Hello everyone 🙂
I only have guitar amp experience so hifi its the first time, i made a schematic and i'm gonna need help to confirm it if possible:
The first part (The preamp) is an existant project from "diyaudioprojects.com" so this one is ok but i'm not sure about the phase inverter do you see an issu there ?
There is also no feedback do you think i need one and where should it be, around R7 (like in guitar amps) or maybe R4 ?
I made also the first version of the power supply, well its a bit exotic 😆
Thank you for your help
Alexis
I only have guitar amp experience so hifi its the first time, i made a schematic and i'm gonna need help to confirm it if possible:
The first part (The preamp) is an existant project from "diyaudioprojects.com" so this one is ok but i'm not sure about the phase inverter do you see an issu there ?
There is also no feedback do you think i need one and where should it be, around R7 (like in guitar amps) or maybe R4 ?
I made also the first version of the power supply, well its a bit exotic 😆
Thank you for your help
Alexis
There is a missing ground in the bias circuit, at the junction of R14 and R15.
The secondary 0 ohms tap is not grounded.
The line stage is not well suited to drive the 47k volume control, or even its own 10k feedback resistor.
The secondary 0 ohms tap is not grounded.
The line stage is not well suited to drive the 47k volume control, or even its own 10k feedback resistor.
I need to reread schematics before post 🙄
Missings grounds added:
Missings grounds added:
What do you mean by not suited ? Not well placed ? or maybe 47K is not enough ?
I think you have to use the 1R (or 10R) resistors in the cathode, not in the heater wiring.
Regards, Gerrit
Regards, Gerrit
Hello Orion 24 !
Congratulations for your first Hi-Fi design attempt 😎 - from a Guy coming from the guitar amp world, it can't be too bad ! 😉
As is, it is possible that your complete circuit may have too much voltage gain - unless you want to add a global NFB look, of course.
That said, I may not understood the purpose of C19, though : local NFB for gain reduction ? 🤔
I usually consider an input sensivity for full power at 0.7 to 1VRMS for my Hi-Fi amp builds.
For instance, my 1974 Audio Research D76 is even rated at 1.5VRMS for 75WRMS output max power.
You probably know this famed Dynaco MKIII circuit - Oh, I just post it as an example of simplicity and efficiency because it also drives a pair of 6550 or KT88 in Ultra-Linear connection, just like in your project :
Good luck for your build ! 🙂
T
Congratulations for your first Hi-Fi design attempt 😎 - from a Guy coming from the guitar amp world, it can't be too bad ! 😉
As is, it is possible that your complete circuit may have too much voltage gain - unless you want to add a global NFB look, of course.
That said, I may not understood the purpose of C19, though : local NFB for gain reduction ? 🤔
I usually consider an input sensivity for full power at 0.7 to 1VRMS for my Hi-Fi amp builds.
For instance, my 1974 Audio Research D76 is even rated at 1.5VRMS for 75WRMS output max power.
You probably know this famed Dynaco MKIII circuit - Oh, I just post it as an example of simplicity and efficiency because it also drives a pair of 6550 or KT88 in Ultra-Linear connection, just like in your project :
Good luck for your build ! 🙂
T
That circuit uses 12AX7 tubes, which cannot drive lower impedances, like the 47k pot or the 10k feedback resistor, very well.
It is also prone to subsonic peaking and instability. Find a better line stage. Or just use a pot and no tubes.
Oh my.... Thank you Gerrit it's crazy after re-checking there is still mistakes 🙄
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Hey Tubelectron, thank you for your input , well actually its not that easy even coming from guitar world because i have made a lot of amps but it was based on existing projects, i always do personal adjustments to fit my personal sound taste tho but its experimental. Of course i Know the basics of electronics and how to calculate amplification classes, psu simulations and love to do pcb and pretty good at wiring everything must be clean (at least now) 😆 but yeah sometime i'm a bit lost when i don't have the tools to understand theoretically speaking. Later i'll buy some Merlin Blencowe books 😀
You right i saw the Dynaco MKIII circuit before, at the beginning i wanted to do something with 12AX7, 12AT7 or 12AU7 because i have a lot of them but schematics are rare and plus i need matched tubes
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So if i understand well, to simplify, i can attack directly the PI with the 47K Pot without the line stage before like this ?:
I also have this one since the beginning but it use 6SN7:
Wich one do you think is gonna be the best ?
Best regards
Alexis
Yes, you can input at C1 in the first circuit if there is enough gain, which there probably is.
But don't build that line stage, it is not good.
I kinda like the 6SN7 circuit, and it allows feedback.
