So, when I was a kid learning how to play guitar, write songs and be in a band I used to dream of recording in hi-tech, expensive, recording studios while I tinkered around with my Fostex X-18 4 track. Having done a bit of that I slowly came to realise that the best music isn't always created and recorded in such state of the art environments and so at the ripe old age of forty COUGH COUGH COUGH, I've decided to get the band back together again and record something low tech and low budget but with enough energy and attitude to compensate for its sonic shortcomings, if my back will hold out long enough, that is.
The reason for this preamble is that one of the pieces of kit that I've decided I can't do this without is a compressor, hence my trawling the interweb tonight for a cheap quad comp that will enable me to compress overheads and bass guitar etc... The cheapest I could find was a second hand Samson for £80, which seemed like a decent enough piece of kit for the money but which then got me thinking, is that cheap and nasty enough and could I build four compressor circuits for less than £80?
My first thought was that the Orange Squeezer +++ might do the trick, plenty of control and a fairly low parts count, but then again maybe the Keeley four knob comp might be more suitable despite the higher parts count? Or maybe something even simpler than the OS+++?
My question is, have any of you ever recorded with a stompbox compressor on anything other than guitar/bass guitar (drums and vocals particularly) and if so, what was the comp and how did it go?
What is your goal here - decent quality on a budget or using something that you build yourself? You should be able to find used gear for well under $100 that would seriously outperform the typical guitar pedal compressor. E.g. https://reverb.com/item/62037484-presonus-acp-22-stereo-compressor-limiter-church-owned-cg00l9q.
Quote from: GGBB on January 03, 2023, 10:52:55 PM
What is your goal here - decent quality on a budget or using something that you build yourself? You should be able to find used gear for well under $100 that would seriously outperform the typical guitar pedal compressor. E.g. https://reverb.com/item/62037484-presonus-acp-22-stereo-compressor-limiter-church-owned-cg00l9q.
Obviously, I'd like the final recordings to be listenable but by the same token I like the idea of working within the limitations of what I already have available to me and what I can realistically afford, with inflation in the UK at over 13% currently (don't get me started on that situation...). There's a strong DIY ethos with this project and I thought it would be nice to extend that to the kit used to record it. I'd love to be able to build four 1176's but I'm afraid the parts count is a little high to make it viable (also, the first nine words of this sentence), hence my looking towards less complex circuits.
I may well buy a rack mounted comp but thought this idea worth exploring and throwing out there to see if anyone has experience of using stompbox comps in unconventional ways.
I wrote several articles about compressors that you can see at:
http://www.muzique.com/lab/compz.htm
tl;dr - build a Dynacomp clone. The Orange Squeezer requires selecting a jfet that has the right properties to make the compression work well, and that can be a little tricky. The Dynacomp needs a CA3080 chip, which has limited availability, but it can be found at several of the pedal parts suppliers.
Best regards, Jack
Quote from: amz-fx on January 04, 2023, 06:29:19 AM
The Dynacomp needs a CA3080 chip, which has limited availability, but it can be found at several of the pedal parts suppliers.
LM13700 also works fine.
Quote from: amz-fx on January 04, 2023, 06:29:19 AM
I wrote several articles about compressors that you can see at:
http://www.muzique.com/lab/compz.htm
tl;dr - build a Dynacomp clone. The Orange Squeezer requires selecting a jfet that has the right properties to make the compression work well, and that can be a little tricky. The Dynacomp needs a CA3080 chip, which has limited availability, but it can be found at several of the pedal parts suppliers.
Best regards, Jack
Thanks for the link Jack, I read all three parts with interest. I found it interesting that the Orange Squeezer, despite its reputation for being quite a subtle compression effect by comparison, is the same type of circuit as the Dynacomp, which by reputation is a little more 'pumpy'. However, my main takeaway was that your Q&D 2 Compressor sounds to me like it would be the best of all worlds! Although, it looks like SMM2166 chips are thin on the ground these days and I've been unable to source a replacement/equivalent chip so I just might take your advice and go with the Dynacomp using the LM13700 as merlinb suggests.
Quote from: Greenballs on January 04, 2023, 09:29:43 AM
I found it interesting that the Orange Squeezer, despite its reputation for being quite a subtle compression effect by comparison, is the same type of circuit as the Dynacomp
Orange squeezer is a minimalist FET compressor, I wouldn't call that the same type as the Dynacomp which uses an OTA?
Or, to toot my own bassoon, this thing:
https://www.diystompboxes.com/smfforum/index.php?topic=128094.40#msg1251519
A FET-based limiter similar to the dynacomp or DOD250 in character. Doesn't need FET matching or selecting and has no hard to get parts.
Andy
Quote from: merlinb on January 04, 2023, 10:15:32 AM
Quote from: Greenballs on January 04, 2023, 09:29:43 AM
I found it interesting that the Orange Squeezer, despite its reputation for being quite a subtle compression effect by comparison, is the same type of circuit as the Dynacomp
Orange squeezer is a minimalist FET compressor, I wouldn't call that the same type as the Dynacomp which uses an OTA?
According to Jack's article, both are peak limiting circuits (as oppose to peak compression circuits a la the Keeley Comp Pro referenced in the same article) which is what I was referring to. Yes, they might have different ways of getting there but the effect ultimately does the same thing by the same means.
The LA Light is a bit of a blast from the past...
https://www.diystompboxes.com/smfforum/index.php?topic=30106.0 (https://www.diystompboxes.com/smfforum/index.php?topic=30106.0)
The circuit is quite simple and it was designed specifically with vocals in mind, while also capable of doing a stand-up job with instruments as well. The links in the post linked above are broken (posted before my .com was ripped off), but they are updated on this page...
http://moosapotamus.net/fatNpretty.html (http://moosapotamus.net/fatNpretty.html)
For recording, I would go with Johan's original and simpler design, LA-Light, rather than my modded stompbox version. The transistors are J201. Looks like synthcube's smallbear parts shop may have some.
https://synthcube.com/cart/index.php?route=product/search&search=j201&description=true (https://synthcube.com/cart/index.php?route=product/search&search=j201&description=true)
[/memories]
Quote from: moosapotamus on January 04, 2023, 05:05:52 PM
The LA Light is a bit of a blast from the past...
https://www.diystompboxes.com/smfforum/index.php?topic=30106.0 (https://www.diystompboxes.com/smfforum/index.php?topic=30106.0)
The circuit is quite simple and it was designed specifically with vocals in mind, while also capable of doing a stand-up job with instruments as well. The links in the post linked above are broken (posted before my .com was ripped off), but they are updated on this page...
http://moosapotamus.net/fatNpretty.html (http://moosapotamus.net/fatNpretty.html)
For recording, I would go with Johan's original and simpler design, LA-Light, rather than my modded stompbox version. The transistors are J201. Looks like synthcube's smallbear parts shop may have some.
https://synthcube.com/cart/index.php?route=product/search&search=j201&description=true (https://synthcube.com/cart/index.php?route=product/search&search=j201&description=true)
[/memories]
Cool! Thanks very much for that, I'll definitely have that on the breadboard over the weekend. I take it the op-amp can be one of several options or is there a specific op-amp that Johan used/works particularly well?
