I have a Jolida JD1501 hybrid integrated amp. Great amp, especially at it's price (US$650 retail), but it's input is way to sensitive. The most I can ever turn it up is 9-10 o'clock, the lowest is 7 o'clock. And, even turned all the way down, there is some bleed through. Also there is some channel to channel mismatch at the very lowest levels. I would like to get up more in the middle of the control. I believe it is an Alps pot.
So, how can I lower the gain? Here is the schematic:
And, while I'm in there, are there any other obvious improvements I should make? I'm currently using NOS GE 12AX7 tubes, I also have some CV4004 laying around. I've read somewhere that a 12AT7 should work and would lower gain, but may increase distortion?
Thanks,
David
So, how can I lower the gain? Here is the schematic:
An externally hosted image should be here but it was not working when we last tested it.
And, while I'm in there, are there any other obvious improvements I should make? I'm currently using NOS GE 12AX7 tubes, I also have some CV4004 laying around. I've read somewhere that a 12AT7 should work and would lower gain, but may increase distortion?
Thanks,
David
Reducing gain.
This one has voltage shunt feedback . If you raise R101 or reduce R103 the gain would go down. It might not be a good idea to drop the value of R103 because it will load the output of the tube even more. It would be better to raise the value of R101.
My simulation shows a gain of 8 and it drops to about 2 with R101 changed to 22k ohms. From what you explained , it might look like a drop in gain by two time may not be enough. So you can try a drop of about 4 times by using 22k. It will also improve the distortion figures. Input resistors in series with the input will contribute to the S/N ratio. But as this is a line level amp you may not be affected much by the increase in noise level--especiallly as the vol pot is after the amp.
Coming to c101 and c102. I would like them to go. In some circuits I tried the sound was much better with the cathode caps removed. As Colt 45 said the gain will also drop. I simulated it and a the gain dropped to 7 with C101 and c102 removed. That is not enough. You could also make R101 15K or so. Change R101 to something between 4.7K and 22K to get the levels you want. In any case just snip off the c101 and 102 first and see if it improves the souind. After that you can raise R101 to get what you want.
Cheers.
This one has voltage shunt feedback . If you raise R101 or reduce R103 the gain would go down. It might not be a good idea to drop the value of R103 because it will load the output of the tube even more. It would be better to raise the value of R101.
My simulation shows a gain of 8 and it drops to about 2 with R101 changed to 22k ohms. From what you explained , it might look like a drop in gain by two time may not be enough. So you can try a drop of about 4 times by using 22k. It will also improve the distortion figures. Input resistors in series with the input will contribute to the S/N ratio. But as this is a line level amp you may not be affected much by the increase in noise level--especiallly as the vol pot is after the amp.
Coming to c101 and c102. I would like them to go. In some circuits I tried the sound was much better with the cathode caps removed. As Colt 45 said the gain will also drop. I simulated it and a the gain dropped to 7 with C101 and c102 removed. That is not enough. You could also make R101 15K or so. Change R101 to something between 4.7K and 22K to get the levels you want. In any case just snip off the c101 and 102 first and see if it improves the souind. After that you can raise R101 to get what you want.
Cheers.
> Here is the schematic:
With the pot settings you are getting, I would scrap everything shown. Well actually, throw away the 12AX7, disconnect the top of W1 from the 12AX7 circuit, and wire the wiper of S1 to the top of the volume pot.
You lose the tube sound, but gain a much higher input impedance. (It is under 10K now, which may be fine for 99% of solid state sources, but seems mighty low to my old eyes.)
With the pot settings you are getting, I would scrap everything shown. Well actually, throw away the 12AX7, disconnect the top of W1 from the 12AX7 circuit, and wire the wiper of S1 to the top of the volume pot.
You lose the tube sound, but gain a much higher input impedance. (It is under 10K now, which may be fine for 99% of solid state sources, but seems mighty low to my old eyes.)
Why not re-engineer the power supply to give around 10mA, replace the 12AX7 with a 12AU7, replace R101 with 10K (leave R103 at 47K), lower the output pot to 22K, and remove the capacitors from the bottom cathode resistor?
This should give you a gain around 3.5, close enough for government work, while lessening the feedback factor around the SRPP maintaining a nice tubey sound, and into the bargain increasing drive considerably without the distortive effect of imperfect caps at the lower cathode...
You will need to fiddle with the cathode resistors, which will probably be around halved.
And you can keep the wiring the same as well, same pinouts!
Cheers,
Hugh
This should give you a gain around 3.5, close enough for government work, while lessening the feedback factor around the SRPP maintaining a nice tubey sound, and into the bargain increasing drive considerably without the distortive effect of imperfect caps at the lower cathode...
You will need to fiddle with the cathode resistors, which will probably be around halved.
And you can keep the wiring the same as well, same pinouts!
Cheers,
Hugh
schematic did not make it w/previous post
The schematic did not make it on my previous post - trying again. This is the schematic for a 6SN7 fixed bias srpp on my bench I am playing with. Use R1 to adjust the gain of the circuit - decrease R1 = decreased gain. Food for thought
The schematic did not make it on my previous post - trying again. This is the schematic for a 6SN7 fixed bias srpp on my bench I am playing with. Use R1 to adjust the gain of the circuit - decrease R1 = decreased gain. Food for thought
Attachments
Hi,
Decrease it any further and you have the entire B+ on the grid.
