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Small mod for tape echo speed control?
Old 3rd May 2014
  #1
Gear Maniac
Small mod for tape echo speed control?

Hi all,
I've got a Marantz PMD222 cool little 3 head cassette recorder. I use it for tape echo. It's a two speed machine, and there is a varispeed/pitch knob. The only fallback in using this machine for echo is that the varispeed knob only works during playback. So I only have two speeds to use....
....Unless I can make the small mod to change the fact the varispeed gets disabled during record mode.

Inside there is a PCB mounted switch that is flipped by a metal extension from the record button. SJ01. This switch serves two purposes: 1: Record! 2: disable pitch knob :(

I am attaching here the two pertinent schematics.. RM51 is the pitch knob variable resistor. SJ01 is the PCB mounted switch that is triggered by the record button. For the pitch disable function, the switch is called SJ01 3/4. For the record function it's called Sj01 1/4. How do these 3/4 and 1/4 digits relate to the physical switch?

Anyone have any suggestions as to how to jump it somehow so that the pitch component of the switch thinks it's always in playback?

I can attach some pics of pcb underside for a sense of it. Will do that in a reply below...
Attached Thumbnails
Small mod for tape echo speed control?-image_585.jpg   Small mod for tape echo speed control?-image_8023.jpg  
Old 3rd May 2014
  #2
Gear Maniac
Here's the PCB underside of the switch (long set of two rows) and the pitch variable resistor (4 points a bottom of second image)
Attached Thumbnails
Small mod for tape echo speed control?-image_7465.jpg   Small mod for tape echo speed control?-image_6288.jpg  
Old 3rd May 2014
  #3
Lives for gear
 

I'm replying here to both of your topics since they both relate to the same specific machine. I used to have a much older three-head Marantz, from their Superscope line, and I used it for tape delay.

I didn't have your issue with dry bleed; that sounds to me like aging components in the mix circuit.

I did however implement the varispeed-on-playback mod you're asking about. Did you intend to only post pieces of the schematic? Because those scans are basically useless as is; the whole schematic is what we need.

But it's not that hard to figure out without the schematic - you just need to find the pair of contacts that gets disconnected when it's in record mode. I did that by trial and error; if memory serves I traced back from the varispeed pot to the switch to get a sense of which contacts might be relevant, then put the machine in record mode and manually connected contact pairs on the switch until the varispeed worked. Solder those together and you're done.
Old 3rd May 2014
  #4
Gear Maniac
Per the faulty mix circuit:
Isn't there no mix circuit? It's just a recorder. Not a proper marketed tape delay. This there is no mix/wet knob. Just input level and output level.

Per the schematics for mod: looking at that zoomed in image of the variable resistor for pitch... It seems to me the playback mode has it's way of communicating w the resistor, and then the record mode has it's way of communicating with it. Your solution sounds perry but doesn't that still leave in tact the playback set of components? Elsewhere in the manual, there is this attached explanation...

Doesn't that keep the resistor nulled if I don't snip the playback/pitch establishment somehow?
Attached Thumbnails
Small mod for tape echo speed control?-image_9688.jpg  
Old 3rd May 2014
  #5
Gear Maniac
Actually I guess there is a chance the source/tape selection process has a fault. I could hunt for where the source signal is being routed to all the various output signals (which then go to headphones, rca, speaker) and out a switch in it's path itself. Or I could just kill the source at that same point, but I might sometimes want source. However 99% of the time I won't care to monitor source.
Old 3rd May 2014
  #6
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Quote:
Originally Posted by coilandmagnet View Post
Actually I guess there is a chance the source/tape selection process has a fault.
Yeah, when I said "mix circuit" I just meant whatever enables you to select a source for monitoring, whether it's a switch, pot, etc.

As for the varispeed pot, I see now where the pitch knob is in your original schematic swatches. You're right; looks like you'd need to cut the trace from the wiper of the pot to the switch (to kill the playback nulling) as well as making the connection from... the other center wiper?... whatever's getting cut by the switch. Maybe that pot does indeed have two connections to the wiper, just to make the layout easier on the board.
Old 3rd May 2014
  #7
Gear Maniac
I'm a little new to some things.. What's a wiper? The knob?
And how does one safely eliminate a trace in a pcb? I'm good with soldering.
Old 4th May 2014
  #8
On SJ01, remove the fixed tap lead on the speed pot and connect the switch pin to the other lead from the pot (the wiper lead). The wiper lead should now connect to both outside terminals of the switch. The speed pot fixed tap now is disconnected.

