SM Pro PR8 Mic Preamps

[aortizjr]

Here is a link to a picture of the stock PR8 with the caps circled to cut:

http://www.intensemetal.com/~aortizjr/projects/PR8/Channel1-caps.JPG

Also here are pics of my modded one:

http://www.intensemetal.com/~aortizjr/projects/PR8/

For OA's. So far I am testing with:

JRC2068
TI NE5532
TI MC33078
OPA2134
ST TSH22IN

So far I can definitely tell differences. But I haven't done a "formal" A/B between them. So far they are all usable and sound pretty nice. Much better than stock. But even with the caps clipped and the JRC4558, it still sounded pretty good. Definitely good enough for such a budget unit.

Even the JRC2068 sounded better though, and they are really cheap to get.

 

[SonsOfThunder]

Nice pics, thanks!

Are those machine pin sockets...or the wiper style? I think over time you will find that the machine pin will maintain a good connection and the other style will not. Weird noises and oscillations will suddenly come and go.

2068 is not a bad OA at all. Its not an OP275, but it is probably the best out of all the JRCs.

Peace!
Charlie

 

[aortizjr]

They are wiper style...

I used those since I have a ton of the wiper style. A few years ago I got a great deal on a few bulk tubes of them. Sorta before I knew better

In other pedals and such I have built, I haven't had any problems. I read a lot of debates over which is better/worse. Some say wiper since it has more contact surface. Others say machine. I think in general machine pinned sockets are much better built. When I run out of my stock of wiper ones I will switch.

Thank you for the info though. When I start having trouble, I will be sure to check there first.

I don't really swap chips much, it is hard on the chip, socket, and solder joints. This one is loaded so each channel has a different chip. Maybe someday I might switch them all to one chip I like best. Then maybe switch all the sockets, and add a gain control of some type.

I am also really toying with designing a whole new pre and boards that match the layout and can use the transformers provided.

 

[aortizjr]

Well I have been using these in the studio for a couple of months now.

Compared to the other budget pre's I have, I have been liking these a lot. Especially where I don't need the features of Pad, Phase Reverse, etc.

Intially these were intended for scratch tracks and additional pre's for drumkits and such.

Still haven't done a formal A/B. But with electric guitar and male voice, I like the OPA2134 the best with the TI NE5532 not very far behind. The others still sound good. But if you are on a budget, I would go with the TI NE5532. They are really close to the OPA2134 in this particular circuit.

Oh and use machined pin sockets. I have already had one channel start acting up with the wipers and had to be replaced. Put in new sockets on that channel and was well.

Anyway just thought I woudl share.

 

[SonsOfThunder]

Cool info. Thanks for sharing.

I am kinda surprised that those wiper sockets gave it up so quickly. I would have thought they would have lasted at least a year or two. Good thing we had already discussed that and you knew the solution ahead of time. Stuff like that can be really frustrating when you don't know the answer!

I have not tried the TI 5532. My 2nd unit has Signetics 5532, but I am keen to try the TIs to see if I can hear any diffs.

Have you tried any cap changes? I need to do that sometime too.

Enjoy!

 

[aortizjr]

I haven't tried any cap changes. Been meaning to. Maybe when my current band recording project is all done.

But right now I have only done the capacitor clips and changed the OpAmps.

I was suprised as well at how fast the problem occured. I changed the sockets first just to see and that was the problem. Thank you for the tip, that really saved me a lot of headache right up front.

The tracks I have been doing right now though I have been keeping. If you went with TI NE5532's, you pay $100 for the box, maybe another $20 in sockets and chips. Then about a couple hours or so with a soldering iron and braid. You have 8 pretty cool pre's. Definitely an upgrade from the Behringer, Mackie, and MOTU Pre's I have.

 

[SonsOfThunder]

Hmm... which MOTU piece?

 

[gavvyt]

Hi all,
Not sure if anyone is still reading this topic, but I have recently gotten my 3 x PR8's from storage and thought it might be nice to mod them.

I am adding db25's for the outputs, as this will fit my 192's easier.
I am also wiring in db25's for the inputs as it fits my work flow nicely.

More importantly, I have one unit open and have snipped the caps mentioned in this thread. Top end improvement noticed.

Now intending to replace the 4558d's with LT1358CN8 op amps.
Can someone tell me if I need to wire in caps to stop oscillation?
If so, what and where do I wire them.

Regards,

Gav

 

[ReRibbon]

Any pictures left? The old ones are gone .