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DIY Stompboxes => Building your own stompbox => Topic started by: jonny.reckless on July 20, 2018, 05:13:43 PM

Title: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on July 20, 2018, 05:13:43 PM
I've been experimenting with using diode bridges in a compressor for a while. It's a very old school approach, but can be made to work really well, and it has a warm character to the tone which I really like. This is an original design, with a precision full wave rectifier feed-forward side-chain.

It's quite warm and characterful, but also can be set to be very transparent. It fits into a 1590BB.

Here is the circuit:
(https://s33.postimg.cc/w0wgi6yu3/Capture.png) (https://postimg.cc/image/w0wgi6yu3/)

Here it is in action:
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: GGBB on July 21, 2018, 06:21:40 PM
Is the dual-rail design necessary? In other words could you do this without the 1044 charge pump inverter as a single rail +9V design?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: pinkjimiphoton on July 21, 2018, 08:09:59 PM
that sounds great, jonny, really clear and a nice squish to it even with the video encoding.
if you end up getting boards burned, please let me know, i'd love to build one up to add to the arsenal.
i usually am not too crazy about compressors, but this one sounds really good, mate, well done!
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: noisette on July 24, 2018, 07:24:07 AM
Great post, thanks!
I have a lot studied diode bridge compressors/vcas but never finalized a circuit.
I like the sound of diode compression, I think its very distinct and well suited for electric guitar.
Is the dual-rail design necessary? In other words could you do this without the 1044 charge pump inverter as a single rail +9V design?
Is that a rhetorical/didactical question?
It could be (has been?) done, and maybe Ill try it, but always better finished than perfect, and telling from the vid, it sounds
already quite tight as it is!

EDIT you could rig it up with dual 9V batteries also, instead of the 1044 circuit...
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: GGBB on July 24, 2018, 08:31:37 AM
Is that a rhetorical/didactical question?

Not at all. The circuit would be simpler, cheaper, easier to build, and potentially have a smaller footprint without the charge pump (I won't use large boxes for pedalboard space reasons). Just wondering why the choice of the +9V/-7V dual rail design - does the circuit require that for some reason?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: noisette on July 24, 2018, 03:55:30 PM
Ah, ok. 
Well, it could surely be done with one 9V battery split to dual +4.5V/-4.5V.
Single supply is possible but unnecessarily complicated (for me anyway).

Examples of simple diode vcas are the KORG MS50 vca (and vcf).
http://machines.hyperreal.org/manufacturers/Korg/MS-synths/schematics/ms50filt.gif (http://machines.hyperreal.org/manufacturers/Korg/MS-synths/schematics/ms50filt.gif)

Examples of single supply diode compressors (HQ broadcast) check Siemens U273/U274
on this site:
http://audio.kubarth.com/rundfunk/index.cgi#u (http://audio.kubarth.com/rundfunk/index.cgi#u)

Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: GGBB on July 24, 2018, 07:47:15 PM
Ah, ok. 
Well, it could surely be done with one 9V battery split to dual +4.5V/-4.5V.
Single supply is possible but unnecessarily complicated (for me anyway).

Thanks. I was actually hoping for an answer from the OP since it's his design. The possibility of doing it obvious - I'd like to know if the designer thinks the circuit might function less well that way, and generally why he went with the extra complexity of the charge pump.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on July 27, 2018, 05:55:12 PM
Yes it's possible to use a single supply and a 4.5V virtual earth. I generally prefer not to. Symmetric circuits are easier to design. The extra headroom of split supplies helps. Mostly I can flood the top layer of the PCB with ground plane. In this case signal ground is real ground. Generally people use an 8 pin op amp for the mid rail so the component count and area are about the same.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: GGBB on July 27, 2018, 06:12:49 PM
Generally people use an 8 pin op amp for the mid rail so the component count and area are about the same.

Thanks. I guess by "people" you mean pro builders. Most DIY designs I come across don''t bother with that unless there happens to be a spare opamp anyway (an unused channel).

