I conceived of this preamp in an effort to have an all tube audio system, which sounds amazing and (equally important)
That I can fix myself using available parts.
Early on I had collected several tube power amps, but the only tube phono stage I had was in a bogen integrated amplifier. It sounded OK, but I knew I needed to be moving towards separates, so that I could put preamplification in front of whatever power amplifiers I manage to collect. Mostly console pulls, organ pulls and that sort of cast off trash. First off I built a line stage preamp, which i really liked, but which didn't actually provide any useful function because all of my music is on the black plastic, still no phonostage....
The line stage got put on a shelf while I continued to use integrated amps, which by this point I was getting rather good at recapping. Then I got a real brain strain across my bench, a Scott 299d with uneven channel balance from the phono section. I changed virtually every component in the stage despite them all testing OK, and still had the same low volume. I looked and looked at the low volume channel and never found the issue, which turned out to be in the higher output channel, specifically the feedback PEC had gone open.
In my frustration I decided to draw a schematic of just the phono stage, with the PEC broken down into individual discreet components.
Soon after hearing this in action, the plan began brewing in my head.
Put the HH Scott feedback phonostage in front of the sRPP line stage I already built. Then I'd have a good, all tube phono preamp and line stage, which I can fix myself and which will drive whatever power amplifiers I build or find...
So I went ahead and built one, which looked OK but soon after became the sloppy copy...
My friend Alan decided that he wanted one just like it, then his friend Roger too, next Anton wanted one, then we decided that Jeremy needed one. Then Anton wanted one for his son, and so on...
Eventually I decided that I was going to build myself another one, and did a much nicer job on one for my personal system.
I gave my original to a friend when he bought a custom ST35 from me.
Here is where the project stands, I've got about 10 of them out there in the world, none of them ever break, the guys that own em, use em, and I've got what I wanted, which is a good sounding, all tube system that I can crank up, buy never blow up, and if I do ever blow it up, I have the parts and can fix it myself.
What do you think of that?
It's got 5 inputs, mm, mc, 3 line level inputs.
Relays to select them, which short unused inputs to ground through a 47k resistor for 0 bleed through.
All tube signal chain using 12ax7, and 12au7 tubes.
(If you have anything negative to parrot about the 12au7 not being linear, go start your own thread about it)
It sounds amazing, everything I put through it sounds right. If something sounds bad it's usually due to a poor recording but that is maybe 3% of the material... It's just good. If it wasn't good I would not have sold ten of em.
That I can fix myself using available parts.
Early on I had collected several tube power amps, but the only tube phono stage I had was in a bogen integrated amplifier. It sounded OK, but I knew I needed to be moving towards separates, so that I could put preamplification in front of whatever power amplifiers I manage to collect. Mostly console pulls, organ pulls and that sort of cast off trash. First off I built a line stage preamp, which i really liked, but which didn't actually provide any useful function because all of my music is on the black plastic, still no phonostage....
The line stage got put on a shelf while I continued to use integrated amps, which by this point I was getting rather good at recapping. Then I got a real brain strain across my bench, a Scott 299d with uneven channel balance from the phono section. I changed virtually every component in the stage despite them all testing OK, and still had the same low volume. I looked and looked at the low volume channel and never found the issue, which turned out to be in the higher output channel, specifically the feedback PEC had gone open.
In my frustration I decided to draw a schematic of just the phono stage, with the PEC broken down into individual discreet components.
Soon after hearing this in action, the plan began brewing in my head.
Put the HH Scott feedback phonostage in front of the sRPP line stage I already built. Then I'd have a good, all tube phono preamp and line stage, which I can fix myself and which will drive whatever power amplifiers I build or find...
So I went ahead and built one, which looked OK but soon after became the sloppy copy...
My friend Alan decided that he wanted one just like it, then his friend Roger too, next Anton wanted one, then we decided that Jeremy needed one. Then Anton wanted one for his son, and so on...
Eventually I decided that I was going to build myself another one, and did a much nicer job on one for my personal system.
I gave my original to a friend when he bought a custom ST35 from me.
Here is where the project stands, I've got about 10 of them out there in the world, none of them ever break, the guys that own em, use em, and I've got what I wanted, which is a good sounding, all tube system that I can crank up, buy never blow up, and if I do ever blow it up, I have the parts and can fix it myself.
What do you think of that?
It's got 5 inputs, mm, mc, 3 line level inputs.
Relays to select them, which short unused inputs to ground through a 47k resistor for 0 bleed through.
All tube signal chain using 12ax7, and 12au7 tubes.
(If you have anything negative to parrot about the 12au7 not being linear, go start your own thread about it)
It sounds amazing, everything I put through it sounds right. If something sounds bad it's usually due to a poor recording but that is maybe 3% of the material... It's just good. If it wasn't good I would not have sold ten of em.
Do you have a schematic to share?
I have good experience with mu-follower replacing srpp stage.
Better psrr(40db), higher gain or lower output impedance when using also feedback.
I have good experience with mu-follower replacing srpp stage.
Better psrr(40db), higher gain or lower output impedance when using also feedback.
No schematic and no measurements but a story of who wanted one? Are you trying to sell more units or what is this about?
This is a site about DIY Audio.
This is an amplifier that I built myself.
I'm not trying to sell you one, as I make my living doing other stuff.
I sell them exclusively to members of my local Audio club.
I post the photos and the story so that others can feel inspired to build what they're dreaming up. I feel like the design aesthetic that my work brings to the table is one that certain types of people crave. If you'd like to have a look at the schematic, send me a Private message, but it's really pretty well spelled out in the text as a srpp line stage preceeded by the HH Scott feedback phonostage.
