Sm Pro Audio PR8E?

[thermos]

Hi, first post. Did a search about this unit, turned up lots o' info on the PR8. Anyone know how similar the layouts are between these 2? Or better yet, any one have a schematic? Or better yet, anyone try modding them yet?

Thanks

 

[Snatchman]

I think the PR8-E is an upgraded version of the PR8. Supposed to be better components..... :roll:

 

[thermos]

Same basic schematic then? I'm guessing. I'll get 2 in a few days, so if anyone wants pics of the guts let me know.

 

[aortizjr]

I am interested in seeing pics. Also schematics if possible. But good pics would be a start.

 

[Pentium]

Hi there, I am new to the forum and have a SM Pro Audio
PPR8E.

I have had a quick look under the hood and it has a split circuit board with a ribbon providing power to the second board from the main board.

I am going to provide a photo of the PCB very soon.

It has the following components that are notable:

2 x JRC4558D per channel (in and out)

2 x C541 transistors and 1 x C1815

There seems to be 7 ceramic capacitors of the values:

2 x 100pf
2 x 470pf
3 x 680pf

on the input side of the board.

It also has a lot of blue resistors which I understand as being of better tolerance.

I am considering removing the 4558's and inserting TI 5532's in there place in 8 pin DIL sockets.

I have seen the considerably long post about the PR8 unit but wondered which capacitors (if any) are worth snipping in the PR8E, I am unsure if the snips and the OA changes will provide a similar imporvement in the PR8E. I cannot easily translate between the PR8 PCB photo's and the
PCB in the PR8E sadly I am not quite knowledgeable. What is does have in common is one ceramic cap right adjacent to the 4558 like the PR8 unit.

I would love a little guidance on improving this a little, seems like the 4558 gains little respect round these parts.

Thanks for your help in advance.

 

[Kit]

seems like the 4558 gains little respect round these parts.

Dont believe everything you read on the internet. Especially if it has anything to do with audio reproduction. :roll:

How does the unit sound stock?

 

[Pentium]

Thanks for reply...

I have only taken delivery of the unit today so I don't know, all I know is
that a lot of people have been modding the units themselves here and Black Lion audio offer a USD $$$ mod option too.

JRC4558 is afterall an older generation op and with a slow slew rate compared with a TI5532 for example (another cheap but later model of opamp)

I am open to what you are saying but people were pulling 4558's out of these devices like there was no tommorrow, are you telling me there is no point, and that there is no improvements to be had by extending these pre amps audio bandwidth and putting a later generation op amp in ?

I am willing to learn here.

In addition the components will cost me about 12 Euros + a little bit of
time, surely it's worth a try at least.

I mainly need to know which capacitors to snip if they are doing the same
thing as the PR8. (i.e. capping the audio frequency range)

Thanks for your help in advance.

 

[Kit]

are you telling me there is no point, and that there is no improvements to be had by extending these pre amps audio bandwidth and putting a later generation op amp in ?

Maybe, maybe not. Many fine recordings have been made on gear with a 741 signalpath.

I dont have the schematics or the unit, so Im afraid I cant be of any further assistance.

I guess what im trying to say is I dont like the idea of modding a circuit just for the sake of modding it.

Try out the unit, listen to it. If it sounds allright, leave it alone.
If it sucks then go ahead, mod the hell out of it.


:thumb:

 

[SonsOfThunder]

Yep, need a schematic. Open it up and trace it out. You can do it!

Peace!

 

[Pentium]

Hi there ok this evenings work involved comparing the SM Pro Audio PR8E
with a Mackie 1604 VLZ pro XDR preamp.

I tried a Studio Projects B1 and a Shure SM58 dynamic.

The SM Pro Audio PR8E is comparably quiet, however a very slight hum was detected when using the SM58 (this was only just audible).

There was an upper mid 5-7kHz agressiveness which could in theory be useful in some apllications with both the condensor and dynamic microphone.Compared to the Mackie pre amps which I am a great fan of
LF's seemed comparable, the Mackie was slightly more open at the extreme HF. (Air I guess you could say)

The SM Pro Audio PR8E is lacking a little smoothness.

Here is the PCB photo as was promised :

http://www.flickr.com/photos/42634417@N00/839512841/

Try "all sizes" to get a big hi res image.

