New compressor project

[free electron]

Hello!
I've just posted a new DIY project on my site:

Tadek the Compressor

It is a nice sounding, easy to build (no internal adjustments necesseary!) TDA7052A based compressor for guitar or bass. Offers rather gentle and elegant compression type. I really like it with my 5 string bass, i find it even better sounding than more advanced THAT4301 based compressor.
The idea was triggered by an article in Elektor but after breadboarding their version i decided to design a completely new compressor from scratch using all the advantages TDA7052A offers.
Because the VolumeControl input is biased at about 1V, the use of LM358 as IC3 is crucial. The other half of  IC3 is used to drive an LED gain reduction indicator. Really handy feature while setting up the compression parameters.

It is difficult to show the operation of a compressor pedal in sound samples, especially not a "squashy" one. Nevertheless i tried it in this video:

No fancy parts, all thru hole. The pcb is in fact a single layer one. I have a plenty of double sided material rest-offs which i wanted to use.

Why the name? Tadek is a common polish name, sometimes used in Poland as a nickname for different TDA chips

Hope you like it!

Piotr

[cacarver]

I love it.  Sounds great especially when played through bass.

[Processaurus]

Thanks so much for sharing your design Piotr, that sounds nice.  Great to have a something new to try, as the world of DIY compressor stompboxes has been confined to a few classic, but very limited and lo-fi designs, when compared to what you get in a rack.

That's neat you were experimenting with the THAT chip, did you use a design out of their app notes? 

Would you recommend the TDA chip as a general purpose VCA for other pedal projects? How do you find its noise performance?

[free electron]

The THAT comp i built is a part of bass recording preamp - typical "fender" type two triode stages with a tonestack in between, followed by almost identical to THAT4301 app note compressor. I had one opamp free, so i decided to put a tilt EQ in front of the sidechain. I need to play more with its center freq, because for now the impact on the sound is, well, not really worth having one additional knob for it
The TDA7052A chip is very nice to work with, i haven't done any more scientific noise measurements, just tried the pedal in front of crunch and lead channel of my amp. The increase of noise is there and will be, as with any other active stage followed by huge gain. But this increase is not drastic and in my opinion really acceptable. The compressor used with clean channel is very quiet.
What really helps to keep the noise floor down is proper driving of the input, low impedance source and enough amplitude to keep a good s/n ratio. That's why i included the InputGain control in the cricuit.
The volume control input is quite sensitive, the best results i got when it was driven directly from low impedance output. The envelope curve needed to be scaled down, DC bias at about 0.9..1V - pefrect job for an LM358.
I think this chip has a huge DIY potential. I already have an idea for a 7052A based tremolo pedal.

And here's a chart showing the gain curves at minimum and maximum compression ratio: