mosvalve power amp doesn't seem too loud = problem?

[moltenmetalburn]

as far as the mosfet goes - you reminded me of what it is. its a P channel (normally on) MOSFET without the outer ring to denote a packaging, and there's 2 of them put together. 6 years of working on circuits and ive never seen a symbol like that. wierd. its on the top right hand corner of the A block channel after a (2k?) potentiometer. the same would exist for block B, however its a cutaway schematic.

as far as the board goes, yes you are right - there is nothing missing in yours. only 4 op-amps in the design and all 4 are accounted for both in trace design, placement, and function.

you might want to email genz benz about it, because you might have a treasure on your hands.... an early run mos-valve prototype that was made before the amplifier was functionally blueprinted and schematics were given out.

as for the op-amp, there is no telling where it came from or why. my guess is that someone could have glued it to the board upside down for an extra, and the glue simply came off.

but in the schematic, as far as i can tell from looking at the schematics those smaller pots are used for tuning the amplifier's frequency range, and the gains themselves are used for volume control. at least thats all i got to think about it.

call genz benz, give them the serial number and a few of these gut shots, and see what turns up. you never know.

i'd also recommend taking all of these pics back down from rig-talk after you are done.

who knows, ive heard people say the 2150 isnt any louder than other power-amps that exist. sometimes the headroom isnt what you'd expect.

thats not the most well designed amplifier ive seen, alot going on there and the design took me a second to figure out. it made sense afterwards, but like i said ive definately seen better designed.

I was just looking at he schematic thinking "either I'm missing what hes seeing or its a mosfet." then after going crazy for ten minutes I saw your post was edited and now reflects the same .... lol!

man that schematic is hard to read, so grainy ...

 

[glpg80]

yeah for some reason that mosfet signature blind-sighted me

o well, cant remember everything on a whim. and you are right, that schematic is so hard to read. i cant tell if a letter is a K or a B or micro from pica lol

 

[moltenmetalburn]

I recently purchased a used Mosvalve MV-942 (500 watt version) power amplifier. Upon taking off the top, because i heard something loose inside, what fell out was an OP-AMP that reads TLO72CP and TI22CB.

Now, the power amp does work just fine but i compared it to my Mosvalve MV-962 (100 watt version) and the MV-942 did not seem to be overwhelmingly louder than the MV-962; louder, yes but not like crazy louder. I did this test by plugging the same guitar and cable into one power amp (mono A channel) and one 4x12 cabinet with the Gain maxed and then the same setup with the other power amp.

My question is, could this OP-AMP just be a spare or something that was replaced? Could it have fallen out of the board, which i really doubt since there didn't appear to be any empty slots on the PCB. There are 4 other OP-AMPS (same exact ones as the "extra") that sit on the board currently but i'm curious because it doesn't seem too much louder than the other power amp.

I also tested it in a W/D/W setup with my powerball and it kept up really well.

yunno, just to backtrack I'm not really sure there IS a problem. You say the amp is louder just not "a lot" louder than the other one....what is the difference in wattage of the two?

I know this is solid state, but in reference to tube amps the difference between 50 and 100 watts in volume is only about 3 DB. If you are expecting a huge difference in volume it just wont be there. to double the volume you need 10x the wattage.

If you were expecting 500 watts to be five times louder than 100 its not. five times louder than 100 watts would be 5000 watts believe it or not. 500 watts should be 1.5db louder than 100. not much, in fact 1db is the smallest increment the ear can discern.

Something tells me its working fine and you just have a spare op amp. It seems like we never answered your original question; "Should this be expected?"

Psychodave chimed in that his Mos Valve was loud, not that he had both models and the higher wattage one was much louder than the other.

who can tell us the DB difference for 100watts vs 500watts Solid State? Is is the same as measuring tube amp wattage?

 

[turmoil]

thanks for the replies guys!!
I contacted BK Butler and their estimate at doing any kind of check or bench-work is kind of pricey, plus there's a long wait time for him to look at anything.

