Echomatic attempt - progress report

[Strategy]

Occasionally posted about, rarely done, it's the Echomatic, from the Stompbox Cookbook. Well, as is often the case with rare DIY projects, it's not what I imagined, but it IS musical and kind of fascinating. On one hand, my dreams of a homebrew echoplex are somewhat foiled; my marantz deck has pitch control, but annoyingly this is DISABLED when record is activated.  Darn. But so, as a 'static' (one repeat speed) delay it has a profound, chorus-y magic that is somewhat akin to a Deluxe Memory Man's space rock wobble, but...even more so. Deep. 

Observations:
- the settings are touchy between the tape deck's gain and the pedal's repeats (feedback) control. there is one little sweet spot where you can get long feedback, but if either control is too loud you can hear a weird background high frequency, a heterodyning whine not unlike a couple ring modulators making noise together.
- the tape deck seems to greatly influence the sound. I can see obtaining a variety of tape machines from large open reel decks to other cassette machines. the key seems to be to find one that has varispeed while record is activated. also for those who don't know, this project requires a three-head tape deck
- did original circuit, so not true bypass, should mod tihs
- mix control does not allow for 100% wet signal, so this effect would not be so great on the auxiliary send/fx bus of a mixer - bummer. Maybe there is a way to put the dry signal on a switchable lift/kill.
- tape type (metal, type 1, type 2) affects the timbre, and so does the selectable tape type switch on the tape deck
- using one of my home made cassette loops is interesting because there's more wow and flutter- more Memory Man vibes.
- the mojo old "reel style" cassette I dug up from my tape bin unfortunately doesn't sound the best - darn.

No conclusions yet. Possible next steps:
- more tape machines to test with it
- Variable speed mod to tape deck - possible? worth it? Can I hack a pot into the motor control? don't want to ruin a perfectly good marantz deck (this gets much use in field recordings and loop playback, so I'm hesitant to hack it)
- modify for true bypass
- figure out dry signal lift

Project PDF:



comments/suggestions/questions welcome!
STRATEGY

[FUZZZZzzzz]

not much to add.. but I'm following this with great interest... do you have soundsamples?

[Mark Hammer]

I gather the annoying heterodyning sound is from the bias generator, or whatever it's called.  We tend to forget that, while tape recording is magnetic, the tape head itself is an electromagnet - a coil that gets turned on, to impose a magnetic charge onto the tape oxide.  The coil gets turned on at a high frequency (see:  http://electronics.howstuffworks.com/gadgets/audio-music/cassette3.htm ), and conceivably, it is that frequency that is heterodyning with something else.

[Strategy]

FUZZZZzzzz, I'll try and grab some quick samples during my lunch break today.

Mark, it's funny about the heterodyning- I mean, I've spent plenty of time trying to get various pedals and synth projects to make this sound on PURPOSE, sometimes with no luck! The high frequency of the tape may be heterodyning with whatever tone the too-loud feedback in the amplification of the circuit is making.

[Mark Hammer]

Or maybe the inconsistent speed of the tape drive results in heterodyning of the bias.  You won't hear 100khz on the tape, but if a tape loop is simultaneously recording and playing back, there's a pretty good chance you'll hear the difference signal of 100khz and 98.7khz.  That's only a 1.3% change in speed, but it may be just enough to result in heterodyning.  I'm just speculating here.

[Strategy]

Sorry, still no time to pull sound samples yet but will do so asap. This thing is definitely some space/stoner rock magic, even if it doesn't do all I want yet.

Right now I'm trying to sort out the signal blend - dry signal is always present at the output, which sometimes you want 100% wet, so a mod is in order. Maybe someone here would have insights based on the schematic in the pdf above.

IC1-D is the output buffer/mixer. I tried disengaging R14 to see if that would kill the dry signal at the output but leave the delayed signal. This goof gave me just very distorted everything, instead. In my still pretty undeveloped schematic analyzing skills, I am seeing now that this was sort of the right type of thinking, but maybe putting a switch between R12 and C10 might be better - might this allow me to disengage the dry signal from going out to R11, the mix pot? How far off the mark am I?

In the meantime, i started looking at ways to modify the Marantz PD-221 tape deck so that the pitch wheel is not for 'playback' only - and sure enough there is this thread http://www.gearslutz.com/board/geekslutz-forum/926423-small-mod-tape-echo-speed-control.html
.... I am not the only person to a) have this problem with the marantz PMD series decks and b) use this tape deck for homebrew tape delay. Unfortunately the thread is light on details but I see the general principle, e.g., find the switch that tells the pitch pot to deactivate when record is pressed, and disconnect. It also looks plausible to put in a different pot value for greater delay pitch/rate range.

advice greatly appreciated!!!

[moosapotamus]

I think it is a misnomer to call R11 a mix pot. I could be mistaken, but it looks a lot more like a delay level pot to me (one lug goes directly to ground). There does not appear to be any level control for the dry signal.

Instead of simply lifting R14, you could try replacing it with a pot connected to IC1a the same way as R11 is connected to IC1c. No promises, but that might give you an independent dry level control to go along with the independent delay level control (R11).