About headroom - are you boosting the circuit enough where this (split rail vs. single rail) makes a difference? Usually guitar signals are far below even what a +9V single rail opamp setup would provide as far as headroom is concerned. It doesn't look like your circuit is boosting a lot but I don't know it well enough.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on July 28, 2018, 01:54:38 AM
I think it would work ok if you wanted to modify the design for single rail operation. The issue I've seen in the past with this approach is that the virtual ground you get at 4.5V is never quite low impedance enough for transients, so it tends to bounce with respect to real ground. Depending on the circuit design this may or may not be a problem. In this circuit there aren't any fast edge transients into ground so I guess you'd get away with it. My first attempt at building the engineer's thumb on vero had a tendency to motorboat due to ground bounce. I got a roughly 1Hz thumping sound in the output until I really carefully strapped everything down with thick short wires and lots of decoupling caps.

I laid out a PCB for this, as seen in the video, which is a 2 layer design with ground plane on the top copper layer. It fits into a 1590BB. Let me know if you're interested in one.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: rankot on July 28, 2018, 03:09:41 AM
This is really interesting Jonny, going to my "to do list" :)
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: Eb7+9 on July 28, 2018, 03:07:26 PM
nice piece of design work Jonny ...

been looking for a solid diode based limiter design for a while now
congrats and thank-you
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: pinkjimiphoton on August 03, 2018, 05:53:50 PM
got my board today, jonny!! thanks mate!! will let ya know how it goes when i get a chance to get to it!
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: domestic-bliss on August 03, 2018, 06:37:17 PM
is this a follow on from the et redux? or a totaly different unit? i realy want to make a et redux :p you guys inspired me lol
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: pinkjimiphoton on August 04, 2018, 12:00:15 AM
hey jonny, total abject moron here obviously, but what the hell is sk3 and sk 4 for? ribbon wire? some kinda socket?
forgive me, but slightly confused. never seen this nomenclature before. thanks man!
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on August 04, 2018, 03:47:16 PM
hey jonny, total abject moron here obviously, but what the hell is sk3 and sk 4 for? ribbon wire? some kinda socket?
forgive me, but slightly confused. never seen this nomenclature before. thanks man!

Take a look at the video. They are for a standard 5x2 way 0.1" box header and 10 way IDC 0.05" pitch ribbon cable to the switch and sockets. You can pick up the parts or ready made cables on eBay.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F282084089830 (https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F282084089830)

You can wire it up with anything you like, I just use these because they're pretty cheap and convenient if you want to take the thing apart a lot.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on August 04, 2018, 03:51:59 PM
is this a follow on from the et redux? or a totaly different unit? i realy want to make a et redux :p you guys inspired me lol

This is a new original design. I also did the redux mods to the ET on a different thread.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on September 01, 2018, 03:59:43 PM
got my board today, jonny!! thanks mate!! will let ya know how it goes when i get a chance to get to it!
Did you get it built yet? Anything I can do to help?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: pinkjimiphoton on September 01, 2018, 05:48:52 PM
not yet, gig schedule has been pretty brutal lately. i will check in when i can bro!
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: R.G. on September 01, 2018, 10:18:59 PM
The diode modulator was a common thing in older RF design. Thomas Organ used a diode bridge modulator in the USA Vox amplifiers. It was a good tremo, very deep. The depth came from buffering the dry signal, inverting the modulated signal, then mixing to get cancellation. That let it go all the way to zero in some part of the sweep where the amplitude cancelled.

The bane of all diode modulators is that you have to work hard at keeping common mode signal out of the signal path, and that it's only a low distortion modulator with signals lower than about 25 to 50mV. Beyond that, the signal voltage swing starts changing the diode's equivalent resistance itself.

You don't have to use a bipolar supply, but it helps.

@ J.R.: since you're driving with a current, you might want to arrange to drive the top of the diode modulator with a voltage equal but opposite to the voltage at the bottom of the bridge. It will take some of the load off the differential amplifier to keep control signal feedthrough. Yeah, I know, diffamps are good, but no sense making the work harder than they have to.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on September 11, 2018, 12:39:11 AM
@ J.R.: since you're driving with a current, you might want to arrange to drive the top of the diode modulator with a voltage equal but opposite to the voltage at the bottom of the bridge. It will take some of the load off the differential amplifier to keep control signal feedthrough. Yeah, I know, diffamps are good, but no sense making the work harder than they have to.