They also said that they won't release any schematics for any of their amps and that only BK Butler himself will be able to do the work.
That made me wonder about this schematic i was able to get

I might try emailing them back with the serial number to see if they can tell me anything specific about this amp. It says it was made in 1991, which is when the schematic is dated for so one would think it would match up better than it does.

About the loudness, i mean it definitely is louder than the 100 watt version i have (MV-962) but i just figured for something that was 500 watts, or at least 250 watts per-side, it would be almost like a, "WOW! this thing is crazy loud!". My reaction was a little more like, huh...this is it? Is this what 500 watts sounds like??

One more thing, why would I want to take down the pictures of the guts?
thanks guys! i really appreciate all the help

 

[glpg80]

lol.

your amplifier PCB board is stamped "1990"

the schematic says 1991.

like i said before - i would try to get an estimate. the copyright date is from a company associated with the amplifier, but the date is earlier than the provided schematic. nothing is wrong with your amplifier as far as im concerned. its what we are trying to say basically, theres no need to send it in.

what you need to do is get some information from genz-benz or whoever owns the series, because you might have a prototype, or a batch of the very first models.

id do some research on what you have because its not the same as whatever is in the schematic, and the schematic you have is probably what everyone else has.

just saying you might be sitting on a gem and not even know it?

if not, then no worries. flip it for a later model with 5 op-amps to buffer the signal and move on. but as far as this one is concerned, theres nothing wrong with it in dealing with an op-amp.

id also hold off on changing out the chips before getting more information on it. just an opinion.

 

[turmoil]

lol.

your amplifier PCB board is stamped "1990"

the schematic says 1991.

like i said before - i would try to get an estimate. the copyright date is from a company associated with the amplifier, but the date is earlier than the provided schematic. nothing is wrong with your amplifier as far as im concerned. its what we are trying to say basically, theres no need to send it in.

what you need to do is get some information from genz-benz or whoever owns the series, because you might have a prototype, or a batch of the very first models.

id do some research on what you have because its not the same as whatever is in the schematic, and the schematic you have is probably what everyone else has.

just saying you might be sitting on a gem and not even know it?

if not, then no worries. flip it for a later model with 5 op-amps to buffer the signal and move on. but as far as this one is concerned, theres nothing wrong with it in dealing with an op-amp.

id also hold off on changing out the chips before getting more information on it. just an opinion.

didn't see the 1990 on the pcb i was looking at the 91 on the sticker on the chassis.

well, i'll try to get in touch with the tech over at Butler audio and see what they have to say about. thanks again

 

[moltenmetalburn]

I'm telling you guys there is most likely no problem

If you had a missing or fried op amp the unit wouldn't work at all.

at 250 watts per channel not 500 as i assumed the volume difference would be even less noticeable.

 

[glpg80]

I'm telling you guys there is most likely no problem

If you had a missing or fried op amp the unit wouldn't work at all.

at 250 watts per channel not 500 as i assumed the volume difference would be even less noticeable.

im not saying there is a problem either?

read all of my post instead of a few words - when i say estimate, im talking value of the model - not for repairs.

 

[just42dave]

You guys a re so frikin smart awesome to even know you if I ever need help

 

[moltenmetalburn]

I'm telling you guys there is most likely no problem

If you had a missing or fried op amp the unit wouldn't work at all.

at 250 watts per channel not 500 as i assumed the volume difference would be even less noticeable.

im not saying there is a problem either?

read all of my post instead of a few words - when i say estimate, im talking value of the model - not for repairs.

I read your entire post. the OP was talking about BK Butler bench prices so it sounded like he was still considering repair...

as for it being an awesome find, dunno...

 

[okgb]

An old thread I know, I have the same amp which loses power after it's been on a while. It would be nice to find a schematic that is more clear.
Mine looks to have been worked on in the past there is some sort of scorch / leaking stain mark under the two power resisters on either side of the relay, they have been replaced from the what pix earlier look like in this thread to a larger wattage but have cracks in them and meter infinite resistance. seems whatever the problem [ overheating drawing too much current ? ] didn't get fixed or occurred again.
Tia for any help , a clear or good schematic would be awesome!