EHX - Full Double Tracking Effect  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.

EHX - Full Double Tracking Effect

Postby Scruffie » 10 Oct 2010, 15:14

Hardly what i'd call a Modern Stompbox but the Schematic dates it as 3 years out on '75.

Anyway, here's a Redraw of the Factory Schematic for those of you with poorer eyesight. I think the Redraw is Correct I can't recall where I got the original Factory one from and nor can I confirm its Authenticity so if someone knows the link to that or if it's correct, that'd be handy.

I might see about converting it to 9V & V3205s as it's quite a nice simple looking Delay Project.

The EH Mans Article on the Pedal and its Predecessors - http://electroharmonix.vintageusaguitar ... &Itemid=45

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Re: Electro Harmonix - Full Double Tracking Effect

Postby madbean » 10 Oct 2010, 17:03

Cool! You could maybe do it with two MN3007s, too.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 10 Oct 2010, 17:14

madbean wrote:Cool! You could maybe do it with two MN3007s, too.

Yeah I don't see why not, it only goes between 50ms & 100mS of Delay on the stock unit so there's really no need for the 3005, a 3008 would probably do fine (although i'm gunna see about modding it if I convert it to V3205 to give one 250mS Repeat... i'm sure I could find a use for that).

And for a single slap back repeat... the 3005 (or any other Higher Voltage BBD) probably isn't gunna let much of its 'Magic' tone through so it may aswell be a 32XX to save those 30XXs for better uses.

Not sure about that power supply when it comes to converting though... I've avoided dealing with how reference voltages and how those sorta supplies work untill now...
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Re: Electro Harmonix - Full Double Tracking Effect

Postby ppluis0 » 10 Oct 2010, 19:51

Hey !!!!

This diagram show the oscillator using the CD4047 wich runs at two possibles frequencies, and both are fixed. This way there are two fixed time delays of 50 and 100 msec available.

What about if we replace the oscillator and the BBD chip, with an PT2399 ?

This maintains the functionality of this design but with more affordable parts, I think.

Cheers,
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Re: Electro Harmonix - Full Double Tracking Effect

Postby oldgravity » 10 Oct 2010, 20:21

ppluis0 wrote:Hey !!!!

This diagram show the oscillator using the CD4047 wich runs at two possibles frequencies, and both are fixed. This way there are two fixed time delays of 50 and 100 msec available.

What about if we replace the oscillator and the BBD chip, with an PT2399 ?

This maintains the functionality of this design but with more affordable parts, I think.

Cheers,
Jose


Indeed, that's what I'd do if I wanted an ADT effect, but if going that way I'd disregard the above circuit completely. No sense copying their buffers specifically, when any of the DIY 2399 projects can do this sound easily, plus a lot more.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 10 Oct 2010, 21:32

oldgravity wrote:
ppluis0 wrote:Hey !!!!

This diagram show the oscillator using the CD4047 wich runs at two possibles frequencies, and both are fixed. This way there are two fixed time delays of 50 and 100 msec available.

What about if we replace the oscillator and the BBD chip, with an PT2399 ?

This maintains the functionality of this design but with more affordable parts, I think.

Cheers,
Jose


Indeed, that's what I'd do if I wanted an ADT effect, but if going that way I'd disregard the above circuit completely. No sense copying their buffers specifically, when any of the DIY 2399 projects can do this sound easily, plus a lot more.

Agreed, there are now much better ways of going about this, but for a simple Analog Delay Project (which alot of people look for over the PT2399 to see what the Fuss is about) I think this is actually pretty nifty, could easily fit it in a 1590B enclosure, plus i'm on a bit of a mission to try and resurrect the lost EHX Circuits (Bad Stone, Zipper, Double Track, Attack Decay etc.) at the moment as I think it's a shame they've died off and become nothing but collectors pieces so if anyone has any suggestions for projects/schematic redraws pass them over while I have the free time.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby oldgravity » 10 Oct 2010, 23:01

Oh for sure, I think this circuit looks cool and probably offers some neat sounds, different from a PT2399. I just meant that if you were going to use a PT2399, there's no point in adapting this circuit for that, since there likely isn't any particular coolness in the buffer and amplification portions of the circuit.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 10 Oct 2010, 23:15

oldgravity wrote:Oh for sure, I think this circuit looks cool and probably offers some neat sounds, different from a PT2399. I just meant that if you were going to use a PT2399, there's no point in adapting this circuit for that, since there likely isn't any particular coolness in the buffer and amplification portions of the circuit.

