Is there really any right or wrong way to audio design? It all comes down to, what sounds best to you.
Sch3mat1c said:
Is this right? I cannot for the life of me find any reference that explains whether this is the case or not.
DanTana said:
Definitly some wrong ways (ie when the design lets the smoke out), but the diversity of possible designs is what makes the field so rich.
dave
Leadbelly, the howler is the "just" in that quote. It's much easier to connect a single network differentially.
SY said:
An example of that is in Allen Wright's circuit... in his Preamp Cookbook he goes to some length explaining that circuit which has all sorts of subtle tricks in it.
dave
SY said:
What I didn't write but was thinking is that this might work for opamps.....I can't find any theory on doing balanced RIAA with opamps!
planet10 said:
It's a nice circuit, but I'm not too crazy about it. If I read it properly, it is passive RIAA after a differential gain stage, so discarding everything after the selector switch probably nets you a weak signal that needs gain somewhere later, no?
leadbelly said:
Yes, but you already have that in your differential 6922 line-stage (ie if you ignore that monster cathode follower at the end your pre is pretty close to the middle stage. Replace the cathode follower with your poweramp output stage and you have a very elegant integrated amp.
dave
leadbelly said:
And it has a nice mix of silicon & glass... you can get the matched FETs from Joe Rasmussen. Keep in mind that the PSRR on the phono stage is quite poor so you need to have a really good power supply....
dave
planet10 said:
Actually, I already have the FET's, one big reason I will build this is that I have the tubes, FET's, and a cheapo transformer. I just have to make the effort to match the FET's as close as possible. As for power supply, what I was planning was a voltage doubler with 1000uF caps and then Morgan Jones' LM317 regulator. I think ripple will be resonable with the bigger caps. I don't want to make it integrated with the power amp but put it in its own enclosure.
A case for sand in the RIAA preamp
I came to tube audio late in life after 35 years in Electronics - the last 15 as a Senior Design Eng. If I had to point a finger at tubes, it would be at their noise performance (which is NOT great). I therefore have always used sand for low signal level stuff like phono preamps.
A caveat on that is that the ONLY tube phono RIAA preamp I've heard is the ECC807 based preamp in my little Rogers Cadet III.
The possible saving grace of tube RIAA preamps is that the RIAA equalisation de-emphasises high frequencies where noise is likely to be most objectionable. However it will emphasise 1/f "flicker" noise. It is also easier to control impedances (especially over an extended lifetime) and therefore obtain accurate RIAA response using sand.
And then there is cost - of course if you were truely worried about cost you would'nt be looking at this forum at all.
On balance its sand for RIAA preamps for me.
Just my opinion for what its worth, and I'm sure there will be plenty of folk to disagree with me.
Cheers,
Ian
I came to tube audio late in life after 35 years in Electronics - the last 15 as a Senior Design Eng. If I had to point a finger at tubes, it would be at their noise performance (which is NOT great). I therefore have always used sand for low signal level stuff like phono preamps.
A caveat on that is that the ONLY tube phono RIAA preamp I've heard is the ECC807 based preamp in my little Rogers Cadet III.
The possible saving grace of tube RIAA preamps is that the RIAA equalisation de-emphasises high frequencies where noise is likely to be most objectionable. However it will emphasise 1/f "flicker" noise. It is also easier to control impedances (especially over an extended lifetime) and therefore obtain accurate RIAA response using sand.
And then there is cost - of course if you were truely worried about cost you would'nt be looking at this forum at all.
On balance its sand for RIAA preamps for me.
Just my opinion for what its worth, and I'm sure there will be plenty of folk to disagree with me.
Cheers,
Ian
Re: A case for sand in the RIAA preamp
The prime reason for the FETs on the bottom of Allan's cascode.
dave
gingertube said:
The prime reason for the FETs on the bottom of Allan's cascode.
dave
leadbelly said:
You'd do better using all of Allen's design by using his power supply which was optimised for his gain stages. The 317 is a jolly handy little device, but at the end of the day it's a 741 plus sluggish power transistor with a few bells and whistles to turn it into the regulator. It's possible to do better...
Re: A case for sand in the RIAA preamp
Hey No excuses..(SDEng)...what's up.. where's your physics ?Some tubes aren't so bad with the noise...ok some are bad offenders . Designing a line /low end preamp with -92dB noise figure. This used to be an early console requiremnt.. Naturally there's a tranny or two stuck in the armoury but it shouldn't be beyond the physics to get to that low noise figurê. The design certainly isn't space conscious as silicon is.
