Hi everyone,
I'm a fairly new (second) owner of an MF nuVista m3 amp and was thinking of doing a service on it: a) replacing the old Jamicon electrolytics and, if at all possible, removing any electrolytic caps from coupling duties; b) checking/setting/re-setting the quiescent current on the channels.
With regard to a) there is one 10uF/63V cap that I just can't find a good-sized film cap to replace it C1 and C101 on the attached diagram (Nuvista_M3_Pre-amp_Line_OP[1].pdf). The other coupling caps in the chain (C32, C40, C41 on the right channel) are already some type of film cap, yellow-coloured with a circled L logo--not sure how their quality is honestly--although I'm going to replace them with WIMA MKP10s anyways. Not all that pricey and I'll have it all apart anyways...thank goodness for suppliers like mouser and digikey etc.
Second item, b), does anyone know how "far" I should set quiescent current, i.e. bias into Class A operation? The SAP15's datasheets indicate 40mA, (so 8.8mV across pin 4,5 or 1,2 depending on N or P type), but some manufacturers seem to like "giving it a bit more." Anyone have any thoughts/experience with MF quiescent currents?
Thanks!
verkion
P.S. Attached the whole bunch of M3 Amp diagrams for people's reference. I'll be replacing PSU caps too as those are the ones that are looking "slightly fatigued." i.e. plastic cover is puckering although the metal under it feels fine...for now.
Copyrighted materials removed by moderation.
I'm a fairly new (second) owner of an MF nuVista m3 amp and was thinking of doing a service on it: a) replacing the old Jamicon electrolytics and, if at all possible, removing any electrolytic caps from coupling duties; b) checking/setting/re-setting the quiescent current on the channels.
With regard to a) there is one 10uF/63V cap that I just can't find a good-sized film cap to replace it C1 and C101 on the attached diagram (Nuvista_M3_Pre-amp_Line_OP[1].pdf). The other coupling caps in the chain (C32, C40, C41 on the right channel) are already some type of film cap, yellow-coloured with a circled L logo--not sure how their quality is honestly--although I'm going to replace them with WIMA MKP10s anyways. Not all that pricey and I'll have it all apart anyways...thank goodness for suppliers like mouser and digikey etc.
Second item, b), does anyone know how "far" I should set quiescent current, i.e. bias into Class A operation? The SAP15's datasheets indicate 40mA, (so 8.8mV across pin 4,5 or 1,2 depending on N or P type), but some manufacturers seem to like "giving it a bit more." Anyone have any thoughts/experience with MF quiescent currents?
Thanks!
verkion
P.S. Attached the whole bunch of M3 Amp diagrams for people's reference. I'll be replacing PSU caps too as those are the ones that are looking "slightly fatigued." i.e. plastic cover is puckering although the metal under it feels fine...for now.
Copyrighted materials removed by moderation. For everyone's viewing pleasure (since we had to take down the original drawings--drawings are copyrighted, but the design is not) I've begun to create the circuits in the free Falstad online circuit simulator, also for my own benefit as I am super rusty on my Electrical Engineering. So, I could be totally wrong about some of the following...and if I am, please do respond so I can correct information!
There seems to be a lot of misconception/misinformation out there about the Musical Fidelity nu-Vista M3, even though it's an old amp. I was on a different website and they were talking about trying to drive 1-ohm loads (which yeah, I probably wouldn't do with this amp!) but someone posted a pic of a modified m3 with downsized power supply filter caps, and then assumed the "transformers" were stuffed into the same case (and were therefore tiny).
As an FYI (and for future reference if anyone else has one--only 500 of them ever built!) I'll add to the thread as I reverse engineer / disassemble / upgrade / replace parts.
Here's the "power-supply" for the 80V or so rails that in turn feed ONE of the Power Amp modules. There are two of these circuits that are fed on the right-hand side from a VAC supply contained in an entirely separate box. That box has 3 toroidals: 1 per channel, and 1 (smaller) one for the pre-amp's 90V rails (which are needed presumably, to heat/power up the 6CW4 nuVistors).
https://tinyurl.com/y33flabp
In any case, the "transformers" that I mentioned earlier that various Internet people assumed were the vastly under-sized power transformers, are actually serving as Common Mode Chokes per side (as far as I can tell).
