Coverting a overdrive into stereo, possible?

[Brandsmannen]

Hi all!

Sorry for my first post being a thread, but I couldn't really find what I was looking for when I searched.

Ok, so the thing is, I like overdrive after reverb very much, but recently I've started to run directly into the mixer with my band in stereo, which sound gorgeous with the delays and reverb. However, the overdrive-after-reverb thing kinda gets lost. I know I could buy another reverb and put it in front of the chain, but I started thinking about making a stereo overdrive and I can't really let the thought go.

Well, I'm a decent solderer, and I can work out a schematic alright, but apart from that, I'm kinda lost in the DIY pedaling. Hence this thread. So do any of you think that it would be possible to make a SD-1, a marshall shredmaster or (preferably, since it's what I use) a barber LTD or just about anything into stereo? With ins and outs? Sorry if this question is utterly retarded and stupid/impossible, after all, I am a noob

[Liquitone]

Welcome to the forum Brandsmannen,

It's not a silly or stupid question at all. Even though you hardly see any stereo drive pedals there are situations where they would be very useful, like in your setup.
Like you I prefer some pedals in front of my overdrive, like a delay and a stereo uni-vibe and made myself a stereo, or rather; dual mono version of the Wampler Plexi-Drive.
It's as simple as running two identical circuits in parallel, each with their own in- and output. Bypass-switching could be done with a 4PDT, but I prefer using relays for this, one for each channel.
If you use stereo-potentiometers you can control both channels at the same time with just one set of knobs.

[R.G.]

A lot depends on what you mean by "stereo".

The term started being used in the mid 60s or so (near as my personal memory goes) to denote two-channel recordings that were recorded so as to preserve the aural illusion of space - the instruments being spread across a mental sound stage which represented in some what where they were in relationship to one another. This was before over-production of recordings manipulated multiple tracks of single instruments/sound into the illusion of spaces that never existed.

If you think about it, "stereo" has to mean something like "more than one channel with differences in phase, delay, and frequency response that gives the illusion to a listener of physical spread of the sound sources." (Obviously, I just made that up on the fly.)

Since the human auditory apparatus detects both phase and time differences in spatial localization, giveing a stereo illusion depends a lot on differences in time and phase between the channels, and trivially if at all on clipping or harmonic content.

So if you want "stereo" to mean "audibly spread out on the mental sound stage", you can't do it with two clipping channels, however similar or different they are, because they tend to run in synchronism in or out of phase. At best, it'll sound like a trick, and at worst, won't make much of an illusion.

If you like the sound of delay, then overdrive, a better way to get something that's palpably stereo is to use your delay, then overdrive, and then after that, then two channels with different phases and/or delays. It's OK to put a different overdrive in each channel for some tonal variation, but the phase/delay is what will inject most of the spatial separation that will make it sound "stereo".

"Stereo" phasers, flangers and such tend to either have multiple delays, perhaps one tapped delay, or go cheap and both add and subtract the delay signal from the dry signal to get two channels that have different interferences with the dry signal for the "stereo" effect. It's better than nothing, and is a cheap way to add a feature to a pedal, in spite of not being what the word used to mean.

IMHO.

[DrAlx]

It's OK to put a different overdrive in each channel for some tonal variation, but the phase/delay is what will inject most of the spatial separation that will make it sound "stereo".

So could you just stick a bunch of fixed all-pass filters into one of the channels to introduce phase changes?

Code Select Expand


                        |---> Left
Reverb ---> Overdrive ---|
                        |---> Fixed All-pass Stages ---> Right


If you use headphones, then there are no phase notches (because the two channels never physically interfere).
There should be enough of a difference in the sounds for it to appear that the sound isn't coming from a single location in the middle of your head.

Not sure what it will be like if you use two speakers in a room though.  Depends on how the phase-shifts from the all-pass stages compare to the phase shifts that occur between sound leaving the speakers and reaching your ears.

[Salvatore]

I use 2 channel distortion after other fx all the time (often for the rougher stuff  I begin with some overdrive, then an fx chain, then stereo distortion, got lots of those, and normally some more stuff like delay and reverb).

The simple answer for you're question is, build the distortion of choice x 2, and decide if you want the 2 channels to have separate controls, or use stereo pots so you control both distortions at ones.

[R.G.]

So could you just stick a bunch of fixed all-pass filters into one of the channels to introduce phase changes?

You could - although like any tinkered-with "stereo" synthesis, the quality of the effect is subject to question.

Just about any different signals in two channels could be called "stereo" - and is. However, the more synchronous the signals are, the less psychoacoustically convincing the effect is likely to be. Stereo was intended (I think) to capture the audible illusion of the 3-d structure of the place where the music was being played. There were long discussions, arguments and advertising blather about the ability of this or that stereo technique to capture the ambience of the "concert hall". There were special recordings made with microphones in the ear openings of human-looking dummies with external ears for listening in headphones so the actual detail of ear-to-ear signal acquisition could be captured.

