This is not fair, John...
How are we supposed to spot the difference by looking at two different schematics, produced years apart, drawn by different people and in addition to that one of the schematics being some sort of pre-production sketch full of mistakes.
I would expect the resistor brand to be listed in BOM, if at all, but not in the schematic of mass produced amplifier.
I knew the question must have some twist, hence I held back.
That's most amazing revelation from a Chinese mass audio product, no one expects that. We could hear something like this from your products like Vendetta or blowtorch or Charles Hansen's Airè products and of course some other DIY fellows.
BTW, which are your favorite brand/type small resistors say 1/4 or 1/2 Watt?
Cheers, Tony
I agree, what is relatively 'obvious' to me, is lost in the scramble.
However the HCA3500 has for the main feedback resistor: 47K VISHAY, R44
the A-21 has for the main feedback resistor: 100K Holco 1/4W, R12
When we attempted to 'fix' the HCA3500, in order to make it sound OK, this was the first thing we did. i.e. changed the 47K 'vishay' to a 47K 1/2W Holco. It made a signficant sonic difference, much to everyone's surprise. However, of course, it was not the only change we had to do to make the HCA3500 into a 'world class' power amp.
However the HCA3500 has for the main feedback resistor: 47K VISHAY, R44
the A-21 has for the main feedback resistor: 100K Holco 1/4W, R12
When we attempted to 'fix' the HCA3500, in order to make it sound OK, this was the first thing we did. i.e. changed the 47K 'vishay' to a 47K 1/2W Holco. It made a signficant sonic difference, much to everyone's surprise. However, of course, it was not the only change we had to do to make the HCA3500 into a 'world class' power amp.
Holco vs. Vishay
This is very interesting indeed. Success or failure of finished product depending on single resistor.... Who would have thought it?
Ok, values are different, but not THAT different. Did you investigate it further, John? What could be the culprit here? Magnetic properties? Contact material? Dissimilar metals? Power rating?
It's just another indication that we're not there yet. More food for thought.
Best,
This is very interesting indeed. Success or failure of finished product depending on single resistor.... Who would have thought it?
Ok, values are different, but not THAT different. Did you investigate it further, John? What could be the culprit here? Magnetic properties? Contact material? Dissimilar metals? Power rating?
It's just another indication that we're not there yet. More food for thought.
Best,
Distortions, i.e. dependence of resistance on voltage and on power. Since the resistor is in feedback, their non-linearities shape non-linearities of the whole amp which amplification factor is close to ratio betwen feedback resistors plus 1. If say resistor changes it's resistance 1% that means already 1% of distortions.
Exactly. For that resistor, voltage coefficient of resistance is a critical parameter. Whether or not that was the cause of market failure or success is a different question...
John,
I always hated "Vishay" Resistors (they give this "look at me, how great I sound" sound that really annoys me), I never even read that part of the schematics...
With hindsight you put in the breadcrumbs, but I kept looking for schinken...
Ciao T
I always hated "Vishay" Resistors (they give this "look at me, how great I sound" sound that really annoys me), I never even read that part of the schematics...
With hindsight you put in the breadcrumbs, but I kept looking for schinken...
Ciao T
To change a Vishay 1% in value would require letting out some of the magic smoke. Full circle again, maybe time for voicing wires.
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I am not John Curl, but I'm almost 100% sure that Mr.Curl, being an engineer with years of experience, didn't overlooked "dependence of resistance on voltage and on power" when specifying parts for his amp. I hope, I'm not wrong here.
ThorstenL,
Vishay produces loads of different resistors, why such general statement? We do not know what resistor type by Vishay was deployed in Parasound.
Best,
Scott,
You know perfectly well that was an overstated example. BUT...
Vishay CCF07 Resistor at 200 PPM/C would require a rise of only 50 Degrees. Hot to the touch but well below the operating limit of 150 C. That requires a dynamic dissipation of only .18 watts to achieve that temperature rise!
Ok, so it is hard to cool it fast enough.