You can also change the speed over a wider range than the existing pitch trim control by replacing RM52 (1.2k resistor) with a 1K trim pot in series with a 1k fixed resistor. That replaces the fixed 1.2k resistance with a variable 1k to 2k resistance value.

The term "wiper" refers to a moving contact inside of the speed trim pot. It's connected to the center terminal on a "normal" 3-terminal pot. A tapped pot is unusual and a PIC is needed to positively identify the correct terminals.

Don't touch the other terminals on the switch.

If you post a PIC of the back of the speed pot, we can point out which terminals are which.

Modified schematic attached.
Attached Thumbnails
Small mod for tape echo speed control?-varyspeed-mod.jpg  
Old 4th May 2014
  #9
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Quote:
Originally Posted by Lotus 7 View Post
On SJ01, remove the fixed tap lead on the speed pot and connect the switch pin to the other lead from the pot (the wiper lead). The wiper lead should now connect to both outside terminals of the switch. The speed pot fixed tap now is disconnected.
Good suggestion to avoid cutting a trace. (With a razor knife, to answer the OP's question; hardly safe or advisable, but it works.)

On a schematic, the wiper is the lead with the arrow pointing to the center of the pot's resistor symbol. Usually pots have three leads and the wiper is the center, as Lotus said, but this pot seems to also have a fixed tap in the center, hence the fourth lead on the PCB.

With a multimeter you can measure the resistance between pairs of pot pins (with the machine off). The outside leads will have a fixed resistance of ~500 ohms, while the wiper's resistance relative to either of the outside leads will change as you move the knob. Assuming the other tap is fixed, it should show up as a fixed resistance around 250 ohms, again relative to either of the fixed leads.

I'd guess the outer pins on the PCB are the two fixed leads, with the wiper and fixed center tap in between. Can't tell which is which from the pic though.
Old 4th May 2014
  #10
Gear Maniac
Ok so here are photos of the switch and the variable resistor.
For the switch, if you look at the previous pic of underside of PCB, the white end of switch is the top end of two columns. (Photo is on angle, but you can still tell)

And for variable resistor (pitch), in orig underside pic u can see the knob sticking out above it as reference.

Thanks much to everyone, this all makes perfect sense. I will need to come up with a physical approach to making this mod..

Originally Posted by Lotus 7
On SJ01, remove the fixed tap lead on the speed pot and connect the switch pin to the other lead from the pot (the wiper lead). The wiper lead should now connect to both outside terminals of the switch. The speed pot fixed tap now is disconnected.

I understand the redesign, but not sure if I should be attacking pcb traces and if so for which component. There are no wires anywhere. It's all surface traces.
Attached Thumbnails
Small mod for tape echo speed control?-image_7004.jpg   Small mod for tape echo speed control?-image_8619.jpg  
Old 5th May 2014
  #11
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First, measure the resistance across the pairs of output pins I mentioned so you can figure out which pin on the pot is connected to what internally.

For my money, if the fixed tap on the pot has a nice discrete trace (i.e., not too close to other traces) from its pin to the rest of the board, the easiest way to disconnect that pin is simply to cut the trace on the PCB with a sharp razor knife and a little sawing action. With a multimeter, you can test for continuity between the pin and the next pad it connects to; when continuity goes away, you've cut the trace.

