Superstar ss158 EDX muffled modulation on Fm

[dxswe]

Hallo
My friend have a superstar radio which sounded muffled on Fm-band.I been heard that many others have the same problem.Is there any mods or other thing to solved it.

Best regards Jan

[dxswe]

This is a solution to modulation sound better at Fm is bypass the echoboard.It's very simple.Unplug J12 connector at the main pcb board then unplug J2 connector at the echoboard.Take J2 connector and plug to J12 at the mainpcb.The fm modulation sounded much better after the bypassing.When you have bypasses the echoboard then the echo will not work anymore.

[captian_radio]

I tried the echo bypass as well but I would also like to disable the talk back, shutting it off does not cancel it completely, can still here the roger beep a bit,I would like to unhook the TB completely,anyone know how?
Tnx Bob

[Brian Morris]

Does anyone have a circuit diagram of the echo board? It seems a shame to bypass the echo board completely, it would be better if we can work out where the audio frequency response is being messed up on the echo board, and then come up with a fix.

Brian.

[Brian Morris]

Right, I think I can see what's causing this problem.

The first three components in the audio path on the echo board form a crude band-pass filter; the value of the resistor (R1) has increased from previous versions of the Ranger echo board, and this has had the effect of making the low-pass cutoff frequency ridiculously low; this is probably what's causing the 'muffled' audio.

For a more sensible pass band, I would change R1 on the echo board from 22k to 10k, and also change C4 on the echo board from 10n to 4n7. See pic in link below:

http://i29.tinypic.com/opsleo.jpg

I haven't actually tried this, as I don't have an SS158 here at the moment, but it can't do any harm so I'd be interested in the result if someone's willing to give it a go.

Regards,

Brian.

[buzz T]

Hi Brian
Thanks for the information regarding the echo board. I have replaced R1 with the 10K you suggested and replaced C4 with a smaller value of 1800pf. Tried a number of different values of capacitor and the 1800pf was the best in this case.
Thanks for your help.

[buzz T]

Hi Brian
Thanks for the information regarding the echo board. I have replaced R1 with the 10K you suggested and replaced C4 with a smaller value of 1800pf. Tried a number of different values of capacitor and the 1800pf was the best in this case.
Thanks for your help.

[Brian Morris]

Hi Brian
Tried a number of different values of capacitor and the 1800pf was the best in this case.
Thanks for your help.

Ok, the reason I chose 4n7 was that in theory it should give a cutoff frequency of just over 3kHz. Was there a vast difference between using 4n7 and 1n8?

Would you say that the mod was a success overall, does the radio sound a lot better on air now?

Regards,

Brian.

[buzz T]

Hi brian

Sorry for the delay on the reply. I've been a bit busy.

The modulation sounded fine with the 4n7 capacitor in but sounded slightly better in my case with the 1n8 capacitor. Overall the modulation is 100% better.

Cheers
Mick T

[Brian Morris]

Ok then Mick, we have a mod, 1n8 it is then!

"The Superstar 158 audio mod" (c)Brian Morris and Mick T.