He turned off the generator which resulted in undefined high generator output impedance seen by the amp input. Thus the rise of noise floor in the "no signal" measurement. The input had to be shorted or closed by a defined impedance, like 50 ohm or 600 ohm, instead. As such is now, the "no signal" noise measurement is pointless.
No. The purpose of that test was to see if the high levels of power supply noise I saw were also there when nothing was playing and that was the case. I also used that graph to minimize mains leakage but strangely, that made the dashboard look worse so I undid that. This is why the noise floor doesn't match in the two measurements.
I heard them early 90's. They were nicknamed "the poor man’s Krell".
Amps like this generally aren't very hard on caps. The average ripple currents are low. Internal temps on most amps are pretty reasonable, and the filter caps usually aren't right next up against the main heatsink. Most don't run 24/7/365. In fact, I've seen a lot of amps of this vintage that show no evidence of PSU capacitor degradation even after extensive use. This amp uses giant can capacitors, which are both expensive and generally have a good lifespan.High voltage electrolytic capacitors simply do not last 30 years… In industrial applications, (AC variable frequency drives) the preventative maintenance recommendation for capacitor replacement is around five years. Given the heat generated by class A/B amplifiers, it is not unreasonable to see capacitor performance deteriorate. Replacing the psu caps in an amp of this vintage is a must.
This does not explain the HF noise however so this suggests that there is more than the power supply caps that require replacement.
I would really like to get my hands on an amp like this to analyze the measurable effects of component degradation.
What if it cost $700+ (as one just went on eBay for)?I'd put this somewhere between "happy" and "postman". It's acceptable - the distortion is around my 0.05% threshold of being a concern. In a nutshell, it's got adequate (if a little unimpressive) distortion performance, quite a bit of power and in a neat-looking enclosure.
Would be interesting - but Bryston typically uses a fairly good, fairly low distortion design. Most of them are rated at 0.01% from 20 Hz to 20 kHz, and I would expect it to be quite a bit better at 1 kHz than at 20 kHz. I feel like I measured a 4B at some point, and I want to say it measured similar to an MC650, (so about 0.005% THD at 1 kHz), but I don't remember the exact numbers. I do remember thinking that the distortion and noise was low enough not to matter.Now I'd like to see how one of the highly reviewed Bryston amps would measure. Something like the 4B or 4BST. I see lots of them around used and have been tempted, but always consider how it would compare to something modern that is well engineered. Thanks for the review, Amir.
I still don't take real issue. I think $700 is a little steep for one of these, but it has a neat look and is built like a tank. Schematics are available, and these should be quite reliable and easy to maintain, even at their current age. Output devices look like they're MJ15003 and MJ15004 (old, slow, bulletproof TO3 devices).What if it cost $700+ (as one just went on eBay for)?
However: These particular amps run quite warm, if not down right hot. Time x heat hurts things. (& if the unit was not in use, was it stored in an attic in a house in the Mojave desert or in the basement of a house in Nova Scotia)? With no way of knowing, if I had one, I would change & modernize all of the things that I could without affecting the circuit design.Amps like this generally aren't very hard on caps. The average ripple currents are low. Internal temps on most amps are pretty reasonable, and the filter caps usually aren't right next up against the main heatsink. Most don't run 24/7/365. In fact, I've seen a lot of amps of this vintage that show no evidence of PSU capacitor degradation even after extensive use. This amp uses giant can capacitors, which are both expensive and generally have a good lifespan.
Motor drives are much, much harder on caps than a typical class AB amplifier.
I don't remember for certain if it was the MK II, although I think it was, but I remember it was $1400 (well, $1395 or $1399 or something like that). I only remember because the funky notched design was very appealing to my younger self (but in the end I decided the money was better spent on "whiskey, women, and wine" than on something that would have just encouraged me to stay home alone more).If anyone knows what it sold for originally please, post.
As a mechanic for well over 40 years, using oil analysis to do oil changes, the 3000 mile oil change was a myth (unless you had a VW Beetle that did not have any oil filter from the factory & was air-cooled, therefore running hotter or only drove on dirt roads & off-road). Since synthetics arrived in the early 70's (Amsoil) I have personally limited even my hotrod cars to one oil change a year (the oil analysis shows that I could go longer) but I believe that condensation due to weather changes & short run times (going to a grocery store 10-12 minutes from home, not allowing a long enough run to maintain operating temperature long enough to evaporate the condensation in the engine) would cause problems in the long run.for example they don't need their oil changed nearly as frequently.