I used NE5532 in my stompbox version. TL072 or similar would probably do as well.
Quote from: moosapotamus on January 04, 2023, 05:59:54 PM
I used NE5532 in my stompbox version. TL072 or similar would probably do as well.
Thanks!
Also, I probably used a VTL5c3 for the vactrol, but other similar or 'roll-your-own' should work, too.
Quote from: moosapotamus on January 05, 2023, 07:43:20 AM
Also, I probably used a VTL5c3 for the vactrol, but other similar or 'roll-your-own' should work, too.
Thanks for the info, I'm going to start with the roll your own variety but its good to know there's a back up plan if I need it. And if I wanted to add a VU meter to show gain reduction where might be the best place to hook it up?
Johan's last revision had a VU meter. I must have lost the scheme in one of my past traumatic hard drive crashes. But I was able to dig it up on the wayback machine...
http://moosapotamus.net/images/LA_Light_last_one_001.gif (http://moosapotamus.net/images/LA_Light_last_one_001.gif)
Also this...
https://www.diystompboxes.com/smfforum/index.php?topic=64291.0 (https://www.diystompboxes.com/smfforum/index.php?topic=64291.0)
Quote from: Greenballs on January 04, 2023, 09:29:43 AM
I just might take your advice and go with the Dynacomp using the LM13700 as merlinb suggests.
In that case, maybe Merlin's Engineer's Thumb is a better choice than a Dynacomp.
https://www.diystompboxes.com/smfforum/index.php?topic=97123
http://www.valvewizard.co.uk/engineersthumb4.html
Quote from: moosapotamus on January 05, 2023, 12:45:48 PM
Johan's last revision had a VU meter. I must have lost the scheme in one of my past traumatic hard drive crashes. But I was able to dig it up on the wayback machine...
http://moosapotamus.net/images/LA_Light_last_one_001.gif (http://moosapotamus.net/images/LA_Light_last_one_001.gif)
Also this...
https://www.diystompboxes.com/smfforum/index.php?topic=64291.0 (https://www.diystompboxes.com/smfforum/index.php?topic=64291.0)
Thanks mate. Am I right in thinking that Johan replaced the Jfets with a second opamp? Also, there's two LEDs and two LDRs there, how are they arranged in practice? All lumped together or separated in pairs?
Quote from: GGBB on January 05, 2023, 01:48:54 PM
Quote from: Greenballs on January 04, 2023, 09:29:43 AM
I just might take your advice and go with the Dynacomp using the LM13700 as merlinb suggests.
In that case, maybe Merlin's Engineer's Thumb is a better choice than a Dynacomp.
https://www.diystompboxes.com/smfforum/index.php?topic=97123
http://www.valvewizard.co.uk/engineersthumb4.html
Yep, its definitely on my list of compressors to try.
Currently my list is:
Engineer's Thumb
LA Light
Q&D 2 (I managed to source two SMM2166 chips).
Level Lacquer V3.7
Quote from: Greenballs on January 05, 2023, 02:08:35 PM
Thanks mate. Am I right in thinking that Johan replaced the Jfets with a second opamp? Also, there's two LEDs and two LDRs there, how are they arranged in practice? All lumped together or separated in pairs?
An additional opamp was added for the VU meter, so adding a dual opamp (or replacing all with a quad) leaves one spare opamp which looks to have been used to buffer the bias voltage. It appears the Jfet stage was simply removed and not replaced with anything.
There are some comments about the LEDs and LDRs in that old thread that I linked to. My interpretation is that they need to be lined up and placed as closely together as possible. But read for yourself and see what you think.
Quote from: moosapotamus on January 05, 2023, 02:54:57 PM
Quote from: Greenballs on January 05, 2023, 02:08:35 PM
Thanks mate. Am I right in thinking that Johan replaced the Jfets with a second opamp? Also, there's two LEDs and two LDRs there, how are they arranged in practice? All lumped together or separated in pairs?
An additional opamp was added for the VU meter, so adding a dual opamp (or replacing all with a quad) leaves one spare opamp which looks to have been used to buffer the bias voltage. It appears the Jfet stage was simply removed and not replaced with anything.
There are some comments about the LEDs and LDRs in that old thread that I linked to. My interpretation is that they need to be lined up and placed as closely together as possible. But read for yourself and see what you think.
Having now read that thread I concur with your interpretation.
Just two more questions and I promise I'll leave you alone! Does it matter which side of the second opamp drives the VU meter? And regarding the resistor and the 'BIG' capacitor in series before the LEDs, will a 10k trim pot suffice as per the 'Jfet' schematic and would something like 4.7uf be in the right ball park do you think? Ok, that's three questions, but I'm done now, honest!
Each section of a dual or quad opamp is the same. Doesn't matter which side you use for what. Whatever works best for your circuit layout.
If you are trying the VU schematic, it does not have the trimmer between the two LEDs. So, I would probably just start with the values as shown in the Jfet schematic, 1k and 0.2uF, and go up from there if necessary. Yes, you could replace the 1k with a trimmer to dial in the best value and then replace it with a fixed resistor if it turns out to be relatively close to a standard value.
Orange Squeezer note, Instructions mention that using 2N5457 is the best, I can vouch for that, if you don't "all bets are off".
Well, I've had both versions of the LA Light schematic on the breadboard and, despite quite a sustained effort switching out opamps, LDRs and LEDs and ensuring that the jfets were matched pairs, couldn't get a peep out of either of them. No sound, no LED lighting up, nada. It's such a simple circuit design that I'm not sure what else I can do? Any suggestions would be greatly appreciated.
