Hi all. First time posting on this forum, I have gotten alot of help over at el34world but I am looking for any more advice where I might find it. I am almost done designing a standalone preamp based on ceriatone chupacabra 50 for my friend. I currently am using valvewizard universal effects loop circuit as the effects loop/output but I am told that this will have significant distortion and impedance issues. I need V3B to output line level to an unbalanced input of a power amp (Like peavey classic 50/50). I have been reading the cathode follower sections at valvewizard but I am really struggling with the theory. I have built a few JCM800s but designing tube stages from scratch is a skill I am trying to learn.
Does anyone perhaps have a circuit I can use for an effects loop and output driver for this application? I do not mind adding more tubes or stages. Any advice really on how I can go about calculating component values? I really appreciate ANY advice, please let me know if I did not post enough information.
Does anyone perhaps have a circuit I can use for an effects loop and output driver for this application? I do not mind adding more tubes or stages. Any advice really on how I can go about calculating component values? I really appreciate ANY advice, please let me know if I did not post enough information.
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Welcome to the forum! 🙂
I moved your thread when I approved it to Instrument & Amps so it gets the attention it deserves.
The output impedance is kind of high, and a function of pot position - driving any length of cable would probably result in a lot of HF roll off. Perhaps a cathode follower output or similar would be a good idea. I would probably use a self biased follower based on a 12AT7A if the PSU can handle the required current. Others with more MI experience than me will likely weigh in.
Well, lots of ways to skin this cat and countless commercial schematics to copy from. The Soldano X88R for example uses a DC coupled CC CF output stage; that would work.
leadbelly that is absolutely perfect. I am just wondering for clarification: the output of a soldano x88r is line level so should be 1v peak to peak? meaning I dont need to add an effects loop to the preamp i can just run effects pedals between the preamp and the power amp units?
If all your effects pedals accept a line level input that'd work fine.
If you want to keep the effects loop, you could add a high voltage MOSFET source follower to gain low output impedance without requiring another tube. The LND150 is a common choice for this sort of thing, but that particular part doesn't seem to be available from any authorized distributor at the moment.
Either way, the maximum output level is a fair bit above typical line level as shown, so you might want to cut the output voltage a bit.
If you want to keep the effects loop, you could add a high voltage MOSFET source follower to gain low output impedance without requiring another tube. The LND150 is a common choice for this sort of thing, but that particular part doesn't seem to be available from any authorized distributor at the moment.
Either way, the maximum output level is a fair bit above typical line level as shown, so you might want to cut the output voltage a bit.
Do guitar effect pedals not usually accept line level input? this is what I am confused about. I would like to do this all tube even if the SS wont affect the signal tone or distortion.
Many do, some don't. Strictly speaking, 'line level' is ambiguous, but many (probably most) pedals will deal with at least a 1V RMS (2.83V pk-pk) signal without issue. Keep in mind that a pedal's supply voltage is usually only 9V, though some use internal boost converters, negative rail generators or other tricks.
Some pedals have a rather high output impedance or otherwise have trouble driving lower impedance (<100k ohm) line inputs.
You can certainly use a cathode follower rather than a source follower, it's just that in this particular application there should be zero audible difference.
Some pedals have a rather high output impedance or otherwise have trouble driving lower impedance (<100k ohm) line inputs.
You can certainly use a cathode follower rather than a source follower, it's just that in this particular application there should be zero audible difference.
Ok fellas how does this look. Stole the output from soldano x88r. will it spit out 1Vrms?
R1, R2, and R3 will have to be experimented with to get the correct voltages.
R1, R2, and R3 will have to be experimented with to get the correct voltages.
No i am getting rid of that. if the output is 1Vrms I can just make a switchbox to go between the preamp and power amp for effects.