A Behringer unit worth modifying?

[Syngriner]

I recently dug up an old Behringer Pre Q dual microphone preamp that I had bought back in the early 90's. I opened it up and was surprised to find that the circuit board and components looked really decent (see attached picture). All the resistors looked like 1% film types. One of the IC's in each channel is a PMI SSM2017P, which is suppose to be higher spec op amp. The other two IC's are Behringer branded; the 14 pin DIP is a BE037 and the 8 pin SIP is a BE027. I assume a dual and quad op amp respectively. Sound wise it's not a bad little unit. Just kind of sterile/bland and doesn't have much headroom. So I am thinking about modding this thing but have some questions-
-I assume the two Behringer IC's are just another manufacturers part that they have rebranded. Is anyone familiar with these/know what they really are?
-Is the pin out's on DIP op amp IC's standard?
-Any ideas where I could get a schematic for this unit?
-What is the best brand of replacement electrolytic capacitor?
-Would there be any reasonable modifications that could be done to the power supply to increase headroom/transient response?
Any information would be greatly appreciated, including letting me know if this would just be a waste of time. Thanks

[Gravity]

Not surprising it's not a bad unit. THis would have been early B-ringer, back when they still designed their own stuff.

Going to be a b*tch to work on though. NO sockets for those ICs.

Best thing you could do is probably a recap with something nice like WIMA or Panasonic, swap out the IC op amps if you can find an equivalent with the same pinout.

Might be fun to try anyway, the parts won't be too expensive, and at worst you'll end up with a slightly better sounding, sterile preamp. ;-)

[sysexguy]

back when they still designed their own stuff

are you refering to two American companies, one that starts with an A and makes exciters and another that starts with R and makes single ended NR?

Andy

[ulysses]

The SSM2017 was less highly regarded than its predecessor, the SSM2015. Different pinouts. But there are some newer replacements that are pin-compatible with the SSM2017. THAT Corp's 1510 and 1512, for example.

The other two ICs can be deduced by looking closely at their pin configurations. Looking at your photo, I think you meant to say there are some 8-pin DIPs which could be single or dual op amps, or something else. A good place to start is by determining the positive and negative power supply pins, and if you can deduce the input and output pins that'll help too. The 14-pin DIP could be a quad op amp or something else. If it's a quad, it could be something very obsolete with very few replacement options, or it could be something slightly less obsolete with very few GOOD replacement options. Again, start with the power supply pins and try to deduce some of the I/O pins as well. The inverting input can usually be identified by the resistor and possibly a ceramic capacitor connected between it and the output. Stare at it a while, try to draw a little schematic, or chart the pin-out, and see what you come up with. Learn to identify pin 1 (there's probably a dot next to it) and count down that row and up the other side. Then you can look at component data sheets to see if a replacement you're considering is pin-compatible. But just because a chip has the same pin-out doesn't mean it's a functional replacement. Power supply requirements, bandwidth, phase margin, unity-gain stability, etc. all come to bear on this.
If you do any chip replacements, start by removing the old chip (sacrifice the chip to prevent damaging the board during removal). Install an IC socket with machined pins and gold plating on the contact mating area (the solder end of the pins don't have to be gold - that's a waste of gold).
To replace the electrolytic capacitors, choose Panasonic FM or Nichicon HE caps from the Digikey catalog. Stick with the same voltage rating, lead spacing, and diameter as the originals. Keep the length under what will fit in the box (probably 25MM). Capacitance will surely go up as a result. That's the general idea.
Be sure to measure and listen as you go, to ensure you're actually improving things.

[Jim Williams]

Use machined sockets. You can sub a SSM2019, that 1510 or BurrBrown INA217 for the 2017 mic pre chip. Also, install a pair of 470 pf npo ceramic caps from pin's 2 and 3 to ground (pin 5). This overcomes some hf instabilities the modern replacements tend to have with unterminated inputs. Most designers only used a single 470pf~1nf cap across pins' 3 and 2.
The 037/027 are rebranded IC's. These are quads so a LT1359 or LME49740 would be ideal as a replacement.