On another note, I had much better success with Bajaman's optical comp, which sounds great, and I curently have the Weak Joe Compressor on the breadboard but so far haven't been able to get that working either.
I've got a + and - 15v bipolar voltage converter built and am aware of a mistake on the schematic with it showing +15v going to the collector of Q1 instead of the correct -15v. Am I right in thinking that the +15v supplies power to all the op-amps also, as oppose to 9v? Also, the opamps are variously connected to ground via pins 3 and 5, do the opamps require grounding via pin 4 also? This is the first time I've encountered such a means of grounding an opamp and it is unclear on the schematic whether or not this is the case. If there is anything else I need to look out for with this build I'd be most grateful for any pointers.
(https://i.postimg.cc/jL82mQz8/Weak-Joe-Schem.png) (https://postimg.cc/jL82mQz8)
assume nothing on that schem,Greenballs, get a complete circuit diagram. generally, if an opamp input is grounded, the opamp will be bi-polar supplies. pin 4 is not ground, but V- or Vcc-, and it always needs a connection to your supply.
Quote from: duck_arse on January 08, 2023, 09:08:37 AM
assume nothing on that schem,Greenballs, get a complete circuit diagram. generally, if an opamp input is grounded, the opamp will be bi-polar supplies. pin 4 is not ground, but V- or Vcc-, and it always needs a connection to your supply.
So, and forgive my ignorance here, does that mean that pin 4 needs connecting to the -15v rail?
unstated. you need to show a schem with the power supply included. if it sez +15V and -15V, then your yes-ish, Vcc- would be -15V.
Quote from: Greenballs on January 08, 2023, 07:08:05 AM
Well, I've had both versions of the LA Light schematic on the breadboard and...
Sorry to hear that. It does require a bipolar power supply. Note connections to -V. Can't think of much else other than double checking everything several times. Sounds like you did give it a pretty thorough going over, tho.
Quote from: moosapotamus on January 08, 2023, 04:36:36 PM
Quote from: Greenballs on January 08, 2023, 07:08:05 AM
Well, I've had both versions of the LA Light schematic on the breadboard and...
Sorry to hear that. It does require a bipolar power supply. Note connections to -V. Can't think of much else other than double checking everything several times. Sounds like you did give it a pretty thorough going over, tho.
I got it working today, once I'd paid attention and realised it needed the bipolar power supply!
It's a nice sounding compression effect, although I did find that it made various static noises/squeals with the pots in certain positions, which I had some success in stopping by changing a couple of resistor values. Its also very low output when the compression is maxed out and could use some gain recovery, which I also attempted to implement but found that it led to more unwanted noises and less range in the compression effect.
Due to the super low parts count I am tempted to persevere with it, but I think I'm going to move onto Merlin's Engineer's Thumb, of which I've heard good things.
8)
Did you consider Guyatone PS-021 ? This one is pure magic.
I built Aion's project, called Meridian, with bass specs, and I use it on everything, guitars, keyboards, drum machine, etc.
https://www.musikding.de/Meridian-kit
https://aionfx.com/app/files/docs/meridian_documentation.pdf
I built the Engineer thumb (5 knobs version) and I almost never use it. It creates some unpleasant distortion quite easily, depending on how you set the controls. To the point that many builders think their build has an issue :
https://www.diystompboxes.com/smfforum/index.php?topic=129237.msg1248160#msg1248160
I think it would be much harder to use it on other instruments than guitar, but I never even tried that. Some of the controls need to be set under 12' or 3' or the circuit won't work correctly. Maybe the 2 knobs version is easier to use....
I spent so much time trying to get rid of the distortion... I'll always remember the quote from Chuck at PPCB forum :
"The design is clever, I wanted to like it, but that never happened."
https://forum.pedalpcb.com/threads/engineers-thumb-compressor-question.12149/
I bought an expensive Walrus deep six, it's good and surely a bit more effective than the meridian on the attack and compression side.
But the Colour and the Exciter controls on the Meridian are very useful to shape the signal. I really miss them on the deep six. Exciter controls odd and even harmonics. This is amazingly good to give more precision and clarity to the signal. Colour pans between bass boost and treble boost, really useful on drums and many other instruments.
You question may come down to:
1. How much compression do you want?
If you are feeding a distortion, you may want to maintain a constant level so the sustain is as long as possible. If you are going on radio, they already compress everything. If you are live, how much dynamic range do you want to retain?
2. At what level do you want the compression to start?
If you are in a studio, you may want a line level compressor. If you are live, you may want something different for amp levels.
3. Do you need variable controls for attack and decay time constants?
Some people want this to be fixed so they know exactly what they are working with and can't accidentally move an adjustment on stage. Some people want it to be variable so they can accommodate any playing style, such as in studio equipment.
4. What do you want to use for a variable gain stage? FET? OTA? tubes?
FET's are easy to find but difficult to match with any consistency and this gets to be more of a problem with push-pull circuits that would be used in a studio setting.
OTA's are easier to use but more diffiicult to find.
My Hammond Solovox uses 6SK7 remote-cutoff tubes for its volume control and I did get a call one time from a guy on a fan forum of a band he was in to see if there were any 6386 remote-cutoff twin triodes in the US for his Fairchild 670 compressor. I gave him a few names of tube purveyors, but he couldn't find any. The 6386's are approaching unobtanium but a pair of variable 6SK7 / 6BA6 stages cascaded would probably give more compression with the added advantage that everybody and his dog carries them.
So you have some criteria here to select a compressor circuit. I hope this list helps clarify what you need to look for.
Quote from: amptramp on January 10, 2023, 08:26:33 AM
You question may come down to:
....
4. What do you want to use for a variable gain stage? FET? OTA? tubes?
Don't forget about VCAs. These are readily available and are great for compressors. THAT Corp. makes some very nice Analog Engines, which include a RMS detector and VCA in one package, and they have a lot of informative app notes and example circuits on their site.
Quote from: EBK on January 10, 2023, 08:50:57 AM
Don't forget about VCAs.
I thought virtually all VCAs are based on an OTA type of circuit or similar configurations using Gilbert cells either as discrete implementations or using ICs.
