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+2 Grey - low 128k sound volume
I'm trying to revive my old grey +2....
First problem was a faulty RF signal, so I bought a SCART cable from Retro Computer Shack on e-bay (it's the one with the 3.5mm jack on it that plugs into the sound output on the +2 to take the audio to the SCART socket). The RF box has now been completely disconnected.
When I first used the SCART cable I had "wobbly" interference on the image, I've discovered that removing capacitor C31 as described here http://hw.speccy.cz/plus2mod.html has made the image rock solid. :D
There was also a bit of interference on the sound initially, but disconnecting the tape deck has removed that - I have a DivIDE and don't need the tape anyway.
The problem that I have now is that the sound volume from the AY-3-8912 chip is very low when compared with the 48k sound effects. If I turn the TV volume up so I can hear the 128k music, the 48k sound is way too loud. For example, the music in Renegade is very low when compared to the punching/kicking sound effects.
It was like this even with C31 in place, I think that all C31 does is mix the sound in with the RF signal so I don't think removing this has caused it.
Any ideas on how I can fix this? Is it possible to boost the 128k sound volume?
First problem was a faulty RF signal, so I bought a SCART cable from Retro Computer Shack on e-bay (it's the one with the 3.5mm jack on it that plugs into the sound output on the +2 to take the audio to the SCART socket). The RF box has now been completely disconnected.
When I first used the SCART cable I had "wobbly" interference on the image, I've discovered that removing capacitor C31 as described here http://hw.speccy.cz/plus2mod.html has made the image rock solid. :D
There was also a bit of interference on the sound initially, but disconnecting the tape deck has removed that - I have a DivIDE and don't need the tape anyway.
The problem that I have now is that the sound volume from the AY-3-8912 chip is very low when compared with the 48k sound effects. If I turn the TV volume up so I can hear the 128k music, the 48k sound is way too loud. For example, the music in Renegade is very low when compared to the punching/kicking sound effects.
It was like this even with C31 in place, I think that all C31 does is mix the sound in with the RF signal so I don't think removing this has caused it.
Any ideas on how I can fix this? Is it possible to boost the 128k sound volume?
Post edited by mappy24 on
Comments
Look on the schematic and you'll see that the AY sound is mixed with the 48k sound with a large resistor, 10k or something. I put a variable resistor with the same value across this resistor, then I run a test program which BEEPs and PLAYs alternately in BASIC, allowing me to tune the volume.
Be aware, though, if you set the 128k too loud you'll get distortion in the 48k (and possibly the 28k).
If you need help, ask me for more info. :)
Good luck!
After reading this page www.worldofspectrum.org/faq/reference/pinouts.htm
I'm assuming this is for the 128k Spectrum and not the +2 as I am unable to locate IC38 on the board, I can see IC11 which is the same IC (MC1376P) though! Can I solder a 3.5mm socket to that or is that a bad idea? :-o
Your advice to use a variable resistor is great, but since I can't understand schematics I'm struggling to locate the large resistor of which you speak!
The sound circuit on the toastrack is different anyway, with resistors in different places.
http://alistairtesting.no-ip.org/r38.jpg (random board photo pinched from google images)
Spirantho said "I put a variable resistor with the same value across this resistor". I'm not sure what that means!
Thanks for all the help, very informative! :D
I assume he means removing that and replacing it with a potentiometer, if you put it in parallel you'd only ever get it up to half that value.
Where does the third leg go? :-?
[FONT=Courier New] _____ -----|_____|--+-- ^ | |_____|[/FONT]Like that.
Sounds like you're on the right track....
My +2 grey is connected via RGB and the sound coming out of the 3.5mm socket, not via RF.
Is R38 the correct resistor to be messing with or does R38 only affect the volume over RF?
http://s-huehn.de/spectrum/hardware1.htm#sp+2b ?
He changes R80 to 330K, R45 to 39K and R37 to 3,3K. Is this the way you normally fix the problem or do you prefer a different attempt?
schombi.de/my-retro-collection.html"
I just stick a 10K variable resistor across the resistor (R37 I think it is on a +2) and change the volume using a short BASIC program which alternately "PLAY"s and "BEEP"s the same note (roughly). When the 128K is too loud, the 48K will start to distort, so you need to find a good balance, but it can be done!
There's the same problem on the Toastrack, by the way.
Your approach is interesting, but would the one I wrote give different/worse/better results? Of course it?s more work. Scott states in his page that R80 would be for EAR, R45 for MIC and Beeper and R37 for the AY.
schombi.de/my-retro-collection.html"
Both of these were Z70700 Issue 1's, where R45 is in a different location to the official schematics which refer to the Z70500 issue 3 board. On the Z70700's, R45 is the resistor immediately north west of the 8 way keyboard connector, standard resistor value here is 10k from the factory.
Apparently R115 is the resistor to change on the toastrack, connect two 3.3k resistors in parallel here (achieving a resistance of approx. 1.65k). As stated above, can't personally vouch for this though.
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zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki
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zx-diagnostics - Fixing ZX Spectrums in the 21st Century (wiki)
Sinclair FAQ Wiki