Re: full stack advise
- From: jh <jh@xxxxxx>
- Date: Mon, 11 May 2009 07:23:37 +0200
adam79 schrieb:
jh wrote:
the reason I wrote about about the "parallel box" has a simple reason.
IIRC the wiring of the big musicmans might *not* be the standard parallel. I don't have an actual unit here to check it.
OK I just looked at the old HD130 schem at
http://www.music-man.com/techinfo/old_amps/2100-130.pdf
The outputs are wired in *SERIES* !!!!!!!!!!
Two 4 ohm speakers would be 8 ohms there. So watch out. The function of the shorting switch is also crucial!
Two cabs with 4 ohms each would be the way to go with the MM set to 8 ohms, but this does not match up with the Peavey. Unless the PV has a 2ohms setting, which i doubt. I'd recommend to have the MM modified for parallel wiring...
Ough.
Jochen
the music-man i have is a hd130 reverb, but i'm assuming the schematics are the same as the ones you found. is the shorting switch you're talking about the "ground" switch that's next to the standby switch on back? what is so important about this switch, besides flipping it if there is too much hum? I'm not familiar with the inner workings of the amps (obviously), but you saying that most music-man amps have the outputs wired opposite from every other amp on the market? Does this also mean that you can't run a full stack where all the speakers are 16ohms with the music-man? I'm really short on cash, and the mod your speaking of sounds expensive..
the peavey actually has 4 outputs (2,4,8,16ohms), which is the way every amp should be, in my opinion.
thanks for this information,
-adam
adam,
if you look at the output jacks in the schem i posted, you will see, that the path of the signal post the output transformer is as follows:
switch - sourced either from 4 or eight ohm winding >>
tip of main speaker out - shorted to its sleeve when no plug is in the jack 1)) >>
tip of ext speaker jack - shorted to ground, if no plug is in the jack 2))
the shorting switches i mentioned are exactly 1)) and 2)).
Your output stage needs a "closed" circuit. Not only the path *to* the speaker is important, the return is also viable. If the "unused" switch gos south because of corrrosion, dirt or mechanical reasons, you will loose one of those paths and the OT would not see any load any more.
NOT GOOD
BTW just for info: th jack of 1)) is usually mounted isolated fro the chassis on MMs
and exactly - you clearly understood what i wrote - you cannot use the MM with two 16ohm cabs; the amp would see 32 ohms.
The mod itself is not that complicated, but if a tech opens the amp, you can count at least one hour until the amp is closed again. Here the amp also takes some responsibility for the device he serviced. W have to make sure that the device does not exhibit certain hazard, so at least a thorough visual check *and some measurements* is/are mandatory.
I don't know the hourly fees in your region, but you can count....
Rewire both amps to 4 ohms, use them with the MM @ 8ohms and with the Peavey @ 2ohms
regards
Jochen
.
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