That's an interesting suggestion. I was considering improving the diff amp by building a 3 op amp instrumentation amplifier or maybe even using an INA103, so both legs of the diode bridge see an infinite impedance load. Do you think balanced diode bridge drive would be superior to this approach? I guess I could go the full monty and do both :-)
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: PRR on September 11, 2018, 12:32:42 PM
20dB better balance in the modulator is worth 20dB better CMRR in the recovery stage.

Which choice leads to better performance or lower part-count, I do not know.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on September 12, 2018, 08:11:37 PM
Thanks, I am going to see what I can do to simplify the design a little and make it more DIY friendly.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: samhay on September 13, 2018, 02:42:24 PM
Thought I saw a revised schematic earlier that used BJTs?

In any case, you can get a pretty closely balanced (in terms of input impedance) diff amp using a single op-amp and I have got this to work  'close enough for rock and roll' in a couple of related designs. Most recent:

(https://i2.wp.com/samdump.files.wordpress.com/2018/04/diode_bias_tremolo_v2.jpg)

Thread: https://www.diystompboxes.com/smfforum/index.php?topic=119901.0
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: Ben N on September 14, 2018, 08:22:09 AM
Watching this thread. Cool design, Jonny, seems like a way superior alternative to Ross/MXR types, and very Strat friendly.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on September 28, 2018, 05:24:02 PM
I've prototyped using a discrete long tail pair as the differential gain stage. It's working quite nicely. I'll post more in a week or two when I've had chance to optimize and debug the design. I found I could get away without the negative supply which simplifies things a bit.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on October 01, 2018, 11:22:46 AM
Here is where I have got to with the revision B circuit. It's simpler than the original with fewer components. I also simplified the side-chain and replaced the time control with fixed attack and decay of 20ms and 200ms respectively. I'll post some clips of the sound when I get chance, but it's pretty sweet.

https://drive.google.com/open?id=1y6zuyUdH2dI2hWFurxAMeCIFM8huKZCV (https://drive.google.com/open?id=1y6zuyUdH2dI2hWFurxAMeCIFM8huKZCV)
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on October 07, 2018, 04:08:43 PM
I've finished developing revision B of the diode compressor. It's simpler, cheaper, has fewer components, and is easier to build than the revision A. It still sounds pretty sweet, but only has 2 controls now: sustain and volume. It's not quite as subtle and transparent as revision A, and has more of a pronounced "quack" at higher sustain settings.

Here is the revised schematic:
(https://i.postimg.cc/RJzxK55h/Capture.png) (https://postimg.cc/RJzxK55h)

Here it is in action. The video also has some photos of the PCB in the case:


Let me know if you would like a rev B PCB.

The music is from my band Saint Wry: https://open.spotify.com/album/76AYXUusxuLu0GiVGBQn6q (https://open.spotify.com/album/76AYXUusxuLu0GiVGBQn6q)

Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: Ben N on October 08, 2018, 02:43:03 AM
Nice squish, no pumping or other unpleasant artifacts that I can hear on the demo, but definitely "there"--not an always-on compressor. Well done, Jonny.

Def interested in a pcb. Is Israel doable?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on October 08, 2018, 11:06:52 AM
Nice squish, no pumping or other unpleasant artifacts that I can hear on the demo, but definitely "there"--not an always-on compressor.

If you would like a more transparent "always-on" compressor, I think the revision A design is slightly better in that regard. It's very transparent due to the full wave sidechain averaging.

I can post you a PCB of either revision. Message me your address and I will stick one in the mail. $5 plus postage, which I am guessing will be a few bucks to Israel.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: bartimaeus on October 26, 2018, 12:50:11 AM
(https://66.media.tumblr.com/763d4a0099ecc1006d79c3ef6f64d397/tumblr_ph6tbjBk9E1u8kzyzo1_640.jpg)

Thought I'd share a pic of my build of the REV C PCB! I'm really happy with how this turned out, it's exactly what I'd been wanting from the compressors I've been trying, plus anything else I could ever want. JUUUUUST barely fits into a 1590BB enclosure – the jacks are a super tight fit, but it's doable. There's even enough room in the front to cram in a 3PDT (or SPDT with a relay PCB), but I'm using it as an always-on compressor so I didn't bother. Maybe I should have gone for a 125-BB (smallbear makes them), but I'm happy. Extra switch is to toggle the treble boost option.

