How can I make my mono EMT 140 become a stereo EMT 140 ?

I bought for a few € an old EMT 140... Unfortunately it's a mono one and opening the box, I realise there were the 2 pickups inside... So I thought : "Cool, I can have a stereo EMT 140 !!!"...

The only problem is that it's a tube reverb, and the tubes are not easy to find nowadays...

The questions are :
- What about a G9 as a stereo pre for the pickups ?
- If I use a G9, must I plug the pickups without the input transfos ?

79 views, no reply

I just looked at the EMT schematics and realise that the first stage was closer to a tube microphone amp than a preamp... So, I think that the solution is closer to a modified G7 or a condenser stage... Any suggestion or comments ???

http://pagesperso-orange.fr/NBNS-Studio/emt/ScheamticMONO-V54.jpg

http://pagesperso-orange.fr/NBNS-Studio/emt/g7%schematic.gif

http://pagesperso-orange.fr/NBNS-Studio/emt/EMT162TS.jpg

http://pagesperso-orange.fr/NBNS-Studio/emt/Neumann_KM83-84-85.gif

Hey lolo-m , I was not any of those 54 lookers. But I have the same plate.And it´s amazing, not like anything else. I have the 162 amplifier and I have changed the 709 toa 5534 to bring down the noise a bit. Its a mic amp with hi.impedance input and its not linear. Ive seen the curves somewhere but I cant find it right now . But copy the V54,s correction. You see it in the feedback of the two EF 804. By the way, the 804 is quite near EF86 but dont have the same pinout.
If you wanna start, just to make a test, this is not a wide range reberb in in frequence terms. Take a OPA 2134 for ex (fet inp amp) with a gain of about 50 dB.Listen to that a go on further. Best of luck. Cheers Bo

:grin: thank you very much , bovox :grin:

I build today a kind of km84 pre with a 10M on the input instead of the 1G. I think that it could be a good buffer for the input. I will check it tonight if I have courage enough or maybe tomorow...
But you pointed to me something I didn't see : the non-linearity of the amp... I think that if my kind of DI works, I will do the second part of the amp with a 5534 to get the non-linear amp into my mixing room with maybe an extra eq...

The goal is to keep the send tube amplifier on, and to receive the two outs through a solid state amp.

I checked the first part of the schematic (upper part) yesterday...
Except the terrible hum I had with (every thing wired in the air without any box I think this is normal), the schematic seam to work...

The second part is what I'm planning to do... I someone think this is stupid or if there's something wrong, you're wecome to tell it !!! :green:
http://pagesperso-orange.fr/NBNS-Studio/emt/EMT 140 MOD.gif

Hey lolo-m, it looks fine..but I had put in a cap infront of and after the 5534 and even at least a 12pF cap (between pin 5&8) to make it stable.Cant you run the fet at typ. +- 15v also? Or choose +-18V and run the fet at + 18V. The signal from the pickups are very lo.
Try it and tell us how it works. Cheers Bo

So here I'm back with results...
It's working but there's not a lot of signal with the non linear amp build around the 5534 :sad: . The level seam to be close to a mic level !!! :? .

Bad point : I've got less level WITH the non-linear amp than WITHOUT it...
Good point : I do not have any noise nor hum with the non-linear amp in the same test conditions (no box around the electronic).

Do you think I must build another stage to amplify the output before driving the transfo ?

Bad point : I've got less level WITH the non-linear amp than WITHOUT it...
Good point : I do not have any noise nor hum with the non-linear amp in the same test conditions (no box around the electronic).

Click to expand...

I just wired the ouput transfo the wrong way, bypassing the two section and not connecting anything together...
Now, I do understand this perfect silence !!! :green:

I wired everything the right way and here it seam to work, I left a buffer on the output to drive the transfo because it's more stable like this... I go and make a few tests... I'll keep you informed...

A NEW PROBLEM

The input transformer is dead !!! The secondary winding is impossible to mesure... My plate is certainly too old not to have any problem... The schematics I have are saying it's a 1:3 tranfo there. I bet it's a 600 ohm input but I'm not sure at all... Does anybody knows ?
I tested it with an OEP tranfo A262A3E (ratio 1+1 : 6.3+6.3) with the input winding serial and only one winding connected on the output... It should give me 1:3.15 ratio. It's working but is it working correctly???

The plate seam to be very very useful ! :thumb:

Don't hesitate to tell me your opinions...
Thanks

PS: I got this plate from a closed studio just before they destroy the building it was in to build another building... I didn't knew anything about plate reverbs before, except it was a program name on digital ones ! It was stored in a sound reinforcement renter office, under dust and moisture... I bought it initialy to save a part of studio history... Now I want to use it !!! :grin:

So here I'm back with some news :
- it's working ! :grin:
- ~~ same gain ! :grin:

But a terrible hum and hiss !

I think hum comes from the non shielded electronic + ground problems and I'm not really amazed by this... But I don't know from where is coming the hiss...

