Grey,
I am in general agreement that simpler can be better as long as things like PSU quality, PSRR .......are given adequate attention.........as you know yhe PSU is half the ballgame.
I agree that Mr.Curl's use of the complementary differentials is nothing short of brilliant.............but I have this nagging idea about attaching the the tails of the differentials to the opposite rails through adjustable current sources (which make balancing the circuit easier).......I know it is not as elegent and noise might be an issue (if any in this circuit)............but what the heck, will it perform better?
Regards,
Jam
I am in general agreement that simpler can be better as long as things like PSU quality, PSRR .......are given adequate attention.........as you know yhe PSU is half the ballgame.
I agree that Mr.Curl's use of the complementary differentials is nothing short of brilliant.............but I have this nagging idea about attaching the the tails of the differentials to the opposite rails through adjustable current sources (which make balancing the circuit easier).......I know it is not as elegent and noise might be an issue (if any in this circuit)............but what the heck, will it perform better?
Regards,
Jam
Chris,
Well all I can say that simple feedback regulators sound worse than CLC filtering, op amps used as comparitors in regulators tend to also impart their own sound and usually the regulators I use end up being far more complex than the circuits they feed..........then again this is only my opinion.
Regards,
Jam
Well all I can say that simple feedback regulators sound worse than CLC filtering, op amps used as comparitors in regulators tend to also impart their own sound and usually the regulators I use end up being far more complex than the circuits they feed..........then again this is only my opinion.
Regards,
Jam
I use fairly elaborate power supplies regardless of the circuit. Since I tend towards multiple rail voltages at various places in the circuit, I either need a custom-made transformer with lots of taps, or multiple regulators. It's faster, cheaper, and easier to go with regulators.
Yes, there have been times that I've used CRC (-RCRC...) filtering, but I'd rather go ahead and nail the voltage to a predetermined value at least once in the chain, even if I use CRC below that.
I have nothing against inductors. In fact, I'd prefer them, but they're difficult to buy at retail, particularly large ones, and awkward to wind for yourself.
I don't know what percentage I'd assign the power supply as far as importance, but it's very, very important. One thing I feel strongly about is the use of film bypasses on electrolytics. Electrolytics just aren't that good; quite far from the ideal cap. Even a smallish film cap can help quite a bit. If the circuit allows, I try to use all film caps in the power supply, but it gets damned expensive. I go to all sorts of lengths to avoid electrolytics in the circuit itself.
Curiously, for all their imperfections, I am not averse to using caps (film caps, that is) in the signal path. This is something I've been playing with for the last couple of years and have had good results. In particular, I have been replacing active devices whose sole function is level shifting with DC blocking caps. As long as you have sufficient current to drive the cap (something many people overlook), it works quite well. I don't guarantee that I'll stay with it, but so far I've been happy with that particular set of tradeoffs.
Grey
Yes, there have been times that I've used CRC (-RCRC...) filtering, but I'd rather go ahead and nail the voltage to a predetermined value at least once in the chain, even if I use CRC below that.
I have nothing against inductors. In fact, I'd prefer them, but they're difficult to buy at retail, particularly large ones, and awkward to wind for yourself.
I don't know what percentage I'd assign the power supply as far as importance, but it's very, very important. One thing I feel strongly about is the use of film bypasses on electrolytics. Electrolytics just aren't that good; quite far from the ideal cap. Even a smallish film cap can help quite a bit. If the circuit allows, I try to use all film caps in the power supply, but it gets damned expensive. I go to all sorts of lengths to avoid electrolytics in the circuit itself.
Curiously, for all their imperfections, I am not averse to using caps (film caps, that is) in the signal path. This is something I've been playing with for the last couple of years and have had good results. In particular, I have been replacing active devices whose sole function is level shifting with DC blocking caps. As long as you have sufficient current to drive the cap (something many people overlook), it works quite well. I don't guarantee that I'll stay with it, but so far I've been happy with that particular set of tradeoffs.
Grey
Yep. If you use enough current to drive a cap, it's actually a fairly low distortion device. Too little current and the waveform gets wonky.
When I see folks trying to run a 30V signal on a large cap with something pathetic like a fraction of a milliamp, I shake my head. It's no bloody wonder caps have such a bad reputation.