Ah I get ya (not that I took it as any kind of insult, it's not like I designed it! :lol: ) I just thought you meant the circuit in general was outdated in practice (which it is if we're honest).

Nah this has its place, it probably isn't the most useful effect ever so personally I wouldn't bother converting it to a PT2399 either when you could get the same thing out of designs already available, I think this is basically as simple a Analog Delay as you can possibly get and it also has a bit of history behind it which gives it its charm, there's not alot to learn from the circuit as far as I can see other than the basics of Delay Design in which case it provides a valuable learning tool.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 12 Oct 2010, 15:23

:slap: Crap Missed a Ground Connection off the MN3005... How come the Vdd & Gnd are linked on it anyway?

Updated Image, Sorry Moderators!

Found where I got the original too - http://sites.google.com/site/electrocon ... Effect.pdf
(Cheers Nelson if you're still around)

While i'm here anyway, Converting this to V3205, could I forego the Power Supply section and just give the whole thing 9V straight from a battery, swap the pin connections on the V3205 as usual and then just use a 5V Zener to give it its bias voltage? (As it's only rated up to 8V and runs best at around 5V).

Or is that a little bit too simple...?
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Re: Electro Harmonix - Full Double Tracking Effect

Postby madbean » 12 Oct 2010, 17:10

That sounds just right, Scruff. I noticed that missing ground connection...I have to admit, I started drawing up a v3205 version. But, I'm already over-extending myself in projects, so I'm anxious to see what you come up with!

I was thinking about a PT2399 conversion, too. I think it might be worth it for the part count alone. I thought of a pretty good outline with one op-amp, the PT2399, two transistors, minimal caps/resistors and one pot to control the blend like this one. Honestly, I don't know how much difference there could be between true analog and "digital" analog in just slap-back. Guess we'll find out :)
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 12 Oct 2010, 17:43

madbean wrote:That sounds just right, Scruff. I noticed that missing ground connection...I have to admit, I started drawing up a v3205 version. But, I'm already over-extending myself in projects, so I'm anxious to see what you come up with!

I was thinking about a PT2399 conversion, too. I think it might be worth it for the part count alone. I thought of a pretty good outline with one op-amp, the PT2399, two transistors, minimal caps/resistors and one pot to control the blend like this one. Honestly, I don't know how much difference there could be between true analog and "digital" analog in just slap-back. Guess we'll find out :)

Sweet, i'll draw up a preliminary schematic, Phibes is also leanding a hand in the process and has another idea to try.

I wont be able to breadboard this for another few weeks as all my stuffs in storage while I move but I think i'll press on with this one afterwards, looks fairly straight forward.

Yeah that's true, it'd be pretty damn small and I doubt I could hear the difference in a slapback other than brighter or darker tones which could easily be compensated for... might be worth a go.

Here's the .sch file if anyone wants it to mess with.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby RnFR » 13 Oct 2010, 01:22

if you wanted to add another knob, it shouldn't be hard to add a feedback loop for repeats as well, correct? also if someone has the slapback echo schem, it might be cool to add the filter from that effect on another switch.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby madbean » 13 Oct 2010, 02:01

RnFR wrote:if you wanted to add another knob, it shouldn't be hard to add a feedback loop for repeats as well, correct? also if someone has the slapback echo schem, it might be cool to add the filter from that effect on another switch.