Hell, yes..The beauty of tubes is that they can take a lot of abuse, but building a SRRP circuit and tieing all the gain down in a FB loop isn't making any sense to me. The FB loop may reduce the distortion and Zo of anything preceding it, it still doesn't make sense.
Get the iron out Asen, if you need help we're here.
Cheers,
Decrease it any further and you have the entire B+ on the grid.
Hell, yes..The beauty of tubes is that they can take a lot of abuse, but building a SRRP circuit and tieing all the gain down in a FB loop isn't making any sense to me. The FB loop may reduce the distortion and Zo of anything preceding it, it still doesn't make sense.
Get the iron out Asen, if you need help we're here.
Cheers,
fdegrove
Thanks for the help. If I get the iron out I'd rather build an Aleph 30 and an Aleph P. But I don't have much time now.
BTW, attenuating the input of the SRPP is quite a good solution as far as the circuit could give an 80V output.
I've been thinking of building a follower (and I have the parts) but wasn't sure it would sound as good as the SRPP does.
Regards
PS - I haven't applied FB, just have added more resistance to the pot I use. It a kind of devider. Maybe you got me wrong.
Thanks for the help. If I get the iron out I'd rather build an Aleph 30 and an Aleph P. But I don't have much time now.
BTW, attenuating the input of the SRPP is quite a good solution as far as the circuit could give an 80V output.
I've been thinking of building a follower (and I have the parts) but wasn't sure it would sound as good as the SRPP does.
Regards
PS - I haven't applied FB, just have added more resistance to the pot I use. It a kind of devider. Maybe you got me wrong.
Lower gain in 12AX7 SRPP
Frank/Asen - The fixed bias mod does increase the grid voltage but, the orginal circuit will have about half B+ on it already ~115V and it will allow you to dial down the gain while still biasing the lower triode - ie. should retain the circuit's orignial voicing. I also agree w/you Frank that should be careful or you can end up going to far with this circuit - Less than 5-10K for R1 (>10:1 R1/R5) is probably pushing it. As I said, I am playing with a 6SN7 version of this circuit on my bench - found a pair of Raytheon brown bases for $5 each that I really want to build something with. Anyway, I played around with several cathode follewers (VTV, AE3, Foreplay), w/wo C4S, etc.. and finally ended up with Bruce Bozenblitz's SRPP - which I think sounds the best. Unfortunately, it has to much gain. From here I tried the buffer circuit in the 12BH7 posts but, the bottom triode is barely on and the circuit did not retain the same voicing. So, in searching for alternatives I found the voltage divider or "fixed bias" circuit in TubeCad. I am still experimenting with the circuit - pulled the grid cap because, it seems to me anyway, that the fewer components I use more open/alive most circuits sound. FYI - circuit as drawn has about 190V on the grid of the top triode and 1V in = 6V out
Asen - another thought - have you considered swapping the 12AX7s with a 12BH7A? It is the same pin out as a 12AX7 and 12AU7, has lower mu than either and IMHO is one of the better sounding 9pin bottles. Should be plug and play in your preamp provided the power transformer can supply the extra filament current - would guess it will be fine. I have a pair of RCA 12BH7s in my Foreplay clone - IMO they sound better than my Amperex's - were hands down my all time favorites until I tried the 12BH7s
Frank/Asen - The fixed bias mod does increase the grid voltage but, the orginal circuit will have about half B+ on it already ~115V and it will allow you to dial down the gain while still biasing the lower triode - ie. should retain the circuit's orignial voicing. I also agree w/you Frank that should be careful or you can end up going to far with this circuit - Less than 5-10K for R1 (>10:1 R1/R5) is probably pushing it. As I said, I am playing with a 6SN7 version of this circuit on my bench - found a pair of Raytheon brown bases for $5 each that I really want to build something with. Anyway, I played around with several cathode follewers (VTV, AE3, Foreplay), w/wo C4S, etc.. and finally ended up with Bruce Bozenblitz's SRPP - which I think sounds the best. Unfortunately, it has to much gain. From here I tried the buffer circuit in the 12BH7 posts but, the bottom triode is barely on and the circuit did not retain the same voicing. So, in searching for alternatives I found the voltage divider or "fixed bias" circuit in TubeCad. I am still experimenting with the circuit - pulled the grid cap because, it seems to me anyway, that the fewer components I use more open/alive most circuits sound. FYI - circuit as drawn has about 190V on the grid of the top triode and 1V in = 6V out
Asen - another thought - have you considered swapping the 12AX7s with a 12BH7A? It is the same pin out as a 12AX7 and 12AU7, has lower mu than either and IMHO is one of the better sounding 9pin bottles. Should be plug and play in your preamp provided the power transformer can supply the extra filament current - would guess it will be fine. I have a pair of RCA 12BH7s in my Foreplay clone - IMO they sound better than my Amperex's - were hands down my all time favorites until I tried the 12BH7s
ALBQ
Thanks for your post. Actually I use E88CC tubes in my pre. I think they sound great. This is the best pre I've ever listend to. I built another pre with 12AX7 some years ago - a McIntosh C22 replica, but the the SRPP is deffinitely better. Anyway, I don't intend to modify the circuit. My future plans are to build an Aleph pre/power amp setup.
Regards
Thanks for your post. Actually I use E88CC tubes in my pre. I think they sound great. This is the best pre I've ever listend to. I built another pre with 12AX7 some years ago - a McIntosh C22 replica, but the the SRPP is deffinitely better. Anyway, I don't intend to modify the circuit. My future plans are to build an Aleph pre/power amp setup.
Regards
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