Best Stereo POKEY Modification?

[VinsCool]

Hi there, I was looking more seriously for getting the POKEYs going on my machines, and I was a bit unsure where to start with this.

 

I do have minimal soldering skills, and some equipment, but I am not sure yet what I can do and what I should not do.

Ideally, I would like to get the least possible amount of destruction if I want to install some modifications, but a few wires is obviously not going to be the worst ever.

 

So anyway, I have seen some boards that have been made at some point, and my question is where I could find such hardware still available for sale, and if possible that ships to Canada?

Ordering extra parts for installation is not a problem for me, as long as I have an idea of what I need in the first place.

 

Thanks in advance!

 

 

Also, I was wondering if anyone actually have managed to take control of a POKEY externally? For something like a musical instrument, for example?

I know that question is pretty much offtopic by itself, but I might as well ask since I do have some chips laying around that are not yet used, and I have a bunch of experiments I wanted to do at one point.

Edited July 2, 2022 by VinsCool
typo

[+DjayBee]

The best replacement seems to be POKEYMAX but AFAIK it currently cannot be built due to unavailability of its FPGA.

 

Regarding using POKEY as a musical instrument you might have a look at MIDIjoy. It is actually not an external device containing a POKEY but an interface to use the Atari as a MIDI device.

 

 

[VinsCool]

34 minutes ago, DjayBee said:

The best replacement seems to be POKEYMAX but AFAIK it currently cannot be built due to unavailability of its FPGA.

Hiya, thank you!

The thing is, I am looking to add another existing chip to one I already have, not a replacement.

Having an alternative is always very nice, I can agree to that  

 

35 minutes ago, DjayBee said:

Regarding using POKEY as a musical instrument you might have a look at MIDIjoy. It is actually not an external device containing a POKEY but an interface to use the Atari as a MIDI device.

Pretty cool indeed!

Not exactly what I had in mind, but it is closer to it for sure, haha!

[+mytek]

This one can be DIY built or ordered from TBA.

 

 

If you don't need the PS/2 keyboard adapter aspect, just leave out the PIC chip which is hard to find currently (same situation as the FPGA shortage).

 

Incorporates electronic Stereo/Mono switching circuit.

 

Link to TK-II-Stereo gerbers and docs.

 

[VinsCool]

Hi there, I have an update since my last post to this thread!

 

Big thanks to @chevymad for contacting me the other day, and kindly selling me these prebuilt units, they arrived earlier today.

 

So excited to give this a try later!

 

[chevymad]

Looking forward to hearing your pokey experiments with them. 

[Beeblebrox]

6 hours ago, VinsCool said:

Hi there, I have an update since my last post to this thread!

 

Big thanks to @chevymad for contacting me the other day, and kindly selling me these prebuilt units, they arrived earlier today.

 

So excited to give this a try later!

 

@VinsCool  Enjoy!! Can't wait to see what you do with things going forward with Stereo capability! I have stereo in one of my 800XLs and hooked up to even basic PC powered speakers the output sounds great for Pokey music tracks like Skyride, Battle Squadron, and a for Stereo (PDS) PDM music conversions. (I often listen to my Fujiconvert'ed PDS conversion of Cowboy Bebop's legendary title track TANK. (https://atariage.com/forums/topic/279232-fujiconvert-01/?do=findComment&comment=4929803)

 

Thanks for all thw work as ever. 

 

[VinsCool]

I've connected the required parts I think now, and stereo works!

 

But I have a bit of a concern... Is it normal the sound appears to be distorted? O.o

I am aware I couldn't driver headphones directly according to the documentation, so I just want to make sure I didn't do something stupid, lol

 

[EDIT] It is pretty loud too, now that I'm actually passing through my USB input card.

Let's see if the quality is also distorted when recorded... Preview headphones jack is very hot for sure, haha

Edited July 20, 2022 by VinsCool
Addendum

[Beeblebrox]

12 minutes ago, VinsCool said:

I've connected the required parts I think now, and stereo works!

 

But I have a bit of a concern... Is it normal the sound appears to be distorted? O.o

I am aware I couldn't driver headphones directly according to the documentation, so I just want to make sure I didn't do something stupid, lol

@VinsCool  Perhaps upload a video of a track playing on your new Stereo setup to illustrate?

[VinsCool]

5 minutes ago, Beeblebrox said:

@VinsCool  Perhaps upload a video of a track playing on your new Stereo setup to illustrate?

For now I have a test audio recording from the jack  

 

As heard, it definitely works, but the signal is so hot!

Did I miss anything important? A resistance I did not see, or couldn't actually find mentioned anywhere? 

 

I followed this as a reference:

 

 

I've salvaged a some pin connector cables and soldered the Bell and A4 lines, but didn't touch the Reset, Option, Select and Start pins, since I didn't need the keyboard compatibility (yet).

Could this be related?

[VinsCool]

Double post sorry

Edited July 20, 2022 by VinsCool

[Mclaneinc]

45 minutes ago, VinsCool said:

For now I have a test audio recording from the jack  

 

 

As heard, it definitely works, but the signal is so hot!

