Watkins Copicat Modifications, Need Help

[d.redfern]

I was wondering if someone could have a look at this schemo I've drawn with some help? I want to add volumes for each seperate tape head and am wondering if what I have in my attachment is the best way to do it or if I should try another way? am a real newbie to electronics so sorry in advance. I have bassically put a 10k pot between the tape head and switching arrangement, will this affect the response of the head, do i need to use an op amp to buffer the signal? would love it if someone out there could help.
regards doug

 

[kepeb]

I like copicats
should work ok. they are summed back together further down so this is the only place.
a complicated hi-fidelity approach would probably be a waste of time for 1/4" loop anyway imo.

this should be real easy to try out without even taking anything of the board as the connections can be put between the heads and switches.

BUT i would add. dont disfigure the poor thing with some unsightly additional drill oles on the front
there are many that were 'modded' really badly just for the footswitch
with a little thought and a bit of time you can make a seperate box/panel that sits snug in the cable compartment for all the I/O
the f/switch is also the effect-wet only out connection so a jack for that is a good idea for choice/studio use
you could also add an IEC to replace the wired plug.
remember to earth it properly if it isnt already too most only have two wire plug 

 

[PRR]

Is that IC2A drawn the way Watkins did it? Tape-head into inverting input is very odd.

IAC, you want a 5K-10K mix resistor off each pot's wiper. Otherwise if any pot is down, all others are shorted to ground.

 

[kepeb]

good point on resistors if your wiring like that.
I think i would have just wired differently, maybe bigger value pot, as below

also, here is a revised schem I did for a rev3 last year.(EDIT: I didnt make it, i went over each section as i checked the unit and redrew the completely illegible sections so you could see values etc.)
its as stock and checked out each component. very similar to rev4 but there were apparently many adjustments made to different versions while the diagram was never updated.
some units just have caps and resistors hanging off that look like afterthoughts.

 

[d.redfern]

Thanks for your reply's so I either wire the pot as I did in my schematic but add a 5 - 10k resistor to the wiper or wire it as a variable resistor but use a larger pot. To PPR Yeah it is how the watkins does it, with the tape head going into the inverting input. The diagram is basically an IC300, and it seems to use all inverting style op amps. kepeb, I'm making it from scrath so am not worried drilling holes and that making it look unsightly its probably gonna look unsightly any how.

I want to add a line input and output i was gonna just use a That 1240 and 1640 and wire them up as the basic diagram shows on the data sheet, is this the best way to do this?

Do you think there are other ways I could make it perform better I.e better s/n more fidelity
Suggestion are greatly appriciated
Doug

 

[kepeb]

cool, from scratch? interested to hear more, what parts etc.
you'll have to keep me updated

the first thing you could do would probably be increase the length of the tape, you would have to think about the overall size of the unit a little more and
some more springs for taking up the slack.
maybe adjustable positions on the heads? more heads?
with a longer loop, a play head could be much further in/longer time delay.
faster speed. or even adjustable speed, not sure if thats part of the IC300 already but it would be more useful. depends what motor you use.

also if your going from scratch i might suggest you find some pots with the dpdt built in for a tidy panel.
let us know how you get on, sounds like a fun project.

 

[d.redfern]

Yeah I'm adding variable speed, im using a dc motor with a mos-fet based speed control, I really want to extend the tape loop but I'm worried about the placement of the tape heads, as they need to be in the right place to make use of the head properly and the distance's should be ratio's of the record to playhead distance. I don't really know how to work this out properly and keep the lovely curve of the tape heads, you got any ideas? It would also mean it would be slightly higher fidelity too. Having an adjustable tape head is also a lovely idea but i dont think it's necessary with a speed control, and there's a engineering and lack of equipment issue here too.

In terms of a power supply the oscillator needs +/- 35V's and the rest of the bits need +/- 15V you got any idea how to get this from a single +/- 35V's?

