Well, I sent two messages to THAT Corp. but look like they don't have any comment about our issue!!......Would be a good idea someone try to contact them again with the same question!!I am very intrigued for a analysis for that analysis......Opacheco.
I think the answer may be even simpler that I thought. I think the gain around the loop sets the threshold and nothing else. The transfer function of the gain element sets the ratio and nothing else. It is similar to an op amp with a switched feedback network. Up to the threshold the gain is one value and above it the switch gets operated and the gain changes. It does not matter if you put some extra gain after the switch in the NFB network it will not affect the threshold. I need to dig out one of my old control theory books to try to turn this into some equations.CheersIan
The 2254 uses a diode bridge as a voltage controlled resistor.I am still working on the theory but other things have got in the way - like moving house!CheersIan
Opacheco, that is correct.The math is pretty simple with regards to this.ruffrecords your statement that the gain in the side-chain after threshold affects ratio only was precisely my original statement, so I'm not sure we disagree at all any more.
I understand what your spreadsheet is basically trying to say, but I couldn't get it to work in OpenOffice properly (I don't use Microsoft Office). Fundamentally, however, the speadsheet is for a feed-forward compressor.Here is a really really simple implementation in Desmos to clarify (for feed-forward): https://www.desmos.com/calculator/oyomsskeqs
While we're digging up old threads... I'm actually quite interested in the U274 design that was coming along here. I've been studying the original schematic, and the various modifications discussed earlier in the thread, and .. I think .. have a fairly complete picture of where etheory left off. I'm going to try building one and see what color smoke it makes.
I'm not sure that mods are my specialty. My analog design skills are meager. I'm just hoping to bring the work already done back to life.While I'm on the subject, one thing I'm not quite sure of: Where would the feedback cap C5 connect to? In the original, it's going to the middle of three pins going to the output transformer. The other two don't look like they're being used. The amp output connects to an outer pin on the top, "0V" to the bottom. Is it safe to assume the middle three pins are taps along the primary coil? If that's the case, maybe C5 would be driven by a 50% amplitude copy of the output signal?AFAICT, this was never shown on any of the schematics etheory posted -- and on the PCB, it just connects to an unlabeled pin in a header block.