Marshall - ED-1 Compressor  [schematic]

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Post by phatt »

Valve Head wrote:C16 (.01) is across pins 4 and 8 of IC1, C17 (.01) is across pins 4 and 7 of IC2 - for maximum RF rejection I guess?

The ED-1 and the other pedals in Marshall's metal beetle series use something that they describe as "passive bypass", but it's not even close to true bypass. Definite tone-suck.
Maybe we could use the inbuilt DPDT switch to make something like Jack Orman's Millenium bypass, which would make these pedals really kick arse.
Nup ,, No tone suck,, unless you are chasing the 27th harmonic of the 49th fret 8)

It's all in front of a buffer and dat'z it's whole purpose, to *isolate* it.

I do own an Ed1 and except for changing R19 (the 10k before level out) mine is stock.
This makes the level pot far less sensitive.

I have also been testing some comp circuits and here is what I've found so far.

If you want to change the *Comp Depth*, double up the diodes (D2,3) or add a switch and flip between say a pair of leds and diodes. that will give you a soft /hard Effect.

Also the *Release Time* can be altered by changing C15 (10uF). hangs off the base of Q5.
all subtle stuff but interesting.
Cheers, Phil.

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Post by roseblood11 »

phatt wrote: Nup ,, No tone suck,, unless you are chasing the 27th harmonic of the 49th fret 8)
Sorry, that´s definitely not true. I just made an A/B comparison with the ED-1 in my true bypass looper. If the pedal is in the signal chain, there´s an audible loss of transparency and treble.
But off course that´s only the case if the guitars high impedance signal goes directly into the ED-1. If you use a guitar with active pickups/electronics, or if you have a pedal with buffered bypass before the ED-1, little Edward won´t suck tone.

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Post by Valve Head »

roseblood11: improving the bypass in the stereo output pedals will be a real challenge. Anyone make a 4PDT footswitch?
Is the loss of treble you are noticeing due to a loading effect on very high output humbuckers, or are you using single coil p-ups?

phatt: thanks for the mod ideas. I used to like my ED-1 much more than I do now, so maybe it's not working properly.
Anyhow, that's a good excuse to dismantle it and tweek.

These pedals use very high input resistances and J202 JFET buffers, so they should be pretty transparent alright.

I will keep an open mind about TB or not TB, and test the JFETs to make sure they're working properly first up.

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Post by phatt »

roseblood11 wrote:
phatt wrote: Nup ,, No tone suck,, unless you are chasing the 27th harmonic of the 49th fret 8)
Sorry, that´s definitely not true. I just made an A/B comparison with the ED-1 in my true bypass looper. If the pedal is in the signal chain, there´s an audible loss of transparency and treble.
But off course that´s only the case if the guitars high impedance signal goes directly into the ED-1. If you use a guitar with active pickups/electronics, or if you have a pedal with buffered bypass before the ED-1, little Edward won´t suck tone.
Yes well it would pay me to read the schematic before I waffle on,, :oops: whoops my mistake.
Yep there is a small cap across the line and this would wipe a little treble with a passive PU setup while in bypass mode.

Not really apparent with my setup as my treble is slammed shut at about 5kHz but thru another amp and using headphones you can hear the loss.
I don't have the modern guitar player dilema because I don't actually want the treble response, way to harsh to my ears.

IME, the gear used today actually hinders progress rather than enhance it simply because the bandwidth of guitar amplification systems now is far to wide.

But hey if it bothers you then easy fix,, cut the cap off the board.
You could put it after the switch to help wipe excess hiss when the unit is on.
Cheers, Phil.

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Post by roseblood11 »

I don´t think that the cap causes the tonesucking. It´s only 47pF. I guess it´s the fact that the rest of the circuit is wired permanetly to the inputsignal...

btw: I don´t play modern "hifi-guitar", I just play a simple strat through a Fender Amp, and I like sparkling clean sounds. The kind of sounds that Leo liked when he invented the whole crap, I guess... :wink:

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Post by phatt »

Valve Head wrote:roseblood11: improving the bypass in the stereo output pedals will be a real challenge. Anyone make a 4PDT footswitch?
Is the loss of treble you are noticeing due to a loading effect on very high output humbuckers, or are you using single coil p-ups?

phatt: thanks for the mod ideas. I used to like my ED-1 much more than I do now, so maybe it's not working properly.
Anyhow, that's a good excuse to dismantle it and tweek.

These pedals use very high input resistances and J202 JFET buffers, so they should be pretty transparent alright.

I will keep an open mind about TB or not TB, and test the JFETs to make sure they're working properly first up.
Hi VHead,
My issue with compressor circuits is the noise they tend to induce hence I've been tweeking some test circuits but the ED came up S/hand for a price I could not refuse so I'll work with it for now.
I had some bad experiences with a CS2 many years ago and it's the noise in most of these stomp type circuts which is the main reason why I've always steered clear of using them but recently I heard some good sounds when used *in front* of a distortion unit so thought I'd re-visit the idea.