Quote from: eh la bas ma on January 10, 2023, 08:12:31 AM
Did you consider Guyatone PS-021 ? This one is pure magic.
I built Aion's project, called Meridian, with bass specs, and I use it on everything, guitars, keyboards, drum machine, etc.
https://www.musikding.de/Meridian-kit
https://aionfx.com/app/files/docs/meridian_documentation.pdf
I built the Engineer thumb (5 knobs version) and I almost never use it. It creates some unpleasant distortion quite easily, depending on how you set the controls. To the point that many builders think their build has an issue :
https://www.diystompboxes.com/smfforum/index.php?topic=129237.msg1248160#msg1248160
I think it would be much harder to use it on other instruments than guitar, but I never even tried that. Some of the controls need to be set under 12' or 3' or the circuit won't work correctly. Maybe the 2 knobs version is easier to use....
I spent so much time trying to get rid of the distortion... I'll always remember the quote from Chuck at PPCB forum :
"The design is clever, I wanted to like it, but that never happened."
https://forum.pedalpcb.com/threads/engineers-thumb-compressor-question.12149/
I bought an expensive Walrus deep six, it's good and surely a bit more effective than the meridian on the attack and compression side.
But the Colour and the Exciter controls on the Meridian are very useful to shape the signal. I really miss them on the deep six. Exciter controls odd and even harmonics. This is amazingly good to give more precision and clarity to the signal. Colour pans between bass boost and treble boost, really useful on drums and many other instruments.
Ah cool, thanks for the tip on the PS-021! The addition of the Exciter and Colour controls sounds like it might be more suited to my needs, I'll definitely be building that on the breadboard.
Quote from: FSFX on January 10, 2023, 09:02:48 AM
Quote from: EBK on January 10, 2023, 08:50:57 AM
Don't forget about VCAs.
I thought virtually all VCAs are based on an OTA type of circuit or similar configurations using Gilbert cells either as discrete implementations or using ICs.
VCAs are usually based on Blackmer cells, which can be thought of as Gilbert cells redesigned for audio.
Quote from: amptramp on January 10, 2023, 08:26:33 AM
You question may come down to:
1. How much compression do you want?
If you are feeding a distortion, you may want to maintain a constant level so the sustain is as long as possible. If you are going on radio, they already compress everything. If you are live, how much dynamic range do you want to retain?
I'm not sure how much compression exactly, just a wide range, say from 2:1 - 20:1.
Quote from: amptramp on January 10, 2023, 08:26:33 AM
2. At what level do you want the compression to start?
If you are in a studio, you may want a line level compressor. If you are live, you may want something different for amp levels.
I'll be using the compressor to do home recordings with. I'll be driving the unit from my Focusrite audio interface, so line level.
Quote from: amptramp on January 10, 2023, 08:26:33 AM
3. Do you need variable controls for attack and decay time constants?
Some people want this to be fixed so they know exactly what they are working with and can't accidentally move an adjustment on stage. Some people want it to be variable so they can accommodate any playing style, such as in studio equipment.
Variable would be the ideal but I could live with fixed if I had to. It depends on the parts count and the cost involved. If I can buy a decent quad comp for significantly less that the cost of building one then I probably, reluctantly, will.
Quote from: amptramp on January 10, 2023, 08:26:33 AM
4. What do you want to use for a variable gain stage? FET? OTA? tubes?
FET's are easy to find but difficult to match with any consistency and this gets to be more of a problem with push-pull circuits that would be used in a studio setting.
OTA's are easier to use but more diffiicult to find.
My Hammond Solovox uses 6SK7 remote-cutoff tubes for its volume control and I did get a call one time from a guy on a fan forum of a band he was in to see if there were any 6386 remote-cutoff twin triodes in the US for his Fairchild 670 compressor. I gave him a few names of tube purveyors, but he couldn't find any. The 6386's are approaching unobtanium but a pair of variable 6SK7 / 6BA6 stages cascaded would probably give more compression with the added advantage that everybody and his dog carries them.
At the moment I'm open to all options, but as I said, cost is the main driver. After cost its about sonics and how suitable the circuit is to the purpose. I still have research to do on compressing drum overheads, for example (I'll be using the Glyn Johns drum mic technique). Once I know what the desirable compression characteristics are for this application I'll be able to narrow my search criteria. I realise that I may be on a fools errand and that I may be trying to force a square peg into a round hole but they're both risks I'm willing to take!
Quote from: amptramp on January 10, 2023, 08:26:33 AM
So you have some criteria here to select a compressor circuit. I hope this list helps clarify what you need to look for.
Thanks for your comments, they've certainly given me food for thought.
Can the Bajaman LA2A style optical compressor be modded to allow control of the attack and release of the effect either by means of a switch, between preset fast/slow modes, or a potentiometer? Or, if anyone has the time, can someone give me a brief analysis of the attached schematic please so I can try and figure it out myself? Thanks.
(https://i.postimg.cc/xkPDprgt/bajaman-schem-2.png) (https://postimg.cc/xkPDprgt)
Quote from: Greenballs on January 14, 2023, 11:52:13 AM
Can the Bajaman LA2A style optical compressor be modded to allow control of the attack and release of the effect either by means of a switch, between preset fast/slow modes, or a potentiometer? Or, if anyone has the time, can someone give me a brief analysis of the attached schematic please so I can try and figure it out myself? Thanks.
(https://i.postimg.cc/xkPDprgt/bajaman-schem-2.png) (https://postimg.cc/xkPDprgt)
It can be done but frankly, the design has so too many issues to bother trying to improve it, imo. Too many superfluous, poorly chosen, and missing components. I would strongly advocate a complete redesign of the side chain. Controlling attack and release in a feed back opto limiter (which is what this is, despite the side chain forking off left of the LDR) in a predictable fashion is tricky in general because the LDR's rise and fall times limit the maximum speed, which makes the infamous dynamic overcompression problem of feedback limiters much worse and nearly impossible to solve on high settings. Also, the current through the LED messes with the release time (unless you add an extra buffer), and the resistance range of the LDR forces us to use high series resistance values, which is not ideal for noise reasons. For those reasons, I pretty much abandoned the idea of opto limiters. You can get the same results (if you want) and much more from JFET or OTA designs.