Thanks!
verkion
P.S. Anyone have a suggestion for substitutions for a Bi-Polar 10uF/63V coupling cap? I was going to drop a WIMA MKP10 in there...but their footprint is too big, and I *think* extending wires to "more exotic caps" is probably worse than using a better quality Bi-Polar Cap? Any thoughts?
There seems to be a lot of misconception/misinformation out there about the Musical Fidelity nu-Vista M3, even though it's an old amp. I was on a different website and they were talking about trying to drive 1-ohm loads (which yeah, I probably wouldn't do with this amp!) but someone posted a pic of a modified m3 with downsized power supply filter caps, and then assumed the "transformers" were stuffed into the same case (and were therefore tiny).
As an FYI (and for future reference if anyone else has one--only 500 of them ever built!) I'll add to the thread as I reverse engineer / disassemble / upgrade / replace parts.
Here's the "power-supply" for the 80V or so rails that in turn feed ONE of the Power Amp modules. There are two of these circuits that are fed on the right-hand side from a VAC supply contained in an entirely separate box. That box has 3 toroidals: 1 per channel, and 1 (smaller) one for the pre-amp's 90V rails (which are needed presumably, to heat/power up the 6CW4 nuVistors).
https://tinyurl.com/y33flabp
In any case, the "transformers" that I mentioned earlier that various Internet people assumed were the vastly under-sized power transformers, are actually serving as Common Mode Chokes per side (as far as I can tell).
Thanks!
verkion
P.S. Anyone have a suggestion for substitutions for a Bi-Polar 10uF/63V coupling cap? I was going to drop a WIMA MKP10 in there...but their footprint is too big, and I *think* extending wires to "more exotic caps" is probably worse than using a better quality Bi-Polar Cap? Any thoughts?
Opps...found a mistake already! The circuit for the power relays and power LED is not actually supposed to be connected where I have it shown. I'm still trying to figure out what is going on there exactly...but I'll leave that bit there for now.
New Power Amp Module Power Supply
https://tinyurl.com/y3ekeh7d
Thanks!
verkion
New Power Amp Module Power Supply
https://tinyurl.com/y3ekeh7d
Thanks!
verkion
MF always used cheap caps, even on their, so called, upscale gear.
Auricap 10uf, 200 volt, kind of big, ~$50 each
Solens are OK-ish, but better than Bipolar: Solen Capacitor 10uF 400Vdc PB Series Metalized Polypropylene (about 1" dia X 1.5" long)
Just part of what's available from Parts Connexion, or similar.
Auricap 10uf, 200 volt, kind of big, ~$50 each
Solens are OK-ish, but better than Bipolar: Solen Capacitor 10uF 400Vdc PB Series Metalized Polypropylene (about 1" dia X 1.5" long)
Jantzen Capacitor 10,00uF 160VDC MKT Metalized Polyester (oval shape, might fit better)
Jantzen Capacitor 10uF 400VDC Standard Z-Cap Series Metalized Polypropylene
Just part of what's available from Parts Connexion, or similar.
@Steve Morley maybe there is no benefit using more expensive cap? in terms of sonical improvement so thats why they use cheaper? dunno
phier,
Greetings. Sometimes, but not always, more expensive caps can sound better. Other times, a different, not very expensive cap, can sound better and maybe even very good, compared to the original cap supplied by the manufacturer.
Greetings. Sometimes, but not always, more expensive caps can sound better. Other times, a different, not very expensive cap, can sound better and maybe even very good, compared to the original cap supplied by the manufacturer.
@Steve Morley thanks, that makes sense and thats the key to the problem...
so many ppl recco so many different brands/typs of caps. So the question would be ... which one can go for ... also i was checking many good caps are sold out as Elna... Was also recco Audio note, but who knows the results?
Thanks!
so many ppl recco so many different brands/typs of caps. So the question would be ... which one can go for ... also i was checking many good caps are sold out as Elna... Was also recco Audio note, but who knows the results?
Thanks!