Sm Pro Audio PR8E?

[SonsOfThunder]

>>>There used to be a schem for the standard PR8, possibly on Black Lion's old site.

Oh yes, Matt posted the schematic that I had traced and drawn after removing my name from it. I protested a bit and he kindly restored the diagram to its original state. But the original is in this thread where it was initially posted for all to see.

I have not tried OP275 in this particular ckt, but it should work well. Let us know what you hear!

Peace!

 

[Pentium]

Wow... is the first word I can say.

The NE5532 has made a very warm sounding preamp of the SM Pro Audio
PR8E, with a thicker and richer sound than my Mackie 1604 pro VLZ

The AD OP275 has also warmed the bass a little and has a nice open high end and lost the upper mid edgyness.

Both are to all intents and purposes noiseless on a speech based recording.

I have modded just 2 channels this evening and the rest are to follow
4 of each I think will be appropriate !

Thanks SOT for bearing with me.

I need to test overload characteristics and long term reliability of the unit
ut I am very very happy.

 

[SonsOfThunder]

Glad to help. Glad you find them useful!

 

[Pentium]

I am quite surprised how ell this went, and how good they sound for the
money. (I love a bargain)

The desoldering of he original 4558 is the part of the job that sucks, it's very
awkward and slightly frustrating but you have to kep patient and calm, I have a solder sucker (desoldering pump) that helps but it's still hard work.

But work worth doing!

I bet there is nothing this side of $1,000.00 (£600.00) that can touch these.

 

[Snatchman]

I'm glad it's working out for you. As I stated, the Op-275s did wonders for my Yamaha console that was full of the 4558s!........

 

[Pentium]

I am so pleased with these that I have ordered 2 more PR8E's
and will have 24 channels of these pre's in 3u space.

Fantatic sound for the money + hours of work.

Very balanced all the way through the spectrum now , even an SM58 sounds a bit smoother through these.

Thanks all

P.S. seems to be ok with high SPL's in general, no problems
with dynamics on snares, I have ordered 4 inline 20dB pads for
unexpectedly loud sources/high output mic combo's.

Not saying they are the same, but some of the DAV Electronics units
use the Analog Devices chips so thats a decent pedegree of unit they are being used in.

The change of opamps have made a significant difference but the circuit
in there does not seem 1/2 bad, it passes signals quietly and nicely, it seems there are 3 transistors in the circuit, 2 close together and 1 further away.

Good stuff !

 

[Pentium]

Sons of Thunder, you don't know what you are responsible for :

Click "All sizes" for hi res images

http://www.flickr.com/photos/42634417@N00/?saved=1

 

[12Bass]

FWIW, I've found the LM4562 sounds better than the NE5532 and OP275 - more transparent and uncolored sounding.

 

[Pentium]

Hi 12 Bass, thanks for the tip, I have been thinking about those
but they are very pricey in the U.K., the cheapest I have seen them for
is £13.50 for 2, that is quite pricey at the moment.

Nice, low current consumption though.

I think I might work with what I have and wait for a price drop.

I guess I could try a couple in 2 channels and see what happens.

Thanks

 

[Pentium]

Ok, "Silver Mica" I have ordered 8 x 22pF ones to replace the ceramic ones
right next to the opamps. (only type i could find 22pF in other than NPo ceramics)

I read that these are unreliable in guitar amplifiers online.

Is there any evidence that they would be inapropriate in a mic preamp
which does need to be reliable.

Someone said they have a nasty habit of shorting themselves without
warning?

 

[Pentium]

Ok, "Silver Mica" I have ordered 8 x 22pF ones to replace the ceramic ones
right next to the opamps. (only type i could find 22pF in other than NPo ceramics)

I read that these are unreliable in guitar amplifiers online.

Is there any evidence that they would be inapropriate in a mic preamp
which does need to be reliable.

Someone said they have a nasty habit of shorting themselves without
warning?

 

[SonsOfThunder]

>>>I read that these are unreliable in guitar amplifiers online.

Can't imagine that to be the case unless they are being run over their working voltage.

You "should be able" to remove those caps without any problems. I say "should" because I have not tried it on that model. I did it on the old PR8 with 5532 and OPA2134 with no oscillations or other problems, ymmv!

HTH!
Charlie

 

[Pentium]

"ymmv"?

Ok SOT, thanks for advice....

Does this capacitor restrict the HF bandwidth of the opamp?

(it's weird, I always thought capacitors passed HF and impeded
LF)

Thanks

 

[SonsOfThunder]

You can look at the schematic I drew for the PR8. Compare with your unit/model at the locations I recommended removing. Those caps shunt HF to ground or restrict the bandwidth because they are in the feedback path. Do a google for caps in feedback path and I'm sure there is a tutorial to explain.

YMMV = your mileage may vary. As in "with that particular layout and your particular unit and the specific opamps you chose, your unit might go into oscillation". Best bet is to check it at full gain with a scope.

Peace!

 

[Pentium]

Oscillation is not an option and I do not
own a scope yet.

I will leave them in for the time being.

 

[Pentium]

I have found the 5532's to be a little too hot in this mod so I am dropping them, they are uncomfortably hot to the touch.

I am now going to run OP275's throughout.

Maybe I'll pop a couple of LM4562's in at a later stage.

 

[Pentium]

Also after further recordings I prefer the NPO/COG ceramics sound
compared to the polpropylene which I believe may go against conventional wisdom somewhat.

But the bass seems a little richer and the mids less prominant in the ceramics, so ceramics it is.

 

[Pentium]

Hi there I have come across another possible improvement on these pre's and it has been suggested to :

Do this bypassing:

It seems I need to solder on a 0.1uF capacitor between power supply pins and ground in the hope of reducing crosstalk between channels, my question is..

Which of the 2 Power supply pins on the opamp will I take to ground with the 0.1uF the positive or the negative?

That would be agreat help.

I am sure there are people here who do "bypassing" all the time.

Thanks

 

[peterc]

Which of the 2 Power supply pins on the opamp will I take to ground with the 0.1uF the positive or the negative?

Both of them, so one cap from +v rail to gnd, another from -v rail to gnd

I would do this for each one of the IC's. Get them as close to the chips as possible.

Peter

 

[SonsOfThunder]

>>>in the hope of reducing crosstalk between channels

Is this a problem now? :wink:
Charlie