MosValve 500 Schematic

Jack Stoner · Post by **Jack Stoner** » 5 Jan 2001 5:14 am

Does anyone have a schematic for this amp? The other thread on Peavey amp pop makes me want to look at he MosValve 500 schematic as the MosValve does not "pop" when turned on or off.

Blake has pretty much isolated the pop (inherent in the Nashville 400 amp) to the power amp section of the Nashville so it would be interesting to see what MosValve is doing, or not doing, that prevents the pop.

Steve Feldman · Post by **Steve Feldman** » 5 Jan 2001 10:46 am

Jack - Steve Bishop is the go to guy at Tubeworks for that stuff. He's a pretty good fella - you might want to give him a call.

Olli Haavisto · Post by **Olli Haavisto** » 5 Jan 2001 1:21 pm

I think many better quality power amps,such as the MosValve,use a relay that mutes the output to speakers until the amp is "settled".As to how this is accomplished I don`t have the vaguest idea..

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Olli Haavisto
Polar steeler
Finland

Jim Smith · Post by **Jim Smith** » 5 Jan 2001 8:51 pm

I think that must be a fairly common circuit. Both my Boss GX-700 and Digitech RPM-1 go through a "warm up" stage before they will produce any output, perhaps for the same reason of not spiking (popping) the circuits.

Robert Parent · Post by **Robert Parent** » 6 Jan 2001 5:19 am

A while back I owned a Tubeworks Blue Tube II and needed a schematic. I just called them and they sent a copy free of charge.

I also purchased a new Tubeworks 1160 power amp that 'popped' when turning it on. I was not happy with the 'popping' noise and the roar of the fan so I sent it to the factory for repair. They returned it telling me that it was normal but did install a somewhat quiet fan. I still was not happy with the noise so I sold the amp even tho it was a very nice sounding unit. Currently I have a Roland GP100 and a Stewart PA100B and every thing is quiet like it should be. The Roland unit is very nice if you guys are looking for a one rack unit that does everything.

Jim Smith · Post by **Jim Smith** » 6 Jan 2001 9:07 am

The Stewart World 1.2 power amp has a sticker on top to remind you that it takes up to one minute after turning on the unit before any signal would be output, again I assume to keep from popping and spiking the circuitry.

Jack Stoner · Post by **Jack Stoner** » 10 Jan 2001 6:27 am

I got a (barely readable) copy of the MosValve 500 schematic. There is a relay on the output, which explains why there is no power on or off "pop".

The relay disconnects the power amp outputs from the speaker jacks. There is a sensing circuit associated with the relay but the schematic is so bad I can't make out a lot of the components.