I think modding it for a single wet/dry control would be a little more involved.

~ Charlie

[danielzink]

not much to add.. but I'm following this with great interest... do you have soundsamples?

Built mine last year - here's a vid :

[Strategy]

Instead of simply lifting R14, you could try replacing it with a pot connected to IC1a the same way as R11 is connected to IC1c. No promises, but that might give you an independent dry level control to go along with the independent delay level control (R11).
~ Charlie

Charlie, THANKS! I thought there might be another angle to attack this from!!! I will try your suggestion. As it happens, to get a satisfying delayed level, the overall volume pot has to be turned up quite a bit, but then this means there's a huge volume jump between bypassed and engaged effect signal levels...It would be VERY useful to have dry signal on it's own path in this circuit.

Strategy

[Strategy]

danielzink, did you try any mods to your version? I referred to your video a few times in preparing for my build!
Strategy

not much to add.. but I'm following this with great interest... do you have soundsamples?

Built mine last year - here's a vid :

[danielzink]

danielzink, did you try any mods to your version? I referred to your video a few times in preparing for my build!
Strategy

not much to add.. but I'm following this with great interest... do you have soundsamples?

Built mine last year - here's a vid :

Nope. Built it straight off the schematic you posted from the Boscorelli manual.

Made my own PCB though.


Dan

[Strategy]

Dan: did you experience any of the squeaky, heterodyning feedback effects on any settings?
Thanks,
STRATEGY

[Strategy]

Progress!

Dry signal kill works by adding a toggle switch at R14. Tried adding a pot in series with R14 but, no luck with attenuating, I think R14 would have to get wholesale replaced by a 25k pot, which I don't have at the moment. will try this soon.

For the tape deck, I did some research and found that others have modded these marantz decks. I have service docs on the way with a goal of:
- tricking the front panel Pitch and EQ controls into being active when record is pressed (rewire switching so that the pots engage during record mode)
- increase range of pitch pot so very slow delays can be achieved

Further experimentation with tape types has revealed that Maxell II-S is far and away the nicest sound quality. Finding some high end mastering cassettes (chrome?) might even be good, though I wouldn't know a current source for these. My loops are imperfect, as splicing 1/8" tape is very difficult, resulting in a weird garbled spot in the delays -- but I think it adds to the magic. I intend to open up the "reel style" tape and replace the crappy tape inside it with a loop of high quality tape instead.

DIY tape delay will be mine before summer's over!!! 

[Strategy]

Bumping old topic as a few folks were following it. My echomatic + modified Marantz deck project is done.

Finished product:

• "dry signal attenuation" didn't work at all, but a "dry kill" works - to an extent. High frequency transient attack sounds from the i/p leak through. It works well enough as a pedal, but the lack of wet-only signal doesn't make it as useful as a mixer effect
• I was able to squeeze the pcb, jacks, wiring, and switching into the battery compartment, but the spaghetti is pretty unstable. I don't think anything's moving now in there, but no gut shots as I don't want to potentially upset the balance, ha ha. Mostly spaghetti anyhow. Would recommend to others, do yours in a separate enclosure with send/return cables, rather than attempt to squeeze it into a tape deck enclosure

How to mod the internal record switch functions on the Marantz PMD221 so that "pitch" control remains active even if Record and Play are activated:


Summary: not a Space Echo or Echoplex replacement but a fun, inspiring musical thing. Well worth the effort and expense of obtaining the tape deck!

[camp tapes]

Bumping old topic as a few folks were following it. My echomatic + modified Marantz deck project is done.

Any luck tackling the high pitched heterodyning noise?

[Strategy]

Kind of. I've observed that if you keep the tape bias setting on 'metal' you can get the longest feedback repeats with the least heterodyning. Using type II tape was a huge improvement over type 1. I still have to find some high-end, studio grade 'metal' cassette tape and try that as well. I just make sure to keep the input level on the tape deck around "8", anything above introduces the heterodyning-- ultimately that sound is kind of in the background and has a spacy quality, I've kind of accepted it as a quirk of this project.

[camp tapes]

Thanks for the reply. I agree about the "metal" setting producing the least amount of heterodyning. I've also found that adding a 3 band EQ in the feedback loop helps a lot. Cut the hi and lo and boost the mids

[Strategy]

I don't have an EQ pedal, I did try a resonant synth filter I built set to bandpass and that didn't produce good results. What's really crazy is put a PT2399 delay with modulation in the return chain - gets pretty bonkers. I'll try the EQ trick may be a good excuse to finally build an EQ pedal of some sort. Not familiar with the DIY options at all.

[TejfolvonDanone]

I've kind of accepted it as a quirk of this project.

Looks like the "It's not a bug it's a feature" type of problem solving. Haha
Anyway nicely done project. I also have the guts of an old tape recorder with the plans of creating a tape echo/flanger. So i just wanted to store this thread for later references.

[Strategy]

Now the trick of finding 'metal' tapes. I used to use those in four tracks in the early 90s to get the best sound. Cannot find them in my local area. I can't even find my other old favorites Maxell II-S. I guess ordering online is probably better for finding cassette stuff.