Don't try it with PSpice or other tube simulated program.....modern programs are hopeless at equalising the noise sources. Unfortunately there is a problem in that most parts of the circuit is patented thus cannot copy it...
Some parts aren't and sometime I will paste the relevant.
richj
gingertube said:
Hey No excuses..(SDEng)...what's up.. where's your physics ?Some tubes aren't so bad with the noise...ok some are bad offenders . Designing a line /low end preamp with -92dB noise figure. This used to be an early console requiremnt.. Naturally there's a tranny or two stuck in the armoury but it shouldn't be beyond the physics to get to that low noise figurê. The design certainly isn't space conscious as silicon is.
Don't try it with PSpice or other tube simulated program.....modern programs are hopeless at equalising the noise sources. Unfortunately there is a problem in that most parts of the circuit is patented thus cannot copy it...
Some parts aren't and sometime I will paste the relevant.
richj
leadbelly said:
For some reason when I see the word "DAC" I think of the actual DAC chip, but here I think you mean the outboard DAC box you connect to the CD transport. Well, obviously the DAC chip has to be silicon, but at the point that you first have analog, that could be tubed. See my
web page of my various tube modified CD players I have hacked
----------------------------
My first time on this forum, though I'm a regular at AudioKarma.
A tube DAC is possible (though not trivial). And it would be quite cool. Or hot. Well, you know what I mean.
Re: Re: Where do you draw the line between tube and sand?
A very interesting page, the only one where I have seen the various common DAC output stages all tried. You don't really seem to compare them for quality. I am planning to build a balanced tube DAC with TDA1541A (no, really!). Based on your experience, would you think that the more promising path forward would be to derive the balanced signal in the digital domain with data inversion or to combine I/V and unbalanced/balanced all together in one step using a transformer?
I was thinking exactly the same thing just recently when I cam across an old Circuit Cellar where Steve C discussed roll-your-own DACs. But who has the energy! 🙂
wa2ise said:
A very interesting page, the only one where I have seen the various common DAC output stages all tried. You don't really seem to compare them for quality. I am planning to build a balanced tube DAC with TDA1541A (no, really!). Based on your experience, would you think that the more promising path forward would be to derive the balanced signal in the digital domain with data inversion or to combine I/V and unbalanced/balanced all together in one step using a transformer?
SY said:
I was thinking exactly the same thing just recently when I cam across an old Circuit Cellar where Steve C discussed roll-your-own DACs. But who has the energy! 🙂
Re: Re: A case for sand in the RIAA preamp
The whole point of patents is to give the inventor incentive to publish the invention. The inventor discloses the invention and in return is granted the right to prevent others from making or using the invention for commercial purposes, for a set period. Any information in a patent can be freely shared.
Sheldon
richwalters said:
The whole point of patents is to give the inventor incentive to publish the invention. The inventor discloses the invention and in return is granted the right to prevent others from making or using the invention for commercial purposes, for a set period. Any information in a patent can be freely shared.
Sheldon
Re: Re: Re: Where do you draw the line between tube and sand?
Do the phase splitting in the digital domain. It's a while since I've looked at digits, but I vaguely recall that to get a true analogue inversion of 2s complement notation you need to add or substract 1LSB. Or something. I could be wrong, but it might be worth checking.
More to the point, there are all sorts of linearity tricks that you can pull once you have both polarities of the digital signal and a handful of DAC chips. Have a look at some of the schemes used in the Burr-Brown (now Texas) data sheets.
There's a lot to be said for using a transformer. I haven't yet tried it myself, but the ground-breaking ability is important.
leadbelly said:
Do the phase splitting in the digital domain. It's a while since I've looked at digits, but I vaguely recall that to get a true analogue inversion of 2s complement notation you need to add or substract 1LSB. Or something. I could be wrong, but it might be worth checking.
More to the point, there are all sorts of linearity tricks that you can pull once you have both polarities of the digital signal and a handful of DAC chips. Have a look at some of the schemes used in the Burr-Brown (now Texas) data sheets.
There's a lot to be said for using a transformer. I haven't yet tried it myself, but the ground-breaking ability is important.
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