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Author Topic: Code-a-phone tape loop machine  (Read 892 times)
mikebike
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« on: December 03, 2012, 10:49:09 AM »

Heres a cool surplus store find: the Code-a-Phone!

it appears to be a phone answering machine, with a 7(ish?) second tape loop.
I'm able to record to the tape and hear it play back through the same jack....

im hoping to make it into a delay, or a looper, but i think its gonna take some hacking.

any ideas, suggestions and the like are appreciated!


* IMG_0233.JPG (702.47 KB, 3072x2304 - viewed 88 times.)

* IMG_0238.JPG (842.13 KB, 3072x2304 - viewed 85 times.)
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mikebike
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« Reply #1 on: December 03, 2012, 10:49:28 AM »

More photos!


* IMG_0236.JPG (623.6 KB, 3072x2304 - viewed 81 times.)

* IMG_0235.JPG (759.82 KB, 3072x2304 - viewed 77 times.)

* IMG_0237.JPG (660.59 KB, 3072x2304 - viewed 85 times.)

* IMG_0239.JPG (836.38 KB, 3072x2304 - viewed 76 times.)
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ve3wwg
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« Reply #2 on: December 06, 2012, 05:54:26 PM »

When you say that you hear the "play back", do you mean that you hear it at the time it is recording? Or do you mean that it will play back the recording after the recording is completed?

For looping, what you're after:
  • is a record head laying down the audio to the tape
  • and a playback head placed at some distance from the recording head

The playback head of course needs an amplifier, when the recording head is also using it's own (two amplifiers are required).

The amount of delay is dependent upon:

  • tape speed
  • distance of the playback head from the recording head

Based upon what I see in the pictures, it appears you have one amplifier (unless there is more somewhere). I only see 3 transistors, so there must be more electronics hidden somewhere else (there is usually an oscillator to erase the tape ahead of the recording head).

So for you to have a functional looper, you'll need two amplifiers that operate simultaneously. One recording, while the other is amplifying the playback head.

To control the delay, you have to be able to move the playback head, or alter the speed of the tape.

The project sounds a bit ambitious to me. But let us know if you can simultaneously playback while recording or not.
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mikebike
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« Reply #3 on: January 05, 2013, 04:49:59 PM »

By play back i mean that it plays back after its ben recorded.

I think you are right about there only bieng one amplifier. there isnt any other circuitry besides the switches

There are 2 heads on the tape, but i wasn't sure if 
A) one was play and the other erase/record
or B) one was play/record and the other erase.

If A is true, i would just i need another amplifier, a feed back pot, and a way to change the tape speed If B, ill need to some how mount another tape head.

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ve3wwg
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« Reply #4 on: January 05, 2013, 07:14:17 PM »

With two heads one will be the erase head, the other the play/record. For a looper, you'll need another head. The easiest one to add is the playback.
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mikebike
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« Reply #5 on: January 14, 2013, 01:49:49 PM »

allright!

currantly installing the 3rd tape head. This one i recovered from a wired portable 8-track player I turned into a "tiny-terror" like head. fortunately, I simply wired a 1/4" jack to the the leads from the tape head, so ill be able to test the head before i get on to the next step, the preamp for the tape head and the feed back stage. I want to find a relatively clean signle booster, so i can use the unit as a tape buffer for recording projects, and potentially add an FX loop for the delays only.

Any ideas on a simple and/or clean preamp that would be suitable for bringing the tape signal back up to line-ish
 

PS: the 8-track amp thing is actually a 2 track tape that was contaned in a 8-track type of tape, this tape had a really long loop. one track contained audio, the other a pulse that would switch on/off a outlet. currently it just serves as a nasty tape distortion desk top amp, with a speaker out put on the rear for driving larger cabinets.
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mikebike
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« Reply #6 on: January 14, 2013, 02:59:06 PM »

heres some pics. i hope to wire the new head right to the spare pins on the conecctor in the last shot!

do you think the shell of the tape head needs to be grounded?


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* IMG_0515.JPG (916.77 KB, 2048x1536 - viewed 58 times.)

* IMG_0517.jpg (1333.46 KB, 2048x1536 - viewed 55 times.)
« Last Edit: January 14, 2013, 03:01:55 PM by mikebike » Logged

ve3wwg
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« Reply #7 on: January 14, 2013, 07:36:38 PM »

If you want a quick "cheat", you can probably hook the playback head up to a practice guitar amp, if you have one handy (it works great for my electric piano with mag pickups).  A magnetic phono pickup amplifier is another possibility. Otherwise, you'll need some sort of tape preamp built. There should be some opamp designs available on the net for that.

The remaining challenge is that you'll need to align that 8-track head. The tracks on it may not align well with the recording head. Ideally you'd have some sort of screwable head height adjustment on the playback head (though you could mess with the record head adjustment if that adjustment is there). This is where having an amp/preamp first would help, because you should be able to hear when you have it aligned.  While the tape is moving, you should be able to hear playback hiss at the minimum.

The case of the head should be grounded to prevent AC hum. You might be able to get away without it, depending upon how bad it is. Just being bolted down to the chassis might be enough to ground it.
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mikebike
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« Reply #8 on: January 15, 2013, 09:15:00 PM »

Sweet.
I was thinking of mounting  the play head with springs between the head-holder and the chasis  and screws to adjust the hight (kind of like a guitar saddle.) But for the time being I'm going to hot glue it to a convenient spot on the tape machine.

I was thinking that way about the amp, I thought the old amp from the new playhead would be a good candidate, i can simply wire the head to a 1/4 jack and plug it in to the existing tape preamp.

I had to forget about the new head for the moment, it seems that the signal is being recorded to quietly to the tape for proper play back. im going to attempt to demagnetize the head (fortunately found the gizmos pictured below) and replace the tape loop before i attempt to modify the existing preamp.


* IMG_0538.jpg (1285.97 KB, 1536x2048 - viewed 59 times.)

* IMG_0539.jpg (1061.93 KB, 1536x2048 - viewed 58 times.)
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ve3wwg
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« Reply #9 on: January 15, 2013, 09:25:22 PM »

You will need a separate play back amplifier. The record head will be using the only amplifier you have in the unit (remember it is designed to only record OR play at any given point in time). So it will only have one amplifier, and use it for the recording function (it gets switched between record and playback by switches).

So I suggest you leave the record electronics as it is (additionally, there is an oscillator and driver for the erase head). For simplicity, don't mess with the record side.

You will need to add an amplifier for the playback head. Then head alignment will be your next problem after that. Smiley
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mikebike
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« Reply #10 on: January 16, 2013, 09:42:29 AM »

I know i need 2 amps.... the second black "8-track amp" will serve the play back purpose, temporarily .

I may need to modify the record amp to get a better signal to noise ratio on the tape.
After making sure i can get a proper signal on the tape, then it will make sense to adjust the playback head

I dont believe head alignment is going to be an issue w/ the spring and screw method i mentioned, i will tap holes in the chasis and probably use some thread-lock to keep the screws from vibrating loose.

I see that i may have got confusing when i was talking about 2 different tape machines (2 heads and amps...)

« Last Edit: January 16, 2013, 12:16:02 PM by mikebike » Logged

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