John Curl's Blowtorch preamplifier part II

[Kindhornman]

I bet the plastic surgeons are making a fortune though!

Back to the discussion, John this is getting interesting, keep it going please.

 

[gpapag]

Thanks, John. Let me follow up with a few more:
1. Does that input capacitance really matter, again restricting ourselves to low output MCs?

Sorry for 🙂Popworm) but I would like to ask (I may be totally wrong): Even assuming constant capacitance with frequency, where does the ac current to charge the gates capacitance of the input fets come from? Doesn’t it come from the cartridge’s coil?
If so, paralleling many fets (for noise reduction), the capacitance increases, therefore the ac current demands too for same charge/time. Can the cart provide this dynamic current? Any consequence on reproducing fast dynamic waveforms?

George

 

[jacco vermeulen]

Can you see

Just wait till it hits rock Bottom.

(In Spain, every ittibittititti counts)

 

[Kindhornman]

Piggy backing on to what you are asking George, wouldn't the output of the cartridge be velocity related and therefor frequency dependent also as to output voltage? If you are producing output into the 100khz range I wonder where this information is coming from, it isn't from the original source material, so what is that and how does it affect the output V of the cartridge in question.

 

[john curl]

MC phono cartridges will work into a direct short, if necessary (summing input), so cap loading is a VERY SMALL problem.

 

[SY]

George, I don't think it's very significant. If we look at the RC time constant between, say, 10R (typical MC) and 1nF (typical multiple high gm FETs in parallel), it's at about 15MHz. Max signal of, say, 0.1mV. So the limiting value of current is 0.1mV/10R = 10uA, and that will only happen at RF. We're down to a single uA at 1.5MHz.

Going at it a different way, let the input impedance be 100R with the FET input capacitance in parallel. The frequency at which the input impedance has dropped by 30% is 1.6MHz.

Clearly, any current drawn at anywhere near the audio band is pretty minuscule for most MCs. You can extend this a bit to see the effect in the audio band of the nonlinearity of the input capacitance and judge how important it's likely to be. If John doesn't, I will.

 

[john curl]

The ultrasonic output from a phono cartridge comes from the MISTRACKING (which happens very often) of the phono cartridge. I used a Sheffield record on a specific track, and I made every MC tested, MISTRACK. It was relatively easy.
However, SOME direct discs, like 'CRYSTAL CLEAR' that were monitored by John Meyer, would not normally MISTRACK. It just depends on the recording.

 

[john curl]

Go for it, SY. I can't do EVERYTHING! '-)

 

[Joshua_G]

The ultrasonic output from a phono cartridge comes from the MISTRACKING (which happens very often) of the phono cartridge. I used a Sheffield record on a specific track, and I made every MC tested, MISTRACK. It was relatively easy.
However, SOME direct discs, like 'CRYSTAL CLEAR' that were monitored by John Meyer, would not normally MISTRACK. It just depends on the recording.

Hi John?
Do we care if the ultrasonic components caused by the cartridge mistracking is being attenuated? Does it affect the signal in the audio band?

As for your phono stage idea.
What if you'll take the Vendetta first stage and have 3 2SK170/2SJ74 in parallel, both in the first left section and in the folded cascade section?
Also, omit the DC servo from the first stage and have one only on the second stage?

 

[bcarso]

I'd add that the series feedback and bootstrapping mentioned drastically reduces the capacitance at signal frequencies and beyond, if this were an issue, which it is at best marginally for low Z cartridges. One should observe some caution terminating the cartridge in a short or near short however. Marsh reported (in a recently reproduced old AA piece on a MC preamp) that he liked how it sounded iirc. But we need to remember that time constants for series L-R are L/R, that is, lower R is a bigger tau, which may or may not be a good fit to what the cartridge manufacturer desires.

And to George's question, with a constant capacitance at the input from whatever source, lumped external or FET internal, the analysis of the R-L-C circuit should be straightforward from linear network theory. But again, the JFET effects can be essentially eliminated with feedback techniques, up to a rather high frequency.

 

[AudioLapDance]

Gilbert's chips, AFA (active feedback amplifier): AD830, LT6552, AD8129/30, TDA856X

I just started a thread on Gilbert's Chips, AFA (active feedback amplifier): AD830, LT6552, AD8129/30, TDA856X, AD844 (Gilbert's Pin)

http://www.diyaudio.com/forums/part...feedback-amplifier-ad830-lt6552-tda856x.html#

In a sentence, Barrie Gilbert stated that his AFA (active feedback amp) "unlike the OPA (vfb opamp), has high open-loop linearity and excellent closed-loop linearity due to its distortion-canceling topology, and a very high degree of versatility arising from its dual fully-differential inputs, has the potential to eclipse the OPA in all applications involving the manipulation of purely voltage-mode signals."



