Adding an audio jack plug lead to a C2N Datasette

Merlin

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Help!

I recently came across a site that described how to add a 3.5mm audio jack lead to a C2N Datasette to be able to record tape files back to tape from a PC's sound card. I would like to modify one of my C2N's to play with this idea, but for the life of me I can't find the web page now!!

Has anyone else come across this site?
 

arnljot

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Just slightly off topic...

Do you record the "disk images" to tapes using special software, or do you have mp3s or wav files of the original data?

I wonder if the data would survive mp3 compression - hehe :)
 

Merlin

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The idea is you convert Tap to Wav files, then use a PC's sound card to record the WAV file back to the datasette. I'd like to record a tape via the audio lead, then try loading it on the C64 and adjust the settings on the PC until I get repeatable good results. The files have to be mono so it will have the same info on both of the stereo channels of the WAV file, unless you can switch the sound card to mono mode.

I have read on Lemon 64 that MP3 C64 WAV files at 128k bit rate can play back OK, but I'm not sure about some of the files that use custom loaders.

The C2N was a bit like a 300k baud modem, so you can't crank the bitrate too high, or it won't transfer the data properly.

I found the site over the weekend and it had really good pictures of where to solder the wires for the audio lead onto the PCB for all of the different 1530 C2N models, but can I find it now? Nope...
 

arnljot

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How about browser history, or were you surfing in "private" mode?:
 

Merlin

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Unfortunately, my browser is set to clear history and temp files files out when I shut it down to stop cluttering up my hard drive, so I've lost the URL.

:roll:
 

jvdbossc

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I would use a portable cd player instead of the datasette, it' will be more comfortable... Why don't you try to hook up a cassettedeck to your pc?

I chatted with a friend about his old tape player, he told me he used an alcohol marking on the volume and just connected the audio out and audio in to the right ports, pressing the enter key and the play together after the load..
 

Merlin

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@ Salaxi54

That's Marcus Brenner's work and I have that site already book marked. The one I'm talking about had several photographs of where to solder wires inside the 1530, to be able to put a 3.5mm mono jack plug on the end and connect it to a PC's sound card, so that you could record the WAV to the 1530 whilst it was connected to the C64. It was just an unusual approach to the problem of transferring tape files that I wanted to try out.

I'll have to go trawling again tonight....:nod:
 

Merlin

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I think I've figured it out...

The audio cable connects to part of the op-amp circuit IC3 - positive to pin 11, ground to pin 7; at least that's how it connects on this version of the C2N. (Check the attached diagram). The op-amp provides the necessary signal conditioning before it gets recorded to the tape.

The positive lead connects to both positive pins of a 3.5mm stereo jack plug, so that it records the same information through both heads, i.e. effectively in mono.

Other versions of the C2N have dual op-amps instead of quad op-amps and the connections will be different. I'll figure those out after I've got it working.

I've got some TAP files ready converted to WAV files and I'll be adding an audio lead to one of my units this weekend.

Stay tuned....;)
 

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protek

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@Merlin: This is great info! I've been trying to find out the same info. Will be waiting how this progresses. :)
 

Merlin

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@ Protek

Thanks! Once I've got the audio levels figured out, it should be possible to record these to a CD, then use a portable CD player to transfer the WAV files to the C2N.

The ultimate end game I'm working towards is a CD or a solid-state MP3 player full of C64 MP3 files, that can be transferred back to a C2N via the audio jack modification. Ipod to C2N, oh the irony of using 'noughties technology to feed 'eighties kit...
 

protek

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@Merlin:

When you created the WAV fiels from TAP, did you invert the audio?
 

Chinners

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The ultimate end game I'm working towards is a CD or a solid-state MP3 player full of C64 MP3 files, that can be transferred back to a C2N via the audio jack modification. Ipod to C2N, oh the irony of using 'noughties technology to feed 'eighties kit...

@ Merlin
Yeah, I had this idea for my Amstrad - however, the problem lies with multi part loaders, or any software which controls the motor.

Another workaround, but not quite as tidy, for playing back wavs into the tape deck is to use one of those adapters that you could get for the car, to plumb a portable CD player into a tape head unit. I am currently using this for my 464, and it works far better than I expected - with certain games I have been able to speed up the wav before writing it to CD, so for example, I can load Starion at 4.3x speed from a CD...

