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Catman's Analog Musings

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I believe the reason why there is sometimes hiss on Australian pressings is that they were cut from copies of copies of copies of the master tapes.  I remember noticing this on an Australian pressing of an Eagles album in the mid 1970s.

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G'day all, listening to a few of my many phono stages of late, I have noticed a slight tendency to occasional roughness/loss of clarity either when driven hard or on dynamic peaks that I've generally put down to phono stage distortion. 

 

In analysing this it seems that my 'cleanest' sounding phono stages tend to be simple full feedback op amp designs with heaps of stage feedback.  Whatever what you think about the use of feedback in audio circuitry, overall distortion is invariably very low thanks to this feedback.  By the same token, my phono stages with passive RIAA equalisation tend to be higher distortion but still very low in absolute terms, yet still occasionally audible! 

 

Sonically I generally prefer the sound of passive equalisation phono stage circuitry especially in terms of excellent dynamic performance, so maybe it is all a question of some compromise in the 'real world'.  Interesting indeed!  Regards, Felix.    

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What do you mean by a phono stage being "driven hard", Felix ... given they have a static gain (ie. no volume control).

 

If you mean "when the music is loud" (ie. an orchestral crescendo - not necessarily a transient) then I suggest the following:

  1. "heaps of stage feedback" will certainly deliver low distortion ... although I suggest there is a sonic penalty which is associated with large amounts feedback ('sterility'!).  So your phono stages with passive RIAA equalisation which, as a result, have higher distortion ... probably sound more engaging.  :)
  2. if you are noticing a "slight tendency to roughness/loss of clarity" with those of your phono stages which have passive RIAA equalisation ... I would surmise this is bcoz the gain of the first stage (prior to the passive RIAA network) is set too high.  Because I haven't noticed any such roughness/loss of clarity on loud passages with my Muse (passive RIAA network between 2 gain stages).

As you probably know, the issue with a phono stage having 2 gain stages with a passive RIAA network in between, is that you can get in excess of 20dB loss in the passive RIAA network.  Now the 1st gain stage is before the frequency adjustments delivered by the RIAA network - so, if you set the gain of the 1st stage too high (in order that the output from the RIAA = the input to the 2nd gain stage, after 20+dB loss, is not too low) then you can cause the output of the 1st stage to exceed the DC rail voltage - ie. clip at at loud HF passages (because the HFs prior to the RIAA network have already been boosted 20dB, during the cutting process).

 

So what is the DC rail voltage for your passive-RIAA phono stages?

 

Andy

 

Edited by andyr

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G'day mate, the way that things are configured in here with most of my phono stages running in the 40 db range with loudspeaker SPL's in the high moderate range, one can detect a general loss of clarity with some phono stages but not others, suggesting that the phono stages are at 'fault'. 

 

It would be nice to have the instrumentation to measure all this, but as it stands I have to rely on my ears!  In radio system analysis a very important concept is that of 'gain distribution', having implications on headroom/clipping/overload behaviour and distortion. 

 

I believe in maximum supply voltages where possible for these reasons, but sadly I see a lot of circuitry with clearly insufficient voltage supplies and degraded performance as a result!  Regards, Felix.    

Edited by catman
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A well designed phono preamp will be biased into class A with the best dynamic range manageable with the available components.

If there's distortion under normal operating conditions, it's a dud.

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G'day mate, yes that would be ideal however one of my  phono stages is supposedly biased into class A, yet does exhibit this occasional distortion/roughness/loss of clarity.  Regards, Felix.  

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Must be something wrong with it or it is of poor design to start with.

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G'day mate, that is indeed a possibility.  Regards, Felix.  

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Could the phono struggling/clipping with dynamic passages be an indication that the power supply is not adequate? 

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3 minutes ago, audiofeline said:

Could the phono struggling/clipping with dynamic passages be an indication that the power supply is not adequate? 

 

Again, if it is..............it's poor design.