For the new connection, you'll need a short length of small wire. I typically use 30 AWG wire-wrapping wire for stuff like this, but anything will work. Just be careful you don't short anything else out when soldering it between the relevant pads on the PCB.
Old 5th May 2014
  #12
Since both the switch and pot are PC mount, you will have to cut some. You will probably have to also uses an ohmmeter to confirm the 'tap" and the "wiper" pins on the pot. To identify the proper pins on the switch, you will have to follow the traces to a few other components, specifically to the emitter of QM52 and the lead to the wiper of the pitch control.
Old 5th May 2014
  #13
Gear Maniac
Here's what I measured..
Attached Thumbnails
Small mod for tape echo speed control?-image_7661.jpg  
Old 5th May 2014
  #14
Gear Maniac
Anyone able to help me determine which is the pin to cut from this here pitch knob?
In the diagram, the markings under the pin set are all unchanged by knob turning, and the markings above the pin set all are changed by the knob as I listed.
Old 5th May 2014
  #15
Gear Maniac
I believe I understand now.. The fixed tap is the pin all the way to the right. It's the one that has 250 fixed to each "outside" lead. "Outside" meaning not the wiper, and of course not the fixed one. The original path is the "outside" ones.
So I should cleanly remove the trace from this pin. Sounds good. Of anyone sees this as wrong give a shout!

On to the more elaborate switch where I have to trace the correct pin to jump at/from/to....
Old 5th May 2014
  #16
Gear Maniac
Oh so I'll just check for this very lead coming out of SJ01 and then jump that pin to the wiper lead. This is all done by the switch, not the pot. Roger that.
Old 6th May 2014
  #17
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I need to do this to my PMD221 as well. But what I'd really like to do is extend the range of the speed control so that it's continuously adjustable from fast-ish to stopped. I usually find a way to do this to all tape decks that I play around with, though the solution is sometimes less than elegant (i.e. building an adjustable power supply for a DC motor).
Old 6th May 2014
  #18
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Yeah, those pins look like (from left to right) outside, wiper, outside, fixed tap. Y'all are making me want to get another Marantz deck. Must... resist... more gear...
Old 6th May 2014
  #19
Gear Maniac
Well it worked! I ended up deciding to cut the trace right before the pin 4 because there was so much room to work right there. It was tougher than I though to saw a trade. You gotta actually dig a little to get all the conductive material dug up. But it was pretty simple.
As for checking for continuity to locate proper relative pins in the SJ01 switch, that was actually more confusing than helpful. All sorts of stuff beeps with continuity to pin 4 of pitch knob. So rather than going full force diagnostic I simply held up a light behind the PCB so the traces were very sharp and I followed the two relevant traces manually. For my PMD222, the bottom right pin (of the two verticle columns pictured) went to Pin 4 of pitch knob, then the pin two above that (so third up from the bottom right pin) went to pin 2 of the pitch knob. This is the wiper lead.

Thus I needed to connect the bottom right Pin of SJ01 switch, to pin 2 of pitch knob, which is the wiper. I just used some regular lead cable, exposed a tiny amount of lead on either end, tinned them just a tiny bit, and very carefully soldered them to the respective pins. I then taped down the wire at various points along board so ease any tension on connections.

It works great!!

Next I'm going to change the resistor of RM52, as Lotus 7 suggests, to something higher. It currently 1.2K ohms or there abouts. Lotus 7 suggested putting in a variable 1k in series with a 1k, this making an adjustable range of 1 to 2 k, which is suppose puts it close to double original range if ine turns that setup to max, but Ive only got a 3.2 k resistor on hand so I might just use that to replace the 1.2K RM52 instead, this will give me somewhere around 2 1/2 X the orig range. I guess that means 30% ish, instead of 12%. Right? Is this too much?

These motors were designed to go pretty all over the place already, given there are already two speeds and 12% +/- either direction. The biggest chance for damage is when I'm at standard speed (as opposed to "slow") and crank it to 30%. I guess I'll just take my chances. Any thoughts on this folks?
Old 9th June 2016
  #20
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Hey @circuitsynth, I'm a complete noob in electronic and even if your explanations seems pretty clear I'd like to summarize to be sure I get it and to not mess up with my PMD222.

As far as I understand I'd do the pictured mod on the recorder. Am I right ? Can I go for it ?
Attached Thumbnails
Small mod for tape echo speed control?-pitch.jpg   Small mod for tape echo speed control?-sj01.jpg  
Old 7th November 2016
  #21
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Bump !

