THE ENGINEER'S THUMB... At last, a better compressor!

[thehallofshields]

Would it be possible to add a switch for Feedback Compression? You know, to have a mode to get the Orange-Squeeze pumping effect? 

[garcho]

if there are settings on existing pots that create the effect you desire, you can always hard wire them to a 3PDT switch for a quick switched dial-in.

[merlinb]

Would it be possible to add a switch for Feedback Compression? You know, to have a mode to get the Orange-Squeeze pumping effect? 

In principle yes, although I haven't tried it.

[rankot]

Another take on combining the best Engineer's Thumb Compressor with Fencepost Noise Gate. I think this is better than the first schematics:

[kristopher612]

Hey everyone, i just finished this on Merlin's original 2 knob PCB, and i'd just like to check my voltages against a known working ET.  i haven't put in a bypass switch, so the issue is i'm not easily able to tell that  it's working.  these voltages were taken with a 1 spot PS.
Modifications: i omitted the millennium bypass portion.  i also put in a 100k attack control and a 100k resistor+500k release control.  i'm pretty sure it works, but i'd just like to verify since i haven't wired a switch up yet. thanks for any help you can give!

Q1 (2N3906)
1 - 4.33
2 - 3.7
3 - 1.3

U1
1 - 4.67
2 - 4.66
3 - 4.24
4 - 0
5 - 4.24
6 - 4.67
7 - 4.92
8 - 9.39

U2
1 - 3.8
2 - 4.41
3 - 4.2
4 - 0
5 - 4.67
6 - 4.67
7 - 4.67
8 - 9.39

U3
1 - 1.29
2 - 0
3 - 4.68
4 - 4.68
5 - 4.68
6 - 0
7 - 0
8 - 0.008
9 - 0
10 - 0
11 - 9.39
12 - 0
13 - 0
14 - 0
15 - 0
16 - 0

[kristopher612]

I have a quick update on my build. I was playing through it, and it started making a rustling sound, turns out I had some cold joints around the socket for the 13700, so I reflowed the solder. Now I've got definite squish once I raise the compression ratio, and the attack and release controls are doing their jobs accordingly. I may get a few smaller log taper pots for the attack control and see if I get more usable range out of it.
All that said, thank you Merlin for a great project. I haven't owned a compressor in years and this was a fantastic way to fill that hole.


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[vefaerdem]

Any chance to have schematic for 5 knobs version with noise reduction meter leds again? It seems all the docs shared on this forum are outdated and unavailable.

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[rankot]

Here they are:





I have built this version with LED indicator and it didn't behave as expected.



I didn't try this one with meter, maybe it works fine?

[287m]

Any chance to have schematic for 5 knobs version with noise reduction meter leds again? It seems all the docs shared on this forum are outdated and unavailable.

GM 5 Plus cihazımdan Tapatalk kullanılarak gönderildi

this?
and welcome

[vefaerdem]

Any chance to have schematic for 5 knobs version with noise reduction meter leds again? It seems all the docs shared on this forum are outdated and unavailable.

GM 5 Plus cihazımdan Tapatalk kullanılarak gönderildi

this?
and welcome

Oh, a pcb layout in a vector file format, that's awesome ) thank you mate!

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[BetterOffShred]

It's becoming abundantly clear to me that I need to take the plunge and start etching some PCB's.   Ring Stinger, This, That Jok3rX high gain thingy..  A lot of cool PCB's to etch..

[effexfreek]

   In the spirit of Jonny.Reckless' mods (FET, NE5534 & VCA "paralleling"), any other low-noise opamps able to be used/substituted for the TL072 in the audio path, for further noise reduction ?