The first 6SN7 needs a 470k resistor from grid to ground.
But R5 should be 22k, not 470R.
But don't build that line stage, it is not good.
I kinda like the 6SN7 circuit, and it allows feedback.
The first 6SN7 needs a 470k resistor from grid to ground.
But R5 should be 22k, not 470R.
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Would it be trouble for you to upload the schematics to diyaudio.com, rather than linking to externally hosted graphics. So often these hosted graphics go away, and readers in a few years can’t see what the discussion was about.
Thank you very much Rayma, well i'm gonna go with the 6SN7 tubes 😊
Let's go for the pcb design !
I'm sorry i did not know, i will use the forum storage for the futures uploads
Let's go for the pcb design !
I'm sorry i did not know, i will use the forum storage for the futures uploads
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With feedback, you may need some compensation after the first stage, a series RC to B+.
I would add provision for that on the board.
Also would increase R7 and R8 to around 470k each.
I would add provision for that on the board.
Also would increase R7 and R8 to around 470k each.
I'd use V2 as an LTP, and a single stage with a 6SL7 for voltage amplification, DC-coupled to the LTP. Saves one tube, and less capacitors on the signal path.
I renamed correctly tubes and power lines for an easiest reading it wasn't clear
Which one is "B+" for you in the renamed schematic ? Usually B+ for me is for power tubes screens
I think i see what you mean i'll do the schematic to see if i'm not too bad 😛
After the first stage you mean after V1A ?
Which one is "B+" for you in the renamed schematic ? Usually B+ for me is for power tubes screens
I think i see what you mean i'll do the schematic to see if i'm not too bad 😛
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So i tried to do and understand some theory about "Long Tail Pair", I had to do some research I did not know what it was 😆
I also try to remove as you said one tube for the all amplifier but here i'm not sure at all 🙄
what do you think of this try ?
I also try to remove as you said one tube for the all amplifier but here i'm not sure at all 🙄
what do you think of this try ?
IOW, short C1, although that still may not be a good operating point for the PI,
so R11 may need to change as well.
so R11 may need to change as well.
This is a basic Williamson design. R1 needs to move to the right, to connect to V1 grid after the 470K grid resistor. This will tame some of the high-frequency response. You also need more feedback, so a much lower value R2. 10K would be appropriate for the standard 20dB of feedback. Otherwise you will have way too much gain and the amp will have poor control. V1 and V2 are 6SN7.
I designed a PCB for the basic Williamson. It would work for KT88s and fixed bias with a few changes and the addition of the bias pots off the board. Eliminate R23, R24, R27, R28 and C6:
The Hammond 1650NA would be a good transformer for KT88s, but any time you have an amplifier with global feedback you need to be able to test the amp on a scope to make sure it is stable. Some tuning of the compensation networks (C1, R5 and C7 on my PCB) is almost always necessary.
Thank you very much for you input 😊
So if i understand well I'm gonna need a scope, it's been at least 10 years since i used one , I'll have to learn again and I'm gonna need a dummy load of 8 ohm
Grovergardner your schematic is very close to the one i was gonna use, now i see what Rayma has suggested earlier about the RC between B+ and the first stage but a question come in mind instantly how I'm gonna determine the value of those ?
This is the new one based on Grovergardner schematic:
Is the 1M Pot Ok at the input ? I raised the value to not reduce R2
For the power supply I'm still hesitating of regulate all of the 6SN7 or maybe i don't need but as i have Reg modules available
Happy New Year 😀
So if i understand well I'm gonna need a scope, it's been at least 10 years since i used one , I'll have to learn again and I'm gonna need a dummy load of 8 ohm
Grovergardner your schematic is very close to the one i was gonna use, now i see what Rayma has suggested earlier about the RC between B+ and the first stage but a question come in mind instantly how I'm gonna determine the value of those ?
This is the new one based on Grovergardner schematic:
Is the 1M Pot Ok at the input ? I raised the value to not reduce R2
For the power supply I'm still hesitating of regulate all of the 6SN7 or maybe i don't need but as i have Reg modules available
Happy New Year 😀
I'm not sure what you mean, but in your power supply I would reduce your "B+" to around 430VDC. Increase R34 to 33K. This will put all voltages just right for the standard Williamson.
You don't really need the regulators, IMO, they seem like an unnecessary complication. Change R32 to 1K ohms @ 5 watts (or something close to that) and that's all you need.
You don't really need the regulators, IMO, they seem like an unnecessary complication. Change R32 to 1K ohms @ 5 watts (or something close to that) and that's all you need.