Be warned with the sustain (which is just max gain it returns to after compression) full up the output level on the ED is un-useabe past 2, Hence the very first mod to R15 which makes it a little easier to control the dreaded hiss they produce.
I blew the test circuits lm3080 chip while messing around so if I find another one I'll have another crack at getting the noise down to a sane level,, if it's at all possible.
meantime I'll leave the ED alone.

Not that I'm an expert but my guess is the studio rack units may have far better circuits to circumvent this niose problem so it must be doable and it would be nice to have a better pedal unit.
Phil.

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Post by roseblood11 »

Studio compressor aren´t build around the old 3080, they run at much higher supply voltage and they use some better parts...
Better opamps reduce the noise a bit in the ED-1, but not much.

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Post by mictester »

roseblood11 wrote:Studio compressor aren´t build around the old 3080, they run at much higher supply voltage and they use some better parts...
Better opamps reduce the noise a bit in the ED-1, but not much.
Exactly right. The 3080 was a poor choice for audio, and tended to be noisy. The BA6110 was better, but is difficult to get hold of. I prefer my transconductance amps in the negative feedback loop of an op-amp - this goes a long way to mitigating the noise and distortion they introduce. The "Pearl" Sustainer was another take on this, using the 3080 to vary the gain of a FET stage.

I've spent a lot of time experimenting with different gain control circuits, and have come to the conclusion that the Vactrol is hard to beat for guitars! I've been experimenting with them to vary the feedback of op-amps and have got some very good results. The response time can be an issue, but the "natural" attack of each note sounds better than something that's squashed flat!

Another approach is the PWM-controlled analogue switch, and this can give very low noise and distortion, though requires good filtering to prevent high frequency clock noise escaping to interfere with other HF-clock operated effects. More to follow soon on this, when I'm happy with the level-sensing circuitry.
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Post by Valve Head »

I decided to play around with the RF bleeder cap C1 on the input; there is a noticeable improvement in tone both bypassed and with compressor on by reducing the value of C1.
I tried values from 3.3pf to 33 pf, and have settled on 10 pf as my fave.

The bypass now seems to have no noticeable treble loss using Strat & Tele-style single coils, and vintage-style humbuckers. Give this a try - it might be a simple (and cheap) improvement for you too.

Hopefully, the ferrite RF bleeder network will keep the nasty interferences away! So far so good.

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Post by roseblood11 »

Why don´t you remove the cap completely? I don´t think that it´s really needed. I guess they use the same design for the complete series of pedals and that cap might be more important in the high gain distortion pedals?
But I can´t understand how a 47pF cap could be the reason for the tonesucking. A 1 meter guitar cable often has a capacity of 100 to 120pF, the lowest value I ever measured was 85pF per meter...

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Post by Valve Head »

Maybe it's something to do with the ferrite network as well as the capacitance and large value resistors.
IIRC the 47pf (or 10pf in my case) C1 is effectively parallelled with R1 (10M) and R6 (2.2M), and forms an LRC network shunting high frequencies to ground - a low pass filter.

Someone with more elec. engineering knowledge than me could do the math and establish the -3db point.
I'm happy to try different capacitor values, or try any other ideas that might work.

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Post by phatt »

roseblood11 wrote:Why don´t you remove the cap completely? I don´t think that it´s really needed. I guess they use the same design for the complete series of pedals and that cap might be more important in the high gain distortion pedals?
But I can´t understand how a 47pF cap could be the reason for the tonesucking. A 1 meter guitar cable often has a capacity of 100 to 120pF, the lowest value I ever measured was 85pF per meter...
Yes but a guitar cord does not have an inductor hung off either end. :shock:
This is an LCL setup, L's in series and C to ground.
Phil.

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Post by phatt »

mictester wrote:
roseblood11 wrote:Studio compressor aren´t build around the old 3080, they run at much higher supply voltage and they use some better parts...
Better opamps reduce the noise a bit in the ED-1, but not much.
Exactly right. The 3080 was a poor choice for audio, and tended to be noisy. The BA6110 was better, but is difficult to get hold of. I prefer my transconductance amps in the negative feedback loop of an op-amp - this goes a long way to mitigating the noise and distortion they introduce. The "Pearl" Sustainer was another take on this, using the 3080 to vary the gain of a FET stage.

I've spent a lot of time experimenting with different gain control circuits, and have come to the conclusion that the Vactrol is hard to beat for guitars! I've been experimenting with them to vary the feedback of op-amps and have got some very good results. The response time can be an issue, but the "natural" attack of each note sounds better than something that's squashed flat!

Another approach is the PWM-controlled analogue switch, and this can give very low noise and distortion, though requires good filtering to prevent high frequency clock noise escaping to interfere with other HF-clock operated effects. More to follow soon on this, when I'm happy with the level-sensing circuitry.
Hi mic,
Can I assume the *Pearl circuit* is a better mouse trap? (less noisey)
I don't wish to embark on lunar module compressor build,, just improve on the basic pedal concept.
What about a CS3,, any better than CS2?
thanks, Phil.

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Post by mictester »

phatt wrote:Hi mic,
Can I assume the *Pearl circuit* is a better mouse trap? (less noisey)
I don't wish to embark on lunar module compressor build,, just improve on the basic pedal concept.
What about a CS3,, any better than CS2?
thanks, Phil.
The Pearl circuit was just another way of implementing a gain control stage, and was a bit less noisy, and much less distorted.

The other approach that I really like is to use the transconductance amp (OTA) in the negative feedback loop of an op-amp. This minimises the ill effects of the poor OTA, and allows the gain cell to benefit from the quality available from the op-amp.

Look at the Morley (Tel-Ray) compressor that uses a 3080 and a TL074. It's simple, but very effective. Also have a look at the (somewhat rare) MXR Sustain Unit - not the Dynacomp. Again, the OTA provides the negative feedback for a TL072 op-amp. MXR's transistorised rectifier was a bit "over the top" in the Sustain Unit, but it worked really well.

The only downside to this configuration is the more limited range of control available, but the smooth control and the low noise and distortion go a long way to mitigating the problems. You can cascade the gain cells for much more control, and I've done this in a commercial product for the broadcast industry. The sequential gain cells were so effective that it wasn't really necessary to use overshoot prevention clippers (with all the distortion they introduce).
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Post by phatt »

Hello Mic,
Thankyou heaps all very helpful. :thumbsup
I can't find any schematics for the Tel-Ray or the MXR sustain but I'll keep searching.

I have placed an order for a few LM3080 chips as I would really like to try the Pearl circuit.
The Ed Comp hiss is just bearable by changing the series resistor just before output from 10k to 47k.
I don't wish to play around with a working pedal to much so I'll have to wait until the parts come in.
Phil.

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Post by phatt »

roseblood11 wrote:I don´t think that the cap causes the tonesucking. It´s only 47pF. I guess it´s the fact that the rest of the circuit is wired permanetly to the inputsignal...

btw: I don´t play modern "hifi-guitar", I just play a simple strat through a Fender Amp, and I like sparkling clean sounds. The kind of sounds that Leo liked when he invented the whole crap, I guess... :wink:
I removed the Cap while it was apart and Yes does make a difference. Remember it's an LCL with C to ground forming a T circuit.
What puzzles me is that there is still some very high freq loss with Cap removed which I assume is the series L affecting it but heck that freq will never be heard in a live venue,, so good enough for me.

Just a note; An opamp wired as per the first Ed stage *without the LCL* should AFAIK have Zilch affect on the signal.
If that was not the case then every mixing desk (where these ideas are often used to *Isolate*) would have major problems :lol:
Phil.

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Post by Tonetweaker »

mictester wrote:Also have a look at the (somewhat rare) MXR Sustain Unit - not the Dynacomp. Again, the OTA provides the negative feedback for a TL072 op-amp. MXR's transistorised rectifier was a bit "over the top" in the Sustain Unit, but it worked really well.
phatt wrote:Hello Mic,
Thankyou heaps all very helpful. :thumbsup
I can't find any schematics for the Tel-Ray or the MXR sustain but I'll keep searching.
I just stumbled into this thread when searching for the MXR Sustain. I just checked and I don't have a schematic for it... but I've got the next best thing... I just bought an MXR Sustain from SniperCentral the other day. Came in the mail today along with a literal pile of other pedals and my new Epi LP. I was so busy playing with the guitar, I was going to leave the pedals for tomorrow... but I'll take some gutshots and start a new thread to avoid completely hijacking this one.

I did have a schematic for the Morley/TelRay Pro Compressor. Here it is...
morley pro compressor.pdf
(255.02 KiB) Downloaded 358 times
Here is the Morley/TelRay Volume/Compressor for comparison...
morley pro compressor.pdf
(255.02 KiB) Downloaded 358 times
I hope they help in the discussion. :D


Cheers...
Steve
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Post by Tonetweaker »

Apologies... I accidentally posted the first schematic inline twice, and then attached the Vol/Compressor as a separate attachment at the end, but they're both there for reference.
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Post by roseblood11 »

Thanx !

Would be great if you could start a retracing thread for the MXR Sustain and post good photos of both sides of the pcb.

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Post by phatt »

Tonetweaker wrote:Apologies... I accidentally posted the first schematic inline twice, and then attached the Vol/Compressor as a separate attachment at the end, but they're both there for reference.
No need to apoligize I'll download it twice to make up for the good work you did. :D

Bin playin around with the *EH Black finger* but it's a split supply,, Grrr.
Not to worry all good practice for my ever expanding electronic skills. :blackeye

I've at least made headway with the Bfinger as it's been tweaked down to a very low noise level and I'm happy with it,,
But I will certainly take these schematics and see how they all stack up.

For me it's not about making the worlds greatest Comp circuit I simply want more sustain without the dreaded hiss that comes with most of them pedal types.

Having purchased a stock ED (Marshall Comp) and being able to improve it's usrless noise issue by just changing 2 things then I feel there is hope for a better pedal sustain unit.
So if the worlds longest sustain comes with 10 times noise then I'll give up but I have a hunch that there is a circuit out there waiting for me.

Grin,, Cheers Phil.

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