etheory - a bunch of projects in progress

[etheory]

12 pos HPF filter, isnt it too much? 3/4 pos would be already cool... my 2 cents!

Sorry, you are quite right, what I should have said was that I'd calculated 12 distinct frequencies and the required resistors, so you COULD (and yes it would be massive overkill for a design like this) up to about 12 positions.
I just happened to have a large quantity of 12 position lorlins I was intending on using, but 3/4/6/12 would be perfectly acceptable also. It's up to you.

No iron there, it should be a cheap build, isn't it?

It should be definitely. The PCB's will be white, gold plated, quite thick and should be of excellent quality. So they won't be as cheap as the usual stuff, but yes, I would imagine this would be probably the cheapest compressor you could make depending on your chosen options. The PCB should support quite a few configurations. I want to try and make it as flexible as possible.

What about PSU, will there be an on-board power section?

Currently No. I was thinking most people would want to build two of these units, so it didn't seem as economically sound an idea to put a separate PSU on each one.
But I am open to suggestions. The low current draw should allow you to run a lot of these from even a modest PSU. My current implementation uses an off the shelf Jaycar plug pack, and the supply is as clean as you could want. It should be quite flexible as to what feeds it the +-15V power (which most people I would imagine already have access to).

Could you linked 2 units for stereo?

This design, whilst somewhat "expanded" from the original is still exceptionally simple. So unfortunately no, you can't.
I would imagine you'd just build two and use them on stereo material independently.
The next project I am already working on, the e273, based on the Siemens U273, will be a decidedly different, and more expensive animal, that will support such "normal" features.

But the e274 is largely a glorified passive diode bridge compressor, with clever makeup gain, some distortion/cv cancellation, and a curious "vintage" topology. It's far from  perfect, and I make no excuses for that, but it will be cheap, small, and simple to build, hopefully more so than any other compressor currently being offered.

I am completely open to suggestions however.

For instance, I'd considered adding a second PCB for the switch mounting. But there is a clear issue here. Poeple might not want rotary switches, as most controls COULD also be pots (I designed it to be flexible in that regard).

So is it better to open that up to the user, or provide a full kit with all of that? The issue then become me supplying people with all the options and them choosing one and throwing stuff out (wasteful).
I think the best option would be to allow people to wire the controls as they wish, without being limited to the PCB I supply. However this does slightly complicate construction for a beginner.

But again, I'm open to suggestion.

 

[evilcat]

You're right, let us wire as we wish, but rotary switch would be cool for recallability.
You say the circuit has a distortion cancellation section. That make me think to the Germanium Compressor of Chandler Limited which have a switch for disengaged this kind of circuit and make the compressor dirtier. Could it be possible (but above all usefull!!!) to have such option?

best,
ben

 

[etheory]

You say the circuit has a distortion cancellation section. That make me think to the Germanium Compressor of Chandler Limited which have a switch for disengaged this kind of circuit and make the compressor dirtier. Could it be possible (but above all usefull!!!) to have such option?

Hi evilcat!

Well.... I think it's best not to think of this design as anything other than a functioning cheap compressor based on an "old" topology. Discrete where it counts, and practical otherwise. I wanted to take a simple old circuit, bring it into 2013 with as close performance as possible to the original, and make it practical for the inexperienced DIYer to learn about the diode compressor topology.

It's DEFINITELY no Chandler Limited compressor.... not by a long shot. I designed it mostly to learn and to share with others my crazy pursuits and thorough testing procedures before I build bigger and better designs. Also it seems there is little to no information on the Siemens Sitral devices out there, but I am fascinated with them. I am still a beginner. I know a lot of stuff, but nowhere near as much as I need to be able to scale up to truly competitive designs.

When I refer to distortion cancellation what I really mean is CV dethumping (though it still lets a sizeable amount through compared to a "high-end" compressor - remember it's still an archaic design really) and some removal of ground-line noise that is induced during compression. I mean, disabling this mechanism would only increase susceptibility to picking up radio interference, line noise and transformer hum - not properties that you'd WANT to accentuate . Plus, it'll save you the cost of another switch!

So in this case, no. It's really a rather boring mechanism to remove ugly additions to the signal where possible.

 

[evilcat]

Ok, I understand.
So it's a lo-fi compressor for beginners. Could it be useful anyway? I've already done some 1176 revA, Mixbuzz and I have a 33609, TubeTech LCA2-b and some LA-4. I'd like to build something cheap, just for fun, but it have to be usable!!!

