Behringer T1953 Mods Anyone???

Hi,

I am brand spankin new to this forum, as of today. I have been trying to find sites that actually cover relevant topics with regards to pro-audio/recording gear and this seems to be the one.

I have a Behringer T1953 Tube Mic pre that I'm wondering about mods for - or for that matter just the schematics. It appears that the mic pre has a couple of minor flaws - the first being too much stuff in the signal path is causing phase distortion, group delay and a few other things... and secondarily, Behringer has increased the frequency response of the thing so much that it's squelched the potential dynamic range of the unit.

Any thoughts on the thing, other than throw it out and buy a new one?

Thanks, in advance.

Dar

welcome

sorry ... no thoughts at all ... never seen one and no schamatic to ponder ... :sad:

but welcome anyway ... :thumb:

Sell it on ebay and build a green pre, or a G9 dual tube mic pre!!!

[quote author="kornowsd"]Hi,

I am brand spankin new to this forum, as of today. I have been trying to find sites that actually cover relevant topics with regards to pro-audio/recording gear and this seems to be the one.

I have a Behringer T1953 Tube Mic pre that I'm wondering about mods for - or for that matter just the schematics. It appears that the mic pre has a couple of minor flaws - the first being too much stuff in the signal path is causing phase distortion, group delay and a few other things... and secondarily, Behringer has increased the frequency response of the thing so much that it's squelched the potential dynamic range of the unit.

Any thoughts on the thing, other than throw it out and buy a new one?

Thanks, in advance.

Dar[/quote]

Dar,

Welcome aboard!
I had this unit and couldn't find a better use, but just completely gut it and use its chassis, trafo, and psu board for another pre project. I got so frustrated looking at its front panel, theat I had to make a new one. Sorry, probably not much help, but I don't think with all the SMD junk inside you could do much there.

Interestingly enough, I have spent a great deal of time w/ the innards of this little gem. The Behringer design is, actually, very well done... the Behringer components are what leave the most to be desired. I have re-built several component sections of this unit with amazing results...

1) I took out all the NJM4580 operational amplifiers. They have the specs of a pre-1970's 741 operational amplifier with low slew rate, narrow bandwith, incredibly high THD+Noise specs, etc. I replaced these with Burr-Brown OPA2228's - high -precision operational amplifiers. This single change impacted the overall tone/accuracy of this box the most.

2) There are 4 primary capacitors in the signal path - they are all 680nF poly caps (green) on the preamp PCB. I removed these and put some high-quality versions of these guys in there. The replacements were poly too, but about 1000 times better.

3) I replaced all the Electrolytics on the preamp, tube and input board with high-quality, low ESR, low di-electric constant (as low as you can get w/ an electrolytic) .

The sound of this unit is now close to the $800 to $900 tube mic pre's. Similar changes can be made to most of the Behringer gear using those NJM4580 operational amplifiers.

I've been thinking about mapping all the ceramic surface mount caps in the unit and replacing those with higher quality tantalum or COG-type ceramics to gain some other minor improvements... but I need some time to take care of that. Going to be traveling too much, in the near future to be able to do that.

Thought that some of you might enjoy revisiting this relatively inexpensive mic-pre that can be made to sound pretty darned ol' good - especially if you have one just laying around.

Dar

So you did a straight swap with op-amps with no issues?

As long as the various elements of the opamps are in-line w/ each other (i.e. input voltages for the rails, pins, etc) they should be able to swap out w/o any issues. The Burr-Browns are much more resiliant than the original JRC's, so it was a nice swap all the way around.

Dar

[quote author="kornowsd"]
1) I took out all the NJM4580 operational amplifiers. They have the specs of a pre-1970's 741 operational amplifier with low slew rate, narrow bandwith, incredibly high THD+Noise specs, etc.
[/quote]

Hmm, that's not really true. Not that I like the 4580, but it's specs aren't that bad. *Much* better than a 741 in any case. You might confuse it with the 4558, which is a really bad chip. The 4580 is an upgrade to the 4560 which can be found in many Mackie consoles and other stuff that most people think of as decent. The 4580 is also widely used by other manufacturers; you see it on lots of soundcards for instance. Even in mid level ones such as RME.

I've also worked on some B*ringer gear, but have avoided SMD ones so far. I've had good success with polyester bypass caps on electrolytics. I know some people don't like bypassing, but I think it improves audio performance of lower grade electrolyics considerably.

I've also swapped a couple of 4558s for 5532 with great success (in Composers). But those 4558s were only used in some older units. You won't find them in newer ones. I don't change 4580s. Of course BB chips would be an upgrade, but more often than not there's other components or design issues that compromise the performance more than those opamps.

