OS/Tangerine Peeler build report

[free electron]

Hi!
I've just finished a little modded and simplified version of the Mark Hammer's TangerinePeeler. I decided to use only feedback signal for envelope follower, added an output buffer after the Vol knob to get a low and constant output impedance.
I think there is a DC blocking cap missing, just between the output of the IC1c and the half wave rectifier. Without the cap there's a bias voltage (- Vf of the ge diode) present at the Q2's gate which makes impossible to set the proper Q2 bias.

I did some mods to the Tone control also. The 2k2 and 10n is replaced with 1k and 33n which gives IMHO more useable treble boost.
What is really cool about this pedal: setting the compression to minimum  gives a you light compressed clean/treble booster.
I haven't seen a full TangerinePeeler build report here, so, maybe someone will find it usefull.
Here's a photo of my version:

And a sound sample. The 1st part is bypassed signal, then i'm increasing the compression parameter, at the end i'm playing with the Tone knob.
SOUND SAMPLE

[Mark Hammer]

Nice work indeed!   Both the build (and PCB layout....which I'd LOVE a copy of ) and write-up, but also the post-hoc detective work and adjustments to the circuit, which are deeply appreciated.

One of the things I never really liked about the stock OS was the manner in which output level and compression were yoked.  Adding the extra gain stage in the sidechain manages to separate overall audio signal gain from envelope sensitivity in a pleasing way.  Your changes to the tone control sound good too.

Admittedly, this was something I've never built.  It was more a thought project whose values were all essentially theory-driven rather than empirically decided upon. Glad to find out they were pretty close to what was needed.

Again, many thanks.

[Renegadrian]

http://reallyrome.com/blog/2007/12/06/chocolate-and-tangerine-semifreddo/

Sorry, couldn't resist...

[snoof]

nice work!

[Pushtone]

Great looking PCB!


I've been wanting to mount a pot in the same way.
I take it you soldered "legs" onto the pot lugs.

Great way to simplify OB wires.

Nice work

Dave S

[Ben N]

Dave, there are board-mount pots with long legs just like that. Mouser has them.

[free electron]

Nice work indeed!   Both the build (and PCB layout....which I'd LOVE a copy of ) and write-up, but also the post-hoc detective work and adjustments to the circuit, which are deeply appreciated.

One of the things I never really liked about the stock OS was the manner in which output level and compression were yoked.  Adding the extra gain stage in the sidechain manages to separate overall audio signal gain from envelope sensitivity in a pleasing way.  Your changes to the tone control sound good too.

Admittedly, this was something I've never built.  It was more a thought project whose values were all essentially theory-driven rather than empirically decided upon. Glad to find out they were pretty close to what was needed.

The idea of taking away from the audio path the gain needed to drive the envelope follower is the best mod to this circuit i think. I've never been a fan of compressors use with guitar, but when the compression is taken down the OS do sound really sweet.
The PCB is a double sided design with some SMT components (there's one cap under the IC) and frankly, it's not enough documented for posting. When designing the pcb for a single project i'm not labelling the components at all. I just follow the schematic when populating the pcb. At the end i found a small mistake (one cap was missing) which would need removing all ground planes to correct. I've used a 0805 smd cap instead. So, better idea would be to design a new one.
Back to OS!
Here's the schem i used:

I've got some other ideas, probably worth checking on breadboard. Since the 82k + FET forms a voltage divider the compression could be also controlled by changing the 82k resistor. So, lets make the 82k variable:

But we'll get a variable signal level. Let's combine it with SWTC technology and use an inverting opamp stage:

To maintain the correct phase we could f.e. add at the end an active, phase inverting EQ, 2 or 3 band and get a very versatile input dynamics and tone correction unit, or use a low gain FET stage at the input to drive the attenuator with a larger amplitude.
Anyway, these are just an untestes ideas i wanted to share. Technically, the way to control the compression by changing the envelope follower gain is probably a better idea.

Great looking PCB!

I've been wanting to mount a pot in the same way.
I take it you soldered "legs" onto the pot lugs.

Thanks! I'm collecting the legs which i cut out from the components. They're sometimes very usefull

[Mark Hammer]

That is brilliant!

