So stone me... I bought a Behringer

[mikka]

I bought an old Behringer Mic 502. :twisted:

My understanding is that these units can be improved by bridging the electrolytics in the input stage with some decent film caps....... thus getting around the increased impedance at higher frequencies.

Also that the ICs can be substituted for newer better ones.

I've asked Behringer for a circuit diagram but I haven't heard anything back yet. Is there anybody here who might have a diagram for this unit or experience in modding it to improve its sound?
:guinness: :guinness:

 

[Rossi]

It's useless to ask B-ringer, they never give you any schematic, no matter how old the unit is.

Can you tell us what's inside, perhaps post a picture? I think I once read that this thing is based on an SSM chip. If so, get the respective datasheet; the circuit is probably similar to one of the schematics in there.

 

[rodabod]

Expensive stuff! :

http://cgi.ebay.com/Behringer-MIC-502-Mic-Preamp-DI-MIC502-Euro-220v-NR_W0QQitemZ190018984137QQcmdZViewItem


Show us some photos of inside!

 

[mikka]

Hey thanks for that. I've taken some photos but my son has taken the USB cable.....doh. I'll post them tomorrow if I can. Couldn't help myself..... had to pull it to bits. Looks to me like the first thing the signal hits is a 22uf/25v electrolytic..... before going into something coded Be 027 which looks awfully like the SSM 2017 it's next to. There's also a 14 pin BE 037, and an LM 339N up near the LED's.

If Behringer won't give me a schematic, I might slowly draw one.... just for the learning exercise. This project is about my level...... if I don't screw it up!

I've got some Tamura input transformers out of an old Tascam mixer. I was also considering adding these, doing a recap, maybe substituting some That 1510's. Somebody called Rossi at Homerecording.com had some really useful info. Are you the same helpful chappy?

Now..... those photos......

 

[emtee]

From that ebay listing -

"No, it's not a super high-end preamp but you can get a cool, distinctive effect using "Phase Reverse" which no other preamp features."

Good old behringer, the leaders in innovation... :wink:

 

[mikka]

Ha.. found the cable..... and had a quick lesson in Photobucket

The overall board.

The input section showing the push on fitting from the balanced in (the wires) the first 22uf/25v cap that the line signal hits is right beside it, and the ICs.

The power supply side. All the pots are stepped..... about 40 positions around the dial. [Added later: Looks like the green Wimas are bypassing two NP electros in the mic section and the red ones bypass two NPs in the line section]

[/url]

 

[Rossi]

Thanks Mikka, so I finally get to see the insides of one of those. Like some early B-Boxes, this one seems to have non polar input caps. That's a little nicer than on the newer units.

The SSM2017 must be the mic input stage. The BE027 is a dual opamp, maybe that one's for the line input stage. The BE037 is a quad opamp. That one is most certainly responsible for the output stage and some other things, maybe hi pass filter and/or phase reverse.

In my B-boxes (I have 2 Ultragain 2000 units, for instance) I usally beef up the power supply. (Often the big electrolytics are a bit small, often there are no bypass caps near the regulator.) From what I can tell by the pictures, your pre looks pretty okay.

Next is the DC blocking cap connected to the gain pot. A bigger cap gives better bass at high gains. 1000u is okay, I think I put in 4700u. 16V should be enough.

I still haven't been able to find any usable info on the BE Opamps. Behringer used to advertize them as upgrades for mixing consoles etc. If I remember correctly they were supposed to replace a number of opamps including such different designs as TL072 and NE5532. One size fits all?!
Doesen't make much sense. From what I can tell, those BE opamps aren't particularly high bandwith. They're quite low noise and low current consumption. Maybe a NJM4558 variety. Some sources suggest a NJM4558DX as a replacement for the BE27 dual.

I replaced some BE037 quads with MC33079 with good results, particularly in output stages. If the BE027 is for the line input stage, replacing it by an NE5532 or MC33078 may improve the sound. Provided you use the line input at all.

Oh, sometimes B omit or simply forget PSU decoupling caps near the opamps. I solder the right on the opamps.

I'm not sure it's worth changing the SSM2017 for something else, because you might have to change parts of the circuit to take advantage of the better performance of an BB INA or THAT chip.

Hope that helps.

 

[clintrubber]

[quote author="rodabod"]Expensive stuff! :

http://cgi.ebay.com/Behringer-MIC-502-Mic-Preamp-DI-MIC502-Euro-220v-NR_W0QQitemZ190018984137QQcmdZViewItem
[/quote]

Sold for US$5.51 ?! :shock:
Seller must have really had it with that box...

 

[rodabod]

That older B*ehringer stuff actually looks ok.... No SMD!

Rossi's comments sound like good advice.

I'd maybe have a shot at socketing and swapping the BE* opamps.

 

[mikka]

You're right.... the input caps are non-polar... there are 10 Non Polar electrolytics per channel. The power supply caps are 220uf/100v, 100uf/63v and 10 uf/50v. The large cap near the long shaft pot is 220uf/100v.[Correction:1000uf/25v also]

Thanks for your input. I'll keep my soldering iron unplugged for now. I am curious whether a transformer input would help the SSM 2017. Is it likely that a cheap transformer is worse than none at all?

Cheers

:guinness: :guinness: :guinness:

Mikka

Sorry guys... I should have put this in "The Lab"....

 

[clintrubber]

[quote author="mikka"]
I am curious whether a transformer input would help the SSM 2017. [/quote]
IIRIC there's an app-note about adding a TX to '201X-style inputs on the Jensen-site.

Regards,

Peter

 

[mikka]

Thanks for that tip......

http://www.jensen-transformers.com/as/as064.pdf

for anyone interested. Very cool.

 

[rodabod]

[quote author="mikka"]Thanks for that tip......

http://www.jensen-transformers.com/as/as064.pdf

for anyone interested. Very cool.[/quote]

Ah, cheers!

I have a very short-run Beyer preamp which uses these.

 

[amorris]

HA-HA!
(in nelson's from the simpson's voice)

 

[clintrubber]

[quote author="mikka"]Thanks for that tip......

http://www.jensen-transformers.com/as/as064.pdf

for anyone interested. Very cool.[/quote]

Ah, nice you found it already. Enjoy :thumb:

 

[rodabod]

[quote author="amorris"]HA-HA!
(in nelson's from the simpson's voice)[/quote]

Hey! What you trying to say?

 

[alk509]

* throws stone *

:razz:

Peace,
Al.

 

[mhelin]

Replace SSM2017 with THAT1512 and BE027 with something you use to replace NJM4558 and BE037 with something similar to LM348 (Behringer recommends those to replace BE parts which originally I think were TL07x replacement opamps hence the number 027 which obviously came from 072).


Nice comparison chart for SSM2017-like amps here:

http://www.thatcorp.com/datashts/AudioPreampComp.pdf

THAT1512 @ 0 dB gain has quite a low input noise indeed 34 dB vs. 90 dB of INA217.

 

[mikka]

Thank you for those comments.

With the Non Polar electrolytics....... any suggestions from anyone? I was considering putting a .01uf or .02uf polypropylene across them but I'm unsure........Sound sensible?

Some people may think I'm polishing a turd..... but the turd is polishing me.

 

[guavatone]

OK, I will :wink: