A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

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JR.
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by JR. »

mediatechnology wrote:Was that your broken link JR or one here? If its mine I'll fix it.

I did find this P100 sch: viewtopic.php?f=12&t=151
If you look at the last edit date on that post, you will see i just reloaded the image a couple hours ago....

the broken link is mine... I have not kept up my personal vanity website so probably more broken links to my old data.

JR
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Hans
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by Hans »

mediatechnology wrote:I still have to think that MC carts capacitively coupled with huge capacitors to elevated transistor bases are going to see peak DC currents in the tens if not hundreds of uA at turn-on.
After a good long warm-up and forming maybe a few uA.
But if capacitor leakage specifications are consistent with 0.01CV for the values required it could be far higher after stabilization in the tens of uA.
Lots of commercial MC stages are this way.
What I don't get is that attempts are made to produce a State of the Art balanced preamp with extremely noise and then to use Low-End MC stages as a reference for the Current flowing into the Cart.
I do not know any high grade MC preamp with a capacitor or a relatively low grade op-amp like the 5532 at its input.

To my opinion this approach makes the design less "balanced".

Hans
ricardo
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by ricardo »

Hans wrote:1) A Cart coil is made from a very tiny wire, that like all wires can only have a max current.
That is said to be the reason why (some) manufacturers mention that you should never measure the internal resistance with a multimeter.
Wanna tell us which makers are these? If they are MC makers, this statement is rubbish. It's rubbish for MMs too but there's a very tiny but higher chance of 'damage' there.
2) The second reason is that a DC current could magnetize the coil to some degree.
There is equipment on the market to demagnetize. Stereophile once did a test and found a positive effect on the sound reproduction.
I have no opinion on this because I never had the opportunity to test it.
This is the second of the "possible problems" I mention in my post. And BTW, its not the coil which is magnetized but the core it is wound on (or the magnetic circuit in a Mc).

It's practically impossible to magnetise the magnetic circuit of a MC with even a passive VOM. Only MMs with poor cores might be affected. MC transformers can be magnetised sufficiently to skew the core and the most sensitive test is increased 2nd harm.

I don't have an opinion about this. I tested it.
3) Testing the effect on DC current for one element gives some insight, but it cannot guarantee that it is true for all elements with their different magnets and coils.
I tested the High End Shure, ADC, Ortofon, Grado, Goldring & Audio Technica cartridges of the time so am pretty sure it holds for their different magnets & coils. Also Ortofon MC cartridges.
4) Measuring is not the same as listening, and that should be the final proof of the pudding. Not everything can be measured.
Einstein once said: Not everything that counts can be counted.
In my previous life, I was a DBLT guru. A DBLT is a 'measurement'. Your instrument is your DBLT panel. It has an accuracy which you need to check and calibrate regularly. I had some of the best ears in the business on that panel.

If my DBLT panel says "there is no audible difference", i'm prepared to wager a large sum of money that there is no audible difference. I'm also willing to wager, my DBLT panel has better ears than you.
5) Last but not least, what should be really helpful is to have a guideline as to how much Cart current is allowed.

I've given you my tested limits. 100uA is a LOT more than I'd expect from any sensible preamp.
And just allowing 100uA flowing into an expensive Cart, is not the kind of risk I would like to take, unless the manufacturer would give his O.K., what they won't do.
Which makers won't allow 100uA through their cartridges? These would not be good cartridges and almost certainly too fragile to use.
What I don't get is that attempts are made to produce a State of the Art balanced preamp with extremely noise and then to use Low-End MC stages as a reference for the Current flowing into the Cart.
I do not know any high grade MC preamp with a capacitor or a relatively low grade op-amp like the 5532 at its input.
Wanna explain what is low end or low grade about 5532?

Wayne has measured his device and shown the current is well under what has been tested to have no effect on the sound through the cartridge.

Wanna link to some High End (?) circuits which you feel have lower noise, lower current bla bla and better "balance"? That would be a constructive contribution.
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mediatechnology
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by mediatechnology »

ricardo:
I tested the High End Shure, ADC, Ortofon, Grado, Goldring & Audio Technica cartridges of the time so am pretty sure it holds for their different magnets & coils. Also Ortofon MC cartridges.
OT, but while you were examining carts did you look at crosstalk polarity? If so were they all the same? I have a theory: http://www.lathetrolls.com/viewtopic.php?f=1&t=6661

Hans:
I do not know any high grade MC preamp with a capacitor or a relatively low grade op-amp like the 5532 at its input.
No one said they were high grade.
High grade is subjective and not a bright line.

But these preamps are out there pumping uA of bias currents into MC and MM carts as we speak and are not blowing up carts.
Many probably have owners raving about how great they sound particularly after cable burn in. :roll:

I see at least four examples of MC preamps here with large value electrolytic inputs: http://www.angelfire.com/sd/paulkemble/sound4.html
Three of the four are commercially-made units. The other is JLH/WW.

