Presonus MP20 - modded it (no pics..)

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Viitalahde

Well-known member
Joined
Nov 7, 2005
Messages
727
Location
Kuhmoinen, Finland
Just wanted to share that I recently did some modifications on an MP20 for a client. He wanted to swap a Lundahl trafo on the other channel and asked if I saw anything else that'd need attention.

So I looked at the schematic and there it was.

A damned balancing driver/receiver combo on the signal path that always does its thing even if the inserts are not in use. :shock: :?

I asked and the guy said he never uses the inserts, so off I solder the SMD op-amp, cut a trace or two, run a couple of wires and things are much cleaner now.

What's the point in making a TwinServo (?) amp when you toss a crappy balanced driver/receiver in the signal path, all the time? Why the hell would you need inserts anyway when you could toss your compressor at the output? Why does this thing have a "mixer" in it, I see very little sense in having a 2-channel mixer with panpots in a 2-channel preamp.

:grin:
 
I have always wondered myself why bother with the servo in the MP20 when you have three caps in the signal chain anyhow. As for all those features, gimmicks sell. IMHO, they should have spent a little more on a better input transformer.
 
I swapped out my input iron for the Jensen iron. If I remember correctly, if you tell jensen it is for a presonus, they give you a discount. I think I paid about 33 bucks each. By the way the ratio is 1:3.5 or maybe 1:4 on those trannies. I used the original presonus' on some API cards, and they sound wonderfull. The lower turn ratio seems to smooth the API out a little. So if you pulled a transformer, keep it... or send it my way.

Joe
 
I have an M-80 -- I think the same circuit in an 8 channel configuration... Don't really want the channel inserts either... I might have to check this mod out -- could you elaborate on the traces/jumpers. If its a pain in the but, no biggie... Also, were the jensens a remarkable improvement?

FWIW, I find the mixer bus function really useful. I got this thing cause I live in an apartment, and can't track acoustic drums there. With the M-80, I can just bring that out and run it straight into my AD converter. Monitoring through the computer you'd normally get some latency, but with this thing I can feed the drummer realtime headphone mix, plus feed some guitar through the aux input so he doesn't lose his place in the song :)

I suspect the mix bus is for similar reasons on the 2 channel -- for DAW guys feeding right to the AD without monitoring latency...
 
[quote author="JRE Productions"]I swapped out my input iron for the Jensen iron. If I remember correctly, if you tell jensen it is for a presonus, they give you a discount. I think I paid about 33 bucks each. By the way the ratio is 1:3.5 or maybe 1:4 on those trannies. I used the original presonus' on some API cards, and they sound wonderfull. The lower turn ratio seems to smooth the API out a little. So if you pulled a transformer, keep it... or send it my way.

Joe[/quote]

My presonus has a JT11-K8-APC in it.
http://www.jensen-transformers.com/datashts/11k8apc.pdf

It also uses OPA604's. There was a schematic for this box floating around at one time. I'll see if I can find it.

I like to have it around because it makes a nice quick mic tester with the built in headphoneamp and pans.
 
Yep thats the ones. Mine did not come with Jensens, so I did the upgrade. Like I said even the stock ones sounded pretty good. The jensen added a little more bottom end and was a little more agressive sounding. Kind of more API ish.
 
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