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Author Topic: BEHRINGER GMX212/GMX1200H SCHEMATIC  (Read 9178 times)

gearhead63

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BEHRINGER GMX212/GMX1200H SCHEMATIC
« on: May 28, 2014, 12:52:23 AM »
Here's the schematic for Behringer GMX212 and GMX1200H amps. Finally found one and thought I'd share. Behringer acts like the the world will end if they give you any information!

J M Fahey

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #1 on: July 20, 2014, 06:09:26 AM »
Thanks a lot  :dbtu:

I´ll hurry to download it before the World ends  :loco   :duh    :cheesy:

EDIT: now I understand why: it´s an absolute ripoff of a Sansamp !!!!!

Worse: it has TWO of them, one on each channel !!!  :trouble   :trouble
« Last Edit: July 20, 2014, 06:33:15 AM by J M Fahey »

difly

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #2 on: April 14, 2015, 06:33:17 PM »
Hello Friend!

I wonder what it means M9 M8 M10 M16 M13 on the first page of the schematics that are connected in 100n capacitors. Could you tell me?

I would like to make his preamp to insert into another poweramp, but I did not understand where they link these capacitors 100n in components denoted with the letter M.

Could anyone help me ? To build the preamp I do like the image ?

Thanks in advance!
« Last Edit: April 15, 2015, 04:24:23 PM by difly »

J M Fahey

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #3 on: April 15, 2015, 10:08:31 PM »
They look like more of the ubiquitous "100n ceramic capacitor" used for RF decoupling, all over the place.

Often they are either not even drawn or drawn "somewhere else", usually the power supply, to lower drawing clutter.

For the same reason tube filaments are almost never drawn, unless they are weird voltage or connected in series.

Go over all of the schematic with a loupe, those "M" parts look like connectors so their mating ones might be on any other board.

As a side note, and not to discourage you ... have you already drawn the PCB?

I guess it will be a very complex one.

difly

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #4 on: April 16, 2015, 07:31:47 AM »
Hi Fahey !
Thanks for the tips!

In fact I'm still learning, I am beginner. I'm researching to see if compensates well. But I drew the first page in Eagle software but not yet converted in PCB, but really think about doing only one channel, more study and learning it.

Best regards!

J M Fahey

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #5 on: April 16, 2015, 08:21:03 AM »
Cool :)

Since the interesting part of that amp is the (ripped off) Sansamps, I'd build just one first and test it, then if pleased build another , then add some switching and maybe some EQ and at last drive a regular SS`power amp with it.

That way you split the workload into manageable chunks.

There's nothing wrong about thinking a complex amp as a series of modules, which can be developed and troubleshooted one by one.

Trying to fit "everything inside a HUGE PCB" works for mass producers because they save assembly time, while we can work at a more relaxed pace.

I often experiment by mounting individual PCBs on an amp sized piece of chipboard, which at the front has an L shaped piece of aluminum, with lots of empty holes for jacks, pots and switches.

Then an amp can be made, modified, tested, the assembly is ugly but stable enough to be carried to a rehearsal room and tested at high power.

Only when I'm happy with it does it get a proper chassis and cabinet.

difly

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #6 on: April 16, 2015, 08:46:13 AM »
great tips Fahey!

I'll do it that way then, modular. Even we do not know if the scheme is totally true.

I will do as you say, divide by modules and testing go into a breadboard!

Once again many thanks for the tips!

teemuk

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #7 on: April 18, 2015, 05:57:42 AM »
The JFET input is actually a circuit idea conceived by Behringer but why, why, did they put it to input where it has least effect? It could have served as a decent "power amp" emulator in the later stages.

Yeah, otherwise pretty much a Sans Amp. Isn't Tech 21's Trademark 60 different from the usual SansAmp, though? I always thought these were nice amps for the money, and never really cared too much if someone was using circuitry similar or nearly identical to someone else's, unless there were legal issues involved. Marshalls, Dumbles, Mesas, whatever, have all started as "Fender circuits" anyway. Fender, on the other hand, adopted circuits from Gibson and so on.... What does it matter? In the end someone get's a "Tech 21"-ish sounding amp more inexpensively. Sounds suspiciously similar to Marshall's plan regarding Fender amps he sold in his shop. When Behringer does it they are big, bad evil corporation. Sigh.

