I’m planning to build a preamp according to the schematics of Croft super micro A. http://soundmovements.co.uk/diyaudio/Croft_preamps.html
Does the schematics look correct? It looks like some components are missing and I suspect the values of the capacitors in the riaa to be incorrect. What do you think? Can I build it with this schematics?
Also, I would like suggestions of a suitable PSU. Any comments on the project is appreciated. (The preamp will be used with Ortofon SPU#1E, Denon 103, Stanton EEE a pair of TD124, Denon AU-340, Quad II:s and stacked ESL57.)
Does the schematics look correct? It looks like some components are missing and I suspect the values of the capacitors in the riaa to be incorrect. What do you think? Can I build it with this schematics?
Also, I would like suggestions of a suitable PSU. Any comments on the project is appreciated. (The preamp will be used with Ortofon SPU#1E, Denon 103, Stanton EEE a pair of TD124, Denon AU-340, Quad II:s and stacked ESL57.)
I would place the 3k9 resistor directly on the grid (grid stopper).
This link gives some more info (very similar amp) :
https://www.diyaudio.com/community/threads/anzai-srpp-line-phono-and-eq-tube-preamplifier.319107/
This link gives some more info (very similar amp) :
https://www.diyaudio.com/community/threads/anzai-srpp-line-phono-and-eq-tube-preamplifier.319107/
The schematic are the original Croft? It works when the amps were build, so why do any changes? I remember that the amp sounded great!
I’m sure it sounds fine if it’s built from Croft’s schematics but I suspect the one I found is not accurate. How about the capacitors of the riaa? 330nF and 150pF looks odd if you compare with for example EAR834. But I have very little experience with electronics. I just want to make sure it’s correct before I start building.
Found this on the internet, the simplier preamp. This sounds great, and I remember that Ken Kessler in HIFI News loved it! I build a clone for 20 ? years ago, and I liked the sound. Easy to build with point to point soldering. http://www.cma4ch.org/chemo/attivita/croftsmic.html
🙂 I’m listening to that one right now and want to try something else. The super Micro A is supposedly way better and looks easy enough to build point to point
I wish I knew how to calculate the riaa correction but hope to get a confirmation that it’s correct as shown in the schematics though I suspect it’s supposed to be 330pF instead of 330nF
I wish I knew how to calculate the riaa correction but hope to get a confirmation that it’s correct as shown in the schematics though I suspect it’s supposed to be 330pF instead of 330nF
I drew that schematic from the preamp I had at the time, and, although I took care reading component values, I can't guarantee correctness. And, in case anyone asks, I sold it years ago...
The Super Micro A had a regulated HT supply, and I will see if I can find a schematic for that.
Alex
The Super Micro A had a regulated HT supply, and I will see if I can find a schematic for that.
Alex
Hi Alex. Thanks for your work with the schematics. I hope to get a confirmation from someone that it looks accurate. I can of course build it and listen but would appreciate if someone can see any obvious misreadings. Again, I wish I could calculate the riaa capacitors. They seem to have odd values.
You could enquire to @Tubekwk and others who modelled a phono preamp, not Croft though, in ltspice. It might also confirm if those values are off. For example: https://www.diyaudio.com/community/threads/rca-phono-preamp-and-reverse-riaa.393290/#post-7202634
A fellow member suggested the Croft to me years ago when I was searching for a tube phono stage to build. I never progressed but it’s got me thinking again 🙏🏻
If I still had the preamp I would be very happy to open it up and have a look to check the values. As I mentioned earlier, though, I sold it a few years ago. And unfortunately Glenn Croft isn't around any more to confirm one way or another
If you had access to a Spice simulator, it would be worth putting all the component values in and checking the frequency response.
Looking at my website, I see I included the HT regulator circuit in the schematic for the Super Micro 3, though I'm not sure whether the HT voltages are the same for the two preamps, and again I can't confirm the values are correct.
Alex