Wow, that's just a bit too much, distortion city..

[VinsCool]

10 minutes ago, Mclaneinc said:

Wow, that's just a bit too much, distortion city..

Yep, I assume I should just add the resistance described for headphones jack input, that's pretty much the only reason I think this gets so hot otherwise.

But hey, regardless, Stereo does work, so that's cool! haha

[Mclaneinc]

Yes, you have fun with it..

[+mytek]

3 hours ago, VinsCool said:

I have a bit of a concern... Is it normal the sound appears to be distorted? O.o

I am aware I couldn't driver headphones directly according to the documentation, so I just want to make sure I didn't do something stupid, lol

Audio output normally shouldn't be distorted without the optional resistor mod installed. Are you sure you have all the right values for the components? Have you tried connecting the output to something other than your USB card, such as an actual stereo system? There is a chance that the USB card expects a headphone level feed, so yes if all the components look correct, then try the mod to see if that fixes things.

 

[VinsCool]

1 hour ago, mytek said:

Audio output normally shouldn't be distorted without the optional resistor mod installed. Are you sure you have all the right values for the components? Have you tried connecting the output to something other than your USB card, such as an actual stereo system? There is a chance that the USB card expects a headphone level feed, so yes if all the components look correct, then try the mod to see if that fixes things.

 

I had tried out with my headphones initially, and the level was actually pretty quiet, and distorted.

I was not very surprised, I was expecting it to not sound right with the headphones

I was surprised by the USB card by how loud and hot the signal was!

You may be correct, however, I think it does expect headphones levels, which would explain the distorted sound.

 

Now that I think about it, I believe the boards were assembled, tested and confirmed working before shipping, so I imagine this isn't the issue.

I can try the other one and see if there is a difference.

Other than that, my Bell and A4 solder points were a bit clumsy (new soldering iron I never used until a few hours ago, and years without soldering came with a price, haha ?), but I am pretty sure they were fine since it did work after all ?

The only other plausible reason for the hot signal is that my machine was already modified with a bunch of upgrades, mainly the extra RAM (256k upgrade) and the OMNIROM/Stock ROM toggle using the RF Channel selection switch...

None of those would be related, by any chance, right? ?

 

Anyway, I will try the second board I received and see if this makes a difference!

At worst, I will need to find some compatible resistances to get a clean audio signal, or maybe I could try mixing the Stereo to the Mono output thru the monitor port, I'm definitely not out of possible workarounds for sure! haha!

Just out of curiosity, I see the required parts are SMD 390 Ohm resistances, is it fine to substitute them with equivalent resistances? I may have some of those around, while I know for sure I have no such thing as SMD resistances in my things at home.

I ask only because I don't really feel like buying some extra parts and wait a bit longer, hehehe  

 

Anyway, I'll swap out the boards and see if this made a difference!

I'll be right back.

[VinsCool]

54 minutes ago, VinsCool said:

I'll be right back.

Okay a bit longer than expected (caught with some unrelated stuff), the result is identical, very hot and fuzzy signal with the second board.

This confirms both are indeed working, but I need to attenuate the signal by a notch, somehow ?

 

Ah well, it's not the worst thing ever, just a mild detail I will have to fix later.

I hope I can find some compatible resistances and see if this will help solving my issue  

[ivop]

If you don't have 390 ohm, you could indeed try 330 ohm or 470 ohm (the closest in the E12 series). The closer the better if you have anything from the E24 series (360 or 430).

 

But it's weird that the current output is not the -10 dBV standard  (0.316 V RMS / 0.447 V Peak) that it should output. Given that both were built by the same person, it might be that one of the installed components is incorrect on both of the boards.

 

Note that if the distortion happens because the transistors are clipping (Fuzz Face, Jimi Hendrix!) it might be that the resistors won't do much. @mytek ?

Edited July 20, 2022 by ivop

[chevymad]

Looking through my digikey order, It looks like all the correct values were ordered. The one board does have a few radioshack resistors that I allready had though. I didn't notice any issue playing through some small pc speakers I use. 

 

Can you post the sound file, so I can play it on my machine. I used Poison's music disk stereo edition for my testing.  

 

 

[chevymad]

Ok.. just did a test between my 1088XLD and my 800xl with this board installed. The 800xl is quite a bit hotter then the XLD's output. No crunch through my speakers though, just alot more volume. 

[VinsCool]

Honestly any file, doesn't matter, it's immediately obvious the signal is way too hot for me here.

It is possible I did something wrong too, so I will just troubleshoot a bit more before trying anything that could permanently ruin the boards.

 

For example, I know my initial solder points were junk, but I am pretty sure they work, so other than the possible resistance needed (which I haven't been able to find anyway :v), or the fact a different mod on my machine caused a conflict, I don't really know what is going on.

 

Also just for fun, I verified and I can still use the original Monitor port AUDIO out connection, which does have very good (Mono) quality, but the sound is much quieter as well.