I have to agree with Rossi:

NJM4580:
SR = 5V/us
GBW = 15.0 MHz
THD = 0.0005% (1kHz, 2kOhm load, 5V output)

LM741A
SR = 0.7V/us
GBW = 1.5 MHz
THD = not spec'd

OPA2228
SR = 11V/us
GBW = 30 Mhz
THD = 0.00005% (1kHz, load not spec'd, 3.5V ouput)
* not compensated for gains below 5 *

Easy to see there is lots of difference in the 741 compared to these, but not so much diff in the "spec" of 4580 vs 2228.

The sound of this unit is now close to the $800 to $900 tube mic pre's

Click to expand...

Could you be more specific? Which models? In what ways does it sound similar to a specific unit? Or different?

Your original post says that you think there are too many components in the signal path, but you don't mention removing any. And then you say that they have increased the BW to the point of decreasing the dynamics. This comment seems rather contradictory, but to each his own.

I have been curious to know a thing or two about this box. Can you tell us what the plate voltages are? I suspect that this unit is more "toob" than "tube".

Peace!
Charlie

Would you by any chance have a schematic, that we could see..?

Schemos are always nice.. :razz:

Jakob E.

Yeah, draw up a schemo, even if it's rough these guys will polish it up over breakfast! It's so fricken cheap I never thought to gut their tube preamp and if it can take 2228's, knowing Uli, won't take these guys long to work out where he nicked the design!! Sorry I can't help, I'm just a hack.

Spec differences between the 4580 and the OPA2228 are SIGNIFICANT...

There are a ton of things that aren't specified in data sheet, or aren't immediately obvious.

First, THD - the specs are determined from a SINGLE frequency, usually 1kHz. THD increases significantly with frequency in the cheaper operational amplifiers. If you measure the output of the 4580's, that Behringer uses, you'll notice that it increases almost 3 orders of magnitude off of the "published" spec. Essentially, this means that all the transient energy (high frequency sibilance, etc.) has a "noise sheen" added to it.

If you read some of the reviews of the Grace Design 101, 201 and 801 series mic pre's you'll find that some critical listeners complain of this issue with the INA103 operational amps from Burr Brown which have THD specs about 4 orders of magnitude less than the 4580's. It can be heard w/ those ultra-accurate op amps it can be heard w/ the 4580's, as well.

Slew Rate determines the effective operational bandwidth of the op amp and the ability of that operational amplifier to accurately follow input changes. For "square wave" type events (severe rise times) the lower slew rate of the 4580 won't track as Behringer has cranked the gain up pretty high on these things to get the gain out of the thing. There 100kHz spec was measured with an extremely low input signal to get the bandwidth out of the thing... their SNR's were measured with high level input signals - skewing the specs to get them to look better is what that's called.

Spec's, out of context of other specs, can really make a device look really good. The reason the 4580's don't have comprehensive specs on that operational amplifier is because in many of the critical areas, where the operational amplifiers accuracy, reallly shows up, it doesn't do well.

Two other areas where the 4580 really doesn't produce are the high/low signal level settle times. The 4580 rings like it has inductors on all the pins... the OPA2228 has an incredibly fast settle time (in the single digit micro-seconds) the 4580 doesn't even print the spec because it's settle time really sucks... As long as you have pure sine waves in the program material the thing performs well. Once you add widely changing transients, it doesn't perform so well...

There's a lot more to an amplifier than slew rate, output voltage and SNR, so to speak... you really have to dig in and truly see how the thing operates at all frequencies, signal levels and with all signal types at various frequencies... just because the slew rate is within the 5V / uS value that the audio community says is sufficient doesn't mean that the thing actually is audio quality. It's important to dig much deeper into the operational aspects of the device.

SCHEMATICS FOR THIS THING I have begged the Behringer folks for them. I'm going to take a signal and inject it and then trace it through the PCB, at this point... it's going to be the only way to actually analyze this circuit and get down to what Behringer is really doing w/ it. I wish I knew what they copied w/ this one so I could start there.

Dar

[quote author="kornowsd"]SCHEMATICS FOR THIS THING I have begged the Behringer folks for them. I'm going to take a signal and inject it and then trace it through the PCB, at this point... it's going to be the only way to actually analyze this circuit and get down to what Behringer is really doing w/ it. I wish I knew what they copied w/ this one so I could start there.

Dar[/quote]

Just got one for its meters, so before it get's trashed/cannibalized/converted I was wondering if there had emerged a schematic or other relevant stuff in the meantime.