I am hoping someone can identify the caps to snip to extend bandwidth.

I wish I could trace circuits but I have very little knowledge
in electronics and so am hoping one of you wizards can help me out
in identifying them.

Hey... I am trying here by doing listening tests and photo's.

With a 1V slew rate on the current opamps Vs 9V on a TI5532
I am wondering if transient response can also be improved.

I am going ahead with the TI 5532 change whatever happens to see
what difference if any.

I really would like help with the caps though.

By trade I am an audio engineer not an electronics expert.

Thanks

 

[SonsOfThunder]

That lack of very HF could be due to the caps or just lack of bandwidth due to limited slew/GBW on the 4558. Tracing the schem would be a HUGE help, but I'll give it a guess. Btw, if you are going to learn DIY, you gotta start somewhere!! If you are not planning on learning DIY, better get yourself a techie friend who can help.

Looking at the schem that I drew, it appears that they have changed from what was originally a 47pF to a 22pF across the 100k feedback resistor on U2.B (my schematic ref) and I see 100pF across 8.2k instead of 470pF in two spots. So this should open up the response quite a bit without actually removing the caps.

Wonder what those jumper pins behind the XLR connector are for?

HTH!
Charlie

 

[Pentium]

Thanks SOT, much obliged.

I understand what you are saying.

They always said a little knowledge was dangerous ; )

I am just a dude who wants the best pre's for £100.00
If you think they are improved cause of those new lower cap values I
leave the caps as is and desolder the 4558's and try 1 of the pre's
with a TI 5532 which I have ordered for £0.29 each and get a some 8pinDIL sockets so I can conduct experiments.

I wonder why they did not change their spec sheets if the HF rolls off alot higher up? You would think that they would want to capitalize on that extension.

Another question, is making a recording at 24/96 and doing a spectrum analysis in software a reasonable test to see if any spurious oscillations are evident?

Thanks

 

[Pentium]

I think the jumpers switch the unit between

SM Pro Audio PR8E mode
and NEVE 1073 emulation mode : )

You know what I thought that too could not think what they were..

States 1 2-3 and 4-5 6 next to them?

SM Pro Audio mentioned the fact they use original JRC4558's mean that they sound better than other 4558's?

 

[mikeyB]

Black Lion audio do a mod of this unit - see what they have to say

 

[Pentium]

I suspect they might say, "Give us $349.00 and we'll mod it for you"

 

[Pentium]

Thanks SOT for trying to identify the caps.

Maybe I can try desoldering and see what happens
1 at a time and then put them back if something is not right.

 

[Pentium]

Oh dear I might have got hooked.

capacitors, I understand electrolytics are frowned upon
(not sure why? is it cause they dry out?)

Can these be replaced with a different (audio grade) capacitor?

Is the difficulty in getting the values in the microfarad range
with anything other than electrolytics?

I guess voltage is a consideration too.

Do tantalum bead capacitors compare?

 

[SonsOfThunder]

>>>mean that they sound better than other 4558's?
I think they are all the same. ST Micro, Fairchild, and TI are the only other manufacturers of that part # currently. I think if I got to choose, I would go for TI, personally, but then again I would go for 5532 instead.

>>>I think the jumpers switch the unit between...
Good one! :thumb:

>>>...who wants the best pre's for £100.00.
And that is what you got. If you want better, you'll have to invest more money or time or a combination of both. :green:

>>>try desoldering and see what happens 1 at a time
Good plan, but I suggest using machine pin sockets as the circuit board will probably not survive a lot of soldering/desoldering.

>>>Oh dear I might have got hooked.
hehehe! Too bad!

You can try all sorts of things in there. You might like two channels with tants, two with electros, two with electros bypassed with films, and two with film caps (good luck on that last one.)

HTH!
Charlie

 

[rodgre]

There used to be a schem for the standard PR8 out there somewhere, possibly on Black Lion's old site. From what I recall, it's not a terribly special op-amp based circuit. I have toyed with getting one of these for the last year or so and still haven't taken the plunge.

Roger

 

[Pentium]

I have also ordered some Analog Devices OP275's

seem like a well specced chip for about $2.00 each

These should be good in this !

I also have TI 5532's on order, should all be with me this weekend.

Thanks all, I promise I will report back after the weekends solderfest.

yes I am putting the chips in 8pin DIP8 DIL sockets