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Reply 201 of 237, by Fagear

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Finally, all of the parts arrived and I've assembled the first prototype (live). 😎
I've not tested it yet.

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Also at the same time I've repaired damaged socket and torn traces for GAL IC on the original board. And I've temporary removed the resistor network SG0309 USI to measure it. This network together with 74HC373 were providing 8-bit DAC functionality.
As I was afraid it is not a regular bus network. This network has R-2R ladder inside and can not be easily found online for a reasonable price. 😵
So I've took some measurements, soldered the SG0309 back to the original board and made another stream, where I with help of my viewers were able to fully reconstruct internals of that network, after that I've made a replacement PCB with high precision SMD resistors to replace that network on my replica. Now it's time to order this board at some production service.

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And the SMD variant of CSM with "resistor DAC" replaced with "proper" AD7524 DAC is almost ready:

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Reply 203 of 237, by Benedikt

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Fagear wrote:

As I was afraid it is not a regular bus network. This network has R-2R ladder inside and can not be easily found online for a reasonable price. 😵

Would it be possible to somehow bodge-solder a Bourns 4310R-R2R-104LF in there? That part is very similar to the one in the Covox Speech Thing but unfortunately has a slightly different pin-out.

EDIT: Its topology is like this:

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Reply 204 of 237, by Fagear

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Benedikt wrote:

Would it be possible to somehow bodge-solder a Bourns 4310R-R2R-104LF in there? That part is very similar to the one in the Covox Speech Thing but unfortunately has a slightly different pin-out.
Its topology is like this:

R2R network pinout is:
1 = GND
2 = output
3...10 = D7...D0
R is 98...100k.
And there is load resistor between output and GND inside of value about 24,9k.

So, if you can get that part from Bourns with R=100k, wire pin 10 as pin 1 and slap a 25k resistor across the output - yes, it can be done.

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Reply 205 of 237, by Benedikt

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Are you sure that R is 200kΩ, or might that be 2R? EDIT: Never mind. You are sure that it's 2R. And yes, the 4310R-R2R-104LF is a 100kΩ part.

I'm asking because the Speech Thing uses a resistor network where 2R is 200kΩ, R is 100kΩ and the load resistor 25.5kΩ. It would have made sense for Covox to use the same part for all their devices.

EDIT 2:

Fagear wrote:

So, if you can get that part from Bourns with R=100k, wire pin 10 as pin 1 and slap a 25k resistor across the output - yes, it can be done.

In that case, my suggestion for the next iteration of the layout is to make the footprint 11-pin, connect pin 11 to pin 1 and add a footprint for an optional resistor, or something like that.

Reply 206 of 237, by Fagear

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Benedikt wrote:

my suggestion for the next iteration of the layout is to make the footprint 11-pin, connect pin 11 to pin 1 and add a footprint for an optional resistor, or something like that.

Done.

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There is a problem with 4310R-R2R-104LF though... It's only 2% part. I'm going to put <0.5% resistors on my R2R board.

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Reply 207 of 237, by Benedikt

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Nice! That adds a bit more flexibility. The 2% tolerance should not be a problem, because they apply to the resistor network as a whole. The resistors within should be closely matched.
Also, the 4310R-R2R-104(LF) and 4610X-R2R-104(LF) are interchangeable, which means that only one of them has to be in stock. If neither is in stock, the factory lead time appears to be approx. three months.

Reply 208 of 237, by shock__

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Benedikt wrote:

Nice! That adds a bit more flexibility. The 2% tolerance should not be a problem, because they apply to the resistor network as a whole. The resistors within should be closely matched.
Also, the 4310R-R2R-104(LF) and 4610X-R2R-104(LF) are interchangeable, which means that only one of them has to be in stock. If neither is in stock, the factory lead time appears to be approx. three months.

Pronounciation on "should" not are. Even within same batches you can get the full 2% span. One way to minimize stray effects would be to use lower value resistors while sticking with the same tolerance (i.e. 1K & 499 Ohms, but would require a different working point of the amplifier).

On another note: Great work as usual Fagear 😀 I'll make sure to get on the list of those interested once the project gets finalized. The SMD-R2R-DAC PCB is a nice substitute to those hard to get SIP-R2R-Networks which existed in the 80s/90s - I was actually thinking on designing a similar board (that can be used on various "carrier" boards/cards) when working on my DSS-StereoCovox recently - good to see that's been taken care of already 😀

Current Project: new GUS PnP compatible soundcard

[Z?]

Reply 209 of 237, by Benedikt

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Mmh... are the optional load resistor and the 10kΩ resistor above it connected in parallel? If so (I cannot see through the board), you could simply install a 7.15kΩ resistor from the E96 series instead of the 10kΩ one and scrap the additional footprint.

Reply 210 of 237, by root42

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Are those two DSUB9 connectors for joysticks?

I could probably make a few ISA brackets for those. I have access to a DSUB9 stencil and a step drill for the audio jack. Would need a PCB of course... 😉

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Reply 211 of 237, by Fagear

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Benedikt wrote:

Mmh... are the optional load resistor and the 10kΩ resistor above it connected in parallel?

No, it's not. The only optional resistor is "24k". "10k" is from the other part of the circuit.

root42 wrote:

Are those two DSUB9 connectors for joysticks?

I could probably make a few ISA brackets for those. I have access to a DSUB9 stencil and a step drill for the audio jack. Would need a PCB of course... 😉

DE-9. I am planning to make bracket from PCB as I usually do, but we'll see.

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Reply 212 of 237, by Benedikt

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Speaking of which: What are the odds that the Keystone 9200-15 bracket fits?
It might not, but if it does, that would reduce the effort to drilling a hole for the audio jack.

Reply 213 of 237, by root42

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That would indeed make sense. Or maybe the PCB layout can be made to fit?

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Reply 214 of 237, by matze79

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Why not simple do it same way like on the SSI 2001.
I like the SSI-2001 bracklet its easy, affordable.
And FR4 is robust.

Who cares about Keystone.

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Reply 215 of 237, by Benedikt

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matze79 wrote:

Who cares about Keystone.

I don't care whether it's by Keystone, just whether it fits. And, comparing the layout to the data sheet, I can now say that it doesn't. So that's off the table.

Reply 216 of 237, by Fagear

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It's 4 a.m. and I'm going to sleep...
But let me leave something here before that.

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https://www.youtube.com/watch?v=wwlXjKm-ZJ0

*assuming the party escort submission position*

New BIG soundcard: FMonster.
Covox Sound Master replica
Innovation SSI-2001 replica & DuoSID.
My audio/video collection.

Reply 218 of 237, by moturimi1

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Fagear wrote:

Is this my Sound Mater Original that you thankfully repaired (due to my terrible desoldering skills) or alreday one of your Prototypes?
Looking forward to the progress...

Reply 219 of 237, by Fagear

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moturimi1 wrote:

Is this my Sound Mater Original that you thankfully repaired (due to my terrible desoldering skills)

Yes it is your board. I've repaired pads and traces around GAL, soldered in new fresh socket and put in a GAL with my firmware. Your *.JED did not work.

moturimi1 wrote:

or alreday one of your Prototypes?

Prototype also works, but has no R2R DAC yet and has some issues with output level.

New BIG soundcard: FMonster.
Covox Sound Master replica
Innovation SSI-2001 replica & DuoSID.
My audio/video collection.