I'm confused.
What I was pointing to is that some parameters are clearly thermally based. That's what is shown in TPC 7.
It's been shown that a lot of the thermal effects are because of the output stage and loading. Makes sense, since the output stage is usually driving the lowest impedance. Some times really low when people want to attach headphones or low impedance test loads. That's why an external buffer might be helpful in some cases.
http://waltjung.org/PDFs/Composite_Line_Driver_with_Low_Distortion.pdf
John,
My faves depend upon the seaon and what was recently in the Sample Envelope and worked out...
BUT, I can tell you about something I did a while back. I needed a decent Phono as a kind of internal reference as to what a "good" solid state Phono would sound like. We found the result superior to Tom Evan's Groove as well as something with Batteries by Ron Sutherland (both of those did rather well) and some other stuff (dross?) I forgot about.
I used an INA103 on the input, set up as howland current pump. This basically produces a Voltage to current converter with low noise.
It was feeding what is basically the fundamental design of the later Vendetta's (that is 100nF cap to ground after the current out stage, 750 Ohm into the inverting input to create the 75uS pole, other poles in the feedback network for the 2nd stage discrete Fet Transconductance Op-Amp).
I used surplus mil-spec polystyrene & tinfoil cap's from east germany for the EQ and decent Metal Film resistors (RC55 standard) for resistors.
Second stage used OPA637.
Direct-couped, offset trim via Multiturn pots on both stages, no servos, DC blocking Cap's etc.
Needs to be adjusted after 24 Hours on and left on all the time, or DC offset can be substantial, a commercial unit would likely need servo's on both stages.
The Power supply used 80uF/30V Polyprop Cap's around each Op-Amp (plus bypasses optimised on an RF analyser) as local PSU decoupling and a bipolar capacitor multiplier with a 1,000uF Elna Silmic Cap on each Base for each (Op-Amp's) supplyfilter R a few KOhm, cannot remember precisely now.
The PSU used four individual 50VA torroidal transformers with ES Screen wired up to cancel leakage from each transformer pair with 40A Schottky rectifier and a 1,000uF Elna Silmic input cap, followed by five 2 * 3.3R & 10,000uF (Nichicon) RC filter cells (that is a 2.5Hz turnover and 32dB attenuation at 100Hz per cell - or 160dB attenuation at 100Hz for the whole chain) and was fully dual Mono.
No 3-Pin regs.
Nothing too special, just swiping ideas from you John, Ron Sutherland and using what was in the junk box...
I am unsure if I really prefer the result over my totally maxxed out "Analogue Addicts 2008".
But that comparison is a little unfair, as the "final AA Phono" used very esotheric parts (including Rhopoint NI Copper Alloy Wirewound resistors everywhere) and by far more extreme power supplies. This one BTW uses either LT1115/LT1028 for MC or OPA637 for MM, single stage, feedback EQ. Socket for gainset resistor (10R MC, 100R MM) and Op-Amp.
I think I also like my "El Cheapo" Tube Phono better, if build with really high quality parts.
I should note that non of my Phono's use buffers on the outputs and always seem to sound worse if one is employed (even in tube circuits).
But I do not connect 600 Ohm input impedance pro-Amp's or 32Ohm Headphones to my Phono's... If I did, I suspect they would sound better WITH a buffer.
Ciao T
My faves depend upon the seaon and what was recently in the Sample Envelope and worked out...
BUT, I can tell you about something I did a while back. I needed a decent Phono as a kind of internal reference as to what a "good" solid state Phono would sound like. We found the result superior to Tom Evan's Groove as well as something with Batteries by Ron Sutherland (both of those did rather well) and some other stuff (dross?) I forgot about.
I used an INA103 on the input, set up as howland current pump. This basically produces a Voltage to current converter with low noise.
It was feeding what is basically the fundamental design of the later Vendetta's (that is 100nF cap to ground after the current out stage, 750 Ohm into the inverting input to create the 75uS pole, other poles in the feedback network for the 2nd stage discrete Fet Transconductance Op-Amp).
I used surplus mil-spec polystyrene & tinfoil cap's from east germany for the EQ and decent Metal Film resistors (RC55 standard) for resistors.
Second stage used OPA637.
Direct-couped, offset trim via Multiturn pots on both stages, no servos, DC blocking Cap's etc.
Needs to be adjusted after 24 Hours on and left on all the time, or DC offset can be substantial, a commercial unit would likely need servo's on both stages.
The Power supply used 80uF/30V Polyprop Cap's around each Op-Amp (plus bypasses optimised on an RF analyser) as local PSU decoupling and a bipolar capacitor multiplier with a 1,000uF Elna Silmic Cap on each Base for each (Op-Amp's) supplyfilter R a few KOhm, cannot remember precisely now.
