Cassette tape delay

[dr pepper]

Nicely made.

 

[Rorut]

Thanks!
I know I maybe should have breadboard it first but I hope the gods are on my side

Should that 20K feedback pot be a linear? According to schematic it does not tell

 

[dr pepper]

Theres always bodge wires!

Dunno, I'd probably try a linear, either is going to work.

 

[Rorut]

Thanks, and is it important to use shielded cables connected to the tape PCB for RCA in/out

 

[Nigel Goodwin]

Thanks, and is it important to use shielded cables connected to the tape PCB for RCA in/out

Yes it is.

 

[Rorut]

Reading about voltage on the IC I bought, I says it needs:
* Dual Supply Operation: +/-5.0V to +/-18V
https://www.electrokit.com/en/mc33079p.44016

I need one for single supply, guess I need to buy a new one ?

 

[Wade Hassler]

Reading about voltage on the IC I bought, I says it needs:
* Dual Supply Operation: +/-5.0V to +/-18V
https://www.electrokit.com/en/mc33079p.44016

I need one for single supply, guess I need to buy a new one ?

Data sheet sez:

Your design has to accommodate this

 

[Rorut]

Yes, no big loss but annoying not to be able to test it today.
Would any of these be ok as a replacement?

**broken link removed**

 

[Nigel Goodwin]

Yes, no big loss but annoying not to be able to test it today.

Have you tried it?, there's no such thing as a 'dual supply only' opamp, the circuit configuration of the design creates a dual supply from the single one - it's an EXTREMELY common technique (and is even demonstrated in the sticky at the top of this very forum).

 

[dr pepper]

You might be able to make your single supply dual with the aid of a regulator, what is the voltage of your current single supply, and what is the requirements of the board?

 

[Rorut]

Have you tried it?, there's no such thing as a 'dual supply only' opamp, the circuit configuration of the design creates a dual supply from the single one - it's an EXTREMELY common technique (and is even demonstrated in the sticky at the top of this very forum).

Not tested yet. Dont want anything to go bad you say it might work and that I already have that dual supply covered in my circuit? Sounds good, but reading the description on different opamps some say dual and some say single and dual and that got me confused. Im happy if I can use this one whithout more hardware.

You might be able to make your single supply dual with the aid of a regulator, what is the voltage of your current single supply, and what is the requirements of the board?

I have a 4.5v-9v 1.5A supply today for the tape recorder.
It needs 4.5v

 

[Nigel Goodwin]

In your post #23, R7 and R8 create the split supply.

 

[Rorut]

In your post #23, R7 and R8 create the split supply.

Thanks Nigel,
Guess Im fine with what I have then
Is there a voltage that would be optimal to use for it?
Or anything between 5.0 V to 18 V?

Edit:
Read about voltage divider
Vin * R2/R1+R2 = Vout ?
If I use a 9v power supply I can take 4.5v from the circuit to the tape recorder? Thats what it needs

 

[dr pepper]

I went back and looked at the schem for the tape echo circuit, it has a supply splitter as mentioned.
The op amp spec'd will work, so will others like an Lm324.
Dont get caught up too much in 'split supply' op amps, for your purposes its not so much an issue.
Nope you cannot take 4.5v from the voltage divider to the cassette deck, the divider cannot provide nearly enough current.
The easiest route would be to power the deck from a separate wall wart, its possible to run them both off one supply, probably using a regulator like a 7805, but you'd be inviting lots of other issues with Dc offsets & ground currents causing hum.

 

[Rorut]

Thanks a lot, i will move on and see if it starts with two separate supplyes and continue from there with a regulator and the problems that may occur.
I have much to learn but the not intended long thread enrich more than I thought, in small steps Thanks!

 

[Rorut]

Connected it together but it did not sound.

Any ideas where to start looking for errors? I went through the pcb paths and I cant find anything wrong, will do i again to be sure. I also measured all compoents before soldering them to the board and they had correct values.
I fed it with 9v, anything I can measure to see if the IC is working correctly?

 

[Rorut]

This is so annoying. Can not see any problems on the PCB (maybe it is) and removed the pot for dry including the added capacitor. Now circuit should be exactly like the original one.

Only thing that sounds is some strange noise/squeling if rec volume is high. If I change the speed button on the front (two static positions for fast or slow), the mechanical sound from operating the button echoes out and is adjustable with the feedbackpot. It is like the music does not transport through the circuit.
Here is a video turning the feedback pot.
https://sendvid.com/bogckujm

Can it be something with the MC33079P?
Connected a 9v power supply. On pin 4 I have 8.3v, (guess some drop because of diode). Pin 11 0v (ground), all other pins about 4v.
(I tested with two different and both act the same)
I dont have any ideas on how to move on

 

[dr pepper]

Hmm,
Sounds like you have record Ok, what are you using for a sound source?
Sounds like the the audio in is not getting to the recorder.
Sometimes these things do odd things when recording like mute the audio out.

 

[Rorut]

I got it working today
No problems with the PCB but i seems that I had a problem with my DPDT switch. Connected the cables together instead and it worked. Pretty cool but not so long delaytime as I thought, even if I run it in the slowest speed. Guess I will have to live with those limits.

But there is a couple of other things:
If I turn the feedback pot more than about half I hear that squelings, almost like an old modem. Can a cap or something solve this somewhere?

And the dry pot is extremely distorted turned to one of the pot ends.

 

[dr pepper]

Good.
Sounds like you have some feedback, did you use screened cable?
Perhaps both issues you mentioned are due to the signal overdriving, if that is the case a resistor on the signal (non ground) end of the potmeter track might fix it.
I cant remember what speed compact cassette runs, 4 track reel to reel is something like 3 3/4" per sec, the 2 heads in a compact cassette are fairly close together so it wont take long to get from one to the other, hence a short delay, moving the heads apart wont be easy!