 

[etheory]

So it's a lo-fi compressor for beginners.

I like to think that the fact it's simple to build lends it well to beginners, sure, and inherently makes it "cost effective". But it's usefulness as a low fi compressor with some attitude is orthogonal to that. I always design and build things that I want to use myself. This project was definitely borne out of a personal want for the sound it now makes. So hopefully other people will also find it useful.

Could it be useful anyway?

Yes, of course! I will definitely be making use of a pair for my own material. I'd conjecture other people could find it equally as useful in their own arsenal.

I've already done some 1176 revA, Mixbuzz and I have a 33609, TubeTech LCA2-b and some LA-4. I'd like to build something cheap, just for fun, but it have to be usable!!!

You can't get much better an indication than sound samples. I've put up as many sound samples of the compressor action as I could. If you have material you want to hear it through I am more than happy to process it for your with whatever settings you want to hear, then you can make up your own mind if it's something you'd like to build or not.

I also have other projects under way that may or may not be more suitable for what you are after. But each will be designed and constructed and tweaked with the same care and attention to detail as this one. So it's up to you to choose what will work best for you. IMO this will work well as an effect processor, or a very nice compressor sound to add to drums or rhythmic/synth/bass material. I personally haven't liked it so far on clean vocal material, but on distorted vocal material it could also be awesome. Again, you could definitely find uses for it imo. I've also tried to outline its areas of weakeness throughout this thread, so if you'd like any more details, feel free to ask, I'm more than happy to answer, or find out, anything you need to know.

 

[etheory]

"Final" prototype PCB layout is close to being finished now. Taking my time on it to ensure it's as good as possible.
Hoping to have some time on Tuesday night to CNC the final prototype, and do some testing before sending the design off to be made professionally.

Will keep you guys updated but it's still moving....

 

[evilcat]

Thanks for the reply etheory. I love dirty compressor, so I guess I'll take 2 of them, or maybe more!!! Do you think I could put 4 of them in 2U, maybe 3U case ;D?

 

[etheory]

Judging on the current PCB size, which is less than 5cm x 15cm - it's probably going to be more like 5cm x 12cm or 5cm x 13cm, you could fit about 5-8 per 1U rack (it's VERY low, so you could probably even stack 2 on top of each other even within the 1U space....), if you were an absolute genius at mounting controls. The PCB is surprisingly small. Else 4-6 would fit quite comfortably, but 4 would be about as many controls as I'd want to deal with in one wiring session....

I'll be making some daughter boards for switch connections that might make that task a tad easier, however....

 

[etheory]

I really need to learn to finish things first, but I just can't help myself - I'm too damn inquisitive....

So the e274 PCB layout is close now. Really taking my time on this one to get it as nice as I can.

But last night I figured out what my next project will be.
Transformer balanced in and out jfet compressor with extremely low distortion and noise and a Fairchild 670 inspired side-chain and timing constants. More soon, but the initial simulations look exceptionally compelling.... Absolutely no feedthrough whatsoever (in a different league entirely to the e274) of the CV, and a stupidly fast attack time is possible. Seems I should be able to get as low as about 50-100 microseconds attack time with no issue with the current circuit I'm messing with. More soon....

This weekend I will do the final proto PCB CNC and testing for the e274 to put it to rest, finally.

 

[evilcat]

And what about your API 225L clone? It seemed interesting too.

 

[etheory]

Still going to do it, but it's quite a bit more complex than anything else I'm looking at for the moment, so I want to work on a few other things to get my skills back up to the point where I can finish it.

 

[etheory]

Rev 2 of the prototype CNC PCB is now done.
A large weekend cookup prevented progress, but for the food, it was well worth the delay ;-)

Here tis, ready to be populated. If it works within expected parameters, I'll be firing off the first professional PCB order within the week (they will be white, silk-screened and gold plated):

 

[Dylan W]

Did you decide whether building in a switch to select between diode types is feasible? (Or alternately a relay... not sure how critical trace length is in the sidechain.)

Also wondering whether it is possible to jerryrig your layout for an external sidechain. Your example at the end of the clip on electronic program material (and knowing that you're an electronic musician) makes me think this might be cool for making stuff pump

Dylan

 

[etheory]

Did you decide whether building in a switch to select between diode types is feasible? (Or alternately a relay... not sure how critical trace length is in the sidechain.)