I really have to thank Jonny Reckless for this excellent compressor!
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: diffeq on October 26, 2018, 03:12:32 AM
(http://66.media.tumblr.com/763d4a0099ecc1006d79c3ef6f64d397/tumblr_ph6tbjBk9E1u8kzyzo1_640.jpg)

Thought I'd share a pic of my build of the REV C PCB! I'm really happy with how this turned out, it's exactly what I'd been wanting from the compressors I've been trying, plus anything else I could ever want. JUUUUUST barely fits into a 1590BB enclosure the jacks are a super tight fit, but it's doable. There's even enough room in the front to cram in a 3PDT (or SPDT with a relay PCB), but I'm using it as an always-on compressor so I didn't bother. Maybe I should have gone for a 125-BB (smallbear makes them), but I'm happy. Extra switch is to toggle the treble boost option.

I really have to thank Jonny Reckless for this excellent compressor!
Nice build!
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: rankot on October 26, 2018, 05:09:48 AM
Jonny, what's the difference between REV A (PCB I have) and REV C?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on October 29, 2018, 02:20:02 AM
Jonny, what's the difference between REV A (PCB I have) and REV C?

He's referring to issue C of the engineer's thumb redux.  BTW nice build, and let's not forget to credit Merlin B for his original design. You couldn't ask for a better starting point for mods. Although this is a different thread :-)

I've only done A and B of the diode compressor. Both have videos so you can compare the tone. Basically rev A is more transparent and rev B is more squishy.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: Ben N on February 13, 2019, 11:43:51 AM
Mine is awaiting some parts, but in the meantime I wish to thank you, Johnny, for keeping it (Rev B) simple in terms of parts. I think there is a total of two resistors in the whole shebang whose values are not multiples of ten, and precious few caps altogether. I think if I was wiring this up on perf, I would try to include some kind of jangle-box option, but a I'm not, I won't--unless you have a suggestion as to how this may be easily done without carving up your nice board.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: dschwartz on February 13, 2019, 12:52:44 PM
What about using a rectifier bridge instead of matching diodes?
I would think that the internal diodes if the bridge should be reasonably matched.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: pinkjimiphoton on February 13, 2019, 01:52:07 PM
been so caught up with work related projects, really lookin forward to the build!
thanks again mr. reckless! ;)
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on February 14, 2019, 03:19:37 AM
What about using a rectifier bridge instead of matching diodes?
I would think that the internal diodes if the bridge should be reasonably matched.

You could do that, but the dynamic impedance of a typical rectifier is going to be a lot lower than 1N4148s, so the transconductance of the sidechain would need to be modified to suit. I'm not sure how well rectifier diodes in a bridge rectifier are matched when only carrying milliamps. If you've got some lying around maybe see what the forward voltages are with a DMM?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on February 14, 2019, 03:26:20 AM
I think if I was wiring this up on perf, I would try to include some kind of jangle-box option, but a I'm not, I won't--unless you have a suggestion as to how this may be easily done without carving up your nice board.

