Cassette tape delay

Rorut · Jan 24, 2018

dr pepper said:
If you want the filters maybe you could put a volume pot before the filter, that way you could trim the apparent volume so that theres no change when you switch the filter in & out, that would enable you to use the bypass switch as an effect, or instead of a pot just a pcb trimmer and trim out the volume difference. You could then possibly do away with the balance pot idea between the filters.
Really glad to have been assistance.

Would this work. Moving the resistor here instead of having it in the circuit before the volume pot in the curcuit?

dr pepper · Jan 24, 2018

With a couple of additions it'd work.
Firstly the mixer might create a whopping thump at switch on and maybe off so leave it on all the time its in use.
Replace the 10k with a Pcb type trimmer potmeter also 10k, connect one end of the track to the mixer and the other to ground (battery -), then connect its wiper to filter inputs as you've shown, of course keeping the switch.
Then adjust the trimmer so the sound when you switch the filters in/out doesnt jump in volume much.

Interesting that Nige, more useless knowledge of old stuff in my head.
I've been experimenting with generating colour pal composite video, must be bored.

Rorut · Jan 24, 2018

dr pepper said:
With a couple of additions it'd work.
Firstly the mixer might create a whopping thump at switch on and maybe off so leave it on all the time its in use.
Replace the 10k with a Pcb type trimmer potmeter also 10k, connect one end of the track to the mixer and the other to ground (battery -), then connect its wiper to filter inputs as you've shown, of course keeping the switch.
Then adjust the trimmer so the sound when you switch the filters in/out doesnt jump in volume much.

Thanks,good idea about the trimmer. Just thought it would be good to be able to shut the echo off and use the unit as a normal player but guess that works anyway without interferance if echo is on, just connect a source to tape in and record.

If I buy this opamp instead. Can I get around the problem with dual supplys and run the echo from the same DC jack as the player 4.5v.
It has lower input settings.
- Single supply: +3V to +30V
- Dual supplies: +/-1.5V to +/-15V
https://www.electrokit.com/lm324n.41733

But it seems like rest of specifications is very different from the MC33079P that I use at the moment.
https://www.electrokit.com/en/mc33079p.44016

audioguru · Jan 24, 2018

Any opamp can use a single supply if it is biased properly. An opamp designed to use a single supply will also not work if it is not biased properly.
The LM324 is horrible for audio. It has crossover distortion, noise and trouble with frequencies above 2kHz.
The MC33079 is made for audio with very low distortion, low noise and performs well up to 120kHz. But its minimum supply is +10V or +/- 5V.

dr pepper · Jan 24, 2018

If you turn the pots down to sero because they are grounded the deck should work as it did.
The Lm324 is what I'd expect to see in something like this, however its probably noisier than the '33079, the reason why they spec it as single supply is that the inputs can work to ground, and the output will drive loads towards nearly ground.
A Tlc274 might also work which is a rail to rail amp, but I havent checked the specs on it.

Rorut · Jan 25, 2018

Ok, Im staying with the MC3379.
Would something like this work to get voltage down to about 4.5v?
Or R2 a 1.5K trimpot?
You talked about problems with hum?

http://www.electrokit.com/en/lm317t.41525

**broken link removed**

dr pepper · Jan 25, 2018

That reg circuit should work fine, the pot is also a good idea.
However do you really need it, the circuit would work fine from 12v, or are you wanting to power the deck from it?, if so dont forget a heatsink for the reg.
Yes hum can be an issue with grounding, a good approach is to put the board in a box or whatever and take all the grounds to one point, a screw with some solder lugs works well.

Rorut · Jan 25, 2018

Yes the circuit is for powering the deck from the same power source. I also have a LM2596 I can try with. The one in the link got very hot above 1.5A when I tested a year ago or so... The deck needs about 500ma
**broken link removed**

audioguru · Jan 25, 2018

The LM317 circuit you posted has resistor values creating an output of 5.5V when it has a load. Its output might be a higher voltage with no load because it uses the 240 ohm resistor that is used with the more expensive LM117. The LM317 should use 120 ohms between its output and the ADJ pin then the other resistor should be a little less than 330 for an output of 4.5V.

Rorut · Jan 25, 2018

diode voltage drop does not affect voltage output?

audioguru · Jan 25, 2018

The diode in the LM317 circuit prevents damage if the input polarity is backwards. It reduces the input voltage about 0.7V and affects the output only if the input voltage to the LM317 regulator becomes less than about 2.5V above its output voltage. The extra 2.5V input voltage is its "dropout" voltage.

dr pepper · Jan 25, 2018

A 1.5a reg is more than enough for the deck, the lm2576 ought to easily cope with 500ma, however I'd prefer a linear reg like you mentioned earlier and a bigger heatsink, up to you.
A diode drop is under a volt, you can compensate by adjusting the reg, a 7805 5 volt reg would probably work fine, you'd get 4.2 - 4.4v, the deck ought to be fine with that, it will be able to run the batteries down to lower than 4.5 anyway.
Just dont put a diode in the ground, put it in the + supply.

Rorut · Jan 25, 2018

Thanks! I have very limited space to put the components inside.
I have one of these very small circuits. Would be great if that could do the job
**broken link removed**

dr pepper · Jan 25, 2018

Not familiar with that chip, but it looks as though it's worth a try.

Rorut · Jan 25, 2018

Is there any risk circuits like this or similar sends full amout of voltage into the deck if fails/gets broken?
Wish the deck had some over voltage protection or something

Rorut · Jan 26, 2018

Tested it today and it seems to work fine, I put in 14v and out 4.5v. Not hot at all.
**broken link removed**

dr pepper · Jan 28, 2018

Good to see it works.
Yes the reg could short putting 12v on the deck, it would need to get over 150 degrees for that to happen though.
The deck might take it, or it might pop, you could if you really want to include a overvoltage crowbar circuit, but that would be a little Ott in my opinion.

Rorut · Jan 29, 2018

dr pepper said:
Good to see it works.
Yes the reg could short putting 12v on the deck, it would need to get over 150 degrees for that to happen though.
The deck might take it, or it might pop, you could if you really want to include a overvoltage crowbar circuit, but that would be a little Ott in my opinion.

Thanks, I will take my chances and trust that little circuit. (Interesting about the crowbar circuit)

Next step is cutting the positive path from the DC jack.
What is the best way to remove the paint for a solder spot?

dr pepper · Jan 29, 2018

I'd scrape it with a knife blade.
You can use sand paper.
I just noticed your using a switching reg to convert 12v to 4.5, you wont get much heat from a switcher they are very efficient.

Rorut · Jan 29, 2018

dr pepper said:
I'd scrape it with a knife blade.
You can use sand paper.
I just noticed your using a switching reg to convert 12v to 4.5, you wont get much heat from a switcher they are very efficient.

Sounds good but what is the downside?
More noisy?
”Switching frequency: 1.5MHz”

Cassette tape delay

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