Personally I didn't like the way the UC3611N sounded nor the zeners, I liked the more intense sound of the 1N4148 array.
Currently you could quite easily add a switch if you wanted, I'll have a think since it's still just a proto board, but, it's more complex than that, since, to stop oscillation, you'll need to also switch in different sidehcain feedback resistors. So in reality, it's just not worth the hassle. You could solder in a 8pin DIL, then push the diodes into that. Test, modify, then when you are happy, I was thinking an 8pin DIL diode daughter board would be useful, as it still allows the user to choose whatever they want. I might even change the sidechain 100R feedback resistor (it an oscillation stopper) for the side-chain to a 10K multiturn trimmer, so you can tune out the oscillation when switching diodes. I mean, imo you wouldn't want to switch diodes, like you wouldn't want to switch 2520 footprint DOA's in the middle of a recording. You can just stop, take off the lid, switch the diodes on a subboard and adjust the feedback trimmer. If that works for you, imo it seems like a better solution. What do you think?

Also wondering whether it is possible to jerryrig your layout for an external sidechain.

Yes, you probably could. I think it would be quite tricky however, as it would be a significant amount of extra circuitry to do it. You'd need a low impedance driver (I guess it's not that hard) to drive the side-chain. Also I'm not sure it's worth the hassle, and it would add to the expense of what's meant to be something cheap and simple. Also an external side-chain would turn it from a feedback to a feed forward compressor, as the input signal would no longer be related to the output signal (unless the side-chain input was a signal modified from the output of the compressor....). It's not really intended as an all purpose compressor.
But I'll have a think and let you know if it's something you think you'd use regularly.

Your example at the end of the clip on electronic program material (and knowing that you're an electronic musician) makes me think this might be cool for making stuff pump

Quite likely it could be, but having said, it pumps pretty crazily already ;-)

Thanks Dylan.

e

 

[Dylan W]

The daughterboard sounds like a great idea. For my intended use (parallel squashing on drum and effects sends) I like the sound of the UC3611N, at least in the clip you posted. Of course... I plan on testing both options, for science.

Was just spitballing with the sidechain thing... must have Daft Punk on the brain since their new record is dropping. Makes sense about FB/FF. This seems like a cool cheap project, and simplicity seems a worthy goal. I usually handle sidechained stuff ITB anyway.

Thanks for the in-depth reply.

 

[etheory]

Cool, in order to accomodate that, which makes sense, the final board, different from the v2 prototype, will have a 10K multi-turn trimmer for the side-chain feedback path, so you can "dial out" any appearance of oscillation, and also you can change the diode choices over with the 8pin DIL daughter boards.

Main difference with diodes that have a low-turn-on-voltage (i.e. schottky diodes) is that the requirement of a higher (around 6.2K, else it squeals loudly with a high-frequency wave like bat sonar) resistance in the side-chain path, limits attack time a little bit (the resistor limits the current flowing into the timing cap). But if you liked the way it sounded, then you liked the way it sounded, and you can't argue with that 8)

cheers.

L

 

[etheory]

Started to solder together the second prototype, looking good so far!
I'll post some pictures soon. Hopefully it works this time! ;-)

 

[etheory]

I found some time to solder up the second revision prototype, I'll test it tomorrow night.
I haven't put in the parts for the second balancing output stage yet, as I'd like to verify I fixed the feedback oscillation bug in the main amplifier stage that popped up in the previous version.

 

[opacheco]

I found some time to solder up the second revision prototype, I'll test it tomorrow night.
I haven't put in the parts for the second balancing output stage yet, as I'd like to verify I fixed the feedback oscillation bug in the main amplifier stage that popped up in the previous version.

etheory, what was the problem with these feedback oscilation??.....How did you fix them?

Opacheco.

 

[etheory]

In my first version I accidentally created a positive feedback loop around the first transistor stage instead of a negative feedback loop.
The simulator didn't pick it up, but when I built the first prototype CNC'ed PCB, it didn't work properly.

I then went back to breadboard, and fixed the issue (simply creating an inverting rather than non-inverting opamp feedback loop).

This new version incorporates all the fixes I verified on breadboard, so I don't foresee there will be any issues this time, but you never know until you turn it on! :