Internal Speaker

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Z80Man
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Re: Internal Speaker

Postby Z80Man » Tue Sep 29, 2020 7:39 am

Many thanks for the precisions.

I'm hesitant to add an internal peaker as for now the headphones in the oudio output jack are allright, and I found the levels between the different sources to be satisfactorily balanced.

It's mostly that my monitors don't have internal speakers, so in case I would like to play sound openly, I intend to insert a small amplifier with a volume potentiometer, either just a trimmer with a hole in the bottom cover to tune it with a screwdriver, or maybe a classical model with an on/off switch at the lowest position. Anyway, I've got supply problems with shipping not allowed to my location for now, so it's not urgent. What's more bothersome is the absence of power switch, so that's the first thing I'll add for now, since I couldn't get a micro SD card slot either to ship to my location...


By the way, as a small note about your choice of speakers :

Using something looking like the original 16K/48K speaker may seem cool, but you should think about using a more serious model here (ideally with a small amplifier, but not only). The best choice should be a model with a seal back (most laptop speakers are shielded, so the rear wave of the membrane is isolated), so you get better response in the bass range.

Then if you can't find that kind of model, or even using one, you should still consider baffling it, i.e. separating the front side from the rear saide of the membrane by fitting the speaker directly against the bottom cover with holes drilled in it (only in front of the speaker membrane, of course, else it would nullify the purpose) and seal the speaker rim with mastic. You'll get better bass and clearer sound at the same time.

Removing the bus cover is fine about getting more noise (well, at least more noise than keeping the speaker enclosed), but won't get you better sound quality with a bare speaker just thrown inside the casing... :p

Of course a shielded speaker will be fine either way, or at least still better than a normal, open one.
Last edited by Z80Man on Tue Sep 29, 2020 11:13 pm, edited 1 time in total.

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Centurion
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Re: Internal Speaker

Postby Centurion » Tue Sep 29, 2020 1:57 pm

Not sure where you are located Z80Man, but hopefully these shipping woes will get better sooner rather than later. I have been avoiding international shipping myself lately. Regarding the power switch, I have been using an Inline Power Switch from ActiveConsult and it's been great.
Z80Man wrote:
Tue Sep 29, 2020 7:39 am

By the way, as a small note about your choice of speakers :

Using something looking like the original 16K/48K speaker may seem cool, but you should think about using a more serious model here (ideally with a small amplifier, but not only). The best choice should be a model with a seal back (most laptop speakers are shielded, so the rear wave of the membrane is isolated), so you get better response in the bass range.

Then if you can't find that kind of model, or even using one, you should still consider baffling it, i.e. separating the front side from the rear saide of the membrane by fitting the speaker directly against the bottom cover with holes drilled in it (only in front of the speaker membrane, of course, else it would nullify the purpose) and seal the speaker rim with mastic. You'll get better bass and clearer sound at the same time.

Removing the bus cover is fine about getting more noise (well, at least more noise than keeping the speaker enclosed), but won't get you better sound quality with a bare speaker just thrown inside the casing... :p

Of course a shielded speaker will be find either way, or at least still better than a normal, open one.
Good suggestions, but trying things one step at a time and hoping to avoid permanent modification of the Next. I will see how the 32 ohm speaker sounds and then move from there. Your idea on a hole drilled for the volume pot could be helpful if using an amplifier for sure, but again hoping to avoid that myself. Not expecting much from the 32 ohm speaker and already thinking about the next step though, which will be an amplifier and possibly a speaker more like one you're suggesting.

I hope you can report your findings here when you get a chance to install a speaker yourself, it could be beneficial to other users too. It would be great if the community could all settle on a certain speaker and/or amplifier setup that's suitable for the masses to avoid all this up and down trial & error so many of us are going through.

It doesn't sound too promising, but if there's any way there could be a software volume control, either through the NMI Sound settings or config file, that'd be wonderful, but trying to not set my hopes too high on that.
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Z80Man
Posts: 21
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Re: Internal Speaker

Postby Z80Man » Tue Sep 29, 2020 11:42 pm

A higher impedance ohms speaker will result in a lower sound volume unless it has a very high sensitivity ; or at least using a lower impedance speaker is a cheap way to get more output power from the amplifier stage, but the sound quality will be worse.

So it's mostly a matter of chosing the best compromise, and considering the simple open collector design, you'll never get much power out of what's at most a preamplifier stage only meant to drive a downstream additional stage.

Adding a small amplifier is therefore the only way to get something decent with a better output voltage range. There's a quantity of choices for miniature amplifiers with low voltage power supply able to share the Next power lines without draining too much current.

