News:

GroupDIY is currently under construction.
Some parts of the site may not work properly.



zmix

MXR DUAL LIMITER no.136 Schematic wanted
« on: January 25, 2005, 10:52:51 PM »
Does anyone have a schematic for this limiter?

Anyone have any information on it?


MXR DUAL LIMITER no.136 Schematic wanted
« Reply #1 on: January 26, 2005, 02:04:32 AM »
I don't have a schematic sorry but I have one myself. These are excellent limiters and were considered a poor mans DBX 160 when they came out late seventies. Can comp as well at 4:1 setting. I was told when I bought it, it has dbx vca's in it but I've never actually looked. Post if you find out more ok?

zmix

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #2 on: January 26, 2005, 05:00:36 AM »
I just got mine today, and I disassembled the entire thing to see what's what.
It's wired Pin3 hot, so yes certainly was a product of the US from the 1970s.

Funny about the 'poor man's dbX' idea, it really bears no resemblance to a DBX comp, from what I was able to discern. Looking over the PCB, it seems to be a FET limiter which uses a peak detector.

I used it today on a mix and thought "poor man's 1178". I did a quick comparison to my Dynamite (2) on overheads, and the MXR was fantastic.


All of the amplification is 5534s, and there is a very long TI chip called the TL336 CN. This seems to be the led meter driver.

I can't say. The board is a bit hard to trace.

It links really well.


Do you have a manual?

-CZ

mig27

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #3 on: January 26, 2005, 05:46:05 AM »
I can't help you guys with a schematic - sorry.

But also owning an MXR dual limiter, I can confirm how cool this box is.
Really snappy, great on percussive stuff.
Like a poor man's cross of a 160VU and an 1176.

Sleeper!

My 2 cents.


Michael

ggoerss

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #4 on: January 26, 2005, 05:46:29 AM »
i have a manual for this give me a day or 2 and i`ll scan it for you.

ggoerss

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #5 on: January 26, 2005, 05:59:43 AM »
Just found the manual and although there is only a block diagram it does have a tech description of its operation.The VCA uses switching devices operating at 250khz which are pulse width modulated to control gain..The pwm is proportional to the control voltage.As the input  signal level increases the control voltage willalso increase proportionally. this causes the pulse width to decrease and reduces the gain of the vca.

zmix

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #6 on: January 26, 2005, 06:14:57 AM »
Quote from: "ggoerss"
Just found the manual and although there is only a block diagram it does have a tech description of its operation.The VCA uses switching devices operating at 250khz which are pulse width modulated to control gain..The pwm is proportional to the control voltage.As the input  signal level increases the control voltage willalso increase proportionally. this causes the pulse width to decrease and reduces the gain of the vca.


That is fascinating. I couldn't identify any VCA, but there was a J108 on each channel.

The Cranesong uses a HF PWM controlling an FET, doesn't it?

Please do post that manual. Great thanks.

zmix

Crane Song Tracker and STC-8
« Reply #7 on: January 27, 2005, 01:06:49 PM »
PULSE WIDTH MODULATOR
Using Pulse-Width Modulation (PWM) to control an FET is what Crane Song uses in both the STC-8 and Trakker compressor / limiters. The technology has been around for about 20 years, having been used by several companies, including EMT. With modern technology, a PWM gain-control circuit can be very fast; from 0 to full gain reduction in 500 nS (0.0005 mS or 0.5 uS) and an audio frequency response to 60Khz or more.

PWM works as a gate, quickly switching the FET from "off" to "more-on" by varying the pulse-width. With careful selection of components and PC board layout it is possible to have very low control feed-through, a very low noise floor and an audio-path frequency response that does not vary with gain reduction. This type of circuit requires costly high-speed components and as a result, there is a fair amount of power consumption (it runs hot). Distortion is very low and does not change with gain reduction.

http://www.cranesong.com/compressorarticle.html

Rob Flinn

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #8 on: January 27, 2005, 07:20:33 PM »
Quote
quickly switching the FET from "off" to "more-on" by varying the pulse-width


I thought the FET is actually switched on or off.  The pulse width just determines how long it on & how long its off.  

There is no grey area the FET is completely chopping bits out of the signal, but at a much higher than audio frequency.  This is why with a bit of heavy filtering you can`t hear it.
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........

verbos

    NYC (where the latest fashions be)
  • Posts: 76
MXR DUAL LIMITER no.136 Schematic wanted
« Reply #9 on: January 27, 2005, 08:34:44 PM »
Quote from: "Rob Flinn"
Quote
quickly switching the FET from "off" to "more-on" by varying the pulse-width


I thought the FET is actually switched on or off.  The pulse width just determines how long it on & how long its off.  

