[540EYE]

I picked up a Mcintosh 2105 off flea-bay. The glass was crakced and almost gone, so the opening bid was pretty low. Otherwise it is pretty clean-chrome is all nice and shiny, no pitting and the black paint on the chassis is almost perfect.
Only had one bidder in 7 days and he bailed.

I did open it up to clean out some accumulated dust, but not too much was there. I hooked it to my rig and it performed beautifuly.
I'm pretty psyched!! I spent the day fabricating an aluminum faceplate to replace the glass......trying to make it resemble a baby 2300!!.....it gots them meters, y'know !!........

I need a little advice on possibly getting that Jerry "clean dirt sound" I understand that there is a power guard feature that will lower the input gain when the output stage is about to clip.(Like Brad's P438). I also remember reading about an intentional speaker mis-match that helps contribute to the "grit". The autoformers are supposed to protect the output transistors in the event of an impedance mismatch...?

I run the typical front end--Resurrection guitar, 3 x Super II's, OBEL, and an early model of the CB1 buffer > Trio > Alesis Midiverb III for reverb. I was running a Marshall 9200--awesome piece--dual mono into (5) JBL K 120's. (2) are 16 ohm wired in parallel for 8 ohms and a second is an 8 ohm wired to these for a total 4 ohm load. This went to one channel in the Marshall. The other channel has(2) 8 ohm K 120's wired in parallel for a 4 ohm load.
It sounds very clear and warm.....but it weigh a ton!!....lotta iron! 2 X power transformers and 2 x output transformers. My goal is to substitute the Mac for the Marshall.

Can you offer any advice on how to "purposely mismatch" speaker load for the 'clean dirt" sound. I'm thinking somehow it makes the amp have less available power and less headroom.........?? Whether or not I can get the dirt sound is not the main issue at all, just wanna see if I can even come close.......
Any guidance you could offer is greatly appreciated. It's all about trying unconventional approaches.

Thanks alot and Merry Christmas
Gerv

[mijknahs]

I can answer a few of those questions.

The MC2105 does not have Power Guard. Only the Sentry Monitor (which protect the output transistors by limiting the output current). This amp is simply the metered version of the MC2100. http://www.roger-russell.com/amplif1.htm#mc2105

Basically just hook up your speaker cabinet(s) to one channel only (100W) to whatever speaker load you have. The "clean dirt sound" will kick in when you play loud enough to overdrive the McIntosh a bit. Basically pretty cranked like playing with loud drums and bass.

I don't know why you need to run 5 speakers. Maybe just try the 2x16 ohm speakers in parallel (8 ohms) from the 4 ohm tap? Or the 2x8 ohm speakers in series (16 ohms) from the 8 ohm tap. This should be less available power.

You will definitely get the dirt sound once you start driving the amp hard.

Jim

[SarnoMusicSolutions]

Yeah,

What Jim said.

[edited because I said something stupid and had my brain on backwards]

Keeping it set in "stereo" keeps both channels truly isolated from each other. It's gonna be loud, so stand back. Tell us what the meters do as well. And watch the speaker cones. Do they "move"? And do they move even if you clip the amp with a high note?

Brad

[540EYE]

Jim,

Thanks for the advice. It's true, I don't "need" 5 speakers..........it simply makes everythng sound bigger w/o being louder. The vertical stack "spreads" sound nicely.

Brad,

Will try your suggestion and report back.

Thanks to all you folks for your input. This forum is a good place to be.

Gerv.

[mijknahs]

Oh, and you'd probably want a pretty hot signal from the preamp (I'm not familiar with your preamp but I set my Twin at about "7"). And the power amp volume at least half way up. That should get you in the ballpark.

Thanks Brad, I wasn't sure if going 8 ohms into a 4 ohm load was advisable. Would that be drawing more power (easier to peak)?

Jim

[SarnoMusicSolutions]

Oops, CORRECTION!!

Thanks Jim. Actually I meant the opposite. I was spacin'. If you have a 4-ohm load then what I mean is to try the 2-ohm tap. But that amp doesn't have a 2-ohm tap. SO, I would suggest using your speakers in an 8-ohm configuration and try the 4-ohm taps. Sorry about the reversed suggestion. 5 speakers is a lot. I get the idea of spread, but there's something to be said for a vertical line array of just a couple, 3 or 4 speakers for that lateral sonic focus.


Brad

[mijknahs]

Thanks for the clarification Brad.

2 speakers vertical (maybe off the ground some) has been plenty for any gig I've ever played.

Jim

[SarnoMusicSolutions]

I agree. 2 vertical JBL's is all I've ever needed.


Brad

[RiverRat]

Oops, CORRECTION!!

Thanks Jim. Actually I meant the opposite. I was spacin'. If you have a 4-ohm load then what I mean is to try the 2-ohm tap. But that amp doesn't have a 2-ohm tap. SO, I would suggest using your speakers in an 8-ohm configuration and try the 4-ohm taps. Sorry about the reversed suggestion. 5 speakers is a lot. I get the idea of spread, but there's something to be said for a vertical line array of just a couple, 3 or 4 speakers for that lateral sonic focus.

Brad

If the goal is to keep the SPL down, go with a higher Ohm tap to get it to peak at a lower level... If the intention is to push the drivers as hard as possible to get them to break up, go with a lower tap.

Jerry's rig was likely setup to achieve both conditions, power amp peaking and maximum driver distortion. Given that it was in a setting where he could run at jet engine sound levels, it worked.

Line Arrays require that the system is design for maximum constructive interference between the drivers, it's a synergistic application (2nd time i've used the term synergy today!). Without proper design and testing, you'll probably get more destructive interference via phase cancellation.

[strumminsix]

I had a few ideas. But then realized I wasn't being paged