminum style heat sink.
But first I had this:
+/_ 32VDC supply
0.9VDC measured across R10 & R11
10mVDC offset at C3
Heat/current was too much for the devices. I think it would be fine if I deployed a larger heat sink. I do in fact have the same ones as the 6L6 build so I may swap them today and try again. No listening tests yet but soon as I can. It took me an hour to to set both sides first time and on second set with lower rails took 20 minutes. I have yet to mount the LED's in the face plate and I want get some ribbon cable to finish that.
I also have a brand new Quantasylum QA401 24 bit analyzer...so it might be nice to take that for a test drive too. Its new in the box, as yet, unused.
Furthermore I have a second BA3 Pre PCB. I am going to China Town to see if I can score some 2SJ313/2SK2013's. Its a long shot and I may only find fakes? In that case I will order FQP3P20/FQP3N30's from Digikey.
+/_ 28VDC supply
0.6VDC measured across R10 & R11
5mVDC offset at C3
This is the highest voltage drop I can get across R10 & R11 while maintaining low DC offset with short aluminum style heat sink.
But first I had this:
+/_ 32VDC supply
0.9VDC measured across R10 & R11
10mVDC offset at C3
Heat/current was too much for the devices. I think it would be fine if I deployed a larger heat sink. I do in fact have the same ones as the 6L6 build so I may swap them today and try again. No listening tests yet but soon as I can. It took me an hour to to set both sides first time and on second set with lower rails took 20 minutes. I have yet to mount the LED's in the face plate and I want get some ribbon cable to finish that.
I also have a brand new Quantasylum QA401 24 bit analyzer...so it might be nice to take that for a test drive too. Its new in the box, as yet, unused.
Furthermore I have a second BA3 Pre PCB. I am going to China Town to see if I can score some 2SJ313/2SK2013's. Its a long shot and I may only find fakes? In that case I will order FQP3P20/FQP3N30's from Digikey.
...and I forgot to center P3 so I maxed them out and carefully turned back 10.5 turns to approximated center position. I thought I should add that although NP or 6L6 and others have noted the method elsewhere.
Try this member:
Selling Zhou Fang’s remaining stocks including some very rare Toshiba transistors
Russellc
China Town did not yield.
I ordered FQP's from Digikey.
I picked up the parts to finish the face LEDs.
Thanks to the leads to purchase the 2SJ/2SK's but I will skip as I am skeptical of all sources unless found in old vintage personal stash.
Cheers!
I ordered FQP's from Digikey.
I picked up the parts to finish the face LEDs.
Thanks to the leads to purchase the 2SJ/2SK's but I will skip as I am skeptical of all sources unless found in old vintage personal stash.
Cheers!
Hello guys, I've been having a look at the whole thread and, apparently, no one is using the universal PSU from this forum. The thing is I want to build this preamp, but I would like to use some spare parts I have in stock and I'm not really sure they will be suitable. I've got a:
toroidal transformer rating 300VA and 2x20V output.
And I've got an empty universal PSU from this forum that I would like to use.
Is it possible to use both of them here?
So many thanks. Lovely builds, by the way.
David.
toroidal transformer rating 300VA and 2x20V output.
And I've got an empty universal PSU from this forum that I would like to use.
Is it possible to use both of them here?
So many thanks. Lovely builds, by the way.
David.
The answer is yes, you can use them but...
The universal psu board is unregulated. Most people making this preamp are using regulated supplies. Even a simple lm317/337 supply will work. The universal psu is designed for power amps so it has much more capacitance than will be needed here. Also, it has no regulation, which is really what's needed here.
Your transformer will make 28-30v rails which is fine. It would be better to have some regulation so you can drop 3-5 volts. But the transformer is massively big for this application. Really you need a 50-100va transformer.
Your transformer and psu board is really for a power amp, not a preamp. I'd save them for a power amp and buy a 100va transformer and appropriate psu...both of which are pretty inexpensive compared to what you have.
But to answer your question, yes you can use what you have but it's not ideal.
I chose to use Salas shunt regulators. I felt they offer a very quiet and stable power source. My BA3 build has resulted in no discernible noise heard from the speakers. I have built a pair of F4 amps which I feel showcase whatever pre you are using. Currently my fav though I recently completed a Salas headphone/line pre. Also very nice.
All of this to say your 300va would be fine for a BA3 build.
All of this to say your 300va would be fine for a BA3 build.