When setting Offset, has anyone had trouble with it not staying steady? I’m now able to bias it to 1V across R10 and 11 but DC Offset I have struggled with settling on both channels.
I have confirmed the preamp works as I set the offset as close to 0 as possible and it played fine but checked the offset after and it’s inconsistent. I also noticed it changes drastically as soon as I remove the cover.
I have confirmed the preamp works as I set the offset as close to 0 as possible and it played fine but checked the offset after and it’s inconsistent. I also noticed it changes drastically as soon as I remove the cover.
Are you measuring dc offset before the output capacitor?
Also use shorting plug or resistor between hot and ground on input.
BA3 pre is so sensitive about temperature change. If you breathe out to mosfets, dc offset may jump all around.
Try not to breathe while adjusting, and if there is air blower or conditioner, turn it off.
When pre heats up, adjust dc offset to "near" zero and be happy with it.
There will be no dc at the output after all, because of the cap..
Also use shorting plug or resistor between hot and ground on input.
BA3 pre is so sensitive about temperature change. If you breathe out to mosfets, dc offset may jump all around.
Try not to breathe while adjusting, and if there is air blower or conditioner, turn it off.
When pre heats up, adjust dc offset to "near" zero and be happy with it.
There will be no dc at the output after all, because of the cap..
That’s why there are caps on output. If it was steady, you wouldn’t need the caps. This is normal behavior for this circuit.
Bias/offset is easier to set if you connect a resistor across the outputs, 10-20k, whatever, just so the circuit has something to look at.
Dennis is 100% correct however - it's not going to be super stable (because of temperature fluctuations mostly) and the cap is there to make it not matter.
Dennis is 100% correct however - it's not going to be super stable (because of temperature fluctuations mostly) and the cap is there to make it not matter.
Amp biased up and is singing! It sounds awesome on my F6 but I would like to see how it sounds on my F4 and then with two F4’s in parallel.
Can I confirm that R13 just needs to be increased for more gain? I have spare 2K 3 watt resistors. Will they work and does the preamp have to be re-biased or can they just be switched out?
Thanks.
Can I confirm that R13 just needs to be increased for more gain? I have spare 2K 3 watt resistors. Will they work and does the preamp have to be re-biased or can they just be switched out?
Thanks.
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Hello,
I intend to build a El34 single ended tube amplifier for which I will need a pre-amp.
I have a set of DIY speakers based on a full range driver plus a bass driver ( Visaton B200 + Visaton TIW200XS).
The tube amp will drive the full range speaker, an Elektor Crescendo the TIW200XS.
So I need to have an active Xover also. I do not intend to build the Xover with tubes. The current solution is based on opamps, I will change to a Nelson Xover eventually.
Since I will not be 100% tube in any case I am leaning towards using the BA3 as line stage.
I am aware that this is all highly subjective but maybe some of you are already using a BA3 to drive a tube amp ? Any feedback would be very much apreaciated.
Thxs,
Emanuel
I intend to build a El34 single ended tube amplifier for which I will need a pre-amp.
I have a set of DIY speakers based on a full range driver plus a bass driver ( Visaton B200 + Visaton TIW200XS).
The tube amp will drive the full range speaker, an Elektor Crescendo the TIW200XS.
So I need to have an active Xover also. I do not intend to build the Xover with tubes. The current solution is based on opamps, I will change to a Nelson Xover eventually.
Since I will not be 100% tube in any case I am leaning towards using the BA3 as line stage.
I am aware that this is all highly subjective but maybe some of you are already using a BA3 to drive a tube amp ? Any feedback would be very much apreaciated.
Thxs,
Emanuel
I-Select installed in BA3 front end
I really like the BA3 FE, but one thing both of mine do I don't care for is a small snapping when operating the selector switch. This also happens to a lesser degree with my Wayne's 2018 line stage.
My BA3 (as well as the BA 2018 linestage) were built just like 6l6's build guide, same parts, including the Tubecad selector switch.
Having just finished the Iron Pre, it switches in total silence. It of course uses relays to do the switching, with selector switch serving to turn on the relay instead of switching signals. Figuring this was reason for the snapless switching, I got a few of Teabag's group buy I-Select kits.
Similar to Iron Pre's selector section, but it has Pads to mount a pot in addition to pads for relays and a tiny power supply that will take A/C and has rectification for separate transformer, or an input for taking D/C from your preamps positive side of power supply.
Once installed, I- Select works perfectly, and switching is now silent. Replaced selector switch with one that came with kit, same unit I used in Iron Pre.
I am going to put one in the Wayne's 2018 BA linestage
When I rebuild it with new board from store.
