Spectrum +3 Sound Distortion Fix Bodge

Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

I have just done the distortion sound fix mod on a +3 (https://spectrumforeveryone.com/technic ... pectrum-3/) and can safely say there is no longer any distortion. As there is no sound…
Well if I load Exolon and put the TV volume up to absolute max I can just hear the title music playing really faintly. So it is producing sound but only just.

I have double checked all the resistors and all are the correct values. I have also checked for solder splashes etc. and cannot see anything untoward.

There was sound (but distorted) before doing this…

I have done this a good few times before without incident.

I am wondering if I damaged TR5 while lifting the emitter to connect it to the resistor? Everything else seems fine. I don’t have a spare to replace it with unfortunately. Possibly a ZTX751 from here? https://www.retroleum.co.uk/zx-spectrum-transistors
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

Well, progress of sorts.

I fitted a BC549C transistor in TR5 after it was suggested that would be a good replacement.

I now get audible music from Exolon at about 50% of volume. The beeper based sound effects are still very quiet however.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

Here is the removed transistor:

77173A15-69EE-44BD-9A98-6807BF1F7805.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

I have fitted a new TR5 and it made no difference.

Back to the drawing board. Next step will probably be to repeat the sound fix and see if I messed up anywhere.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
User avatar
1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by 1024MAK »

When you say that you have “double checked all the resistors and all are the correct values”, was this by testing with a multimeter or reading the colour codes?

Are you using metal film types (normally have a light blue coloured body) or carbon film types (normally have a light brown or yellow/cream coloured body) resistors?

Apart from a multimeter, what test gear do you have? Do you have a battery powered audio amplifier?

Does the lack of volume affect all the audio outputs of just some?

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
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Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

Thanks Mark.

The audio was fine, but distorted, before the so mod so it is something I have done.

I am using the carbon film type of resistor.

I have rechecked each resistor by taking a resistor out of the appropriate packet, checking it with a multimeter and then putting it next to the resistor I have fitted on the board.

I don’t have an audio amplifier, just a multimeter and logic probe.

I have only tested with Exolon and Manic Miner, both at max volume on my TV.

With Exolon I get quiet AY music and sound effects.
With Manic Miner I can’t really hear anything so I think the beeper is either extremely quiet or not producing audible sound.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
User avatar
1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by 1024MAK »

Lardo Boffin wrote: Sat May 28, 2022 12:58 pm I don’t have an audio amplifier, just a multimeter and logic probe.
Not even a shoebox tape recorder that can be set up in audio monitor mode?

Here is a simple BASIC program to test the bleeper:

Code: Select all

10 FOR a=10 TO 20
20 BEEP .5,a
30 NEXT a
40 GO TO 10
To hear this on a issue 3 48K board ZX Spectrum, waddle over to YouTube :P

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

1024MAK wrote: Sat Jun 04, 2022 11:51 am
Lardo Boffin wrote: Sat May 28, 2022 12:58 pm I don’t have an audio amplifier, just a multimeter and logic probe.
Not even a shoebox tape recorder that can be set up in audio monitor mode?

Mark
Ah, I do have one of those I think. Not thinking outside the box. :oops:
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by Lardo Boffin »

I have made use of the Sound In port of my trusty WHSmiths tape player and at about 25% volume I can hear your beep program.

Spurred on by this I loaded Manic Miner and can hear all of the music and sound effects. Obviously the sound quality is reflective of a 1980s cheap tape player but it is there none the less.

I also loaded Exolon and got the lovely intro music so it seems that all of the sounds are being produced but are now very, very quiet…

Thanks Mark! At least I don’t seem to have really killed anything.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
sP1d3r
Posts: 118
Joined: Mon May 16, 2022 9:20 am

Re: Spectrum +3 Sound Distortion Fix Bodge

Post by sP1d3r »

I was looking at my 128 +2B and I noticed a mod I did some time ago, which was to lift the 3.5mm jack socket, cut the track that links the two contacts and run a wire down to by the memory chips.
I think the purpose of this was to allow a stereo signal though I can't remember much about doing it.

Your quiet sounds make me think you've only got one channel output instead of two.

I'm going to try the distortion fix on my +3, I wonder if I'll get the same problem!
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