But the point of stereo is psychoacoustic localization, and from what little I know of psychoacoustics, that's dependent on phase delay and time delay. The issue gets very tenuous when any "soundstage" is made up by the guy mixing down multiple performance tracks each made in a nearly anechoic room.

So - sure, fixed phase delays might be a useful tool. I think that there were some quadraphonic encoding schemes that used something like that back when "quad" was topical. One version of the phase delay line that might be useful is the Hilbert or dome filter. This introduces a broadband 90 degree phase delay between two versions of a single signal. Could be interesting.

If you use headphones, then there are no phase notches (because the two channels never physically interfere).
There should be enough of a difference in the sounds for it to appear that the sound isn't coming from a single location in the middle of your head.

Not sure what it will be like if you use two speakers in a room though.  Depends on how the phase-shifts from the all-pass stages compare to the phase shifts that occur between sound leaving the speakers and reaching your ears.

Pretty much any difference concocted between the channels will cause some audible difference. But simply doing two different distortions leaves the fundamentals in synchronism, and isn't likely to tickle the human auditory apparatus into thinking the signal is spread out. A slight frequency modulation in the form of a small amount of vibrato-doppler would be useful, probably.

But it's open to experimentation.

[samhay]

Does the OP's reverb spit out a stereo / dual channel output?

[karbomusic]

Ok, so the thing is, I like overdrive after reverb very much, but recently I've started to run directly into the mixer with my band in stereo, which sound gorgeous with the delays and reverb.

Sounds to me like they want to overdrive an already stereo signal so how it  became "stereo" mostly doesn't matter. The thing that matters is having two separate signal paths from end-to-end in the overdrive. It really wouldn't matter if the overdrive introduced slightly more stereo but the real point is to not "de-stereo" what is going into the overdrive.

Actually I take that back, the sentence is confusing me.

[petemoore]

 Dual Mono is required to play ''Stereo''. 2 each: source/pre-amp-amp/speaker systems, ie 2 complete channels, referred to as right an left channels.
L/R is a common way to refer to a couple channels used for ''stereo''.
In the stompbox it is possible to split the signal, process each 'side' differently [say for instance remove the highs and compress the remaining LF's on one side, Fuzz and bandwidth control the other side, use breakout jacks here or there to include additional effects] , then mix them back to 1 output, ..phrased as "split signal processing"?
For everyone to understand A/B or L/R, "Stereo", Dual Mono, and split signal processing, a block diagram or even schematic reference may help clarify meaning.

[ashcat_lt]

This could be as easy as a pair of back-to-back diodes to ground for each of the stereo channels.  Especially if you use germanium or shottky's you should have plenty of oomph from the mixer or other line level devices to push them into clipping.  With the diodes box in series between the reverb unit and the mixer you'll get rat/ds-1 type distortion.  With them in parallel - spilt from the output of the reverb or on a second set of sends to separate return points - you'll get something very similar to TS style overdrive.  I would probably try to bring the diode path back to actual channels on the mixer so that you can use the EQ to tailor the tone a bit.  If you can find a way to get EQ before the diodes, it's even more flexible.

[PRR]

> The term started being used in the mid 60s or so (near as my personal memory goes)

"STEREO!!" as short for Stereophonic was commercially available in the 1950s, a buzz-word by late 1950s.

Experiments run back to 1881. Stereo music over telephones was commercial 1890 to 1932. Fletcher and Blumlein worked through the 1930s. Fantasia 1940 had multiple sound channels, but was so costly it was remixed mono.

2-track tapes were commercial early 1950s.

There was a whacko disk player with two needles on one arm, 1953, records of locomotives and thunderstorms.

The Blumlein X/Y Stereo LP (invented in 1931) was commercial in 1958. FM Stereo in 1961.

What you may be thinking.... traditional mono record players would rip the grooves out of stereo pressings. Most 45s/LPs were issued mono and stereo well into the 1960s, when compatable and stereo needles became common.
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I have a hard time imaging "stereo" from an instrument only a foot wide. You have to have a mental picture of why a small instrument should have "width". Pink Floyd used a small image moving left/right and even 4-speaker around the concert hall. This is just a cross-fader, and usually manual.

[Ben N]

I understand the requirement as a kind of doubling effect. Anyway, I recall having a small boombox with a simulated stereo feature for adding space to mono (or even stereo) material, consisting, IIRC, of comb filters emphasizing complementary frequency bands on the two channels to enhance separation. I'm not sure how one would implement such a thing in DIY without several high-order filters, although it must be doable, and the resulting smear and phase cancellation effects probably aren't objectionable in a distortion.