Iron Pre board very well thought out, would be great if later broken down do selector section board and separate board for the shunt supply for preamps. But, this is DIY after all. Maybe it's time to learn circuit board making!
Russellc
I really like the BA3 FE, but one thing both of mine do I don't care for is a small snapping when operating the selector switch. This also happens to a lesser degree with my Wayne's 2018 line stage.
My BA3 (as well as the BA 2018 linestage) were built just like 6l6's build guide, same parts, including the Tubecad selector switch.
Having just finished the Iron Pre, it switches in total silence. It of course uses relays to do the switching, with selector switch serving to turn on the relay instead of switching signals. Figuring this was reason for the snapless switching, I got a few of Teabag's group buy I-Select kits.
Similar to Iron Pre's selector section, but it has Pads to mount a pot in addition to pads for relays and a tiny power supply that will take A/C and has rectification for separate transformer, or an input for taking D/C from your preamps positive side of power supply.
Once installed, I- Select works perfectly, and switching is now silent. Replaced selector switch with one that came with kit, same unit I used in Iron Pre.
I am going to put one in the Wayne's 2018 BA linestage
When I rebuild it with new board from store.
Iron Pre board very well thought out, would be great if later broken down do selector section board and separate board for the shunt supply for preamps. But, this is DIY after all. Maybe it's time to learn circuit board making!
Russellc
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This is the unit I used, as in 6L6's build guide:
Stereo selector switch
The little switch used with the relay set up is light and inexpensive, but I know it isn't handling signal itself, just a switch to turn on relays.
So if I had just wired Tube-Cad selector it would continue to pop? Tube-Cad does not mention if it was make before break or not...guess it isn't? I have this switch in another BA3 FE with the slight pop, and in Wayne's 2018 BA linestage too....but I have another I-Select kit and when I stuff my newly acquired store boards I intend to implement this. Think I will also try just the switch hooked up regular style in the other BA3 FE, and see if it alone stops the snapping.
I thought that the relay being in between switch and input killed the snaps, not the case?
Oh well it was a learning experience and cleared up a lot of hook up confusion I've had concerning preamp input selector wiring.
Russellc
Funny you mentioned that. When I first fired up I-select the slight click of the relay wasnt loud enough I could hear...I thought, actually it was occurring at the same time as the slight mechanical noise switch made when switched. Slowing the turn of selector, just before "clunk" of switch you could hear the relay click. I suppose this is coming up on the "make" causing the click of relay, and the "break" where the mechanical clunk would have obscured the mild click of relay.
Russellc
Russellc
Just looks like a switch to me! I tend to follow build guides closely, to make potential problems easier to diagnose. It was the switch used, so I went with it. Very inexpensive, snap slight, just enough to be irritating. But there is a slight snap with it, seemed to help to put shorting plugs in the one unused input...maybe my imagination but seems to help somewhat. Plus I use his A/C on off switch and power supplies. So I just threw in the selector switch too. Used them in two BA3 FE, and Wayne's 2018 BA lineamp. One of the BA3 FE has now been cured and I learned a little beginner preamp input selector hookup.
Russellc
Russellc
look at close
if you see , while rotating shaft from one position to next , that wiper in mid position is riding on top of both adjacent contacts - then it is make before break
if you see it not making contact with both, in mid position - it is break before make
simple as that
in plenty of cases using either of them is going to be the same, but in case of more complicated construction, chosing proper one is crucial for non-popping operation
I didn't checked,by mistake got those break ones from regular vendor, and used them in one phase of development of Iron Pumpkin balanced, which is sorta complicated having additional relay for automatic switching between SE or Bal In modes, and I pretty much threw through the window entire afternoon, chasing why I have pops on output, whatever I have brain to do..... only to find that damn Lorlin switch is non-shorting
go figure; when dealing with inductive potentials in gadgets, one must obey all rules
anyway, enough babble, do your homework
if you see , while rotating shaft from one position to next , that wiper in mid position is riding on top of both adjacent contacts - then it is make before break
if you see it not making contact with both, in mid position - it is break before make
simple as that
in plenty of cases using either of them is going to be the same, but in case of more complicated construction, chosing proper one is crucial for non-popping operation
I didn't checked,by mistake got those break ones from regular vendor, and used them in one phase of development of Iron Pumpkin balanced, which is sorta complicated having additional relay for automatic switching between SE or Bal In modes, and I pretty much threw through the window entire afternoon, chasing why I have pops on output, whatever I have brain to do..... only to find that damn Lorlin switch is non-shorting
go figure; when dealing with inductive potentials in gadgets, one must obey all rules
anyway, enough babble, do your homework