Jim Williams
Audio Upgrades

[Syngriner]

This is great, I appreciate your replies and thanks for all for the good information. What is your opinion on bypassing larger value audio path electrolytic caps with small value film/poly caps to improve high frequency response/linearity? Also is it worthwhile to replace the filter caps in the power supply (main and phantom power) with larger values? Does this improve S/N ratio or transient response?

[ulysses]

Bypassing signal-path electrolytics with film still isn't as good as just not having electrolytics in the signal path, but that's a design decision, and not always something you can mod around. Still, bypassing them is better than not.

Yes, improving the capacity of the power supply can lower the noise floor and improve a number of performance parameters. If the original construction included adequate capacity, increasing it wouldn't be beneficial. That seems unlikely in this case.

[Snatchman]

I had this pre and as stated ,it's not bad but lacks head-room. I had it modded with sockets installed with Burr/Browns ( OPA-3124 ?), Nichelon caps, etc. opted out for the output trannys even tho there's a place on the PCB for one..It became a queiter, warmer sounding pre after the mod, but didn't change the headroom issue tho..BTW.. if you are interested in other Behringer gear made during this same era ( topolgy as this..) I have some EQs, compressors, etc. for sale..!..Good luck..

[headwerkn]

You could always rip out the entire guts and put in a 1081 or similar esoteric circuit. Better yet, you can put the Behringer circuit into an esoteric case and mess with 'Slutz heads ;-)

[Jim Williams]

You will need to keep the large 2200 uf gain set cap and a blocking cap on the output of the mic pre chip as they tend to have significant dc offset. Following that you may be able to remove some of the electrolytic signal caps if you use a very low offset opamp like the quads I suggested. You need to measure it first to determine if it's below 5 mv or so of dc. Otherwise, place a Wima MKP-2 .01 uf cap across the el caps, a .1 across the large gain set cap.

This is not a bad design, it's very similar to the "revered" DAV BG1 and Trident S-20 mic preamps, designs praised here. Don't let the brand sway you, it's what's under the hood that counts. Picking up one of these instead of spending $100's on those other versions can save you $$$, if you can afford the "B" word in your rack. Even a broken clock is right 2 times a day.

Jim Williams
Audio Upgrades

[Syngriner]

Well, I have all the parts on order. I went with the Burn Brown INA217 as the replacement for the SSM/2017 and the LT 1359 for the 14 pin dip - BE037. In visually tracing the signal paths it appears as if the other 8 pin dip, the BE027, is just for the line input, which I don't intend to use. So I am not planning on replacing it. In fact I am considering just removing and hardwiring past the mic/line selector switch to get it out of the microphone input signal path.
-A few more questions -
Is it necessary to capacitor bypass the power supply and/or signal inputs on the LT 1359?
Is the DC voltage level of the power supply the primary determining factor in the audio signal headroom for a unit like this?

Thanks again for your help and I will let you know how it turns out.

[Jim Williams]

Headroom translates as dynamic range. That can be increased at the high end or the low end of the dynamic range. Increase psu voltage rails and you gain a db or so, big deal. Lower the noise at the low end and you can get more db's than that depending on the design, parts selected and resistor values. If that is done, levels can be lowered without a noise floor increase = more headroom.

Do add a pair of .1 uf mono ceramic caps from pin's 4 and 11 to ground. Add another across the rails, pin's 4 and 11. That assumes they are missing from this design. Don't bother with signal hf bypass caps, they lower slew rates. Also audition the SSM2019 and the that 1510, users report both are superior to the BB INA217, even DAV switched to that from BB.

Jim Williams
Audio Upgrades

[Aerophone]

Hi. Sorry to dig up this old thread.