Yes, Feedback from right before the Blend knob. Just send it back to the input of the BBD and put a trimmer and cap in-between. This is the kind of effect that would excel with a "Slam" switch, which takes the feedback to maximum. Add a couple of back to back 1n914s to ground from the feedback control to keep the oscillation under control and it will sound hella cool.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 13 Oct 2010, 15:15

RnFR wrote:also if someone has the slapback echo schem, it might be cool to add the filter from that effect on another switch.

http://sites.google.com/site/electrocon ... H-4700.jpg :thumbsup It's actually readable too!

Sounds like you guys have quite the plans for this unit! Although I don't really know if it's going to have a sound worthy of such mods yet being such a primitive design, could be fun to try, i'll try and get the basic unit verified and a PCB layout sorted though.
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Re: Electro Harmonix - Full Double Tracking Effect  [schematic]

Postby phibes » 22 Nov 2010, 06:35

I threw this on the board bread with a Cool Audio 3205 and it's pretty cool. Super simple but right up my alley. I'll attach a schematic if anyone wants to try it out or mess with it. I left the power supply simple at 9v for the BBD because that's where it sounded best and it keeps the parts count low. Another obvious problem with being an old non true-bypass effect, it doesn't reach unity gain if converted for true bypass. As mentioned above there is definitely a lot of room for improvements. I like keeping vintage circuits as close to the originality as I can so I didn't dive too heavily into it. It's definitely box worthy in my opinion. Anyway, it's verified with the Cool Audio Chip if anyone wants to draw a layout.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 23 Nov 2010, 04:55

Okay... here's my first ever attempt at a PCB layout for a pedal so go easy on it... it's not the greatest and I haven't checked it or tidied it up but it's a proof of concept atleast to get this into a 1590B with a Board Mounted Pot (Pot Mounted on Back) and hopefully battery too.

Do any of the PCB gurus have any tips from what i've done? If I used stand up resistors or upped the enclsoure to a 125B I could probably get it in but i'd much prefer not to, I know it's kinda ugly in places but I quickly lost room, hence the 3 large jumpers (although mounted on the back they might be okay and would only add to the authenticity of an EHX pedal :lol: ) aswell as five smaller ones and the generally squished areas.

From the schematic Phibes has posted I dropped the 0.1uF Cap and 1N4001 from the power supply section (Kept the 100uF though, C14) and added a 1k5 from 9V to the 3205 Ala the Aqua Puss (R19), R11 is mislabelled R33 too.

Board measures 53.34 x 53.34

Any feedback however harsh will be appreciated :thumbsup

FullDouble SS.gif

FullDouble PCB.gif

Full Double.gif
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Re: Electro Harmonix - Full Double Tracking Effect

Postby Scruffie » 24 Nov 2010, 03:23

Tidied Up, Reshuffled & Checked PCB!
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Re: Electro Harmonix - Full Double Tracking Effect

Postby phibes » 15 Mar 2011, 18:29

Saw one on the bay so I inquired about a top board shot for fun.
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Re: Electro Harmonix - Full Double Tracking Effect

Postby chi_boy » 16 Mar 2011, 15:12

I'm really torn about this effect. I like the idea and have actually toyed with the idea of of replicating it with a Rebote 2 as a foundation. I even bought the board.

The thing that has me torn is that if a good analog delay can do the same thing, why build this? Or can it do the same thing?

Am I mistaken in my understanding of what this does?

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Re: Electro Harmonix - Full Double Tracking Effect

Postby pinkjimiphoton » 12 Oct 2012, 23:30

just picked up one of these, and converted it to run with a charge pump instead of the two batteries.
had to mess with it a little to get it working right, but it's actually a pretty cool effect...definitely smells like 1978 or so with a fuzz in front of it.

trim pot setting is pretty crucial...only really a narrow window where it works right.

the 50ms setting is barely noticeable, but there..
the 100ms is more pronounced. it really does kinda sound like playing along with a tape.

i'd build one of these again if i needed to, even thinking about adding it to my live board.
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