Thanks,

Peter

As others warned already, those boxes are indeed empty. Not much more empty than most DIY-boxes we often see here though. It's still quite heavy however.

FWIW I took some pics:




I saw +/-16V, +48V & two times +24V. The U-shaped cooling-fin seems a bit of a waiste; the box sucks only 25W from mains and the regulators could have used the full bottom plate of the case, which they're actually already touching.

Relays, torroid-TX, meters, power-cord, light-bulbs, not bad :wink:
Box seems neatly build, but the plastic wannabe knobs feel flimsy.

Mine (just bought second hand) has Sovtek-tubes, could these be original ?
I'll be trying some Philips ECC83 before the box might be entering the realm of re-use.

Regards

as has been said before, 13v/us is just about the lowest limit I would want in an opamp at it's normal working setup for full audio bandwidth. some opamps change slew signifigantly as their bandwidth is changed via feedback.

I was looking at an AD part that had some amazing slew at gains higher than 3 or 4, and was also stable at higher gains. feedback for stability at gain of +1 dropped slew to nothing more than a 5534. it then became .20$ opamp vs 5$ opamp for the same performance.. :shock:

and we wonder why some expensive desks($$L) use "cheap" opamps...

Clint,

Thanks for the pics. Nice to see that they gave up yellow LED's behind the tubes and resorted to filament lamps. Much prettier light.

It would be interesting to know what voltages (and aproximate currents, judged from fuses and/or capacitor values) are available from the powersupply?

Maybe that part could be re-used..?

Jakob E.

I have this unit too. The semi conductor preamp has e.g. a lower performance (frequency response, thd, noise...) than a SSM preamp.

But the tube circuit can be used as a fx. The more you turn the "warmth" poti to the right the more distortion and the frequency response shows much more highs and less lows.

I chanced the cheap and bad sounding factory tubes to the IMHO very fine sounding SED 12AX7 and was really surprised by the result: Snare track for example got much more "life" when treated with this unit!

So, it is not bad at all... depending on the tubes and the mission... and if your prejudice against Behringer are too strong: At least it is a cheap spare part source... :grin:

[quote author="gyraf"]Clint,

Thanks for the pics. Nice to see that they gave up yellow LED's behind the tubes and resorted to filament lamps. Much prettier light.[/quote]
And there's more prettyness ! :wink: I hadn't seen the top-lid of these boxes in the flesh before. The top has the Beh-name in a 'perforated fashion', right above the lamps'n'tubes. So just imagine how the 8-tube T1950 would look :wink:
This T1953 has just two, so only the last few letters of the name are illuminated. All part of the hype of course, it doesn't contribute to the sound.
To be honest, I had expected a block of lead inside this box - given the emptyness it's actually quite heavy.

It would be interesting to know what voltages (and aproximate currents, judged from fuses and/or capacitor values) are available from the powersupply?

Maybe that part could be re-used..?

Jakob E.

Click to expand...

I had added voltages already, but didn't pay attention to the cap-values & fuses. Will make some notes the next time I open the box. :thumb:

I didn't measure the voltages yesterday, but the PCB stated +/-16V, +48V & twice +24V. Those 24's will be going to the tubes I guess, not the 48V. Don't know about the 'ff', maybe they run both tubes in series on one of those 24V-sections. The whole box draws 25W.

The supply section sure looks re-usable - looks a nice self-contained unit.
Maybe this is a one-supply-fits-whole-range unit, so the boxes with more tubes are using the same supply-PCB and/or supply-TX. In that case it'd be rated for 'doing' all eight tubes for the T1950 (and the fins probably getting very hot) but for the two tubers it'll be having an easy life.

Regards,

Peter

[quote author="Wolferl"]I have this unit too. The semi conductor preamp has e.g. a lower performance (frequency response, thd, noise...) than a SSM preamp.[/quote]
Sounds like you've been measuring etc - got any notes saved ?
So far I haven't peeked inside much further - what's it using ? As I undertood the usual recipe of a few discretes and in Beh.'s case a 4580 for the mic-pre ?

But the tube circuit can be used as a fx. The more you turn the "warmth" poti to the right the more distortion and the frequency response shows much more highs and less lows.

Click to expand...

Will try other brand - so far it's been of no use that warmth-thing.

I chanced the cheap and bad sounding factory tubes to the IMHO very fine sounding SED 12AX7 and was really surprised by the result: Snare track for example got much more "life" when treated with this unit!

Click to expand...

Yours had Sovtek as factory tubes as well ?

Regards,

Peter

Anyone know if we can do anything with OT-1? also mine has TL074CN the Burr-Brown are still a big improvment, Right?

Joe