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Messages - Oooscar

Quote from: Jazz P Bass on March 11, 2022, 12:04:57 PM
I would 'cut' the traces coming out of the SA21111 at pin 13 (R OUT) & pin 14 (L OUT).
Solder in your aux input after the cut in the traces.

Heyy, thanks a lot for your reply... That's what I did, yes... And It works... I cut the jumpers on the output tracks, and added a female 3.5 stereo Jack with five pins, so that I can listen the radio and also an aux input...
Yes, exactly. Just modding the radio circuit. Actually, later I checked
the SA211 ic, the radio IC, and I looked at the tracks of its outputs.
I think there are some jumpers/resistors along those tracks that I can
open, maybe, and connect there the 3.5 female Jack stereo, with
double pole. I Will try that, similar to this example

Hello all,

Maybe a bit off topic, but maybe you can give me some help...

I am trying to add an aux input to a boombox radio I have at home
I have not found the schematic of the main board, it's a MX-Onda
MX-MCP6428Mp3. So far, I don't want to use the tape player or the
CD player. I want to modify the circuit on the radio Mode.
It has an analog volumen pot with six pins, and the following ICs,
SA2111 is the radio IC, and NEC1316C is the power amp IC.
I can't see any sort of Jumper wire that would allow to connect an
stereo 3.5 female Jack with 'two poles' to keep the radio on, but
connecting an aux instead of the radio. Everything seems printed
on the board.

I have tried to connect directly my smartphone to one of the inputs
of the NEC1316C ic, but the sound is barely heard, It's like the IC
ignores that signal, and the radio signal keeps there. The volume pot
does not improve the situation. Something is going on, but I am lost.

Anyone here has any clue how can I make It if it's possible?

Thank you very much for your attention. Thanks for stopping by.



I have around two small speakers from a pair of phones. 8 ohm 0,25 watt each one.
I have tried It today with an lm386 amp I have. And the sound from the low strings is not as good as the sound of the first three ones. I know small and tiny speakers have problems with low frequencies, I even tried It with the smartphone, and It sound quite high, bright, treble. Is there any way to balance the sound at least a bit? Changing the output capacitor, etc. I would like to make a very small guitar amp, like a smokey amp, but with the "best" possible sound.

Regards, cheers
Just to share with you...

I have tried the g1xOn with a generic TDA7297 stereo amp board bought on eBay, and I can get louder volumes without the squeal... (I am bit experimental... But it seems you can get nice volume and sound in a cheap DIY way) I have been told as well that cheap pickup coils can also contribute to produce that squeal, due to microphonic effects. Wax potted ones have less microphonic effect. In the future I will try better pickups also.
Yes... Well, I learned today that the g1xon has different level controls, one of them, the master level can make a difference. I will keep trying. Maybe I can use my nice diy amp after all...
I have tried with a different lm386 amp that I have with volume control, and at some point starts to happen. I also have tried disconnecting the pins 1 and 8 of the amp of the photograph, and the problem still remains at some point. I noticed that when I touched the strings with my hand the squeal disappears, but when I touch the strings with some fabric, textile, for instance, the squeal does not vanish.

The other road to go is buying some device. I would prefer not to do it, or buying something economical.
The idea for this small amp was to make it as simple as possible, and to get the maximum of it. So I decided to control the volume with the guitar volume control, and the gain of the LM386 is set to maximum. Pins 1 and 8 are connected together with a wire, like in a smokey amp. Some of the patches give me more trouble than others, but in general, as soon as I crank up the volume control of the guitar, the squeal comes in. I would like to get still a nice volume to fill the room,  ;)
Hello all,

Recently I bought a Zoom G1xon effects processor, and I am trying it with a homemade amp I did based on an LM386 ic. I didn't expect to work properly. What happens is that any guitar I connect to the g1xon and to the amp produced in general a lot of noise, and if I turn the volume of the guitar up, a high pitch squeal, like feedback sound starts to sound. Have you had these sort of sounds in any unwanted situation? Maybe I can get some tips to solve it. The amp by itself with just a guitar works well, with a bit of hum of course, but fine. I attach a photograph of the diy amp.

The Newcomer's Forum / Re: Tda ICs Pentawatt PCB
May 29, 2020, 04:14:06 PM
I see, thanks a lot... I have read about mica washers. The idea is to use a washer that transfers well the heat but not the electricity. Usually, go together both properties. The reason to do that is to avoid kind of antennae effects? I have not thought in those issues. Sorry... Too many questions...

About the heatsink, I have a piece of solid metal from a car radio, this piece is one the sides of the whole radio. Pretty impressive heatsink.
The Newcomer's Forum / Re: Tda ICs Pentawatt PCB
May 29, 2020, 06:59:43 AM
Thanks a lot...  :tu: About the heatsinks, do you think any piece/sheet of metal will do the job, or it is worth to use a proper one. Aluminum or denser... ?
The Newcomer's Forum / Tda ICs Pentawatt PCB
May 28, 2020, 04:29:39 PM

I have some TDA ICs, 2030A, 2003, 2006. The Pentawatt package pins do not fit on a typical perforated board. Is there some specific socket to use it with a perforated board? Otherwise I have to make bigger holes. Any suggestion? Maybe some of you have more experience.

Another question. I heard that Jfets with low pinch off voltage are better to use them as buffers, boosters? I guess it affects to the clipping, taking into account that a guitar signal has 200 mV peak to peak, let's say.



I am studying different preamp schematics. I am inclined to minimal amps or amps with not so many parts, just the ones needed to produce a given sound for guitar practice/bedroom playing purposes. I have several questions:

1.- Is it good to add a boost stage initially before any overdrive/soft clipping in terms of sound?
2.- Is it better to add a tone control stack before any clipping or after, in terms of sound?
Let's say you make: guitar, boost, tone control/tone stack, soft and/or hard clipping, out.
3.- Does it worth to add a classic tone stack with bass, trebble, mid respect a single pot tone control, or a BMP with some mid control (Jack Orman mod I believe...)?

It seems to me that with a simple tone control (or maybe two pots) you can get a wide range of sounds, but I am learning, and I would like to understand how many stages can have a guitar amp, and the purpose of those, to see how can I simplify or minimize them, and still get a good and wide range of sound. For instance, adding preamp stages to an LM386 can give you a good sound with control. I have tried hard clip diodes with a TL072, and the sound to me gets better. Nicer.

Thank you very much for your attention.

Regards, cheers.

Looking forward for the schematic...
Here it is.

The first issue is solved. I added a 100n capacitor to isolate the filter from the dc of the second op amp as well, and it seems to work.

The second issue with the JRC386D remains. The picture shows both schematics.