There is no grey area the FET is completely chopping bits out of the signal, but at a much higher than audio frequency.  This is why with a bit of heavy filtering you can`t hear it.


that's right but it never fully attenuates the signal. The FET isn't able to do that, because of how it is configured. So either it is letting the signal through or is is letting the signal through attenuated, but never stopping it entirely.

mark


CJ

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #10 on: January 27, 2005, 10:21:58 PM »
DW Fearn now has a vacuum tube PWM compressor. I believe the side chain is solid state.
If I can't fix it, I can fix it so nobody else can!
Frank's- www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar- http://tdsl.duncanamps.com/schematics.php

zmix

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #11 on: January 30, 2005, 08:21:49 PM »
Hmmm... Is the 4016 used as the gain reduction element by switching it on and off using  the 250kHZ PWM signal?? Not the J108 I spied on the PCB?

kvintus

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #12 on: February 02, 2005, 05:10:32 PM »
The schematic can be bought here for 15$

http://www.schematicconnection.com/store/asp/prodtype.asp?prodtype=66&ph=cat

If someone buys it I could pay a couple of bucks to have a look at it. If no one wants to buy it I'll have to do it myself.

/Anders
...not perfect, but close enough for rock 'n' roll...

strangeandbouncy

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #13 on: February 02, 2005, 06:00:35 PM »
Zmix said -


    PULSE WIDTH MODULATOR
Using Pulse-Width Modulation (PWM) to control an FET is what Crane Song uses in both the STC-8 and Trakker compressor / limiters. The technology has been around for about 20 years, having been used by several companies, including EMT. (HOW DO YOU GUYS GET THOSE QUOTES? I;ll BE F@@ked IF I CAN FIND HOW!)

    The Pye compressor works the same way, I believe, and they are at least 30 years old . . . .


     MXR's ROCK! Especially drum/percussion sub-grps . . . . but Sssh! Don't tell everyone, or they will become outragiously expensive like everything else!

      Andy P
. . . . RUH ROH . . . . .

fum

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #14 on: February 02, 2005, 06:08:19 PM »
the quotes are by clicking on the quote button up top in the post window, typing or pasting what you want quoted, and then clicking on the quote button again.

once you see what it puts in when you click the quote button (open and close), you can just type that in yourself, if you'd like =)

ju

strangeandbouncy

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #15 on: February 02, 2005, 06:34:49 PM »
Quote from: "fum"
the quotes are by clicking on the quote button up top in the post window, typing or pasting what you want quoted, and then clicking on the quote button again.

once you see what it puts in when you click the quote button (open and close), you can just type that in yourself, if you'd like =)

ju


   Oh Yeah! Thats Cool :oops:  :oops:  :oops: that'll be the Quote button in the right hand top corner - DUH!!!!! Hgow did I miss that?

    Erm . . . . just one more thing, how do you attach photos(Jpegs) :oops:  :oops:  :oops:

   thanks Ju!
. . . . RUH ROH . . . . .

strangeandbouncy

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #16 on: February 02, 2005, 06:38:45 PM »
Thats still not right . . . . .everyone else's quotes are outlined in white . . . .
. . . . RUH ROH . . . . .

fum

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #17 on: February 02, 2005, 06:46:27 PM »
edit the above message, and insert a space after the ]  in quote] and a space after ] in[/quote]

images work the same way

Regards

ju

strangeandbouncy

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #18 on: February 02, 2005, 06:52:07 PM »
Fum,

    yet again, Thanks!

      Andy P
. . . . RUH ROH . . . . .

zmix

MXR DUAL LIMITER no.136 Schematic wanted
« Reply #19 on: February 02, 2005, 11:54:23 PM »
Quote from: "strangeandbouncy"
Zmix said -


    PULSE WIDTH MODULATOR
Using Pulse-Width Modulation (PWM) to control an FET is what Crane Song uses in both the STC-8 and Trakker. The technology has been around for about 20 years, having been used by several companies, including EMT.

    The Pye compressor works the same way, I believe, and they are at least 30 years old . . . .


     MXR's ROCK! Especially drum/percussion sub-grps . . . . but Sssh! Don't tell everyone, or they will become outragiously expensive like everything else!

      Andy P


Yes it's true. I paid $33 for mine last week on e-bay. I'll never sell it.
Also, I wouldn't want to spend $15 on a schemo...

The MXR is nearly 30 years old, too...FWIW


 

Related Topics

Subject / Started by Last post
Last post December 22, 2012, 06:47:34 AM
by evil grill
Last post August 12, 2004, 04:11:21 AM
by dramadisease
Last post October 15, 2007, 04:55:55 PM
by SSLtech
Last post April 10, 2013, 12:59:35 AM
by opacheco
Last post March 01, 2014, 03:30:25 AM
by Brizco