I won an ebay auction of Behringer Mic pre Q and, of course, i want to mod it.
Hi Jim! Always follow your posts! Are you sure BE027 and BE037 are compatible with the Quad/Dual opamps you mentioned? I already got the ssm2019's and the machined sockets ready thumbsup. Should add psu bypass caps from the power pins to ground?

Syngriner, what successful mods have you already done to your Pre Q?

thanks!

[Jim Williams]

I would check the work with a scope. On a quad opamp the corner pins are the outputs. Set the scope to 20 mv sensitivity and time base to 1 ms. Look at the output pins on the corners. You should see a clean flat line in the absense of any signal.
I also have a superior replacement mini pcb to substitute the ssm2017, ssm2019, INA217 and that 1510 mic pre chips, the PIP or plug in preamp. It has lower noise and THD with greater bandwidth and slew rate. Output current is 100 ma.
On that Behringer layout you would need to bend over one of the phantom input blocking caps, replacing them is a good idea anyway. See the PIP at:
Audio Upgrades

Jim Williams
Audio Upgrades

[Syngriner]

Hello Aerophone
I ended up replacing the two main mic path IC's with the That1510 (8 pin) and the LT1359 (14 pin). I did not replace the line input IC since I have never used that. I replaced all the audio path electrolytic capacitors with Panasonic FM caps and bypassed them with Wima film caps. I soldered the Wima's on the bottom of the PC board. I did find one signal cap in each channel the did not measure any DC voltage across them so removed and jumpered them. The only thing I replaced in the power supply were the two power supply filter caps with somewhat higher capacitance values. I added the small bypass caps around the IC power supply legs as per Jim's suggestion. I have toyed with the idea of installing output transformers in the Pre-Q but I think I am just going to make an external dual transformer box that I can run inline with any of my preamps. All in all the mods did improve the preamp and I learned new things in the process. Good luck with your project and please let me know if you have any further questions. - Bernie

[Aerophone]

Hi syngriner!
Good to read from you. Can you tell wich cap you removed? i have no scope to measure dc offset. Also did you added psu decoupling caps to stabilize the lt1359? And rf filtering ceramics for the that1510?

[Syngriner]

Sorry, I don't remember specifically which caps I removed. I would have to pull the pre-Q out of the rack, open it up and take a look. I did add the bypass caps on both IC's. Seemed like I had to do some interesting kludging to get the caps as close to the IC's as possible. As far as figuring which caps had any DC offset I just used a simple volt/ohm meter on the DC millivolt setting. I just measured using the common side of the power supply filter caps as my ground reference.

[Aerophone]

This thing does not have a gain set cap. Should i add one?

And what's with the lack of headroom? it is a simple circuit, shoudn't be hard to pin down the problem.

There are bipolars on audio path. They're refered as polars in the schematics (22uf/25v) but on the circuit they are BP. All i've got is Pana FM's polars, will the substitution be an improvement over the non polars?

Another thing. In the schematics shows three EL caps with 220uf/63v and one 100uf/100v but in my behringer i have three 100uf/63 and one 220uf/100v. Is there an error in the schematics or on the assembling of my behringer? Should i change the 100uf/63 to 220uf/63v to improve the voltage doubler capacity?

I already:
Changed BE027 to LM4562 with psu decoupling caps (0,1uf to ground);
Changed SSM2017 to SSM2019 with psu decoupling caps;
Changed BE037 to LME49740 with psu decoupling caps;
Changed input caps to Panasonic FM's 100uf/63v with Wima bypasses;
Changed the PSU 1000uf/35v to 2200/35v and added paralell 0,1uf bypasses;
Added a gain set Cap with the minus side to pin 1 of the ssm2019 (2200uf/10v);
Removed the EL cap marked with red arrow.

Do you guys (Jim and Syngriner) recommend other mods?

thanks a lot.

[antoniosolo]

I wanted pretty badly to modify the vintage looking Behringer Tube Compressor but felt like painting it and all was not worth it. I went with an SSL G series clone.