Anyone can confirm that by doing what's on the pictures of the previous post, it will enable the pitch variation while recording ?
I really don't want to mess up with my PMD 222.
Old 3rd August 2017
  #22
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asulauz, did you get it working? Now I want to make this mod to my 222
Old 3rd August 2017
  #23
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Unfortunately not. I've never had any advice and because I was scared to mess everything up I've never did the mod.
However, if you have some information I'll be really really interested.
Old 8th August 2017
  #24
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Quote:
Originally Posted by asulauz View Post
Hey @circuitsynth, I'm a complete noob in electronic and even if your explanations seems pretty clear I'd like to summarize to be sure I get it and to not mess up with my PMD222.

As far as I understand I'd do the pictured mod on the recorder. Am I right ? Can I go for it ?
What I understood from circuitsynth explanation, you are correct and I did these steps to my PMD222, now I am able to adjust pitch during the record, but internal speaker started act strange, I need some time to figure out how and when source/tape button needs to be pressed.

Here's todays result:
https://www.instagram.com/p/BXiK7JFD...-by=karolis.va
Old 9th August 2017
  #25
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Great !
I'll do it as soon as I find some time.
Did you find what's wrong with your speaker ?
Old 10th August 2017
  #26
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Quote:
Originally Posted by asulauz View Post
Great !
I'll do it as soon as I find some time.
Did you find what's wrong with your speaker ?
Nothing is wrong, it just looked like it's acting strange from the fist time, but it works ok to be true.

Now I'm trying to extend pitch range and planning to add this:
Echo-Matic: how to turn a cassette deck into a delay
Old 26th August 2017
  #27
PES
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Thanks for the thread! Received a Marantz PMD221 today and followed your findings. Works like a charm.

Now I hope to find a way to extend the delay time further without having to disassemble the circuit boards. As in, do it from the (under)side with the solder points.
Old 26th August 2017
  #28
PES
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update:

Found this site which shows how to disable the 1.2k resistor mentioned above (albeit on the 221, which I have - not the 222) simply by removing the solder around one leg, so no further disassembly was required (just make sure the leg doesn't touch the conductive trace or solder remnants around it).

When using a 90 minute tape, I could go down to a 560 ohms resistor before the transport stalled (so about half the value of the original resistor). Then I made the tape into a simple tape loop, so that there is less mass to move around. This allowed me to go down to 270 ohms without the transport struggling.

This is equals more than a second of (very low fidelity) delay time.

Since I don't want to deal with the transport dropping out below 270 ohms, I placed a 270 ohm resistor in series with the new 1k trim pot. I might change the trimpot for a 1k resistor instead, and use a switch to switch it in and out.

So far that new circuitry is on a small breadboard that I keep in the battery compartment, which means it is easy to modify it, and the unit looks the same.





Old 30th August 2017
  #29
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I did the pitch mode too yesterday following the instructions of my post #20 and it works
However, I don't know if I did something wrong but now, in play mode, I can't mute the speaker. It's not a big deal because I'll always use the recorder in rec mode for the delay.

I did not mesure it but the delay time is pretty short, even with the "low mode" and the pitch all the way left. I'll try to do a tape loop, as @PES suggest it, but I doubt it will increase the time that much. @PES, do you think I can do the same mod you did on the breadboard on my 222 ?
Old 30th August 2017
  #30
PES
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Quote:
Originally Posted by asulauz View Post
I did the pitch mode too yesterday following the instructions of my post #20 and it works
However, I don't know if I did something wrong but now, in play mode, I can't mute the speaker. It's not a big deal because I'll always use the recorder in rec mode for the delay.

I did not mesure it but the delay time is pretty short, even with the "low mode" and the pitch all the way left. I'll try to do a tape loop, as @PES suggest it, but I doubt it will increase the time that much. @PES, do you think I can do the same mod you did on the breadboard on my 222 ?
If you mean the ext. speaker on/off, I don't think that's the onboard speaker. You need to use the level knob on the front.

Looking at your pic of the PCB, it seems the traces from the pitch knob are different on the 222 from the 221. So I don't know where you can find the resistor that must be changed in order to get longer time. But it should be possible like on the 221.

It is once you have done that you will find that the motor can't handle a fully loaded tape on the lowest speeds (potmeter at the lowest value). Then you can make a loop. I tend to use a fully loaded tape though, as the delay time is long enough on the lowest possible resistance, and I haven't managed to make a seamless loop yet (there is some dropping out when the section with the splice moves across the heads).
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