Andy
Quote from: Fancy Lime on January 14, 2023, 01:44:47 PM
Quote from: Greenballs on January 14, 2023, 11:52:13 AM
Can the Bajaman LA2A style optical compressor be modded to allow control of the attack and release of the effect either by means of a switch, between preset fast/slow modes, or a potentiometer? Or, if anyone has the time, can someone give me a brief analysis of the attached schematic please so I can try and figure it out myself? Thanks.
(https://i.postimg.cc/xkPDprgt/bajaman-schem-2.png) (https://postimg.cc/xkPDprgt)
It can be done but frankly, the design has so too many issues to bother trying to improve it, imo. Too many superfluous, poorly chosen, and missing components. I would strongly advocate a complete redesign of the side chain. Controlling attack and release in a feed back opto limiter (which is what this is, despite the side chain forking off left of the LDR) in a predictable fashion is tricky in general because the LDR's rise and fall times limit the maximum speed, which makes the infamous dynamic overcompression problem of feedback limiters much worse and nearly impossible to solve on high settings. Also, the current through the LED messes with the release time (unless you add an extra buffer), and the resistance range of the LDR forces us to use high series resistance values, which is not ideal for noise reasons. For those reasons, I pretty much abandoned the idea of opto limiters. You can get the same results (if you want) and much more from JFET or OTA designs.
Andy
It sounds good though, feels good under the fingers and doesn't suck tone (at least, not until it's near maxed out, then it loses a little high end I'll admit).
So, its great to hear your opinions -
I get that the feedforward claim is possibly false, but I'm unsure why?
I understand that the LDR and the LED affect the attack and release times and that adding an extra buffer (somewhere? in front?) will solve the LED side of the problem but I'm guessing the LDR/high series resistance values issue is just one that we have to live with?
I'm unclear as to which parts of the circuit you consider superfluous, poorly chosen and missing? Or how you'd go about redesigning the side chain?
Genuinely interested in your response.
> despite the side chain forking off left of the LDR
But "after" the dominant 68k.
So yes: 96% feedback. The 4% kick is a hack to extend the compression when the LDR loses linearity.
Time "constants" (not constant at all) are entirely up to the LDR. The LA2 people worked with the LDR bakery and did a LOT of selection to get "nice" time response. I did a lot of playing-around in the 1980s, and even by then "good" LDRs were hard to find. I used the scheme for "rude" limiters to protect drivers against accidents and abuse.
When I heard the RNC1773 I stopped paling-around with obsolete chemistry. Yes, four separate channels of RNC is not cheap. I think "all" PA gear companies have a 4-channels compressor on similar technology, it's not obscure. If you convince THAT Corp you have factory and distribution, they can be eager to help.
Behringer MULTICOM PRO-XL MDX4600 V2
4-channel Compressor/Limiter/Gate
Rated 4/5 3 reviews
Item ID: MDX4600V2
$159.00
It's a cheap box and jacks but you can't touch it DIY for that price, even before you build and test guts.
If you like the way it sounds and feels, you were probably lucky in the vactrol lottery. In that case, there is nothing wrong with using the design as it is. Don't fix what isn't broken, no matter what some dude on the internet sais :icon_wink:
However, in my experience feedback limiters do not respond well to long attack and release times. For this type of circuit you want your attack as fast as possible and your release just slow enough to avoid rippling on the lowest notes. Slow attack causes duck-and-swell and long decay causes pumping. Both rarely wanted. Seems that your vactrol happens to give you good values as is is, so no need to make it worse, imo.
There are a few things you should add, though. Add a 100 Ohm resistor between the vactrol LED and 1/2V and do the same for the indicator LED. This is called current sharing and makes it so that both LEDs light up even if they have different thresholds.
If you want to experiment with slower attack and decay, just place a cap from the top of the LEDs to ground. This is called the holding cap or timing cap. I would start with 22uF or even 100uF. If that has too little effect, try increasing that 56 Ohm resistor before the LEDs to 220 Ohm.
The buffer I was talking about would go between the holding cap and the LEDs. In the scheme described above, the holding cap discharges through the LEDs, which is not at all linear and cannot easily be controlled or changed. The buffer separates the discharging if the holding cap from the charge necessary to drive the LEDs, allowing to then use a (variable) resistor to set the discharging rate.
Andy
Quote from: Fancy Lime on January 14, 2023, 05:57:44 PM
If you like the way it sounds and feels, you were probably lucky in the vactrol lottery. In that case, there is nothing wrong with using the design as it is. Don't fix what isn't broken, no matter what some dude on the internet sais :icon_wink:
However, in my experience feedback limiters do not respond well to long attack and release times. For this type of circuit you want your attack as fast as possible and your release just slow enough to avoid rippling on the lowest notes. Slow attack causes duck-and-swell and long decay causes pumping. Both rarely wanted. Seems that your vactrol happens to give you good values as is is, so no need to make it worse, imo.
There are a few things you should add, though. Add a 100 Ohm resistor between the vactrol LED and 1/2V and do the same for the indicator LED. This is called current sharing and makes it so that both LEDs light up even if they have different thresholds.
If you want to experiment with slower attack and decay, just place a cap from the top of the LEDs to ground. This is called the holding cap or timing cap. I would start with 22uF or even 100uF. If that has too little effect, try increasing that 56 Ohm resistor before the LEDs to 220 Ohm.
The buffer I was talking about would go between the holding cap and the LEDs. In the scheme described above, the holding cap discharges through the LEDs, which is not at all linear and cannot easily be controlled or changed. The buffer separates the discharging if the holding cap from the charge necessary to drive the LEDs, allowing to then use a (variable) resistor to set the discharging rate.
Andy
Thanks for taking the time Andy, much appreciated. I'll learned some useful things there that I'll certainly be experimenting with over the next couple of days.
Quote from: PRR on January 14, 2023, 05:17:39 PM
Behringer MULTICOM PRO-XL MDX4600 V2
4-channel Compressor/Limiter/Gate
Rated 4/5 3 reviews
Item ID: MDX4600V2
$159.00
It's a cheap box and jacks but you can't touch it DIY for that price, even before you build and test guts.
