Hi all!
I just wanted to run my design for my preamp past you before I commit and send of for final components and PCB's 🙂
make sure everything is safe and works as intended, here is the schematic of the power supply:
And the preamp:
I will add another board for input/output switching and a relay delay on the output.
The low output impedance is needed for my usecase as I'm driving a MOSFET source follower to the speakers and will be experimenting with different output stages in the future.
I am a little concerned about gain-matching the L R channels, and have considered a bypass capacitor and trimmer pot in series with R10 in order to address this.
What do you guys think? any input is much appreciated.
I just wanted to run my design for my preamp past you before I commit and send of for final components and PCB's 🙂
make sure everything is safe and works as intended, here is the schematic of the power supply:
I will add another board for input/output switching and a relay delay on the output.
The low output impedance is needed for my usecase as I'm driving a MOSFET source follower to the speakers and will be experimenting with different output stages in the future.
I am a little concerned about gain-matching the L R channels, and have considered a bypass capacitor and trimmer pot in series with R10 in order to address this.
What do you guys think? any input is much appreciated.
Out of interest, has anyone tried a boot-strap approach as follows:
It seems to have very good distortion numbers and can be done with just one valve, halving current consumption from the filament.
It seems to have very good distortion numbers and can be done with just one valve, halving current consumption from the filament.
Anyone had experience in the SRPP and/or bootstrap circuits? what are the pros and cons of each? the bootstrap also uses negative feedback so I don't have to worry about gain matching there but can also apply feedback to the SRPP I guess 🤔
See you are thinking of using the Russian equivalent of the ecc83, which is a high gain tube. When the volume control is at 9 o'clock, is the power amplifier at maximum power? Better with a srpp with ecc82, or a preamp with a 12B4A tube? I build the SRPP preamp with ecc82 found in diyaudioprojects. It was a great preamp
Can you link the preamp from diyaudioprojects? I know there's a fair few on there. And yeah I went with the 6N2P as I got a few much cheaper than the ecc83 (or 12AX7) 7 of them for 21USD! 👍
There seems to be a fair bit more gain with the boostrap. 38.5db vs 33db.
Even so 33db should be well enough, the output stage can do 30Vp-p being single ended class A with no voltage gain (follower). It will be clipping at an input of about 700mv.
I think I'm going to go with SRPP with switchable feedback, something like:
Is there a need for input protection on a feedback design like this? to ether protect the tube or especially the device driving the input (DAC)?
Would this be better than the bootstrap?
There seems to be a fair bit more gain with the boostrap. 38.5db vs 33db.
Even so 33db should be well enough, the output stage can do 30Vp-p being single ended class A with no voltage gain (follower). It will be clipping at an input of about 700mv.
I think I'm going to go with SRPP with switchable feedback, something like:
Is there a need for input protection on a feedback design like this? to ether protect the tube or especially the device driving the input (DAC)?
Would this be better than the bootstrap?
//diyaudioprojects.com/Tubes/ECC802S-ECC82-12AU7-Tube-SRPP-Preamp/ I built this one a couple of years ago. Build it point-to point soldering.. Simple and a great preamp.
Nice 👍 did you have any issue gain matching the left and right channels? I am completely new to tubes so not sure about stuff like that.
When I build both preamps and power amplifiers, I often use a volume control for each channel, i.e. two knobs, and it becomes easier to get the same signal out then, if the two tubes are not completely matched. Look at "old" Croft preamps. One tube per channel, if you think SRPP. If you're new to tube amps, I'd build something simpler first, like the SRPP preamp mentioned earlier. A very simple power supply, perhaps a choke in the high voltage, and perhaps a 7812 voltage regulator for heaters.
The way I see it if I'm going to the effort, I may as well make a preamp that's versatile and I'll be happy with for years
I'v just found some really good information at https://sound-au.com/valves/preamps.html and the best one looks a lot like my #2 post
Basically just replacing the V2 cathode follower for a mosfet source follower, I'd try and do away with the V1's bypass capacitor also.
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Hello Mr_Zener:
When designing an amp.
A couple of rhetorical questions to consider.
Do you know the voltage swing you are trying to achieve for the next stage in your amplifier.
Do you know the input voltage from your source. You have set the Q point for this stage to -2V does that meet or slightly exceed your source voltage.
If you have these simple questions sorted out you should be good to go. Go forth and build!
If not time to read some more on amp design to understand what is going on. Lots of info out there.
Good luck
When designing an amp.
A couple of rhetorical questions to consider.
Do you know the voltage swing you are trying to achieve for the next stage in your amplifier.
Do you know the input voltage from your source. You have set the Q point for this stage to -2V does that meet or slightly exceed your source voltage.
If you have these simple questions sorted out you should be good to go. Go forth and build!
If not time to read some more on amp design to understand what is going on. Lots of info out there.
Good luck
Yes, the input signal will not exceed 2Vp-p and I will set the gain at about 23.6dB for 30Vp-p output. Though I would like this switchable to a more normal lower line level using a simple onboard switch.
I have more faith now that Rod Elliott's page has reported very good results with the bootstrap circuit, I have a noob question though, if I use 1/2 of the dual triode for left channel and the other half for right channel, will there be any problem with cross-talk, especially given this high gain setting?
I have more faith now that Rod Elliott's page has reported very good results with the bootstrap circuit, I have a noob question though, if I use 1/2 of the dual triode for left channel and the other half for right channel, will there be any problem with cross-talk, especially given this high gain setting?
Hello Mr Zener:
A quick look at the data sheet shows that pin9 is a shield between the sections. If you ground the shield you should get very good isolation between the sections.
A quick look at the data sheet shows that pin9 is a shield between the sections. If you ground the shield you should get very good isolation between the sections.
If you don't have much experience building tube amps, build something that others have built before. Don't reinvent the wheel. As mentioned before, the 6n2p tube has high amplification, and is actually mostly suitable for phono amplifiers and input tubes for power amplifiers
stenak: I don't really see that its a complex amp, and I do have solid state circuit experience, perhaps I could breadboard out a JFET equivalent.
Anyway seems like I'm going for something very close to the circuit in my #2 post, if I felt the need to simplify, I could simply leave out the bootstrap capacitor and feedback resistor from the board.
I will be running my PCB design past folks before the build for any errors and checks
Anyway seems like I'm going for something very close to the circuit in my #2 post, if I felt the need to simplify, I could simply leave out the bootstrap capacitor and feedback resistor from the board.
I will be running my PCB design past folks before the build for any errors and checks
In the 12V regulator circuit, enough voltage is needed for the 14V zener to stabilize as a reference. Without load, the voltage may increase a bit, but when connected to the load, it will be close to 12. So check it. Meanwhile, this The circuit is more suitable for the headphone drive.There are such circuits for headphones on the Internet/
The 12V(ish) out is only used for the input selector and output relays (about 60mA) so tight regulation isn't crucial, the zener is there more to prevent over voltage really.
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Why did you put a regulator circuit? used 12 volts directly. The construction of the device should be based on a logical design so that you can improve and the rest will learn something.10k resistor for led in 12v !!