This is one of the secrets of "tube sound." Tube equipment runs on high resistances and impedances. When's the last time you saw a 10 Ohm resistor in a tube circuit? It just doesn't happen. So with all those high resistances, you can get away with...wait for it...really small capacitances. The small caps are easy to charge and discharge, even with the relatively modest currents available in a tube circuit. You can run a 6SN7 or a 6922 at 3-5mA maybe even 10mA and do wonders with a .1uF cap.
So then some solid state guy walks in and thinks he'll cap-couple something. Only...because he's working into a 10k load (or less) instead of 1M, he's using a much, much larger cap in order to keep the low frequency cutoff point down below 1Hz. The punchline is that he's trying to charge ten or twenty times the capacitance with, say, 2mA. It doesn't sound the way he wants. It doesn't measure the way he wants. So he walks away bad-mouthing coupling caps without ever once thinking of anything so obvious as slew rate. He just rants about "obsolete technology."
I'm a non-conformist. I'm willing to use coupling caps in solid state gear. A year ago I did a line stage for a guy. Cap-coupled at the output. But...the final stage of the circuit was an IRF MOSFET pair biased out the wazoo (15-20mA? Something like that.) so as to have plenty of current to drive the cap.
Simple.
Grey
When I see folks trying to run a 30V signal on a large cap with something pathetic like a fraction of a milliamp, I shake my head. It's no bloody wonder caps have such a bad reputation.
This is one of the secrets of "tube sound." Tube equipment runs on high resistances and impedances. When's the last time you saw a 10 Ohm resistor in a tube circuit? It just doesn't happen. So with all those high resistances, you can get away with...wait for it...really small capacitances. The small caps are easy to charge and discharge, even with the relatively modest currents available in a tube circuit. You can run a 6SN7 or a 6922 at 3-5mA maybe even 10mA and do wonders with a .1uF cap.
So then some solid state guy walks in and thinks he'll cap-couple something. Only...because he's working into a 10k load (or less) instead of 1M, he's using a much, much larger cap in order to keep the low frequency cutoff point down below 1Hz. The punchline is that he's trying to charge ten or twenty times the capacitance with, say, 2mA. It doesn't sound the way he wants. It doesn't measure the way he wants. So he walks away bad-mouthing coupling caps without ever once thinking of anything so obvious as slew rate. He just rants about "obsolete technology."
I'm a non-conformist. I'm willing to use coupling caps in solid state gear. A year ago I did a line stage for a guy. Cap-coupled at the output. But...the final stage of the circuit was an IRF MOSFET pair biased out the wazoo (15-20mA? Something like that.) so as to have plenty of current to drive the cap.
Simple.
Grey
Grey,
When you say
"Yep. If you use enough current to drive a cap, it's actually a fairly low distortion device. Too little current and the waveform gets wonky."
What are you test conditions? and if your test device impedence is constant how would a high current DUT (Device Tnder Test)differ from a low current DUT using the same capacitor in both cases?
Jam
When you say
"Yep. If you use enough current to drive a cap, it's actually a fairly low distortion device. Too little current and the waveform gets wonky."
What are you test conditions? and if your test device impedence is constant how would a high current DUT (Device Tnder Test)differ from a low current DUT using the same capacitor in both cases?
Jam
What I am trying to point out is that coupling caps only have a dV/dt problem with very low impedance loads. If you are coupling from a source to a load, either directly or through a cap, it makes little difference, current-wise. It only makes a difference IF the load is too low or actually ground. Then, direct coupling will work as badly as any cap, or even worse, you will be driving a short-circuit. In either case, the cap does not REQUIRE more current. Caps have other, REAL problems, and, by the way, I like high current too, just to drive the residual cable capacitances with ease.
However, a related situation is VERY important. This is the capacitance to ground of long cables, or the RIAA caps in a traditional phono stage. For example, the DYNA PAS-3 phono stage is SLEW-RATE limited by the RIAA cap(s) attempting to drive a 1K input resistor from a 100K load resistor. What a problem! I lived with the DYNA preamp for 10 years, before I realized this. No wonder it tended to 'soften' the sound.
However, a related situation is VERY important. This is the capacitance to ground of long cables, or the RIAA caps in a traditional phono stage. For example, the DYNA PAS-3 phono stage is SLEW-RATE limited by the RIAA cap(s) attempting to drive a 1K input resistor from a 100K load resistor. What a problem! I lived with the DYNA preamp for 10 years, before I realized this. No wonder it tended to 'soften' the sound.
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