So obviously any sound quality issues must be blamed on using op-amps!
(In reality you actually could get .05 to .1% distortion on the A part of ADSR.)
ES
T, this is a controversial area. I have to move slowly, especially under moderation, to make any point that will make sense to any interested party.
Of course, Wavebourn is correct, and I was quoted in print about 30 years ago, by Peter Moncrief, in his publication, that the feedback resistor was the 'template' of the transfer function of an amplifier.
I originally chose Holco (old, non-magnetic) types as a rational improvement for the RIAA of the Vendetta Research Phono Stage, over the existing Resista parts I was using. They also had the advantage of being 0.5% accurate and that made my RIAA tracking more consistent. What I really like about these parts is their relatively thick leads that gives us more thermal capacitance over most similar resistors.
Early on, with Parasound,(more than 20 years ago) I recommended, in writing, to use Holco for the primary feedback resistor in every power amp I was associated with. I could not predict the quality of the rest of the resistors, as they would be sourced in Asia.
This worked OK until the HCA-3500, which was modified with a very strange, almost miniature resistor, made by a relatively unknown Asian company, owned by Vishay. It had GREAT SPECS, throwing out any 'scientific' approval, and it NOT make the measurements bad in the amp, either. It just sounded 'lousy', had virtually no thermal capacitance (if that did anything important) and when we replaced it, it changed the sound of the amp, almost completely. Why? Who knows? This to me, is the ESSENCE of what I have tried to convey on this thread for many years. I can sometimes only give RESULTS, and technical speculation, not HARD EVIDENCE. Tough nuts! '-)
Of course, Wavebourn is correct, and I was quoted in print about 30 years ago, by Peter Moncrief, in his publication, that the feedback resistor was the 'template' of the transfer function of an amplifier.
I originally chose Holco (old, non-magnetic) types as a rational improvement for the RIAA of the Vendetta Research Phono Stage, over the existing Resista parts I was using. They also had the advantage of being 0.5% accurate and that made my RIAA tracking more consistent. What I really like about these parts is their relatively thick leads that gives us more thermal capacitance over most similar resistors.
Early on, with Parasound,(more than 20 years ago) I recommended, in writing, to use Holco for the primary feedback resistor in every power amp I was associated with. I could not predict the quality of the rest of the resistors, as they would be sourced in Asia.
This worked OK until the HCA-3500, which was modified with a very strange, almost miniature resistor, made by a relatively unknown Asian company, owned by Vishay. It had GREAT SPECS, throwing out any 'scientific' approval, and it NOT make the measurements bad in the amp, either. It just sounded 'lousy', had virtually no thermal capacitance (if that did anything important) and when we replaced it, it changed the sound of the amp, almost completely. Why? Who knows? This to me, is the ESSENCE of what I have tried to convey on this thread for many years. I can sometimes only give RESULTS, and technical speculation, not HARD EVIDENCE. Tough nuts! '-)
I am not John Curl, but I'm almost 100% sure that Mr.Curl, being an engineer with years of experience, didn't overlooked "dependence of resistance on voltage and on power" when specifying parts for his amp. I hope, I'm not wrong here.
As John Curl uses to say, "Learn and grow!"
Vishay today is a huge corporation that bought lots of brands. However, it started when it's founder escaped from basement where they used to hide from German soldiers at the end of WW-II. In that basemebt he met an engineer who taught him a lot. And the name of the village was Vishay. There in the basement he got a dream to create the best in the world electronics' company. And to buy Telefunken. He did that, later. But started from invention of bulk foil resistors, extremeny temperature stable. But it does not mean that all resistors marked Vishay today are all the same, some of them have quite high temperature coefficient of resistance, that means modulation of resistance by signal, that means distortions.
John already said you can't measure the difference. Vishay's 1/2W leaded resistors are speced at -130db thirds (no conditions stated).
Maybe just rotating the Vishay's would help, who knows?
Or placing tiny feedback resistors further from strong heat radiation, or putting inside of some small can?
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