It doesn't sound different from before the Stereo mod, too, I guess that's worth mentioning.

 

my next idea was to poke around with my multimeter and see if I'm getting voltage higher than it should be, or just see if my connections are all actually making good contact.

I can believe it's either something stupid I did (most likely) or something my machine had kept hidden to surprise me, just like how my colours potentiometer acted all weird a little while ago (fixed now).

 

[darn it Atari Age died unexpectedly and the message was not sent]

 

10 minutes ago, chevymad said:

Ok.. just did a test between my 1088XLD and my 800xl with this board installed. The 800xl is quite a bit hotter then the XLD's output. No crunch through my speakers though, just alot more volume. 

interesting... so maybe that goes into why this happens.

So now it is not unrealistic to want some extra resistance to reduce the distortion a bit.

Would there be any other vector I could explore by any chance for a possible fix?

For example, would I be able to tap the AUD OUT from the POKEYS and grab them directly, as a workaround, I would actually be more fond of using PHONO jacks than STEREO HEADPHONES, so if that could work around that extra fuzz I am totally not against it, assuming I cannot fix it with the resistances.

[+mytek]

13 minutes ago, chevymad said:

Ok.. just did a test between my 1088XLD and my 800xl with this board installed. The 800xl is quite a bit hotter then the XLD's output. No crunch through my speakers though, just alot more volume. 

The 1088XLD already has that extra resistor in each channel's audio driver section as part of the design. By the time I got to designing both the XEL and XLD I already knew this was a good idea.

 

If you look at this schematic (click to enlarge) you'll see that R29 and R33 are the 390 ohm resistors we are talking about.

 

1 hour ago, ivop said:

If you don't have 390 ohm, you could indeed try 330 ohm or 470 ohm (the closest in the E12 series). The closer the better if you have anything from the E24 series (360 or 430).

Yes this resistor's value is non critical, so any of those suggested values should work as a substitution.

 

2 hours ago, VinsCool said:

Okay a bit longer than expected (caught with some unrelated stuff), the result is identical, very hot and fuzzy signal with the second board.

This confirms both are indeed working, but I need to attenuate the signal by a notch, somehow ?

Even without the 390 resistor mod, it shouldn't distort. So I really believe the distortion is caused by the USB card you are using being too sensitive to input level and thus being over driven. As I suggested earlier, try hooking it up to an alternative amplified speaker or stereo system to confirm this.

 

2 hours ago, VinsCool said:

Ah well, it's not the worst thing ever, just a mild detail I will have to fix later.

I hope I can find some compatible resistances and see if this will help solving my issue  

The 390 ohm resistor will drop the level a bit, and that may be enough for your USB card to work without the distortion. Although SMDs are called for, any THT resistor would work if you can figure out a good way to bend its leads to fit. However the SMDs will look much nicer and fit much better.

 

[VinsCool]

6 minutes ago, mytek said:

Even without the 390 resistor mod, it shouldn't distort. So I really believe the distortion is caused by the USB card you are using being too sensitive to input level and thus being over driven. As I suggested earlier, try hooking it up to an alternative amplified speaker or stereo system to confirm this.

Yup this was the impression I got as well.

The problem is, I do make use of this device specifically for audio recording sessions, which is unfortunate for me to get the sound overdriven as much as it is right now.

I was going to try different devices hookups and see if anything displayed the same distorted sound issues or not.

I'll make sure to keep this thread updated with my observations.

 

7 minutes ago, mytek said:

The 390 ohm resistor will drop the level a bit, and that may be enough for your USB card to work without the distortion. Although SMDs are called for, any THT resistor would work if you can figure out a good way to bend its leads to fit. However the SMDs will look much nicer and fit much better.

Awesome, this was what I was looking to see, so as a last resort I could simply add the extra resistance and call it a day.

in any case, the modification does work, and that's what truly matters for me  

Very easy to install, too!

[VinsCool]

Ok so while the site keeps killing itself every 2 minutes, I managed to test directly on my Commodore 1702 Monitor and frankly I can give the exact same observation:

the volume is very loud and distorted, compared to the exact same level of the original (amplified) AUDIO out signal.

 

It's really something I cannot describe without being in person, but yeah, it is quite nasty as it is right now ?

I'll see if I can find anything like an amp, computer speakers, etc.

But honestly I'm pretty much expecting this same loud and distorted output on other setups, but I hope I will be wrong with the expectation.

 

It does actually sound better through the monitor speaker, I get each POKEY play independently just fine, but it's the clipping fuzz that is leading the entire headroom audibly, and this isn't much enjoyable even at love volume.

It's definitely the sound of overdriven levels, haha ?

 

I'll carry on with more tests!

[+mytek]

Very interesting, and a bit odd as well. I've connected my TK-II-Stereo board (without the 390 ohm resistor mod) to just about every amplified widget I have, and it never distorts. Not to say that covers all bases, but it is odd that even your monitor has an issue.

 

Now I do know that without the resistor mod the use of headphones will sound fuzzy and at a low volume.

 

That's about all I can add for the moment