The PSU used four individual 50VA torroidal transformers with ES Screen wired up to cancel leakage from each transformer pair with 40A Schottky rectifier and a 1,000uF Elna Silmic input cap, followed by five 2 * 3.3R & 10,000uF (Nichicon) RC filter cells (that is a 2.5Hz turnover and 32dB attenuation at 100Hz per cell - or 160dB attenuation at 100Hz for the whole chain) and was fully dual Mono.
No 3-Pin regs.
Nothing too special, just swiping ideas from you John, Ron Sutherland and using what was in the junk box...
I am unsure if I really prefer the result over my totally maxxed out "Analogue Addicts 2008".
But that comparison is a little unfair, as the "final AA Phono" used very esotheric parts (including Rhopoint NI Copper Alloy Wirewound resistors everywhere) and by far more extreme power supplies. This one BTW uses either LT1115/LT1028 for MC or OPA637 for MM, single stage, feedback EQ. Socket for gainset resistor (10R MC, 100R MM) and Op-Amp.
I think I also like my "El Cheapo" Tube Phono better, if build with really high quality parts.
I should note that non of my Phono's use buffers on the outputs and always seem to sound worse if one is employed (even in tube circuits).
But I do not connect 600 Ohm input impedance pro-Amp's or 32Ohm Headphones to my Phono's... If I did, I suspect they would sound better WITH a buffer.
Ciao T
Hi Pavel,
Which is besides point. The point was that attaching 600 Ohm to the AMR PH-77 is operating it outside the design parameters (and outside the limits stated in the manual) and that attaching the same load to John's Phono also is operating it outside the design parameters.
If that is done the results may be "interresting", but pointless.
If you need a Phonostage that drives 600 Ohm don't buy my one or John's.
Ciao T
Which is besides point. The point was that attaching 600 Ohm to the AMR PH-77 is operating it outside the design parameters (and outside the limits stated in the manual) and that attaching the same load to John's Phono also is operating it outside the design parameters.
If that is done the results may be "interresting", but pointless.
If you need a Phonostage that drives 600 Ohm don't buy my one or John's.
Ciao T
Well, someone has to tap into that market of all those line preamps with a 600 ohm input impeadance.
It should be pointed out that most designers know quite well the distortion free limitations of most op amps made today. The designers seem to 'steal' output quiescent current in order to put it into other stages or to get the desired overall operating current. I have always worried about this, especially when trying to get the ADVERTISED performance with realistic value feedback resistors. Even the AD797 suffers from this. Why I should be called out for designing just under the worst case conditions, is a surprise. This thread is full of surprises! '-)
OK, the Blowtorch thread turns to opamp audio thread with output stages idled at 1mA. I can digest it, no problem, but please address marketing practices to someone else. I would call it a 180° shift in one day 😀😀😀
Well, PMA when the exact schematic for the JC-3 comes by you, as the JC-1 and JC-2 before it, please contact my boss and show us the way to improve the product, as you have before. I would appreciate it.
Thorsten, I like the current pump conversion, but would it not be easier just to make a trans amp? I guess not, compared to an IC, like I use, but I don't use a current pump in this application. The last time I used that approach was making current drive electronics for the driver stages of my master tape recorders. Used them seriously since 1969.
PMA, we finally agree on something. The ADA4898 looks to be an outstanding op amp. I will have to get some.
I have already recommended the part a year ago. It has extremely low voltage noise. Open loop DC gain is not very high (103dB), and OLG corner is about 1kHz. The output stage is quite powerful. The part has warm, rich sound, not sterile. This is very seldom for a bipolar input opamp. I prefer it compared to AD797, LT1028 and National circuits.
The good sound quality might well be a result of the multi-tanh input circuitry? Given the notion that undegenerated LTPs are bad owing to poor linearity, this one should have more or less licked that particular problem. I'd like to get some too 🙂
I do not even the simplified circuit diagram, maybe Scott might tell us more (in case it is not covered by NDA).
Now I remember why I didn't audition this part: The package was NOT mini-dip, and the board was designed for mini-dip more than 1 year ago. Later, I had to get adaptors, anyway, so the problem is not so great, today. I WAS going to use the AD797 and it IS mini-dip, but the National part sounded slightly different, but both were OK to use. The final decision was actually the price. The AD797 appears to cost about twice as much as roughly equivalent designs, so we chose the National part. However, we 'could' change over to the 4898, but I would have to audition it first. Maybe someday.
Would you kindly explain what you mean 'opamp_distortion'?
I have some measurements we made, but they are not a general answer.
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