Sinclair ZX80 / ZX81 / Z88 Forums

Hey guys,

I originally created a post some time ago (viewtopic.php?f=21&t=3292&p=42854#p42854) about the sound problems I was having with a ZX Spectrum but I've only just now come back to the project, so I've created a new post here because I don't know if a post from over a year ago will be seen or responded to.

Apologies if this is bad form and please delete if this isn't allowed.

I bought the 2PCS LM386 Module 20 Times Gain Audio Amplifier Module F Raspberry Pi Arduino, as @1024MAK kindly suggested might solve the problem, from ebay but as a newbie to the world of repairing Speccies, I was hoping someone could tell me what my next step is? I'm guessing I need to solder it to the Spectrum's board but I have no idea where to start with it.

Could anyone point me in the right direction? If anyone's got a photo of an installed module, that would be really useful.

Cheers,

Kieran.

A new post in an old topic will appear at or near the top of the list in the ‘active topics’ page (use the quick links drop down menu in the top left corner), on the ‘new posts’ page, on the ‘unread posts’ page and at or near the top of the relevant sub-forum page.

But, as it’s been a while, there is no problem in starting a new topic. Especially as you included a link back to your earlier topic.

The normal usage of the audio amplifier module (you only need one) can be internal to a ZX Spectrum or external.
I recommend external for rubber key machines due to the lack of space in their cases.

This is a very brief description of how to use it externally:

The output from your audio source (smartphone, MP3, music player, laptop, PC) goes to the audio input on the audio amplifier module.

The output from the audio amplifier module goes to the Ear socket on the ZX Spectrum.

The audio amplifier module also requires a DC power feed. This can either be a completely separate DC power supply unit (PSU)/power adapter/wall wart or similar. Or you can use a power splitter cable/adapter and use the 9V supply from the Sinclair PSU.

I’ll do a more detailed post tomorrow when I have more time.

Mark

Hi Mark,

thanks for getting back to me. I appreciate it after it took me so long to get back to my original post!

Having read your reply, I'm wondering whether I've bought the right amplifier or should I have bought something more like this: https://www.ebay.co.uk/itm/262610277188

Cheers,

Kieran.

petercushion wrote: ↑Tue May 18, 2021 8:29 pm Having read your reply, I'm wondering whether I've bought the right amplifier or should I have bought something more like this: https://www.ebay.co.uk/itm/262610277188

Hi Kieran

I’ve not had good results with one similar to the one you linked to

I’ve not had time to get any further with this subject today, in court as a witness in the morning and had to make use of the dry weather in the afternoon, before the rain came...

So I’ve not forgotten

Mark

No worries, Mark.

Good luck with court, I hope it went well.

Cheers,

Kieran.

@1024MAK

I was just re-reading the post you previously directed me to about boosting the audio viewtopic.php?f=7&t=3541&start=10#p36670 and noticed the part about old PC speakers being something to try. Guess what I threw out two sets of last week?!

I'm off out in a bit, so I'm going to have a nose in a few charity shops and see if I get any luck with picking a pair up!

Cheers,

Kieran.

Connect the +9V DC input to the positive of a 9V battery (use a battery box that takes six AA cells rather than a PP3). Connect the battery box negative to one of the two 0V / GND terminals.

Connect the audio in terminal to ONE channel of your audio source (e.g. the left stereo channel if your device is stereo, ignore the other channel). Use the other 0V / GND terminal for the audio ground.

You can cut up some DuPont type connectors to fit on the input terminal pins.

Connect the audio out terminal to the signal (tip) contact of a 3.5mm mono (single channel) jack plug. Connect the 0V / GND terminal next to the audio out terminal to the ground / screen / outer of the 3.5mm mono jack plug.

This jack plug then goes into the ear socket on the ZX Spectrum.

Play a tape file and adjust the volume control. Hopefully you will now be able to load up games

Mark

It's worth noting that at X20 gain this chip is working on internal bias only hence the low gain factor, however should the gain not be enough and you feel brave then a 10uf electrolytic capacitor soldered between pins 1-8 (positive to pin 1)will take this up to X200 gain

At X20 it's very nearly line level which may be on the weak side whereas X200 is enough to power a speaker at a good volume and is the kind of level kicked out by the earphone socket on the old shoebox type cassette players and is the kind of level which the Sinclair computers expect.

Cheers, guys.

@1024MAK

Looks like I need to gather together a few bits and pieces but hopefully this'll sort the problem!

@Moggy

My soldering skills aren't fantastic but they're adequate, so if I don't get any luck with the amp x20, I'll get the soldering iron out.

I'll probably be a few days sourcing the bits I need but I'll let you know how I get on.

Thanks again.

Kieran.

Guys, I bought an amp to try and take the workload out of putting one together but it didn't work. The amp works fine with my other Speccy but I had the usual problem on the problematic console.

Attached is a spec for the amp. In your opinions, should it be powerful enough to do the job? If not then I guess I need to get building!

Cheers,

Kieran.