I'm gonna add mic and line input , and a filter and LFO and a dub siren, the whole project is gonna be modular so you can choosethe routing and do strange things to the dub siren with the lfo and vice versa.

What you think?
D

 

[kepeb]

sounds cool, some good ideas.

the distance's should be ratio's of the record to playhead distance. I don't really know how to work this out properly and keep the lovely curve of the tape heads, you got any ideas?

well thats more of a physical/mechanical design issue and all about which parts you get and which features you include.

It would also mean it would be slightly higher fidelity too.

because of faster speed? your still using 1/4" right?

Having an adjustable tape head is also a lovely idea but i dont think it's necessary with a speed control, and there's a engineering and lack of equipment issue here too.

I think you may of missed the point with adjustable tape heads...
the speed will change the rate of each delay's occurrence but not the relative space between each delayed repeat.

for example, if you were to move the third head further along the tape you would get two fast repeats then one would be delayed further according to how far along you pushed the head, move it all the way around to right before the erase head for instance.
this creates some great effects, and at whatever speed you adjust to.

I think a great idea would be to have each heads placement variable.
if I were so inclined, I might try adjustable 'tape take-up' arms between each playback head instead of moving the heads at all.

In terms of a power supply the oscillator needs +/- 35V's and the rest of the bits need +/- 15V you got any idea how to get this from a single +/- 35V's?

the best way to do this is probably something i would be asking the smarter people on this board

I'm gonna add mic and line input , and a filter and LFO and a dub siren, the whole project is gonna be modular so you can choosethe routing and do strange things to the dub siren with the lfo and vice versa.

What you think?
D

I vote 'go for it'

 

[d.redfern]

Ah yes I see you're point about the adjustable tape head,

"if I were so inclined, I might try adjustable 'tape take-up' arms between each playback head instead of moving the heads at all."

its a good idea but you would have to have a longer length of free tape, it would work better with a RE201 type design i think.

Cheers for your suggestions
D

 

[Whoops]

Hi,
nice ideas, Im also modifying a copicat unit at the moment.

How is your project going?

thanks

 

[d.redfern]

Well My project works which is great, and I have got some old tape machines that i'm going to incorporate into it, I had trouble with my motor spindle being to thin among other things . My project was a complete rebuild and it isn't finished yet, but does work.

What are you're ideas?

Good Luck With It
Doug

 

[StephenGiles]

You might try contacting Phil Kelly, lead guitarist in Bruce Welch's Shadows. He uses a rebuilt Meazzi echo, but he may be able to put you in contact with a tech with serious Copycat knowledge.

Also try here, very helpful guys who also may be able to help

http://shadowmusic.bdme.co.uk/viewforum.php?f=11

 

[d.redfern]

I've had help from a guy called john form www.amp-fix.com,

He's great and was really helpful.

 

[Whoops]

Best place for Copicat repairs, spare parts or info.

John Beer is a great guy.

I've had help from a guy called john form www.amp-fix.com,

He's great and was really helpful.

 

[Tubetec]

I've recently modded my copicat mkII to make the level from each playback head adjustable. I removed the original three button switch assembly,and replaced it with  three linear 25k pots,wireing them in series.So now, instead of just six variations in echo ,I can blend any desired combination from either of the three playback heads.This mod allows great versatillity in the echo settings of the unit .I made a number of other small modifications which drastically reduce  the amount of 50hz hum in the MkII, making it much more useable in a recording studio situation,without having to resort to gateing.One final change I made was to connect a  jack socket in place of the foot switch,in such a way as it can be used as an echo only output.
Yet another lease of life for my Cat ,over 50 years old at this stage!
I had also been thinking of useing a system of  three tape guide rollers,from redundant vhs machines  ,in between the record and first playback head,to vary the delay time .Havent quite got around to making this happen yet ,
any suggestions most welcome,seems a lot easier than varispeeding a synchronous motor though.