Yep, even the Drawmer DL441 is only £250 second hand these days. I think I might struggle to match even that price. Still, I'm enjoying the process of breadboarding different types of compressor and learning about how they function (with help from the good folks here), so its not a complete waste of time and effort! :D
One general observation with hardware these days is that DIY has long stopped being the "economy option". All the standard stuff like studio compressors, mic preamps, headphone amps etc. can be had for much cheaper brand new from a dozen or so companies than you could ever make it yourself, even if you value your working hours at zero. And these things that are cheap new are very cheap used because people feel the need to upgrade from Behringer to something more reputable as soon as they can, whether it sounds better or not. From a purely economic standpoint, DIY only makes sense now if you want something extraordinary that is so far out of the mainstream that the cheapo companies don't bother with it. So my advice on the "you need a quad compressor" front would also be to get a used cheap one. As long as it works at all, It'll do just fine for your stated purpose of getting drums and bass and other stuff into a computer. Complicated compression (if that is what you want) is best done in the DAW these days anyway. To scratch the DIY itch, it is still fun to create your own "secret sauce" compressor for a particular purpose. One goal of the FET compressor I linked earlier in the thread, was to accentuate the nice fat overdrive of this type of control element in extreme settings and also to allow to dial in some rippling to taste. Both things that commercial designs try to minimize because you rarely want them. But I happen to like them a lot on the niche application of fretless finger style funk bass lines. Hot, fat and dirty, like all the best street food :icon_wink:
Andy
Quote from: Fancy Lime on January 14, 2023, 05:57:44 PM.... in my experience feedback limiters do not respond well to long attack and release times. For this type of circuit you want your attack as fast as possible and your release just slow enough to avoid rippling on the lowest notes. Slow attack causes duck-and-swell and long decay causes pumping.
IMHO, this applies just as much to feed-Forward topology. If you have a rapid attack instrument (guitar, piano) and slow-attack limiter (your tiny demon was out carousing all last night), it's gonna splatt.
Even so, I wish you would consult for my cable TV company.
duck and
SWELL indeed. Not even good for business: frequently the name of the product is swallowed-up by an overblown first transient. Though this is more about over-compressing pre-compressed crap than about time factors.
True, the same problems apply to feed forward designs. I just don't have any hands-on experience with those. There are ways of tackling these problems, like clipping the side chain, adaptive attack speed, etc. But all the ones I know or tried are hacky and finicky and not well suited for production circuits.
Quote from: Greenballs on January 14, 2023, 11:52:13 AM
Can the Bajaman LA2A style optical compressor be modded to allow control of the attack and release of the effect either by means of a switch, between preset fast/slow modes, or a potentiometer? Or, if anyone has the time, can someone give me a brief analysis of the attached schematic please so I can try and figure it out myself? Thanks.
(https://i.postimg.cc/xkPDprgt/bajaman-schem-2.png) (https://postimg.cc/xkPDprgt)
I've built this one some time ago and never made it work as intended. It always distorts the sound. Tried different vactrols, both rolled or factory made, they made some changes, but newer succeeded to remove distortion. NSL32, LCR-0202 and VTL5C10 (original NOS) work the best, but non of them is perfect. :(
Quote from: moosapotamus on January 04, 2023, 05:05:52 PM
The LA Light is a bit of a blast from the past...
https://www.diystompboxes.com/smfforum/index.php?topic=30106.0 (https://www.diystompboxes.com/smfforum/index.php?topic=30106.0)
The circuit is quite simple and it was designed specifically with vocals in mind, while also capable of doing a stand-up job with instruments as well. The links in the post linked above are broken (posted before my .com was ripped off), but they are updated on this page...
http://moosapotamus.net/fatNpretty.html (http://moosapotamus.net/fatNpretty.html)
For recording, I would go with Johan's original and simpler design, LA-Light, rather than my modded stompbox version. The transistors are J201. Looks like synthcube's smallbear parts shop may have some.
https://synthcube.com/cart/index.php?route=product/search&search=j201&description=true (https://synthcube.com/cart/index.php?route=product/search&search=j201&description=true)
[/memories]
I've built Fat'n'pretty few years ago and never made it work at all. No idea why. I didn't use that isolated DC converter, used LT1054 negative voltage generator, maybe that was the problem? No idea.
QuoteI've built this one some time ago and never made it work as intended. It always distorts the sound. Tried different vactrols, both rolled or factory made, they made some changes, but newer succeeded to remove distortion. NSL32, LCR-0202 and VTL5C10 (original NOS) work the best, but non of them is perfect.
The half-wave rectification doesn't help but designs like this rely 100% on the opto time constants to reduce distortion. Without redesigning the whole thing it's probably worth playing with caps across the opto LED maybe 10uF upto 100uF, just enough to shave off the distortion. Not ideal but maybe enough to push it over the line.
Quote from: Rob Strand on January 16, 2023, 09:23:33 PM
The half-wave rectification doesn't help but designs like this rely 100% on the opto time constants to reduce distortion. Without redesigning the whole thing it's probably worth playing with caps across the opto LED maybe 10uF upto 100uF, just enough to shave off the distortion. Not ideal but maybe enough to push it over the line.
Thanks Rob, I'll try that. I've built https://stompville.co.uk/?p=50 (https://stompville.co.uk/?p=50)
Clean Squeeze compressor and it has that parallel cap across the opto LED, but I forgot about that option. :-[
QuoteThanks Rob, I'll try that. I've built https://stompville.co.uk/?p=50 Clean Squeeze compressor and it has that parallel cap across the opto LED, but I forgot about that option.
You can only try it to see if it can be saved. The distortion comes from the release time being too short. However the parallel cap affects both the attack and release times. What happens is by the time the cap is big enough to fix the release time the attack time becomes too long. So it's a careful balancing act tweaking the parallel cap. For feedback type compressors it not as bad as it seems since the release time gets stretched compared to the attack time by nature of the feedback.
The four diodes around the opto LED on the John Hollis compressor (from your link) will give you full-wave rectification, that helps reduce distortion too. Which is useful. However you can't use the same trick on the BAJA compressor since it adds a DC bias using the two small diodes. To get full-wave and the DC bias on the BAJA you need to redesign that part of the circuit - which will make it more complicated.
Quote from: rankot on January 16, 2023, 05:05:09 PM
Quote from: Greenballs on January 14, 2023, 11:52:13 AM
Can the Bajaman LA2A style optical compressor be modded to allow control of the attack and release of the effect either by means of a switch, between preset fast/slow modes, or a potentiometer? Or, if anyone has the time, can someone give me a brief analysis of the attached schematic please so I can try and figure it out myself? Thanks.
