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

[samhay]

Will a charge pump do any good?
A max1044 voltage doubler specifically.
I searched the thread and can only find a mention of it from midwayfair early on but no follow up.
The IC and transistor datasheets will allow it but what other considerations should I be taking into account?
Thanks

http://www.diystompboxes.com/smfforum/index.php?topic=97123.msg912480#msg912480

[tombaker]

thanks sam

[merlinb]

Higher / bipolar rail voltages are not directly applicable to this circuit. It is optimised for 9V. With more voltage the circuit needs modifying to ensure the OTA can't be burnt out by excessive control current. The end result is that this doesn't really buy you any extra headroom, because you have to turn the gain up proportionally to get the same level of comrpession as with the stock 9V circuit. This might be suitable for studio applications, but not direct guitar use.

[tombaker]

Higher / bipolar rail voltages are not directly applicable to this circuit. It is optimised for 9V. With more voltage the circuit needs modifying to ensure the OTA can't be burnt out by excessive control current. The end result is that this doesn't really buy you any extra headroom, because you have to turn the gain up proportionally to get the same level of comrpession as with the stock 9V circuit. This might be suitable for studio applications, but not direct guitar use.

Hey Merlin,
Thanks for addressing that. I have the ET installed in a small DI box in front of a transformer and I use it between my soft synths and the FOH desk at live gigs.
It helps to keep the different synth/piano/organ patches closer in loudness and the transformer smooths out some of the nasty high frequencies from the computer.
But I still run it off a 9V onespot along with my guitar pedals.

[Cozybuilder]

Finally got around to finishing mine- thanks Merlin for a superb circuit design. This build uses 16mm Alpha pots, ¼ watt resistors (except the LED 22K), follows the original schematic.





Obligatory gut shot



What's under the card

[mth5044]

Nicely done! You are indeed a cozy builder. That's tight.

Merlin - I'm not familiar with studio type compressors and whatnot - what does a gain reduction meter indicate? A real time level of compression?

[duck_arse]

I see letraset, just as I remember it ^. nice work, cozy, I like the thumb-print.

[orangepit]

Wow, your pedal looks remarkably similar to mine:

[Cozybuilder]

@orangepit-
Real nice!

[orangepit]

Thanks. It's funny how we both envisioned our future pedals as yellow with a black thumbprint on it 

[merlinb]

I'm not familiar with studio type compressors and whatnot - what does a gain reduction meter indicate? A real time level of compression?

Yes, it shows by how much the signal has been squashed compared with what it would have been without the compressor working. It allows you to see when the compressor is actually doing something!

Cozybuilder- it's sooo tiny! 

[bloxstompboxes]

Gotta ask a dumb question here. I see there is a 10M resistor at the input going to gnd. It's in the usual pull-down position. Any reason why so high a value? i have none of these and neither does smallbear. I haven't wired this up yet as i need to order the NJM13600D. Seems a 1 meg would be fine. I went ahead and put in the largest I have, a 4.7M. Just wondering.

[samhay]

A 4M7 will work just fine as an input pulldown resistor.
I suspect that Merlin specs a 10M as it is an order of magnitude bigger than the input bias resistor. It can thus be largely ignored in determining the input impedance, which is ~ 1M - a fairly common modern standard.

[bloxstompboxes]

Kk, thanks Sam!

[wacko]

Here you go, a single-sided version:
https://dl.dropboxusercontent.com/u/57831278/115x60mm.bmp
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf

Are these still available? Dropbox says the file is not found

[merlinb]

https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf
Are these still available? Dropbox says the file is not found

I have fixed the PDF link, but I can't seem to find the bitmap at the moment...

[bloxstompboxes]

I have my own layout available if necessary. Might be larger and not as tidy, but it works.

[wacko]

https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf
Are these still available? Dropbox says the file is not found

I have fixed the PDF link, but I can't seem to find the bitmap at the moment...

That is great, thank you!!!

Was the bitmap the same black&white mask that's in the pdf?

[merlinb]

Was the bitmap the same black&white mask that's in the pdf?

Yes the very same.

[wacko]

Was the bitmap the same black&white mask that's in the pdf?

Yes the very same.

Thanks