As noted previously, it's probably a better idea to power it from the 9V line rather than risking to add noise to (and possibily weaken) the +5 V regulated line. In addition, the said noise could affect both parts, i.e. not only cause drops in the +5 V chips power supply, but also add switching noise to your audio output. In all cases, adding an eletrolytic capacitor in parallel on the supply line will help dampening all of these unwanted effects.

If it's difficult for you to source one, a small amplifier stage could probably be scavenged from an old active device, such as a small amplified speaker pod for mobile phone, a defective bluetooth headphone, an old battery powered miniature radio receiver, and so on.

Then generally speaking (because some top quality miniature design exist), the smaller the speaker you'll use, the lower the quality you'll get, so you don't really need an expensive amplifier there. However, since there's quite some room under the right side of the Next top cover, you could still use a decent wide range speaker if you don't try to place it in the cramped dedicated area on the motherboard. Remember you'll have to drill some holes in the bottom cover and fit your speaker there on its membrane side if you want to get a decent sound quality and an as full as possible range.

There quite a lot of available wide range speakers meant for car hi-fi center channel you could use, usually around 1.8 to 3 cm wide, that could fit into the casing. They're usually not very flat, but some of them are around 1 cm thick and should fit without a problem.

Anyway, you'll do this only if you intend to use the internal audio as your main audio output, else it'll always be simple to just use the audio output jack. I've noticed there's a bit of noise (especially when plugging an HDMI monitor or TV, strangely), but the sound quality is really good, the dynamic range is perfect with rich bass and and an excellent resolution (each channel is sharply detailed), and the balance between each source is excellent.

So maybe if you have a small pod for mobile phone, the simplest could be just to plug its 3.5 mm jack in, though dismantling it and fitting it inside the casing could work too. :p

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Centurion
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Re: Internal Speaker

Postby Centurion » Wed Sep 30, 2020 10:37 pm

At the moment, I'm mostly concerned with bringing the volume level up vs quality. Probably sounds funny, but I would really be happy just being able to hear the beeps a bit when navigating menus and playing some games casually. Something along the lines of how my Harlequin sounds. You have some really good suggestions Z80Man and I appreciate them, just unsure how much of that is necessary for what I'm going for right now.

I just installed the ABS-231-RC 32 ohm speaker and it seems about the same as the piezo speaker volume wise. Actually maybe a hair louder, but still next to silent when using the BEEPer mode on ALL and just very faint in the Int mode. Removing the expansion cover did help a bit but not much.
ABS-231-RC.jpg
ABS-231-RC.jpg (653.61 KiB) Viewed 2759 times
Next phase of the adventure will be trying an amplifier. The guy on Facebook used a TDA1308, which is considered an Earphone amp, but I'm also seeing one on eBay that's considered a Microphone amp, which looks more appealing to me since it has a volume pot onboard. Do you folks know if there would be any issues using the Mic amp rather than the Earphone amp?? Thanks, I really appreciate the help and discussion. Learning a lot!
TDA1308vMicAmp.jpg
TDA1308vMicAmp.jpg (237.8 KiB) Viewed 2759 times
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Montala
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Re: Internal Speaker

Postby Montala » Sat Oct 03, 2020 10:46 am

I am folowing this thread with interest, and would like to thank all those who have contributed such useful information!

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Centurion
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Re: Internal Speaker

Postby Centurion » Tue Oct 06, 2020 5:08 am

Montala wrote:
Sat Oct 03, 2020 10:46 am
I am folowing this thread with interest, and would like to thank all those who have contributed such useful information!
That's great. Glad someone is getting some help from all of this. :)

Well, yet another fail on my end. This evening I tried a 5-12v LM386 Mini Amp on both the J15 5v line and J16 9v line. Neither allowed the Next to work. The power light on the Next wouldn't turn on and no video, so I'm lucky I didn't blow my Speccy up! :o
Next_LM386_Amp.jpg
Next_LM386_Amp.jpg (866.08 KiB) Viewed 2640 times
Unless I am doing something wrong here (Which I most likely am), I would suggest any readers to avoid this particular amp. The guy on Facebook has installed a variable gain pre-amp to his internal setup and seems to be getting some great results.

EDIT: Sure enough, it wasn't this amp that was bad, it was that the Negative pins 1 & 2 on the Next's J3 have 3.3v and I had a wire connected to my input ground on the amp. Yikes! :o
Last edited by Centurion on Tue Oct 13, 2020 5:15 am, edited 2 times in total.
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mitchelln
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Joined: Wed Jun 07, 2017 10:18 am

Re: Internal Speaker

Postby mitchelln » Tue Oct 06, 2020 1:14 pm

It doesn't matter what speaker you try, there's simply not enough current available to drive it.

