Presonus M80

[evm1024]

I picked up a Presonus M80 preamp over the weekend. This unit does not have Jensen transformers. So this thread is the holding place for a DIY transformer swap, BB OPA627 op amp swap and perhaps a few more mods.

I've scoured the web for data on the MP20 and M80 mods and think that I got most of them. I know that one of our moderators was involved a few years ago....

I'm thinking of a few before and after clips as well as a howto that might have more details/photos than the existing howto.

Please feel free to make any comments.

--Ethan

Current status: transformers and opamps on order. ETA a week or so.

 

[evm1024]

cleaning....

The PO of this preamp said that a few channels were not outputing at the same level as the others....

I spent the last few days taking the preamp apart and cleaning things up. 9 years of dust and hair are gone. It was not that dirty to start with so the job was easy.

The cover has been taken off and of course some of the screws were lost. They were replaced with some that were about 3 times too long. Shorting out a few send and return jacks. Now we know why those channels did not work quite correctly.

So far the front panel cleaned up OK. I did need to bend the ears to get them (near) straight and wash off some ink. Not all the ink is gone but leaving well enough alone is good.

I've been having a great conversation with Presonus. They have send me a replacement set of knobs for the ones replaced by the PO and some new jacks.

Presonus agrees that just replacing the transformers and opamps is the way to go. Going after more upgrades gives very little in return.

It turns out that you can upgrade to a Jensen transformer or to a Cinemag transformer. The Cinemag was made for the M80 (and thus MP20 and perhaps the eurika).

I might have to try a breadboard preamp with the Cinemag. Model number CMMI 3.5

I'll be stalled out waiting for the replacement parts to get here so it is time to wax the front panel and make it shine.

--Ethan

PS Here is the main board

 

[evm1024]

So many projects on the fire....

I've been plugging away on this preamp for a while. Time for an update.

So far here is what has been done:

- swapped out the stock (China) transformers for Jensen JT-11K8-APC. Let Jensen know that these are for a Presonus and get a discount ($30 each)
There is a good writeup on how to do this here:

http://www.imjohn.com/PresonusJensenXfrmrs/TransformerSwap.htm

- Installed BB OPA627PA IC in place of the 5534

- Installed 3 new insert jacks to replace those damaged by a PO using screws that were too long on the cover.

- Installed a new set of original knobs.

Changing the transformers is a big job that should be done carefully and without haste. Most can do it if careful.

The top cover uses 1/4" long screws (I need to measure so don't quote me). Some were lost by a PO and longer screws were used. There are a few places where the longer screws went down into the insert jacks and messed them up. This is a good time to talk about Chad Kelly and Presonus support.

In looking for replacement jacks I contacted Presonus. The degree of support hat I got from Presonus and from Chad Kelly was outstanding. I can recommend Presonus fully based on the support I got. It turns out that Chad had done the final testing on this unit when it was new. His signature was in it. Support above and beyond! Plus a lot of information on the unit.

TODO: Right now the biggest thing is that the gain pots are noisy. I have a set of replacement pots coming from Presonous that I will install soon.

I might replace the output coupling caps. They are Nichicon and not bad but I might want to try some Muse there. Chad says that there is minimal (if any) audable gain.

Testing:

I have done a few tests just singing (if you cn call it that) into the preamp. I'll post the clips sooner or later for your review. The tests are:

CH xformer, stock 5534 IC
CH xformer, OPA627 IC
Jensen xformer, stock 5534 IC
Jensen xformer, OPA627 IC

THe signal chain is an Oktave MK-012 SDC (with modded electronics), Presonus, Tascam BR-20 and later to CD on a Tascam CDRW-5000 and then to an mp3.

Those 4 tests were done at the same time and in the same configuration (distance to mic and levels).

I hope to add some like tests later of other preamps (DMP3 before and after mods, GR MP2, DIY MPC1, and a few others)

FUTURE:

Well I have 8 Chinese transformers to play with. I'm thinking that a FET to OPA627 to 49860 preamp might be nice to DIY....

Regards, Ethan

PS: I really want to say thank you to Presonus and Chad Kelly for their outstanding support.

 

[CalgonStudio]

After 5 years are you still using this M80? , I've thought about buying...how do you feel about it today , if you still have it.

 

[ecc83]

Just a thought. D.Self gives the OPA627 a good enough comment especially if you want high DC precision. However, he points out that it is some 100X the cost per section of the NE5532 and is in fact slightly noisier. The 5534 has a much lower input noise at microphone impedances.

I wonder if there are any before and after noise figures for the OP's pre amp?

Dave.