[Brandsmannen]

Wow, thanks everybody for the replies!!! I have had few busy days and kinda forgot about my own thread for a while. 

I think I'm going to try and build an overdrive with stereo ins and outs, and use (as mentioned in the first post) a 4dpt and stereo potentiometers. Does anyone know of a easy overdrive projects where the OD doesn't color the sound to much?

Thanks everybody again

[ashcat_lt]

Ahem...

Any overdrive you choose will consist of a very few components:

1) Some filtering either before or after...
B) A gain stage which boosts the signal enough to clip...
III) Some diodes

You have 1 and B built into the mixer.

[wavley]

I run a what I would call dual mono rig to be technically correct I guess, although with everything bypassed and all levels set properly my guitar images in the middle of the room, we do the same with the bass when we record... on both sides of the drums and captured by both close mics and a Mid/Side pair in the room.

I run separate signal paths after a certain point in my rig so I can have a phaser in one or both channels, ping pong delay, delay only in one channel... whatever.  The majority of my major clipping, fuzz, or whathaveyou actually happens in the mono portion of my rig, BUT I use fairly low wattage and very touch sensitive amps that will clip depending on dynamics, one single ended single 6CA7 amp that clips before my modded out Vibrolux making for a lot of complex tonal possibilities.  That said, I find playing phase tricks (as in fixed all passes or 180 degree flips) or delay tricks (as in delaying one channel in a time less than a discrete echo) often sound novel, tiresome, and not very useful, phase tricks in particular will completely screw with you in the recording process.

I guess this is my long way of saying that if I were to build a stereo (or dual mono or two channel or whatever you decide to call it) dirt box, I would consider doing a couple of things:  1. Personally, I would keep the controls for the two channels separate for a few reasons (taking advantage of the characteristics of two different amps, a broader stereo image, simulating two guitars...)  2.  I like the idea of using a 4PDT to turn the whole thing off, but you might also consider just putting two 3PDT switches close enough together that you can hit them at the same time but still have the option of drive in just one channel.

[Brandsmannen]

Thanks for the ideas wavley. I was gonna go with stereo pots, but now I'm not very sure anymore. I only own one amp right now (although in the band we play stereo right into the mixer) but I'm gonna buy another amp soon enough, which will be a lot different i suspect. Separate controls might not be such a bad idea. I found a cheap enough overdrive project with only two knobs, which i think would suit me well. This one: http://www.musikding.de/The-Llama-Overdrive-kit

It might color the sound more than I would like, but meh, it might be great as well

[Ben N]

If that is a Red Lama clone (itself a clone of the Craig Anderton Tube Sound Fuzz), then you might as well skip the kit and make it on perboard (it's a simple design, very few parts) so you can take advantage of the 3-4 unused inverters already on the chip for your second overdrive. That is to say there are six inverters on the chip, and the RL uses only 2-3 of them, so it is perfect for a stereo/dual overdrive.

[bool]

>>> You have to have a mental picture of why a small instrument should have "width".

The why: so it sounds big(er) on a small set / radio, laptop, headphones etc.
The how: various methods, ranging from source capture techniques to re(up)mixing and manipulating mono or narrow image stereo sources.

[merlinb]

Does anyone know of a easy overdrive projects where the OD doesn't color the sound too much?

Wha   Surely OD is by definition colouring the sound by adding distortion? Unless it's switched off...  Or do you mean very mild distortion?

[Ben N]

A much hashed-over topic, and indeed, "transparent overdrive" is a bit of a contradiction in terms. And that's not just because the purpose of an OD is to distort the signal; it's also because producing a distortion unit that does not sound like poo generally involves emphasizing certain parts of the signal spectrum and deemphasizing others. For example, distortion units fed a full-range signal tend to fart out from bass indigestion, so most of them have some hi-pass filtering at the input to keep the bass under control. Another thing distortions do is emphasize high harmonics, which if not controlled tend to become an annoying mass of ice-pick; ergo, low pass filtering at the output. Put the two together, and if they are not subtle you have a notable mid-range emphasis that in some cases can sound nasally.

Still, I think I know what you mean, and I generally have tried to have two overdrives on board, one with a flattish eq profile and low-to-medium gain, and another with more mid-emphasis, like a tubescreamer/SD-1-alike, Klon-alike, what-have-you for stacking and driving the amp. My flattish ODs have included a DOD FX-50 (quite underrated IMHO, and easy to DIY), a Boss BD-2 (one I have wanted to love, but just could not get comfortable with), a Boss OD-3 and an OCD clone. Also worthy of exploration are the Barber LTD (schematic available--do a search here) and Timmy, both of which have nice options for tailoring the eq so that at low gains you preserve as much of the original frequencies as possible.