(https://i.postimg.cc/xkPDprgt/bajaman-schem-2.png) (https://postimg.cc/xkPDprgt)
I've built this one some time ago and never made it work as intended. It always distorts the sound. Tried different vactrols, both rolled or factory made, they made some changes, but newer succeeded to remove distortion. NSL32, LCR-0202 and VTL5C10 (original NOS) work the best, but non of them is perfect. :(
The Baja Optical Limiter is
by far my favorite compressor, and it's been on my board for close to 10 years now. I didn't test any legit vactrols, but I had to try a few combos of LDRs (with different off resistances) and LED colors to get the right one. I think I ended up with a red LED & a quite low off resistance LDR.
Definitely worth troubleshooting if you still have it.
Quote from: bowanderror on January 27, 2023, 11:30:19 PM
The Baja Optical Limiter is by far my favorite compressor, and it's been on my board for close to 10 years now. I didn't test any legit vactrols, but I had to try a few combos of LDRs (with different off resistances) and LED colors to get the right one. I think I ended up with a red LED & a quite low off resistance LDR.
Definitely worth troubleshooting if you still have it.
I'm just about to start buildng this today, with a couple of the minor mods suggested by Fancy Lime. Fingers crossed I won't have any issues with it.
I've also had AMZ's Q&D 2 compressor on the breadboard and was very impressed with it's range and versatility, not to mention the HUGE amount of output it has on tap, so I'll definitely be building that too, maybe with the addition of a switch (between different cap values) to change the decay time of the VCA.
Just out of interest, is there any way gain reduction and output meters could be hooked up? Schematic attached.
(https://i.postimg.cc/47RkYvjD/AMZ-comp-schem.png) (https://postimg.cc/47RkYvjD)
Quote from: Fancy Lime on January 14, 2023, 05:57:44 PM
If you like the way it sounds and feels, you were probably lucky in the vactrol lottery. In that case, there is nothing wrong with using the design as it is. Don't fix what isn't broken, no matter what some dude on the internet sais :icon_wink:
However, in my experience feedback limiters do not respond well to long attack and release times. For this type of circuit you want your attack as fast as possible and your release just slow enough to avoid rippling on the lowest notes. Slow attack causes duck-and-swell and long decay causes pumping. Both rarely wanted. Seems that your vactrol happens to give you good values as is is, so no need to make it worse, imo.
There are a few things you should add, though. Add a 100 Ohm resistor between the vactrol LED and 1/2V and do the same for the indicator LED. This is called current sharing and makes it so that both LEDs light up even if they have different thresholds.
If you want to experiment with slower attack and decay, just place a cap from the top of the LEDs to ground. This is called the holding cap or timing cap. I would start with 22uF or even 100uF. If that has too little effect, try increasing that 56 Ohm resistor before the LEDs to 220 Ohm.
The buffer I was talking about would go between the holding cap and the LEDs. In the scheme described above, the holding cap discharges through the LEDs, which is not at all linear and cannot easily be controlled or changed. The buffer separates the discharging if the holding cap from the charge necessary to drive the LEDs, allowing to then use a (variable) resistor to set the discharging rate.
Andy
@FancyLime
Hi Andy,
Can I just check that the attached schematic (simplified to show just the relevant parts) is what you were describing regarding the buffer/holding cap in your previous post?
I have the Bajaman compressor built and it works but there is a little bit of background distortion, which I'm trying to figure out ways of eliminating. Am I right in thinking that the correct value holding cap should help to reduce the distortion?
(https://i.postimg.cc/dDk03DVq/Screenshot-2023-01-31-at-07-34-16.png) (https://postimg.cc/dDk03DVq)
I think that loading opamp output with a capacitor is a bad idea. Put it across LEDs.
(https://i.postimg.cc/mtZZPnsR/Baja-indicator.jpg) (https://postimg.cc/mtZZPnsR)
Quote from: rankot on January 31, 2023, 01:12:33 PM
I think that loading opamp output with a capacitor is a bad idea. Put it across LEDs.
Would it not be better to make U2.2 an integrator by having the capacitor in its feedback path or am I missing something here?
QuoteI think that loading opamp output with a capacitor is a bad idea. Put it across LEDs.
It's not that bad as the opamp drives the cap via a resistor. On that design you are pumping a fair bit of current through the LEDs anyway.
FWIW, I had some thoughts later. You might have more success placing a rectifier further back in the signal chain. At least that lets you keep a faster attack and you can still set the time constants. It also removes the need for large caps.
Here's the idea. You could use a Schottky diode.
(https://i.postimg.cc/wy3J0wSJ/BAJA-LA2-A-time-constant-tweak-hack.png) (https://postimg.cc/wy3J0wSJ)
Please don't think of this as a working circuit. It's only showing the general idea of shoe-horning a way to tweak the time-constants into the circuit. It's still a half-wave rectifier.
There's an assumption that the distortion is caused by the time constants, while highly likely, it's not yet proven.
Quote from: Rob Strand on January 31, 2023, 04:26:22 PM
It's not that bad as the opamp drives the cap via a resistor. On that design you are pumping a fair bit of current through the LEDs anyway.
FWIW, I had some thoughts later. You might have more success placing a rectifier further back in the signal chain. At least that lets you keep a faster attack and you can still set the time constants. It also removes the need for large caps.
Here's the idea. You could use a Schottky diode.
(https://i.postimg.cc/wy3J0wSJ/BAJA-LA2-A-time-constant-tweak-hack.png) (https://postimg.cc/wy3J0wSJ)
Please don't think of this as a working circuit. It's only showing the general idea of shoe-horning a way to tweak the time-constants into the circuit. It's still a half-wave rectifier.
There's an assumption that the distortion is caused by the time constants, while highly likely, it's not yet proven.
It seems to be working, at least in LTSPICE. Adding 330n across R11 on your schematic will further smooth the envelope curve, but it will also slower the attack a little. I will test this circuit later today, because I have one almost complete unit on the desk.
Also, would it be possible to adjust compression ratio with R15 as a potentiometer?
QuoteIt seems to be working, at least in LTSPICE. Adding 330n across R11 on your schematic will further smooth the envelope curve, but it will also slower the attack a little. I will test this circuit later today, because I have one almost complete unit on the desk.