[Aerophone]

bump?

[CZ101]

How did it all work out Aerophone? I picked one of these up for cheap on eBay a couple of months ago - interested in trying some of these mods...

[Frank DeWitt]

Originally Posted by CZ101

How did it all work out Aerophone? I picked one of these up for cheap on eBay a couple of months ago - interested in trying some of these mods...

My guess is it started to go intermittent, lots of crackle noise, then quit.

Sorry, I know it's an old one, but Behringer just bothers me. I will do all I can to warn others away.

Frank

[CZ101]

Originally Posted by Frank DeWitt

My guess is it started to go intermittent, lots of crackle noise, then quit.

Sorry, I know it's an old one, but Behringer just bothers me. I will do all I can to warn others away.

Frank

These are actually pretty well built and carry a high mod potential. The Behringer hate, however passé it may be, keeps this stuff cheap, and that's fine by me!

[Frank DeWitt]

Originally Posted by CZ101

These are actually pretty well built and carry a high mod potential. The Behringer hate, however passé it may be, keeps this stuff cheap, and that's fine by me!

I am really glad there are some good ones out there, and I wish you well. No hate here, Just a bit sheepish about learning the hard way. I kept reading that the ADA 8000 was an exception. I believed it and bought 5 ten months ago. I am down to two.

I read many years ago that the average unhappy customer will tell 13 people. I want to do much better then that.

Good luck, and God bless

Frank

[drtechno]

remove the 5v6 diodes as they are not very good quality.


if you are using dynamic mics or condensers with a separate power supply:

remove the twe 6.81k phantom power resistors.

remove the two 100 uf 63 V input caps and replace them with a piece of wire.

[Jim Williams]

Not recommended. That will cause you to lose phantom power and risk front end damage. Just use good caps like Nichicon HE 47uf, 63V. Bypass with a good film cap.

I would also check the chip outout DC at +60 db of gain, there may be significant DC gain without that large value gain pot blocking cap. If so, add a large 2200 uf 10 V HE cap with a .1 uf polyprop bypass.

Those 5.6V zeners are there to protect the chip front end from voltage transients, those come from audio spikes and turning on/off phantom power. Remove them and you may fry the chip. I would replace them with 1N752 series zeners as they have less stray capacitance/leakage and will measure better THD specs. They can also be re-arranged to dump to the voltage rails instead of the ground buss.

[S2udio]

Originally Posted by drtechno

remove the 5v6 diodes as they are not very good quality.

As they are there for protection only they will have absolutely no effect on
anything,as for poor quality,where on earth did you get that from..

[jensenmann]

Originally Posted by S2udio

As they are there for protection only they will have absolutely no effect on

Unfortunately not exactly.... Zeners are a source of noise. In voltage regulator circuits you´d want to bypass them with caps. In a mikepre scenario that´s not possible. Their noise will be amplified by the adjusted gain. But keeping the chip alive is a higher goal (for me) than maximum sonic purity.

[Jim Williams]

Originally Posted by jensenmann

Unfortunately not exactly.... Zeners are a source of noise. In voltage regulator circuits you´d want to bypass them with caps. In a mikepre scenario that´s not possible. Their noise will be amplified by the adjusted gain. But keeping the chip alive is a higher goal (for me) than maximum sonic purity.

That's why you use the 1N700 series, less stray capacitance and current leakage. Those diodes should be bypassed with small 470pf caps to remove hf noise and damp rf and input instabilities. There are plenty of alternate topologies if you don't want to use zeners, like fast rectifiers dumping overvoltage spikes to the rails.

However, I've never been able to measure a contribution to the EIN specs with/without zeners on the front end, there are greater noise sources to see.

[S2udio]

Originally Posted by Jim Williams

However, I've never been able to measure a contribution to the EIN specs with/without zeners on the front end, there are greater noise sources to see.

Exactly ,the ears will detect no difference,and so nothing to gain unless you want to stray into audiophool territory.........