Note that while the variable sidechain gain allows one to dictate the amount of compression, it does not dictate the compression ratio.  Both of these elements play a role in the "feel" of the compression.  So, in theory, at least, the adjustable input leg of the "virtual pot" is a good idea, and your use of the moving wiper approach is an elegant way to do that.  Why?  Because it offsets the softer ratios (which is what you'd get as the wiper gets moved to the left in your drawing) with decreased gain in the op-amp stage that follows.  Conversely, if you make the compression ratio more severe by moving the wiper to the right, you simultaneously increase the gain of that inverting stage to compensate for the more drastic level reduction one will experience at higher ratios.  Like I say, brilliant.

The challenge is one of likely finding a "target gain" in the inverting stage, and perhaps paralleling the right-hand side of the Ratio pot (from wiper to right-hand/output lug) with a fixed resistor so that one gets the appropriate amount of gain compensation.

You know, undoubtedly Dan Armstrong knew enough about studio-quality compressors and limiters to be able to extract the bare minimum from them and whip up a bare-bones compressor that did as much as was felt to be needed for budget-conscious guitarists.  I say this to emphasize that all of this modification is not a reflection of what Armstrong didn't understand, but more likely a reflection of what he had pared away to get down to the simplest possible configuration that would work with an on-off switch.  When you consider the typical consumer of the original extruded aluminum boxes, over 35 years ago, that was probably a wise decision.  Nowadays, our tastes are a little more refined, our expectations a little higher, and our needs more varied.  So, bit by bit, we're adding back what he had so artfully carved away.

[free electron]

You know, undoubtedly Dan Armstrong knew enough about studio-quality compressors and limiters to be able to extract the bare minimum from them and whip up a bare-bones compressor that did as much as was felt to be needed for budget-conscious guitarists.  I say this to emphasize that all of this modification is not a reflection of what Armstrong didn't understand, but more likely a reflection of what he had pared away to get down to the simplest possible configuration that would work with an on-off switch.  When you consider the typical consumer of the original extruded aluminum boxes, over 35 years ago, that was probably a wise decision.  Nowadays, our tastes are a little more refined, our expectations a little higher, and our needs more varied.  So, bit by bit, we're adding back what he had so artfully carved away.

True. The OS circuit with its topology of enveloper controlled attenuation followed by a constant make up gain stage is more close to the big rack compressor brothers than a most known guitar compressor - Ross and the family, which are atually an automatic gain controllers.
If i'll start a guitar compressor project someday it will have for sure a threshold knob. I like the idea of interfering in the amplitude just above a certain level, but leaving the signal below alone.

[gigimarga]

Can this version of Orange Squeezer to be modified to obtain a distorstion in which the amount of the distortion is controlled by the force of picking (like Boss Dynadrive)?

[free electron]

Can this version of Orange Squeezer to be modified to obtain a distorstion in which the amount of the distortion is controlled by the force of picking (like Boss Dynadrive)?

There are a several ways to get an envelope controlled gain, or amount of distortion. The Dynadrive is digital, but it's not too complicated task and can be easily done in analogue world. Basically what we need is an expander with some sort of clipping producing the overdrive sound. So, let's combine a TS type overdrive with OS/TP's  side chain and variable resistance part:

In this case the FET transistor controls the gain of the opamp stage. This is just a preliminary idea and probably needs a lot of tweaking. The same thing could be done with an OTA or using LDR to control the gain.
About a year ago i had an idea of combining the patented Crate "tube simulating technology" with a TS based overdrive. This time the envelope's influence is focused on the harmonic content of the sound. The picking strength controls the assymetry of the clipping. My idea was to add a Sensitivity pot to control the amount of the bias voltage shift. Here's the schem:

[snoof]

interesting, thanks for posting these.

[gigimarga]

Woooow...very nice..thx a lot free electron!!!

[rnfr]

great stuff! being a sound engineer, i've always been rather unimpressed by guitar specific compressors.  i like how you have started to "sophisticate"  the design a bit.

[buildafriend]

Do you have a layout for this and a BOM? I would like to etch it and give it a shot.