I initially tried just the TDA1308 headphone amp as seen in my Facebook post. However, it doesn't quite supply enough gain even when maxed out.
The output of the dac has a tiny range -
around 0.7V to 0.9V.

So I added a pre-amp board. The output is now LOUD. I then made a little plug in board that's takes power off J15. The aux keyboard connector adds a little complication...

I've updated the Facebook page with this setup.
https://m.facebook.com/groups/237301699 ... ef=m_notif

Only issue now is a little noise from the WiFi module. It's on the Next's rails, so not much that can be done without hacking other than turn off the module. Ideal solution would be to power the ESP8266 off its own regulator. I think the Next team are considering options for the issue 3 boards.

mitchelln
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Re: Internal Speaker

Postby mitchelln » Tue Oct 06, 2020 10:07 pm

Centurion wrote:
Wed Sep 30, 2020 10:37 pm
Next phase of the adventure will be trying an amplifier. The guy on Facebook used a TDA1308, which is considered an Earphone amp, but I'm also seeing one on eBay that's considered a Microphone amp, which looks more appealing to me since it has a volume pot onboard. Do you folks know if there would be any issues using the Mic amp rather than the Earphone amp?? Thanks, I really appreciate the help and discussion. Learning a lot!

TDA1308vMicAmp.jpg
I doubt the microphone amp will be able to drive low impedance loads such as a speaker. Need to check the spec of that chip

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Centurion
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Re: Internal Speaker

Postby Centurion » Thu Oct 08, 2020 12:20 am

mitchelln wrote:
Tue Oct 06, 2020 1:14 pm
It doesn't matter what speaker you try, there's simply not enough current available to drive it.
Seems like we're learning that the hard way. :lol:
I initially tried just the TDA1308 headphone amp as seen in my Facebook post. However, it doesn't quite supply enough gain even when maxed out.
The output of the dac has a tiny range -
around 0.7V to 0.9V.

So I added a pre-amp board. The output is now LOUD. I then made a little plug in board that's takes power off J15. The aux keyboard connector adds a little complication...
How did you 'max out' the TDA1308?

I was able to find a TDA1308 board here in the states and ordered one.

I am curious to know how you wired everything up with your plug in board and connected it to J15 if you're willing to share that info. Did you run into issues with the aux keyboard header blocking pins 3 and 18?
I've updated the Facebook page with this setup.
https://m.facebook.com/groups/237301699 ... ef=m_notif

Only issue now is a little noise from the WiFi module. It's on the Next's rails, so not much that can be done without hacking other than turn off the module. Ideal solution would be to power the ESP8266 off its own regulator. I think the Next team are considering options for the issue 3 boards.
I just installed the WiFi module on my Next. Is there an easy way to turn it off and on that you know of?

I really appreciate you posting here and keeping your FB post updated. Helpful information! It's a shame about the noise on the Next's rails and wonder if anyone will figure out an easy solution for that on our boards.

I like that you've found a way to avoid hacking away at the Next while bringing the volume up. That's exactly what I'm looking for, minus the noise of course!

Thanks
Last edited by Centurion on Thu Oct 08, 2020 1:49 pm, edited 1 time in total.
ZX Spectrum Next Backer №1,104 / ZX Spectrum Harlequin Rev. G owner / USA ZX Spectrum enthusiast

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Centurion
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Re: Internal Speaker

Postby Centurion » Thu Oct 08, 2020 12:25 am

mitchelln wrote:
Tue Oct 06, 2020 10:07 pm
Centurion wrote:
Wed Sep 30, 2020 10:37 pm
Next phase of the adventure will be trying an amplifier. The guy on Facebook used a TDA1308, which is considered an Earphone amp, but I'm also seeing one on eBay that's considered a Microphone amp, which looks more appealing to me since it has a volume pot onboard. Do you folks know if there would be any issues using the Mic amp rather than the Earphone amp?? Thanks, I really appreciate the help and discussion. Learning a lot!

TDA1308vMicAmp.jpg
I doubt the microphone amp will be able to drive low impedance loads such as a speaker. Need to check the spec of that chip
Here's a link to the LM386 Datasheet:

https://www.jameco.com/Jameco/Products/ ... 839826.pdf
ZX Spectrum Next Backer №1,104 / ZX Spectrum Harlequin Rev. G owner / USA ZX Spectrum enthusiast


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