If you need to extend the release time to reduce the distortion you can use a larger cap and reduce the 1k in series with the diode to keep the attack the same. The threshold pot is fixed at 10k so you can play with the resistance to modify the release time. Another angle is to change the 10k pot to a 100k pot - that will let you get longer release times with smaller caps and avoid small resistances on the output of the opamp.
QuoteAlso, would it be possible to adjust compression ratio with R15 as a potentiometer?
In use it might give that impression but what it is really doing is limiting the maximum attenuation. If the compressor sits at full attenuation it stops compressing at higher inputs and you get less (incremental) compression. I haven't analysed it in detail and sometimes the details screw you over on these circuits.
Hi Greenballs,
sorry for being slow to respond. I put together a little snippet demonstrating what I meant with "buffering". Word of warning: this is just a sketch intended to demonstrate the principle, it is not tested, the values mostly pulled from thin air, the schematic may well be riddled with errors and I am a bit deliriously tired at the moment. The input buffer was changed to an opamp because using a 2SK117 for an input buffer is a waste of a grate JFET to use it in a role where it actually performs rather poorly. JFET Opamp is much better and probably cheaper for this.
(https://i.postimg.cc/CBsghDRg/Comp-snippet.png) (https://postimg.cc/CBsghDRg)
I mean that the time setting cap (C8) should be separated from the LEDs and not be charged or discharged through the LEDs. This allows you to use a variable resistor for discharging (Release control), without messing with the sensitivity of the optical element. This is achieved here with Q1, which can be pretty much any moderate to high gain NPN BJT. Now this does modify the release characteristic, which you may or may not like. With the time cap directly at the LEDs, initial discharge would be very fast and becomes very slow as soon as the LEDs drop below their threshold voltage. This is the way the DOD280 handles this and it leads to very inconsistent attack, depending on how long the silence before a note was. If that is what you want, let me know, I'd have to move a few parts around. But I personally much prefer the consistent release and this is more or less what most people expect from a compressor. By tuning the Release control, you should be able to get this thing mostly ripple free (assuming that is the cause of the unwanted distortion).
A really simple and flexible ratio control is to simply mix uncompressed signal with the limited signal at the end. You then have the option to stick a tone control in the uncompressed path to have a frequency dependent ratio control. It can be quite nice for funky guitars and such to only add a bit of topend in parallel. Likewise for bass, you might want to tame the high end in the uncompressed path a bit to tame the pop-n-slap transients but keep the punch. The big drawback of the parallel approach is that you have to watch out for phase cancellation, especially if you put in a tone control. This can be designed properly (I think) but it requires some careful simulation and testing.
HTH
Andy
Andy L. - your Q1 would have a series base resistor in a real world vershun, wouldn't it?
Quote from: duck_arse on February 03, 2023, 07:22:03 AM
Andy L. - your Q1 would have a series base resistor in a real world vershun, wouldn't it?
Yes, sticking a 1k to 10k in front of the base would prolly be a good idea.
Quote from: Fancy Lime on February 02, 2023, 03:33:03 PM
Hi Greenballs,
sorry for being slow to respond. I put together a little snippet demonstrating what I meant with "buffering". Word of warning: this is just a sketch intended to demonstrate the principle, it is not tested, the values mostly pulled from thin air, the schematic may well be riddled with errors and I am a bit deliriously tired at the moment. The input buffer was changed to an opamp because using a 2SK117 for an input buffer is a waste of a grate JFET to use it in a role where it actually performs rather poorly. JFET Opamp is much better and probably cheaper for this.
(https://i.postimg.cc/CBsghDRg/Comp-snippet.png) (https://postimg.cc/CBsghDRg)
I mean that the time setting cap (C8) should be separated from the LEDs and not be charged or discharged through the LEDs. This allows you to use a variable resistor for discharging (Release control), without messing with the sensitivity of the optical element. This is achieved here with Q1, which can be pretty much any moderate to high gain NPN BJT. Now this does modify the release characteristic, which you may or may not like. With the time cap directly at the LEDs, initial discharge would be very fast and becomes very slow as soon as the LEDs drop below their threshold voltage. This is the way the DOD280 handles this and it leads to very inconsistent attack, depending on how long the silence before a note was. If that is what you want, let me know, I'd have to move a few parts around. But I personally much prefer the consistent release and this is more or less what most people expect from a compressor. By tuning the Release control, you should be able to get this thing mostly ripple free (assuming that is the cause of the unwanted distortion).
A really simple and flexible ratio control is to simply mix uncompressed signal with the limited signal at the end. You then have the option to stick a tone control in the uncompressed path to have a frequency dependent ratio control. It can be quite nice for funky guitars and such to only add a bit of topend in parallel. Likewise for bass, you might want to tame the high end in the uncompressed path a bit to tame the pop-n-slap transients but keep the punch. The big drawback of the parallel approach is that you have to watch out for phase cancellation, especially if you put in a tone control. This can be designed properly (I think) but it requires some careful simulation and testing.
HTH
Andy
Hi Andy
Thanks very much for the detailed response, much appreciated! I'll definitely get that on the breadboard as soon as I have chance and have a good tinker with it.
So, my interpretation of what you were describing regarding the buffer was obviously different in that I have the LEDs coming off the emitter to the +4.5v instead of the collector tp +9v. Is there any reason why my interpretation won't work or won't work optimally? I only ask because I built the Bajaman Comp with this buffer arrangement (minus the holding cap because I couldn't hear or feel any discernible difference with or without it) and while the LEDs light up and it
sounds like it's compressing I'm fully prepared to be told that my ears must be deceiving me and that something else is at play!
(https://i.postimg.cc/bSNGVGZL/Screenshot-2023-01-31-at-07-34-16.png) (https://postimg.cc/bSNGVGZL)
Hi Greenballs,
well, you answered your question yourself: in your arrangement, the holding cap does not work, hence the not hearing a difference. The thing will still compress, only slightly worse than without the JFET, but the holding cap cannot do anything useful if you feed it the whole AC signal from the opamp. You need those Schottky diodes (D1 and D2 in my schematic) to feed it a half certified signal for the holding cap to work as intended.
If the LEDs go to +9V or +4.5V or ground does not fundamentally matter very much as long as everything is arranged such that they light up when they should.
Andy