   There's a couple I can get real cheap at a near-by surplus shop (they even have old SSM2017s, a buck-a-piece !) :


-OP27                                    noise : 3 nV/"Hz
-I have some LM4562 (dual)    noise : 2.7 nV/"Hz
-I might order some AD797      noise : 0.9 nV/"Hz (used in the Forrest Green comp, I reckon... oh : $18 !)
-LT1115, maybe ?                    noise : 0.9 nV/"Hz as well (but way cheaper at $6)
-any other ? (money's no object : the way I see it, even a $20 chip would be worth it, in my Quest for the Holy-Grail Noiseless, Endless, Extreme Compression DIY pedal ! )


TIA !

[PRR]

Welcome.

There's always hiss.

We say the limiter "turns down the loud parts", but in fact we always use it to turn up the soft parts.

Including the hiss.

The guitar hisses.

Hiss is not just voltage hiss. At guitar impedance, current noise also matters significantly.

The TL072 is very nearly as low-hiss as a guitar's self-hiss impedance. You can do a little better. Not a lot.

You will generally be looking for FET input. Bipolar input tends to be too much hiss current. If not, then the input is so starved the voltage hiss comes up. I know there is a "better FET input" chip, but don't recall its name.

[effexfreek]

Thanks PRR !


   Yeah, I know  : chasing after noise is sort of a  pointless endeavour in the world of RAWK guitar ; but, I love the Engineer's Thumb sooooo much, 'though : can't blame a guy for trying.

   I'd die for a real lush, chorused & heavily compressed chord, to slooowlyyy fade into... pure silence ! (there's a volume knob for that, I know...  )

   And : I'm also looking into DIY very-low-impedance pick-up (I built a prototype flat-mount, 1mm thin, stealth over-bridge-pu/under-pu-cover, 35 Ohm hex pu, needing preamps & nearly-silent, heavy compression for well...  Belew-esque experimental extravaganza ! Looking at CYC-FI schematics for the moment...)


Anyways, whenever you recall the opamp number : i'm all ears !

[effexfreek]

Paul,

   Were you thinking of AD743/AD745 by any chance ? Lowest noise BiFET inputs opamp I can find, so far : 2.9nV/rootHz...

   I was doing some reading : how 'bout "paralleling" 4 opamps, for 1/2 the noise ? (Or 8 ! Go big or go home, I say ! ) I'd go with 4 parallel LT1115 (o.9nV/rootHz-$6 a-piece) using Jonny.Reckless's 2N5457 "buffer" in front, for a "theoretical" noise contribution of 0.45nV/rootHz ? Does this make any sense ?

   It'd be worth the $24 to me, fer sheeeur... if : it works, that is...

[PRR]

The resistance of a gitar in the hiss band is near 20K.

In a 20KHz bandwidth, that is about 2uV.

2.9nV/rootHz over 20KHz is about 0.4uV.

Try them all. You can do a bit better than TL072. I submit you can't do a "lot" better, the guitar self-hiss dominates.

Turn down the amp, strum harder.

[digi2t]

Turn down the amp, strum harder.

And there folks... is my new sig line. 

Thanks Paul!

[garcho]

are you building a guitar pedal for stage? or a rack unit for the studio? if it's for stage, forget about hi-fi hiss concerns, especially if you play with a drummer who uses cymbals. if you have a house gig at Orchestra Hall and they're micing you with a pair of $10,000 Schepps or something, ok, then bring your rack gear, leave the pedals at home. If you're building recording gear, just build an SSL clone or something. gonna find a low noise OTA?

any other low-noise opamps able to be used/substituted for the TL072 in the audio path, for further noise reduction ?

that matters for mic pres, for instance, basically doesn't matter for guitar stuff, like what Paul said. if you ever get a chance to look in a top shelf console, check out the op amps, you might be shocked

[brett]

For less noise.... lower that 10M pull-down resistor at the input to 220k. You'll lose those 100kHz highs that bats and dolphins love but I doubt you'll miss them.
(and yes, I do know that the input impedance is already much less than 10M)

[merlinb]

For less noise.... lower that 10M pull-down resistor at the input to 220k.

No no no, that will increase noise i.e. worsen the signal to noise ratio!