MC preamps with 5532 inputs may not have the best NF but they're out there.
Most I've seen are a flat +20 dB pre-preamp stage ahead of the MM stage.
Others just have 20 dB boost switch in the lower feedback arm of a 5532 preamp.
I looked at one this way for a customer. I'm sure it was noisier than it had to be.

I see and read far too much over-the-top obsession with phono stuff.
I have zero interest in that.

Are vinyl fanatics not aware that most Neumann lathes use a 709 op amp in the RIAA pre-emphasis stage?
Talk about slew rate limiting...
After listening through a slew rate-limited 709 stage am I to believe that a few uA of cart current is going to make a huge change in what I hear?

I can assure you that people who make records don't buy into vinyl fanaticism because they know how the sausage is really made.
Like JR I have no interest in the fanatic phono preamp market.
My goal is to make tools for people who create content not consume it.
They seem to be more reasonable in their expectations.

ricardo:
Wayne has measured his device and shown the current is well under what has been tested to have no effect on the sound through the cartridge.
I think I may have stumbled upon a very well-matched pair at 80 nA but I'm pretty sure a highly-unmatched pair would come in well under your 100 uA limit.
Maybe 10 uA worst-case Ios?
Hans
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by Hans »

ricardo wrote: Wanna link to some High End (?) circuits which you feel have lower noise, lower current bla bla and better "balance"? That would be a constructive contribution.
Sorry to say, but I find your response to my open questions, meant to give a constructive contribution, rather harsh.

Answerring your bla bla question first, it makes no sense to put a Ferrari engine in a Fiat 500. That will make the product unbalanced.
Designing a pre amp with great care by making a fully balance design and striving for ultra low noise is not a quick and dirty job and needs quite some attention.
As cart current is one of the design criteria, it seems quite logical to pay attention to this aspect with the same care and attention.
Whether or not 100uA cart current can be allowed is a question that is not supported in the specs of any cart manufacturer.
So the easy way is to go as low as possible, just like was done with the extremely low noise.
So with high grade I mean: Low noise, low cart current, low phase distortion from 20-20kHz, accurate Riaa curve, high overload margin, very few caps in the signal path etc, etc.
Only when all these criteria are met, you have a balanced design.

What may be a fact of life for you, will not be perceived by others when things are not outspoken.
It did nor read before about you having tested many elements.
The design in this thread is from the beginning concentrated on a MC preamp, so only MC carts are of concern here.

Your opinion that all elements can have 100uA is a point that I missed in your posting.
And I only read about testing harmonics but not at all about all the listening you have done in a team.
It would therefore be interesting to hear whether you contacted Cart suppliers and if any to hear what their response was.
But whatever may be true, when the supplier does not guarantee this possibilty, why take the risk?

I contacted the supplier of my Benz LP Cart and their response was: the lower the better, but no more than in the low nA region.
For that reason I will never take the risk to allow 100uA, although their answer may be much too conservative.
Wanna explain what is low end or low grade about 5532?
It is low grade with respect to high grade RIAA preamps, the way I have explained at the beginning of this posting.
For a Riaa preamp 65dB SNR A-weighted is about the border where noise becomes noticeable from the speakers at normal listening levels, so this value must be seen as a lower limit.
This 65dB is for a MM ref 5mV@1kHz and for a MC ref 0.5mV@1kHz.
To have some room for Carts having less output, a target value of 75db SNR A-weighted seems appropriate.

Now coming to the 5532: For an MM its voltage noise is perfectly adequate but the current noise spoils this figure.
The input short circuited gives very nice noise figures, but the cart connected tells another story.
For that reason a Fet op-amp like the opa2134 or even better the opa1642 are to be preferred.
And for an MC application it voltage noise is to high to meet the 75dB.

Hoping the discussion can be continued in a more amicably manner.

Hans
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JR.
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by JR. »

To say vinyl and associated electronics are a mature technology is an understatement.

Perhaps your choice of words is also contributing to animus. Yes, 553x is totally inappropriate for MC gain stage because of it's ein, so further analysis is moot.

