Interesting design, one thing you might want to consider is that the actual gain is rather low. Bob D. lists it as ~24dB @ 1kHz - this is typically anywhere from 14 - 20 dB less than convention. The issue here is that the line stage is going to need to make up the missing gain or the volume levels you can achieve are going to be rather low.
Changes to the second stage can be made to address this issue, for example a 12SL7/14N7 could be substituted with certain other changes - note because the eq is spit between the two stages the value of R9 will need to be reduced to compensate for the required increase in R8 and the tube's higher rp.
You could increase R8 to about 100K, and start with R9 at around 221K - 226K - you may need to trim this to get it just right as my numbers are an estimate from an off the cuff calculation. (Not modeled) Change R11 to about 82K to keep cathode current in an acceptable range. (couple of mA) This will net about an additional 10dB of gain and put you in the range.
Note that you can get additional gain by adding cathode bypass caps to each stage, however this significantly affects rp of the associated triode requiring a trim upwards in value of R4 and R9, this also makes the eq more sensitive to tube variations than with unbypassed cathode resistors.
Best if you have some way to measure the RIAA response that way you can trim to your heart's content.
Changes to the second stage can be made to address this issue, for example a 12SL7/14N7 could be substituted with certain other changes - note because the eq is spit between the two stages the value of R9 will need to be reduced to compensate for the required increase in R8 and the tube's higher rp.
You could increase R8 to about 100K, and start with R9 at around 221K - 226K - you may need to trim this to get it just right as my numbers are an estimate from an off the cuff calculation. (Not modeled) Change R11 to about 82K to keep cathode current in an acceptable range. (couple of mA) This will net about an additional 10dB of gain and put you in the range.
Note that you can get additional gain by adding cathode bypass caps to each stage, however this significantly affects rp of the associated triode requiring a trim upwards in value of R4 and R9, this also makes the eq more sensitive to tube variations than with unbypassed cathode resistors.
Best if you have some way to measure the RIAA response that way you can trim to your heart's content.
burnedfingers said:
Issues above all addressed in my previous post...
Reread carefully, further questions will be answered and further assistance happily provided. For whatever reason one of my diversions is designing passive eq phono stages. Once upon a time I played a lot with 6SL7...Tweak C3 to compensate for increased miller capacitance in 12SL7 2nd stage.. (reduce value)
Hi,
If you look at the circuit imagine what could go wrong....
Noise? YES.
Microphony? YES.
Lack of gain? YES.
PSU requirements? As pointed out this circuit as so low PSR it needs babying beyond reason.
Al in all, I agree with Analog-SA's assesment and say look at something else.
Every circuit performs to what it's PSU allows but this one definitely's going to require ***-tight regulation to perform at all.
Some people do read circuits easily, Joe. One day you will too.
Your friend,
If you look at the circuit imagine what could go wrong....
Noise? YES.
Microphony? YES.
Lack of gain? YES.
PSU requirements? As pointed out this circuit as so low PSR it needs babying beyond reason.
Al in all, I agree with Analog-SA's assesment and say look at something else.
Every circuit performs to what it's PSU allows but this one definitely's going to require ***-tight regulation to perform at all.
Some people do read circuits easily, Joe. One day you will too.
Your friend,
fdegrove said:Hi,
If you look at the circuit imagine what could go wrong....
Noise? YES.
Microphony? YES.
Lack of gain? YES.
PSU requirements? As pointed out this circuit as so low PSR it needs babying beyond reason.
Al in all, I agree with Analog-SA's assesment and say look at something else.
Every circuit performs to what it's PSU allows but this one definitely's going to require ***-tight regulation to perform at all.
Some people do read circuits easily, Joe. One day you will too.
Your friend,
Hi Frank,
Not to disagree, but I am going to disagree
while agreeing that all the limitations you mention above are true.. Confused? I have built a number of generally similar phono stages in the past, and some not so similar. Ones based on this topology while not necessarily the ultimate actually do sound quite good, and as you say are also very sensitive to PSU performance. I would actually recommend building as designed (including psu) and then making the changes I and others have suggested to get additional gain. (Great opportunity to learn.)Bob Danielak is quite well known in this neck of the woods and his amplifiers generally sound quite good (I've heard more variations of the darling than I could shake a stick at.. ) so I expect he put some effort into this design as well.
FWIW I only build my own designs, and opinions expressed are subject to that caveat..
Quote:
If you look at the circuit imagine what could go wrong....
Noise? YES.
Microphony? YES.
Lack of gain? YES.
PSU requirements? As pointed out this circuit as so low PSR it needs babying beyond reason. ****************
Yes, but if I were to look at any tube circuit I could probably say the same. Granted it would be a challenge and that is probably part of the reason I want to tacke it. As I mentioned before Mapletree has a phono preamp that is very similar and it performs quite well. I really like the sound of a 6SL7 tube and don't care for the run of the mill 6922 or 12AX7. So what else is left? Do I dust off my SS phono preamp or do I give it a shot and try to build this?
Frank..good seeing you on the board again
If you look at the circuit imagine what could go wrong....
Noise? YES.
Microphony? YES.
Lack of gain? YES.
PSU requirements? As pointed out this circuit as so low PSR it needs babying beyond reason. ****************
Yes, but if I were to look at any tube circuit I could probably say the same. Granted it would be a challenge and that is probably part of the reason I want to tacke it. As I mentioned before Mapletree has a phono preamp that is very similar and it performs quite well. I really like the sound of a 6SL7 tube and don't care for the run of the mill 6922 or 12AX7. So what else is left? Do I dust off my SS phono preamp or do I give it a shot and try to build this?
Frank..good seeing you on the board again
Hi,
To both of you, yes you can make it work.
All I'm saying is that with careful attention to tight regulation of the PSU it will be that much better than what can be expected from the mere circuit alone.
The circuit and the choice of tubes suggest to me a tendency towards noise, microphony and a touch of euphony that's not going to be close to the truth.
You may like what it does but it may well be just another deviation of the recorded ruth.
@Joe, cheers pal. Respect.
Cheers,
To both of you, yes you can make it work.
All I'm saying is that with careful attention to tight regulation of the PSU it will be that much better than what can be expected from the mere circuit alone.
The circuit and the choice of tubes suggest to me a tendency towards noise, microphony and a touch of euphony that's not going to be close to the truth.
You may like what it does but it may well be just another deviation of the recorded ruth.
@Joe, cheers pal. Respect.
Cheers,
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