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Fixing audio on a grey +2

Posted: Sun Mar 11, 2018 9:48 am
by MonkZy
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?

Re: Fixing audio on a grey +2

Posted: Sun Mar 11, 2018 11:48 am
by MatGubbins
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.

Re: Fixing audio on a grey +2

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

Re: Fixing audio on a grey +2

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

Re: Fixing audio on a grey +2

Posted: Sun Mar 11, 2018 1:37 pm
by MonkZy
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 :)

Re: Fixing audio on a grey +2

Posted: Wed May 13, 2020 5:52 am
by WDeranged
MatGubbins wrote:
Sun Mar 11, 2018 11:48 am
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.
This is a problem I'm getting with my +2. I don't suppose you ever found a cause/solution?

Re: Fixing audio on a grey +2

Posted: Wed May 13, 2020 8:53 am
by MatGubbins
WDeranged wrote:
Wed May 13, 2020 5:52 am
MatGubbins wrote:
Sun Mar 11, 2018 11:48 am
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.
This is a problem I'm getting with my +2. I don't suppose you ever found a cause/solution?
Sorry, never found out why my grey +2 RF has a beefy bass sound. It is a lot better than the tinny sound socket output. I've tried a few different TVs (flat screen) since then and they all gave the better beefy bass sound over the RF connection. I've tried my other grey+2, that too has better RF sound.

Re: Fixing audio on a grey +2

Posted: Wed May 13, 2020 7:54 pm
by WDeranged
That's a shame. The sound quality through RF is far better than what you get from the rear jack, apart from the digital chatter. If it's just a +2 issue I'm surprised more people haven't noticed.

Re: Fixing audio on a grey +2

Posted: Sun Jul 26, 2020 12:11 am
by dobbo2k
Hi all, having been a long time owner of a Spectrum 48k, I recently acquired a Spectrum +2 (grey model, issue 3) and noticed the audio imbalances when using a SCART cable that combines the RGB signal with the audio from the mono 'sound' socket.

Not only was the overall audio output really low, but the AY sound was tinny and quiet, the beeper sound was relatively louder and the tape loading sound was extremely loud. I tried replacing the R37 (10k) resistor with a 3k resistor as recommended but it made little difference. Looking at the schematic I noticed that R37 was fed a signal from the 100nF capacitor C28, so I replaced that but again it made no difference.

Then what I did was effectively basically bypass both the capacitor and resistor by soldering a wire between the upper most leg of C28 to the rightmost leg of R37. Immediately the sound was much louder and fuller, just like it sounded when taking the RF signal. The AY sounded great but this now meant the beeper was relatively quiet, so I replaced the R45 (10k) resistor with a 1k resistor and that brought it up to a reasonable level. The added bonus is that the tape sound is now relatively very quiet (but still audible), so no more headaches when loading.

TLDR: The solution to tinny/quiet sound on the +2 grey issue 3 is to solder a wire between the upper leg of capacitor C28 to the right leg of resistor R37, and replace resistor R45 with a 1k resistor.

Hope that is useful to people :)

Re: Fixing audio on a grey +2

Posted: Thu Sep 03, 2020 3:43 pm
by dougal
Hi, I want to do this because the balance on my grey +2 is horrible between AY and ULA. But problem, my motherboard is different, it is a Z70700 and I cannot find the mod for this or a layout to where the capacitors and resistors are and the markings for many components on the silkscreen are covered by the components themselves.