I apologize for my p-100 not being balanced. :lol: My earlier p-10 was balanced.... :D (I did offer a version of my earlier balanced p-10 preamp using 2sB737 for MC carts. Since the MC cart was bridging between the two input bases, the current flowing in the MC cart would be a small fraction of the difference between the two input base currents. )

Coincidentally some guy actually patented the concept of a balanced input MM preamp in the '80s, and came after me for my published (balanced) design, demonstrating how ignorant some patent examiners are. I found a balanced (transformer input) phono preamp in an old tube manual, so his patent was bogus (the examiner was completely unfamiliar with the concept of a balanced audio input). :roll:

JR

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Hans
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by Hans »

mediatechnology wrote: High grade is subjective and not a bright line.
I regard your design as high grade simply because of all the effort invested to what you have designed, i.e. extremely low noise, full balanced design etc.
Noise is much lower than strictly needed and a full balanced design is also quite a step above the average Riaa preamp.
I see at least four examples of MC preamps here with large value electrolytic inputs: http://www.angelfire.com/sd/paulkemble/sound4.html
Three of the four are commercially-made units. The other is JLH/WW.
Thank you for sharing this interesting list, I haven't seen it before.
From the 12 MC designs, 4 have input caps, but most are almost 30 years old vintage designs and incomparable with your much more modern design.
Only the Douglas Self design is probably from a more recent date.

I see and read far too much over-the-top obsession with phono stuff.
I have zero interest in that.
What do you mean by that, given all the care and attention you have given to your design.
It suffices to take a single AD797 or a LT1028 to make a low noise MC pre amp, but you obviously wanted to go one big step further.
There is nothing wrong with that or in any way over the top.
It is an intellectual challenge trying to find the border of what makes sense and what not, and you are quite a bit out of the way from a simple standard design.
My goal is to make tools for people who create content not consume it.
So obviously they need the best of the best.
That's what makes this thread interesting.

Hans
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by Hans »

JR. wrote:Perhaps your choice of words is also contributing to animus.
That may certainly be the case, I try to do my best but it should be quite obvious that English is not my native language.
English is a complex language with all its understatements and double meanings.

Hans
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mediatechnology
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by mediatechnology »

JR.
My earlier p-10 was balanced.... :D
Really? :lol:
And a real source of inspiration: viewtopic.php?f=6&t=423
Thank you John.

Hans
I regard your design as high grade simply because of all the effort invested to what you have designed, i.e. extremely low noise, full balanced design etc.
Noise is much lower than strictly needed and a full balanced design is also quite a step above the average Riaa preamp.
Well thank you for that!
I'm more inspired to finish it now.
I wanted to see if the ZTX really had that low rbb so I pushed current hard and got the resistors about as low as practical.
I see and read far too much over-the-top obsession with phono stuff.
I have zero interest in that.

What do you mean by that, given all the care and attention you have given to your design.
It suffices to take a single AD797 or a LT1028 to make a low noise MC pre amp, but you obviously wanted to go one big step further.
There is nothing wrong with that or in any way over the top.
It is an intellectual challenge trying to find the border of what makes sense and what not, and you are quite a bit out of the way from a simple standard design.
I can't take credit for the design since its been seen many times before.
A hat tip to Demrow for the topology.
Another nod to Cohen for his brilliant double-balanced output.
Horowitz and Hill get the credit for finding the ZTX851 1990-era sleeper part.
bcarso alerted me to their work in the Third Edition of Art of Electronics.

I can take the credit for plugging in the ZTX851 though!
That's about it.
So obviously they need the best of the best.
They just need stuff that works good.

My clients for the most part have been mastering facilities or people doing archival transfer and restoration. (The MM preamp.)
For the ME, they want something quiet and free from electrical interference in difficult environments. (The Lathe.)
These folks are not op-amp swappers, they charge hourly, want something that works and isn't finicky.
Rather than buy hundred or thousand dollar phono cables they use shielded CAT-5.
They have a keen realization that adjustment of the Lathe is going to affect everything downstream and its errors eclipse just about every impairment downstream that people lose sleep over.

I have some vinyl that sounds like pure crap because it was cut that way.
And it may have not been the mastering facility but the elements they were given.
No cable, special capacitor or anything else is going to make it better.

I also have some vinyl that sounds good on the smallest most crappy speakers I have.
Its all about the performance and capture and less about the playback.

Thank you for your compliments and joining us Hans.

I don't speak a second language but have a limited understanding of Spanish.
They say humor is the most difficult to understand in a foreign language and that if you can tell a good joke in foreign language you've mastered it.
I'm not so sure: I think sarcasm is the most difficult nuance of a language.
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Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

Post by Gold »

mediatechnology wrote: They just need stuff that works good.
Yes.

Phono preamps are the most ridiculous example of specs meaning almost nothing in the real world. I have never met a phono preamp that was noisier than environmentally induced noise. Except the PTS. I like minutia as much as the next guy. Shorting the input and measuring the output is great for literature but any real world installation will be multiple magnitudes greater.

Reducing environmentally induced noise is so obviously where the greatest improvement lies I can't believe it's not talked about much. It's like it's a dirty secret. Until that noise is not a problem in 99% of the setups talking about a nanovolt of noise is pretty academic.

I am paying attention because I would like to try this transformless design next to a step up transformer and Wayne's MM pre, which I am using now. I'm betting the CMRR of the transformer bests the better noise specs of the transformerless design. But I'd gladly be proven wrong.
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