And you guys might get a kick out of an an old thread (2004!) I reference at the end (post 5) when talking about the AD844

http://www.diyaudio.com/forums/part...plifier-ad830-lt6552-tda856x.html#post3392798

With ... Holy Heavy Hitters Batman! Charles Hansen, John Curl, Walt Jung, ... and the old gang! Jocko, PMA, CarlosFM, Pedja, Elso ...

 

[Esperado]

Do you know you can buy plug-ins for your digital audio workstation to emulate vinyl sound? I wonder what the algorithms are...

Adding rumble, surface noise, random clics & scratches of various levels, distortion a high levels +high frequencies, HQ resonance in ultra low basses (the arm), mutiples HQ resonnances at HF, re-equalized plus a special compressor to bring a curtain between you and the music..
All what make the charm of vinyls 😀😀😀😀

 

[Kindhornman]

Esperado,
My vinyl albums don't have all that noise, I just put them in the dish washer and they come out sparkly clean.....! 😱😀

 

[john curl]

It is sad, I really like phono playback, yet I don't hear noise, rumble. Perhaps a few ticks and pops that I can readily ignore, but that is with a 'hi end' playback system and properly handled vinyl records. An exception to the rule, I suppose.

 

[31697B]

I just started a thread on Gilbert's Chips, AFA (active feedback amplifier): AD830, LT6552, AD8129/30, TDA856X, AD844 (Gilbert's Pin)

http://www.diyaudio.com/forums/part...feedback-amplifier-ad830-lt6552-tda856x.html#

In a sentence, Barrie Gilbert stated that his AFA (active feedback amp) "unlike the OPA (vfb opamp), has high open-loop linearity and excellent closed-loop linearity due to its distortion-canceling topology, and a very high degree of versatility arising from its dual fully-differential inputs, has the potential to eclipse the OPA in all applications involving the manipulation of purely voltage-mode signals."



And you guys might get a kick out of an an old thread (2004!) I reference at the end (post 5) when talking about the AD844

http://www.diyaudio.com/forums/part...plifier-ad830-lt6552-tda856x.html#post3392798

With ... Holy Heavy Hitters Batman! Charles Hansen, John Curl, Walt Jung, ... and the old gang! Jocko, PMA, CarlosFM, Pedja, Elso ...

Looks great. OK I'm in.

 

[john curl]

Joshua G, please do not jump ahead in my descriptions of these phono stages. It will just confuse the majority who might be interested in learning about advanced phono stages. Tomorrow, I hope to describe the Vendetta input stage.

 

[scott wurcer]

I just started a thread on Gilbert's Chips, AFA (active feedback amplifier): AD830, LT6552, AD8129/30, TDA856X, AD844 (Gilbert's Pin)

http://www.diyaudio.com/forums/part...feedback-amplifier-ad830-lt6552-tda856x.html#

In a sentence, Barrie Gilbert stated that his AFA (active feedback amp) "unlike the OPA (vfb opamp), has high open-loop linearity and excellent closed-loop linearity due to its distortion-canceling topology, and a very high degree of versatility arising from its dual fully-differential inputs, has the potential to eclipse the OPA in all applications involving the manipulation of purely voltage-mode signals."



And you guys might get a kick out of an an old thread (2004!) I reference at the end (post 5) when talking about the AD844

http://www.diyaudio.com/forums/part...plifier-ad830-lt6552-tda856x.html#post3392798

With ... Holy Heavy Hitters Batman! Charles Hansen, John Curl, Walt Jung, ... and the old gang! Jocko, PMA, CarlosFM, Pedja, Elso ...

The AFA has a pretty big noise penalty, for phono the feedback to null pin techniques might be more promising. Walt has published this (the AD745 is great run open-loop this way).

 

[Pano]

My vinyl albums don't have all that noise, I just put them in the dish washer and they come out sparkly clean.....!

Me too - but I quickly learned not to use the heated dry cycle - they warp! Use air dry only.

 

[scott wurcer]

The ultrasonic output from a phono cartridge comes from the MISTRACKING (which happens very often) of the phono cartridge. I used a Sheffield record on a specific track, and I made every MC tested, MISTRACK. It was relatively easy.
However, SOME direct discs, like 'CRYSTAL CLEAR' that were monitored by John Meyer, would not normally MISTRACK. It just depends on the recording.

I think the mistracking thing is overstated, I have pictures of large scratches where the stylus clearly leaves the groove and the signal has integrity immediately after it lands back on the groove. No pre-amp misbehavior.

 

[scott wurcer]

Me too - but I quickly learned not to use the heated dry cycle - they warp! Use air dry only.

I use my old LAST brushes and liberal quantities of the Wholefoods version of Windex (the uncolored one). I made a lable protector out of a couple of plastic circles and some cryo rubber sealing material that uses a wing nut and bolt through the hole.