I found the info useful in your investigations - I was planning on completely replacing the internal cassette deck of my 464 with a cheap CD player - this info helps a lot, especially with my limited knowledge of electronics. I have the schematics for the tape deck, but now have a slightly better understanding of what they mean :)

(y)(y)

:D
 

protek

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Another workaround, but not quite as tidy, for playing back wavs into the tape deck is to use one of those adapters that you could get for the car, to plumb a portable CD player into a tape head unit. I am currently using this for my 464, and it works far better than I expected - with certain games I have been able to speed up the wav before writing it to CD, so for example, I can load Starion at 4.3x speed from a CD...

How do you use that? Do you load the program into the memory from the CD using the tape adapter and then save it onto real tape?
 

Chinners

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Another workaround, but not quite as tidy, for playing back wavs into the tape deck is to use one of those adapters that you could get for the car, to plumb a portable CD player into a tape head unit. I am currently using this for my 464, and it works far better than I expected - with certain games I have been able to speed up the wav before writing it to CD, so for example, I can load Starion at 4.3x speed from a CD...

How do you use that? Do you load the program into the memory from the CD using the tape adapter and then save it onto real tape?

I use a program to convert the tap file to wav. I then edit the wav in [insert favourite sound editing program here], ensuring it ends up at 44,100 in stereo (both channels the same). I then burn it to CD. (rewritables are the best).

I then use one of these:
View attachment 3461
Bob the tape side into the tape player, plug the other end into a cheap CD player, press play, then wait.

The "speeding up" of the wav is not needed, but if you can do it, and get away with it, I see no reason not to.

You can get the adapters most places, for example ebay, or amazon:

http://www.amazon.co.uk/HQ-CLP-003-CD-Cassette-Adapter/dp/B00077DDGO

I never actually save it to real tape - I see no need to tbh.
 
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Merlin

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The problem is in how the C2N works compared to tape units for other formats. Spectrums and Amstrads use straight forward audio coupling whereas the C2N uses TTL logic. The unit is 'smart' to a degree, the same as other Commodore peripherals right up to the Amiga.

The MP3 adapter may cause an issue with the "end of tape" lever inside the C2N. There have been discussions on Lemon 64 about these and you basically have to gut them out, so that the tape lever doesn't cause issues. Also, this approach needs you to be pretty speedy on the C= key on the C64, as the unit won't stop once it's found a file.

I'm trying to make this hack as simple as it can be, so that you only need the jack lead to initially record the WAV file down to the C2N and it won't affect how it normally functions. This cable approach is as simple as it gets whilst still allowing the signal processing to take place, so that the C64 sees a clean signal in the format it wants.

The op-amp will invert the audio, so the standard TAP to WAV programs shouldn't need to invert it; I'll know for sure when I test it.

Edit: The 'op-amp' I mentioned is actually a Hex Schmitt Trigger Inverter, e.g. 74LS14 or AN6564 dependent upon the variant of the C2N, however, it will invert the audio signal as required.
 
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Merlin

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OK,

Tonight I installed the audio lead into one of my spare C2Ns. I've connected the +ve to pin 11 and the shield ground to pin 7, as per the diagram. Both +ve leads were soldered together at the C2N end of the audio lead before being soldered to pin 11.

The neatest hack would have been to install a 3.5mm jack socket to the C2N then use a male-to-male cable, but a flylead will do for testing.

I've also got some new blank tapes for test purposes.

I'll record a WAV file down to it tomorrow evening and see it it loads back to the C64 once recorded.
 

Merlin

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Hmm, after a bit of tinkering this weekend I'm not having much success. I can convert T64 to Tap, PRG and WAV with no issues, but recording them to the Datasette results in an unreadable tape. Possible causes for this are:-

1. The WAV conversion is amplified too much, causing corruption of the tape signal. I need to find out the optimum dB for the tape signal in order to correct this with Audacity.

2. I'm not sure if the audio signal needs to be inverted or not. The point where I am feeding in the audio signal is before the op-amp so the signal will get inverted as it passes through. Until I get the optimum audio level I can't solve this part.

3. I'm not 100% sure if any of the Datasettes I have are correctly aligned for azimuth. Differences in azimuth may be cocking up my fiendish master plan here.

During the week I'm going to make a Markus Brenner C64S tape adapter and see if I can create a tape using Ptap via the parallel port.

To make matters worse, it seems as though my C64S has lost it's sound...:(
 

cosmicfrog

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why can`t you just take the audio out of the c64 where the tape connects ??

though would like to see how you fit and audio jack to the c2n and one of those vu meter things aswell (y)

edit:

Just read last line :(
 
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