Um, on the HCA1200 schematic, Pchannel source follower transistor Q121 (type = 2SJ200) incorrectly shows the source and drain terminals reversed. The bulk is internally connected to the source, which should be connected to the higher voltage node (R134) while the drain should be connected to the lower voltage node (bottom rail). It's just a schematic symbol drafting error, I'm sure the PCB is routed correctly.
- anxious CMOS guy
- anxious CMOS guy
I spotted something worth mentioning. On the HCA1200 the cascode BJTs on the differential front end have caps on the bases for AC grounding.
This is not so on blowtorch-like schematics where fets are used for folded cascoding. Maybe the caps are not necessary because of much higher gate resistance?
What if we omitted the base caps, would they still behave close to common-base / cascodes?
The same PSU noise is injected at the bases and therefore should cancel out with good matching of the whole front end.
This is not so on blowtorch-like schematics where fets are used for folded cascoding. Maybe the caps are not necessary because of much higher gate resistance?
What if we omitted the base caps, would they still behave close to common-base / cascodes?
The same PSU noise is injected at the bases and therefore should cancel out with good matching of the whole front end.
I think the resistances would have to be much lower for omitting those caps.
Feedback 47k resistor - Caddock TF 020
Cascode 10k (r107, r113) to 5 green LEDs
10pf feedback cap to polystyrene,
C109, C103, C106 to polystyrene
Output zobel cap to film and foil - Rel cap or Wima FKP
Bias bypass caps to smaller film type only - maybe 1 uf with .01 bypass - no electrolytics
Relcaps or FKP Wimas for all bypass caps
Non magnetic metal film Vishay/Dale or PRP for signal path resistors
Lower noise dual op-amp for servo
Refresh board level electrolytics - Silmics for local bypass
Cascode Q9, Q10 - harder to do on existing pc board and some loss of output voltage - maybe a db of maximum output
Soft recovery diode bridge - or correct C / RC snubbing of existing diode bridge (Mark J specialty if I recall)
Cascode 10k (r107, r113) to 5 green LEDs
10pf feedback cap to polystyrene,
C109, C103, C106 to polystyrene
Output zobel cap to film and foil - Rel cap or Wima FKP
Bias bypass caps to smaller film type only - maybe 1 uf with .01 bypass - no electrolytics
Relcaps or FKP Wimas for all bypass caps
Non magnetic metal film Vishay/Dale or PRP for signal path resistors
Lower noise dual op-amp for servo
Refresh board level electrolytics - Silmics for local bypass
Cascode Q9, Q10 - harder to do on existing pc board and some loss of output voltage - maybe a db of maximum output
Soft recovery diode bridge - or correct C / RC snubbing of existing diode bridge (Mark J specialty if I recall)
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Ticknpop, you are NOW in dangerous territory! Of course, you and I would agree that your upgrades make a difference, but the 'critics' here will consider it a waste of time and money. Of course, more modern amps have these sort of 'improvements', with my best stuff having all of them, in one way or another.
So will any rational designer or engineer if it lacks evidence of the desired improvement. If the desired improvement is, "A good story to tell which will allow a higher price," that's going to be evaluated by a different metric than, "Makes the amplifier sound different in a way that can be discerned and preferred."
It's a tribute to the robustness of your design that people can do willy-nilly changes and not degrade its performance significantly.
I think Sy and I could never split a pizza (or an amplifier) , we'd never agree on the ingredients, a bottle of wine I'm more flexible on
I have shared Italian with SY, and I can assure you that he is very reasonable.
😎
Amplifiers, maybe not so much.
I like symmetry. In fact, I think that my reliance on symmetry for my designs, when possible, has made my designs stand out and actually work better than many asymmetrical designs.
Normally, I would use two fixed resistors of the same value and a pot in between.
This NODE is very high impedance, so my approach would balance out the capacitance to the case, from each side. A small change, but it would keep me more comfortable. This sort of circuit is compromised enough.
The opposite case is the circuit for the Quad 405. That is a treatise on asymmetry!
Normally, I would use two fixed resistors of the same value and a pot in between.
This NODE is very high impedance, so my approach would balance out the capacitance to the case, from each side. A small change, but it would keep me more comfortable. This sort of circuit is compromised enough.
The opposite case is the circuit for the Quad 405. That is a treatise on asymmetry!
Guess what? There never were two 1K trimpots. One is a lower value for fine adjustment. It is just another error on the schematic.
Scott, I do not recommend that you bother with changing out the caps, resistors, etc. The speakers that you are using (MET 7's I presume) will probably forgive any small differences. Just get the amp up and running, and go from there.
Tipo Fino 00 flour, San Marzano tomatoes, garlic, salt, pepper, olive oil and fresh mozzarella (preferably bufala). The Neapolitans figured this out.
John, thanks for the clarification, that makes much more sense.
That I can agree on, I was in Chicago in June, had Brazilian instead.
Probably knows where to get a great cannoli too.
Probably knows where to get a great cannoli too.
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Still can't taste any difference in bottles of wine... but I do like some labels better than others...
_-_-
Pizza? Yep big differences. But I am sighted.
_-_-
Pizza? Yep big differences. But I am sighted.
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