Anyway, sorry for the "off topic".
« Last Edit: April 18, 2015, 05:59:03 AM by teemuk »

LateDev

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #8 on: June 26, 2015, 06:58:39 PM »
Hello Friend!

I wonder what it means M9 M8 M10 M16 M13 on the first page of the schematics that are connected in 100n capacitors. Could you tell me?

I would like to make his preamp to insert into another poweramp, but I did not understand where they link these capacitors 100n in components denoted with the letter M.

Could anyone help me ? To build the preamp I do like the image ?

Thanks in advance!

In each case given that they are next to a VR? which is not used, I would presume decoupling either across or to the wiper of the unused VR to suppress noise. No idea as I have not seen the M? symbol used before. Easy enough to check if you have the machine.
If you look at the diagram, all IC decoupling is shown relative to the IC's, as on the first sheet which shows IC 9,10,11,14 with decoupling caps.
I am a bit surprised that full decoupling has not been done on the digital IC's as in 10uF Tant with 100n decoupler, but guess it is cheap.
I have no idea about the earlier comment about this
Quote
EDIT: now I understand why: it´s an absolute ripoff of a Sansamp !!!!!
as there is nothing about that circuit that can be attributed to anyone in particular.
As far as circuits coming from somewhere is concerned, there are only so many ways you can design an amp circuit, some people can design some really good amps, but goof up in small areas, so why not improve upon something.
Quote
The JFET input is actually a circuit idea conceived by Behringer
No it isn't, I designed an amp late 1970's with FET front ends, so no that is not original either.

Every design you can think of has similarities to other amps, it matters little where it came from as long as long as there is no patent.

I just wonder why you want to use a Behringer circuit for the front end to a power amp ?

What you really need to do is write down your criteria for a pre-amp as in what is its usage going to be and do you want something that is make do, or do you want something a bit special.

As far as power amps are concerned, when you design a system, you match your pre-amp to the power amp. So it is not just a question of banging an output into some power amp, and expecting quality.
« Last Edit: June 26, 2015, 07:04:03 PM by LateDev »

g1

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #9 on: June 27, 2015, 01:46:39 PM »
I just wonder why you want to use a Behringer circuit for the front end to a power amp ?

Who said that? 
Teemu mentioned using it for power amp emulation in the "later stages" by which I think he meant later stages of the preamp.

LateDev

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #10 on: June 29, 2015, 06:53:57 AM »
To answer that question.

I would like to make his preamp to insert into another poweramp,

Could anyone help me ? To build the preamp I do like the image ?

Thanks in advance!

To answer the jfet question of why it is used at the front end. You have to look at the characteristics of Valves, Transistors and FET's, which will make it become clearer.
Both Valves and JFETS are Voltage amplifying devices, whereas a transistor is a current amplifying device.
 
What difference does this make I here some saying. Well when a transistor starts to distort, it is the second harmonics which effect it the most, which gives, to me, the horrible course sound. Now compare that with a Valve, which has its distortion effected more by the third harmonic, which gives the characteristic waveform. This tends to not clip as badly as the transistor, and sounds a hell of a lot better.

Another thing with FET's is that their impedance at the gate is very high, so is less likely to effect the input signal, it also makes input impedance matching easier. Read up on small signal analysis with a transistor taking particular attention to how all the resistors at the input effect the input impedance.

g1

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #11 on: June 29, 2015, 12:01:40 PM »
Ok, we are just misunderstanding terminology.
Front end of a power amp is the differential input or whatever circuit is at the input in the power amp itself.
Preamp is preamp.
At least that's how I was always taught.
When you said "front end" in reference to the preamp, I thought you meant the input stage of the power amp.

LateDev

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Re: BEHRINGER GMX212/GMX1200H SCHEMATIC
« Reply #12 on: June 30, 2015, 12:37:07 PM »
I must admit, people do get hung up on terminology.

An amplifier normally consists of two parts, the pre-amplifier which usually boosts the signal up to line level, and the power amp which takes this higher Voltage and increases it to whatever the amp is designed for.

Line level can be different depending on when the amp was built and for what purpose.

Whenever someone speaks of a front end to an amp, they can either mean the front of the power amp, or the front of the preamp. It all depends on their point of reference.