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21 hours ago, stevoz said:

Tape hiss can be heard on some of Kraftwerk's earlier stuff, pre digital sampling, where they would insert a sound effect that was on a tape loop and hiss was evident until that particular effect ends. I always liked the sound effect and while the accompanying hiss may have added a certain 'ambience' to the sound, I never really found it 'magical'.:P

When CDs were very new, I was in my favourite record store and a nerdy regular customer was talking to the sales girl, telling her in detail how impressed he was with the Kraftwerk CD (that I presume she had previously sold him) because he could hear the different hiss levels in the recording.  The salesgirl was lovely, but the look on her face indicated that it was evident she didn't care less about these technicalities. 

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5 minutes ago, audiofeline said:

When CDs were very new, I was in my favourite record store and a nerdy regular customer was talking to the sales girl, telling her in detail how impressed he was with the Kraftwerk CD (that I presume she had previously sold him) because he could hear the different hiss levels in the recording.  The salesgirl was lovely, but the look on her face indicated that it was evident she didn't care less about these technicalities. 

 

Geeks trying to crack on.................always good to watch!

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1 hour ago, LogicprObe said:

 

Geeks trying to crack on.................always good to watch!

Yes....I've always found 'The Big Bang Theory' hard to believe!:lol:

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One of the advantages of a good valve circuit running on a couple of hundred volts.  No problems with clipping and because the signal is such a small fraction of the operating point, the device behaves extremely linearly. 

 

More to the point here though, it is often suggested that 9 volt batteries are not enough for a good opamp based phono preamp.  Could that be the problem here?

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G'day all, firstly apologies for my large number of phono stage related threads of late!  It is interesting that listening to all my phono stages over recent weeks, my humble DIY efforts are in absolute terms, every bit as good! 

 

Of my DIY efforts I consider my DIY ESP P06 and my various DIY versions of the Bruce Heran single op amp stage, my favourites.  For various technical reasons my DIY P06 'should' be my best, however my various versions of my Heran op amp design (aka 'Mimic' designs) sound much, much better than they have any right to! 

 

I am always looking for new designs to build but these two already set a very high standard, even compared against high performance commercially made units I have.  Are there any other DIY/kit designs worthy of consideration?  Regards, Felix. 

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G'day mate, yes I have seen that design before which is very interesting, especially the use of the little used common base amplifier configuration.  The design is optimised for low output moving coil cartridges as far as I can determine.  Regards, Felix. 

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14 minutes ago, catman said:

G'day mate, yes I have seen that design before which is very interesting, especially the use of the little used common base amplifier configuration.  The design is optimised for low output moving coil cartridges as far as I can determine.  Regards, Felix. 

 

It's a head amp (aka pre preamp), Felix - hence, yes it is to be used with a LOMC ... to get its output voltage up to MM levels.

 

Andy

 

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Not for the faint hearted. ......but hey if I can put one together any one should :lol:.

Have built a few phono stages in the past, haven't felt the need to build another since.

 

https://tavishdesign.com/collections/frontpage/products/classic-vacuum-tube-phono-stage?variant=1252476071

 

Will take a little longer than the average DIY phono stages and is probably over kill for what you want or need.

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14 hours ago, awty said:

Not for the faint hearted. ......but hey if I can put one together any one should :lol:.

Have built a few phono stages in the past, haven't felt the need to build another since.

 

https://tavishdesign.com/collections/frontpage/products/classic-vacuum-tube-phono-stage?variant=1252476071

 

Will take a little longer than the average DIY phono stages and is probably over kill for what you want or need.

 

But it looks like a great piece of kit.   Worth the effort.

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Definitely cornet 3 for me but it's no longer available as kit I think

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6 minutes ago, mloutfie said:

Definitely cornet 3 for me but it's no longer available as kit I think

That's a pity.

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I would say that the cartridge is more important - at least in the sense that the range between good and bad is much larger.  On the other hand it may be wiser to invest more dosh in the phono stage as that will outlive several cartridges.

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