What's a jangle box? I am guessing some compression / EQ hybrid? I've thought about adding pre-emphasis and de-emphasis filters around the compressor, so that the gain reduction is more balanced across the frequency spectrum rather than being defined primarily by the low end. I've experimented with a couple of graphic EQs in front and behind the compressor, but never really gotten to a sound I like. I did consider adding an insert into the side chain so you can do this sort of thing. You'd basically put a 1st order highpass filter in front of the sidechain so the compressor kind of "ignores" low frequency more. I think Joe Meek used this trick with compression in the 60s.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: Ben N on February 14, 2019, 04:19:07 AM
IIRC, the Marshall ED-1 has some kind of filtering in the sidechain for this purpose--which it calls "Emphasis"--although I'm not sure if it controls threshold or the amount of compression. As for the Janglebox concept, yeah it is some kind of treble emphasized compression, as exemplified by the onboard Rickenbacker compressor as used by Roger McGuinn back in the day. Somebody put out a commercial stompbox with than name, which was probably a slightly modded Dynacomp, and there have been a few discussions around here about implementing it as a mod.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: pinkjimiphoton on February 14, 2019, 10:22:20 AM
jang;enbox is an mxr dynacomp with a switch for the high end snubber in and out. noisier, but more of a treble boost . jim ....err... roger mcguinn does use them, or at least did endorsements for a while. but nothing as cool as an extra eq or treble boost circuit, just undoing one component on the mxr.
i believe the second series may have been a slightly different circuit with a couple more options.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: Ben N on June 13, 2019, 09:08:38 AM
Just want to report that my Reckless Comp (Rev B) on pcb supplied by Jonny is at long last done, and it is instantly my "main squeeze" for clean, better sounding and quieter than my old Dyna even at high compression settings. Loves a Strat. Sorry no pics, both because my phone camera died, and because I butchered the pretty powder coating on my 125B (tight fit with top mounted jacks) with a runaway drill bit. Eventually I'll figure out a way to rehab the finish, but in the meantime I'm playing it, and loving it. Thanks, Jonny.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: andy-h-h on June 27, 2019, 12:18:56 AM
I just made a vero for the Rev 4B if anyone is interested.   Sitting over on Guitar FX Layouts in the forum (unverified section).   It does however work, as I just finished making one.
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on June 27, 2019, 02:51:54 AM
I couldn't find the layout - can you post a link please?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: andy-h-h on June 27, 2019, 04:32:04 AM
Sure - hope you don't mind me making the vero.  I did credit you  :icon_biggrin:

http://guitar-fx-layouts.42897.x6.nabble.com/file/n46845/Reckless_Diode_Compressor_Rev_B4.png


(https://i.postimg.cc/TynTpDWq/Reckless-Diode-Compressor-Rev-B4.png) (https://postimg.cc/TynTpDWq)
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: snk on June 27, 2019, 08:45:10 AM
Thank you, Andy.
Is this design a "typical guitar comp" (aiming at long sustain), or can it be used like a "regular" eq ?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: andy-h-h on June 27, 2019, 08:56:14 AM
Thank you, Andy.
Is this design a "typical guitar comp" (aiming at long sustain), or can it be used like a "regular" eq ?

This is definitely not EQ, and for the record, it's not my design.  I just did a vero layout for Jonny's design as I liked the sound of the demo.  If you want EQ, try a preamp of some description.   :icon_smile:
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: snk on June 27, 2019, 09:33:13 AM
Oops, sorry, the last word was definitively a mistake on my side  :icon_redface:
I meant : "is this designed as a "guitar comp" (aimed at increasing sustain, with a limited bandwidth), or can it be used like a "regular studio comp" on bass, drums, full mixes, etc. (if we add pots for attack and relase) ?
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: andy-h-h on June 27, 2019, 05:39:25 PM
Hey snk,

It was designed by Jonny Reckless for guitar, and while I have not tried it on anything other than guitar as I only built one yesterday, I'm guessing it will not be very effective on drums / vocals etc.

Reason being - If you try to use this as an insert on a channel, or plug anything other than a guitar or bass into this, you will most likely run into level and impedance issues.  Running at 9v restricts dynamic range too.

If you want something for studio work, I'd say run with proper rack-mount gear or some nice plugins.  :icon_wink:  As far as studio grade compressors go, I'm yet to find a cheap way of getting there. 
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: jonny.reckless on June 28, 2019, 12:21:33 PM
I doubt it would be much good as a studio compressor. Typically you would want separate controls for threshold, ratio, attack and release, and some way of doing stereo linking of the sidechain for studio use. It was designed specifically for electric guitar, although I have tested it with bass and acoustic guitar and it works pretty well for those purposes. There is no EQ - the circuit has a flat frequency response. It's a feed-forward architecture with a peak detecting sidechain.

I just thought it would be fun to see if I could make a diode compressor actually work  :icon_cool:
Title: Re: Reckless compressor - an original feed-forward diode based compressor
Post by: roseblood11 on June 28, 2019, 02:35:09 PM
The  "THAT Jam" is much closer to a studio compressor: https://www.uk-electronic.de/onlineshop/product_info.php?products_id=2945