Fixing audio on a grey +2

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MonkZy
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Fixing audio on a grey +2

Post by MonkZy » Sun Mar 11, 2018 9:48 am

I have recently obtained a grey +2. I have managed to clean up the composite output by removing C31. I have no need to feed this signal to the RF, so I simply removed the capacitor. My next problem is the abysmal sound. I am fine with the sound coming out of the mono audio jack already on the +2, but I do need to address the awful mixing of the two sound signals. I have looked at the aftermarket offerings but I am hesitant to solder items to the ULA or AY chips, also I am not too fussed about having a stereo output. While googling around for the composite fix I stumbled across a thread which showed two resistors on the motherboard that can be swapped for better values to get a nice balanced output on the original mono socket. I cannot seem to find this thread again :( Can anyone tell me the numbers of the two resistors that set the audio balance, and also the appropriate values for these two resistors to give a better balance?
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MatGubbins
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Re: Fixing audio on a grey +2

Post by MatGubbins » Sun Mar 11, 2018 11:48 am

There is a big thread on WOS regarding the +2 Grey audio fix. I hope the mods here don't mind me linking.

https://www.worldofspectrum.org/forums/ ... -errors/p1
There's a lot to read, along with few mistakes by me misreading the values of resistors.
-------------------------------------------------------------------------------------------------------------
There is this page, in German, that has lots of helpful info:

http://s-huehn.de/spectrum/hardware1.htm#sp+2b

Scroll down to 'ZX Spectrum +2 - Verbesserung des Sound-Ausgangs'
and it mentions the
R80 ändern in 330k (für EAR)
R45 ändern in 39k (für MIC und Beeper)
R37 ändern in 3,3k (für Soundchip)
along with a nice picture to show where they are, with red dots on the solder points.


After fixing the audio on my +2 Grey I found that was best to keep the AY slightly quieter than the BEEPer noise as the music would be distracting to some games when the BEEPer noise was important. I also found that the RF sound had a lot more bass (both AY and BEEPer) than the SOUND output socket, this is on the same TV. I wanted to mess around putting a AY volume control on the side of the +2 so that I could have the AY louder or quieter than the BEEPer, but I've not progressed any further as my +2 is working and I don't want to balls it up.
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Ast A. Moore
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Re: Fixing audio on a grey +2

Post by Ast A. Moore » Sun Mar 11, 2018 11:57 am

The simplest way to balance the audio between the ULA and the AY chip is replace two resistors with different values, as I show here. This brings the audio levels on par with the +2B. Feel free to change the values to your liking.
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1024MAK
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Re: Fixing audio on a grey +2

Post by 1024MAK » Sun Mar 11, 2018 1:16 pm

MatGubbins wrote:
Sun Mar 11, 2018 11:48 am
There is a big thread on WOS regarding the +2 Grey audio fix. I hope the mods here don't mind me linking.

https://www.worldofspectrum.org/forums/ ... -errors/p1
:arrow: That's okay, saves me linking to my own thread :lol: :ugeek: :mrgreen:

Mark
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MonkZy
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Re: Fixing audio on a grey +2

Post by MonkZy » Sun Mar 11, 2018 1:37 pm

Thank you, I think the WOS thread may be the exact thread I am trying to find. I will most likely make the relay mod to cut the tape player input when not in use. I used a cassette audio adapter (dummy cassette with a wired tape head inside) to load up some games, it worked well but when I amplified the audio from the spectrum I created a rather loud Theramin!! Was fun playing tunes by waving my hand around near the tape deck, but the novelty wore off a bit quickly :)
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