All very simple publicly available stuff if you care to spend 3 minutes searching...
BTW, @schiirrn, I looked and I couldn't find any postings of your work here at DIY Audio. Lots of critique of others, but bo photos of your work, at least not that i could find. Could you point to me in that direction?
One Gentleman on Audiokarma asked if he could build himself one, and I sent him a care package, schematic, and a few other pieces...
His works and he likes it...
I do not own a Reverse RIAA setup, otherwise I could test it and post the results, I don't feel it's necessary, simply because it does in fact sound great, it doesn't matter to me...
If it was good enough for Herman Hosmer Scott/ Daniel VonRecklinhousen then it's good enough for me.
This is an amplifier that I built myself.
I'm not trying to sell you one, as I make my living doing other stuff.
I sell them exclusively to members of my local Audio club.
I post the photos and the story so that others can feel inspired to build what they're dreaming up. I feel like the design aesthetic that my work brings to the table is one that certain types of people crave. If you'd like to have a look at the schematic, send me a Private message, but it's really pretty well spelled out in the text as a srpp line stage preceeded by the HH Scott feedback phonostage.
All very simple publicly available stuff if you care to spend 3 minutes searching...
BTW, @schiirrn, I looked and I couldn't find any postings of your work here at DIY Audio. Lots of critique of others, but bo photos of your work, at least not that i could find. Could you point to me in that direction?
One Gentleman on Audiokarma asked if he could build himself one, and I sent him a care package, schematic, and a few other pieces...
His works and he likes it...
I do not own a Reverse RIAA setup, otherwise I could test it and post the results, I don't feel it's necessary, simply because it does in fact sound great, it doesn't matter to me...
If it was good enough for Herman Hosmer Scott/ Daniel VonRecklinhousen then it's good enough for me.
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I can send you a reverse riaa pcb . But you still need a tonegenerator and analyzer or soundcard with software.
Can’t comment on anything else, but that’s a beautiful build. 👍👍👍
Oh hey that's much simpler than I imagined.
I've got a few HP sine wave machines, a 334 distortion analyzer and at least one spate RMS meter, all HP, all work correctly.
My square wave machine bit the dust and I've not had a chance to obtain another one.
I can probably build my own reverse RIAA, if I just remember to add those parts to my next mouser order.
Thank you!
It is an easy schematic.
They used it here:https://www.diyaudio.com/community/threads/mini-me-phono-preamp.242855/#post-3642692
They used it here:https://www.diyaudio.com/community/threads/mini-me-phono-preamp.242855/#post-3642692
I always use a simple resistive voltage divider and use a spreadsheet for the inverse RIAA correction. It's less convenient, but that doesn't matter much, as I only measure RIAA correction networks every twenty years or so. It's also more accurate - no tolerances of the inverse RIAA circuit to worry about.
A spreadsheet?
I do all of my measurements using dedicated hardware and I don't own a computer. Forgive my ignorance but how is a spreadsheet going to help me Reverse the RIAA equalization of my phonostage?
I do all of my measurements using dedicated hardware and I don't own a computer. Forgive my ignorance but how is a spreadsheet going to help me Reverse the RIAA equalization of my phonostage?
I measure with sine waves at a number of frequencies over the audio band, say about two per octave. I measure the gain at those frequencies and then use a spreadsheet to multiply the results with
K √(1 + 4 π2 f2 tau12) • √(1 + 4 π2 f2 tau32)/√(1 + 4 π2 f2 tau22)
where
tau1 = 0.00318 s
tau2 = 0.000318 s
tau3 = 0.000075 s
are the RIAA correction time constants and K is some constant needed to make the expression equal to 1 at 1 kHz (as the nominal gain of RIAA preamplifiers is usually specified at 1 kHz).
It's easy enough with a spreadsheet, it gets rather difficult with a calculator or a slide rule.
(You can rewrite the equation to something with only three squares and only one square root, but that requires more parenthesis and becomes less readable when you put it as formatted text on this forum.)
Of course you can also convert the measured voltage gain into decibels and then add the inverse RIAA in dB:
10 dB • 10log((1 + 4 π2 f2 tau12) • (1 + 4 π2 f2 tau32)/(1 + 4 π2 f2 tau22)) + 20 dB • 10log(K).
K √(1 + 4 π2 f2 tau12) • √(1 + 4 π2 f2 tau32)/√(1 + 4 π2 f2 tau22)
where
tau1 = 0.00318 s
tau2 = 0.000318 s
tau3 = 0.000075 s
are the RIAA correction time constants and K is some constant needed to make the expression equal to 1 at 1 kHz (as the nominal gain of RIAA preamplifiers is usually specified at 1 kHz).
It's easy enough with a spreadsheet, it gets rather difficult with a calculator or a slide rule.
(You can rewrite the equation to something with only three squares and only one square root, but that requires more parenthesis and becomes less readable when you put it as formatted text on this forum.)
Of course you can also convert the measured voltage gain into decibels and then add the inverse RIAA in dB:
10 dB • 10log((1 + 4 π2 f2 tau12) • (1 + 4 π2 f2 tau32)/(1 + 4 π2 f2 tau22)) + 20 dB • 10log(K).
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I have been wondering if a 12ax7 or 6j1 may be a perfect mm phono front end.
More stuff to try !!
More stuff to try !!
Thank you for explaining that.
Given my circumstances, I think the reverse riaa network is a much easier solution