you are right. It sounds silly.
The advantages and disadvantages of SRPP are well outlined and discussed in many articles, most germainely John Broskie's SRPP Deconstructed
The advantages and disadvantages of SRPP are well outlined and discussed in many articles, most germainely John Broskie's SRPP Deconstructed
If you use cathode capacitor at the bottom tube cathode resistor, the sound character is greatly influenced by that capacitor. Sound is also very dependent on the PSU (I prefer C-R-C filter, but again the C matters). Finally, the tube itself. I prefer ECC88/6DJ8 for line stage, it has clean, a bit analytical sound. If you prefer "soft tube sound", go for ECC83, but this is unnatural for some. SRPP requests high load impedance, otherwise distortion goes up.
SRPP was actually used for video scan, not audio amps (See Amos and Birkenshaw). The circuit was indeed most useful for low impedances, especially with capacitive reactances and the high voltages needed for scan circuits. Merlin Blencoe published a very nice article showing that the distortion actually has a minimum at a relatively low load and it's a pretty sharp minimum. It's not as low distortion as a more conventional circuit, but definitely lower than running the circuit into a high impedance load. A variable load is not a good idea.
Topologies don't have a "sound." Specific implementations can, but presumably we want hifi, which means that the electronics do not contribute a "sound." if one wants an effects box, there are more efficient ways of achieving it.
Topologies don't have a "sound." Specific implementations can, but presumably we want hifi, which means that the electronics do not contribute a "sound." if one wants an effects box, there are more efficient ways of achieving it.
I use that topology routinely (see His Master's Noise on this site and the ImPasse in AudioXpress for examples). You do have to buffer the output or account for the next stage load. It's very low distortion, and if you choose a good operating point and a low distortion tube, it's audibly transparent.
Could be. In the original application, the SRPP was meant to drive over a kilovolt into 400R and 500pF at 3MHz. It became, for reasons I absolutely don't get, extremely fashionable, especially in Japan and (consequently) China. First time I saw it used in audio was the Purple Cow amp, but it may predate that.
Don't forget the Loftin-White, back before TV even existed!
http://diyaudioprojects.com/Schematics/images/2A3-SE-6SL7-SRPP-Loftin-White-Tube-Amp.jpg
I prefer a mu stage with a tube on top, or better yet a solid state gyrator. I used to fool around with the above kind of a preamp stage (on my DC Darling), but never quite got it sounding right. Haven't gone back since going mu follower.
http://diyaudioprojects.com/Schematics/images/2A3-SE-6SL7-SRPP-Loftin-White-Tube-Amp.jpg
I prefer a mu stage with a tube on top, or better yet a solid state gyrator. I used to fool around with the above kind of a preamp stage (on my DC Darling), but never quite got it sounding right. Haven't gone back since going mu follower.
I covered this type of stage in my article (see half-mu amp). Since the stage is DC coupled, the load presented to the bottom triode is simply a resistance. There is no bi-directional flow of signal current, so it is not push pull in any sense. There is practically no difference in taking the output from the upper cathode or from the lower anode, which is very different from the SRPP.
You may, of course, accuse me of pedantism
You may, of course, accuse me of pedantism
About that DC coupling.. first time I have seen that - I see the designer has swapped the usual coupling capacitor design for one that sits at 144V holding up the cathode, which seems like a neat idea.
What advantages and disadvantages does this have over a coupling capacitor and fixed negative bias that is usual (to me at least)? I guess it saves finding a negative supply but what would it do to the sound as you now have two capacitors in series with the drive to the primary instead of one - but no interstage capacitor.
What advantages and disadvantages does this have over a coupling capacitor and fixed negative bias that is usual (to me at least)? I guess it saves finding a negative supply but what would it do to the sound as you now have two capacitors in series with the drive to the primary instead of one - but no interstage capacitor.
I covered this type of stage in my article (see half-mu amp). Since the stage is DC coupled, the load presented to the bottom triode is simply a resistance. There is no bi-directional flow of signal current, so it is not push pull in any sense. There is practically no difference in taking the output from the upper cathode or from the lower anode, which is very different from the SRPP.
You may, of course, accuse me of pedantism
I don't mid pedantism at all if I understand it.
The input stage is loaded by (essentially) the 390k resistor in parallel with the input impedance of the 2A3. If I understand you correctly, you're saying that if that 390k resistor were smaller, then the stage would be an SRPP rather than half-mu?- Status
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