Please, tell me if the C4-C5 is non-sense to get a Non Polarized cap.
Please, tell me if there's something wrong somewhere...

Here's the exact schematic of what I've wired :
http://pagesperso-orange.fr/NBNS-Studio/emt/EMT140MODv1.bmp
And ExpressSCH file :
http://pagesperso-orange.fr/NBNS-Studio/emt/EMT140MODv1.sch

Bonjour Lolo-M,
A few months ago I fixed a big hum coming from the outputs of a EMT140S that a friend of mine bought from another studio : the wire link that connects the audio ground of the amplifier module to the chassis ( round metal tubes ) and the plate itself had been removed, probably during transport.
Was a VERY loud hum !
Also the amplifier module is very sensitive and must always have its cover closed, otherwise you get a big hum too ! !
Just one idea...
Guy

[quote author="bovox"]I have changed the 709 toa 5534 to bring down the noise a bit. [/quote]
Did you only exchange the opamp or change some other components all around ???

[quote author="guy_4"]Bonjour Lolo-M,
A few months ago I fixed a big hum coming from the outputs of a EMT140S that a friend of mine bought from another studio : the wire link that connects the audio ground of the amplifier module to the chassis ( round metal tubes ) and the plate itself had been removed, probably during transport.
Was a VERY loud hum !
Also the amplifier module is very sensitive and must always have its cover closed, otherwise you get a big hum too ! !
Just one idea...
Guy[/quote]
Bonjour Guy_4 ,
Thank for your idea...
The hum problem is for sure a shielding + ground problem and I'm not frightened by this...
My real problem is something like white noise... The signals are so small that changing the first stage of the preamp with a fet opamp I made a radio receiver !!! :?

The old electronic is working perfectly now I've changed the input tranfo. And the reverb is simply terrific but mono... :sad:

Yesterday test results :
- I used a metal can around the electronics and the 50/100 Hz hum disappeared (of course !)
- My problem comes from the first stage (2n3819) which generates a lot of white noise... I tried to change C3 unpolarized MKT to a tantalum : no change... I tried to change C2 polarized electrolitic to a tantalum : no change... I tried to remove C2 : got less signal gain and still to much white noise...

There is 2 solutions I see :
- The first solution is to copy the original input stage but the 2N4303 is close to be impossible to find nowadays... A web search gave me some equivalents : 2N4302 , 2n4416 , 2N5245 , 2N5362 , 2N5458 , 2N5459 , BC264LC BFS80 , BFW11 , E102 , ECG457. Some of them seam easy to find, others are really expensive... Does anybody knows which one is the more suitable ??? :?
- The first stage around the 2N3819 have too much gain... Does anybody knows how I can lower it's gain ? On the EMT schematic the input fet is used only as a buffer... 3mV IN and 2,5mV OUT !!! I don't know a lot about fets so if someone can help me on that... :thumb: Maybe I just have too much gain here.

50 views in only 2 days, more than 800 views total and only 2 persons posting...

Sometimes I feel really lonely... :sad:

I tried a copy of the original input with a 2N3819 and a 2n5457 (lowering the PSU to +12/-12 ) and still have too much white noise on the output...
I STILL NEED HELP ON THIS POINT !

But trying to find infos on the input fet, I realize that a lot of studios had a MARTECH (Martinsound) EMT 140 MOD installed in their plate reverbs... I tryed this morning a "a la Martech" Mod... And it's working perfectly. Without any effort I had no hum, no white noise and the sound was really interresting... :grin:

I don't give up on the original pick up but they're so difficult to use... I manage to buy some EF804S at a resonable price so I will try to do a second tube preamp for the plate... I think it's interresting to have both possibilities tube original sound and a new Solid State sound.

What does this Martech MOD contain?
I am having an old EMT plate and by moving it into our new studio rooms I want to play a little with it, cause it is realy noisy.
Btw. it is the solid state version.

[quote author="DerEber"]What does this Martech MOD contain?[/quote]
You can find the most important lines here :
http://www.groupdiy.com/index.php?topic=10718&postdays=0&postorder=asc&highlight=emt+140&start=30
At least, before reading this I did some pickups for accoustic instruments with piezzo speakers. And it was amazing how much it was sensitive to sound without any noise... I was thinking I'd better use the original pickups but now I'm not sure at all... My mono ( :sad: ) tube electronic works but the piezzo pickups are a lot less noisy...

Damm! I even posted in this treat. :green:
So now I know. You meant this one.
Sorry for beeing a fool.
:guinness:

[quote author="DerEber"]Sorry for beeing a fool. :guinness:[/quote]
So do I !!! :green:
I don't know the amount of noise there is with a 162 electronic... Any way to have an idea (sample : no sound then reverb) ? Maybe I'm not so far to reality with the last version I didn't post (but I don't think so) ?

Do you have a tuning tool ?