EM5 Echomachine build

[gcwills]

Hi all,
For some time I've been aware of the obsolete Ibanez Soundtrack EM5 Echo machine delay. It has garnered a lot of fans for its tone.
So decided to bite the bullet and build one.
The heart of the EM5 is the Matsushita M65831 karaoke echo ic which although obsolete seems to be still available via Ebay and other online sellers.
I simplified the circuit somewhat by eliminating the fet switching and using a TL074 instead of the two dual opamps.
Also, the delay clock was simplified to a simple LC arrangement with a hex BCD switch to set delay time.
Here is the original Ibanez EM5 circuit:

[chuckd666]

This site has a PCB of it: https://www.3pdt.com/products/tape-echo-machine

[gcwills]

Thanks for that. Yes 3pdt have the PCB and a full kit.
Unfortunately the post cost is prohibitive to my part of the world.
However it is a great resource for anyone in the US.

[chuckd666]

Yes indeed, it makes sense if you're somewhere on the Pacific! Alas...

[gcwills]

Below is the circuit of my simplified EM5 Echomachine.

As mentioned, I have removed the FET switching and now the wet signal is switched in and out with a SPST pushbutton.
To simplify the clock generator I used a pi LC network of two 470p capacitors and a 100uH inductor between pins 2 and 3 of the M65831. Delay time is now set with a hex BCD switch to allow 16 increments of delay time from approx 25ms to 400ms.

These simplifications allowed me to build the EM5 on a small perfboard which can fit in a 1590B box.
I am really liking the sound of this delay pedal and can see why it receives such good reviews. Of all of my delay pedals, it sounds closest to a tape delay. Repeats do not get in the way of the dry signal, in spite of being brighter than BBD or PT2399 designs.

To come are some photos of the populated perfboard

[sergiomr706]

In the original, first posted schematic, what is CP1? from 8 pin of 74HCU04? I was looking pictures of this from another post

http://www.diystompboxes.com/smfforum/index.php?topic=112429.msg1037476#msg1037476

and cant figure it out.
Thank you

[gcwills]

The CP1 reference on the original circuit is a test point to allow measurement of the clock frequency. The 74HCU04 inverters form an oscillator to generate the clock which is fed into pin 2 of the M65831.
In my circuit, a simple LC pi network is used instead of a crystal as the clock oscillator.

[gcwills]

Here is an image of the populated perfboard:



Not much to it apart from the M65831 and TL074. Not shown is the hexadecimal BCD switch and outboard pots etc.
It makes for a fairly small footprint which allows for mounting in a small 1590B diecast box.

[sergiomr706]

Thanks a lot fot that information and a great effort. Im not ee, so excuse me if im wrong but in your perf version, is delay time not working progressively? Does it make 25 msconds jumps? I know its not much, just curious if you know wich crystal oscillator is that original one. Getting rid of the switching system is great too in order to save space

[roseblood11]

Please share the layout!

[suryabeep]

Sorry if this is really basic, but :
1)what are the symbols that look like capacitors but with diagonal lines across them?
2)Also what is the loop with 100 uH written next to it?
3)Whats a hex BCD switch? will one of these do? https://www.mouser.com/ProductDetail/Apem/PT65103/?qs=sGAEpiMZZMsfGXvUAbE5P3hZRUxdvcGfyDbePER4rkE%3d . How would I connect one of these to the schem as shown?
Thanks!

[gcwills]

Thanks for your interest in my EM5.

Re the delay time, the hex BCD switch increments the delay time in 25ms steps from 25ms to 400ms in 16 steps.
Re layout, I don't have a perf board layout, but here is a photo of the underside of the board:



Re the circuit symbols that look like caps, they are ground connections. The "loop" is a 100uH RF choke available from most sellers.
A hexadecimal BCD switch comes in a few varieties. The one you link is fine but not easy to adjust. I used one like this: http://www.conrad.com/medias/global/ce/7000_7999/7000/7010/7010/701084_BB_00_FB.EPS_1000.jpg

[duck_arse]

....
1)what are the symbols that look like capacitors but with diagonal lines across them?
....
Thanks!

I think this is referring to the electrolytic capacitor symbol, the two plates with the diagonal lines between.

[gcwills]

Oh yes, thanks for that.

[Ice-9]

....
1)what are the symbols that look like capacitors but with diagonal lines across them?
....
Thanks!

I think this is referring to the electrolytic capacitor symbol, the two plates with the diagonal lines between.

You often see electro's drawn like that on older circuit diagrams. 

[digitalunderdog]

Very cool! I love the EM5 and this is very interesting. Was the reason to use the HEX because of size? I'd like to build this but with the ability to use a pot for delay time. There's some nice mods for the EM5 also, especially the tone mod which makes the repeats gradually darker like a tape delay.

[gcwills]

Thanks for your interest. The BCD switch was a way to simplify the EM5 and allow it to fit in a 1590b. There is no reason that you couldn't build the extra circuitry around the hex inverter and extra transistors to generate the clock signal.
BTW, I recently found a source of M65831s for $2 posted on Aliexpress.

[digitalunderdog]

Yes! Aliexpress is a good source for those, I picked yup a few. Thank you. I am trying to add a modulation board to my EM5 but am having trouble connecting it to a contact point. I built the 1776 modulation board but it doesn't seem to work on non PT2399 delays. Do you have any ideas on creating a modulation effect on the EM5, and if theres a modulation circuit that would work with the EM5?

[gcwills]

To add modulation to the EM5, one option is to use the LFO/clock oscillator circuit from the EH DMM.
As time permits I might breadboard this to see if it is suitable. The "pi" LC network in my EM5 would be removed, and one of the clock outputs from the 4047 used to drive pin 2 of the M65831

[vortex]

Perhaps of interest as a mod.

I often run my EM-5 on batteries. One day I noticed that the repeats were extra long with very cool warped artifacts. As expected, the battery voltage was rather low.

I figured that I could recreate this great sound with an external sag control I have boxed up. It didn't work. I don't have the schematic handy but if I recall correctly the voltage gets regulated seperately for the ic's. If you 'sag' just the one of them you should be able to get the longer repeats with warped artifacts.