Juno 106 style analog synth possible?

[msi]

I don't believe it can be but can a 74HC595 be used to provide an oscillator if it is modulated at the correct speed. If not can J10 off a core module provide a base oscillator and control an AOUT module? The data lines of the 82C53 can be controlled by a 74HC595 but there are a few pins that cannot, and looking at the way the SID attaches to the core (via J10) it would appear we'd need two cores. One to control the DCOs, and another for CV.

I suppose we could hook the 82C53 to the 74HC595 exactly like the SID module, and provide a base oscillator for each 82C53. This means that every group of three DCOs (each 82C53 provides three outputs) would then have it's own dedicated oscillator and using an RC oscillator would be out of sync with other groups of DCOs.

Also, I have not read of the SID having any frequency errors on high notes like the Juno. I am unsure why that would be. My studies show the SID runs off a 1Mgz clock where as the Juno an 8Mhz clock. It seems to me that the Juno should have higher accuracy at higher frequencies than the SID. If the SID is more accurate how so?

[jojjelito]

I don't believe it can be but can a 74HC595 be used to provide an oscillator if it is modulated at the correct speed. If not can J10 off a core module provide a base oscillator and control an AOUT module? The data lines of the 82C53 can be controlled by a 74HC595 but there are a few pins that cannot, and looking at the way the SID attaches to the core (via J10) it would appear we'd need two cores. One to control the DCOs, and another for CV.

I suppose we could hook the 82C53 to the 74HC595 exactly like the SID module, and provide a base oscillator for each 82C53. This means that every group of three DCOs (each 82C53 provides three outputs) would then have it's own dedicated oscillator and using an RC oscillator would be out of sync with other groups of DCOs.

Also, I have not read of the SID having any frequency errors on high notes like the Juno. I am unsure why that would be. My studies show the SID runs off a 1Mgz clock where as the Juno an 8Mhz clock. It seems to me that the Juno should have higher accuracy at higher frequencies than the SID. If the SID is more accurate how so?

In theory you could control the HC595 to output a square at the right frequency, but that means that you'll have to write to it each time you need the output to go either low or high. This in turn means that the CPU must take care of this very exact timing and issue the command exactly when due. This could run off a timer on an interrupt but that won't be more exact than using the 82C53 or 82C54 timer (which also won't use up a ton of CPU cycles better used elsewhere) plus other interrupts will make this very jittery.

So, the 82C53/54 is connected somewhat like a SID instead. The other pins can be controlled by a second 74HC595 (look at how the DOUT module can connect 4 of those). For prototyping you can use the J10 timer output (easier to do range switching), then move over to dedicated oscillators (since you may need to implement range switching between 2,4 and 8MHz via controlling some flip-flops). Then we'll follow the 1 osc per timer IC idea as above. The AOUT or AOUT_NG are connected to either J10 or J6 on the old core module or to J19 on the Core32.

The SID uses a 24-bit phase accumulator design using dedicated, programmable hardware. You could wire this up, but it would be a large hot mess for sure. See the Bob Yannes interview for some in-depth info. Or you could start using a 24-bit or even 32 bit counter and do it all in software (see DDS on the Electric Druid pages) but with earlier discussed caveats. Anyhow, the larger number of bits for the counter plus the usage of dedicated hardware is the key to precision in the SID case. For us, we could attempt to use a higher base clock for some troublesome parts of the scale -> halved errors for double frequency (which the timer chips won't accept). Or we switch to a more suitable time base. The effects of that could be studied using a spread-sheet.

[msi]

So after thinking about it I think I've decided going with the replacement chips that are available for the juno for the time being is a viable choice. With that decision here is what I've come up with. The timing is handled by an 82C53 connected to a pair of 74HC595 chips connected to J10 of the core. I'm sure a DOUT could handle the 74HC595 chips but this seems like a better way to start at the moment.

Currently I have the output of the 82C53 going into a MC5534 VCO chip. The chips are only 25 euros plus shipping I believe so there is no reason not to utilize them. The CD4052 handles the saw amplitude like in the juno. There is the transistor connected to the Vee pin of the CD4052 that I am unsure what it's purpose is.

Questions I now need answered is can this be extended to multiple modules on a single core? I don't see why not but I could be wrong. Also can a core handle both the DCO and an AOUT module.

[jojjelito]

So after thinking about it I think I've decided going with the replacement chips that are available for the juno for the time being is a viable choice. With that decision here is what I've come up with. The timing is handled by an 82C53 connected to a pair of 74HC595 chips connected to J10 of the core. I'm sure a DOUT could handle the 74HC595 chips but this seems like a better way to start at the moment.

Very SID-modulesque choice of port. Either alternative should be fine.

Currently I have the output of the 82C53 going into a MC5534 VCO chip. The chips are only 25 euros plus shipping I believe so there is no reason not to utilize them. The CD4052 handles the saw amplitude like in the juno. There is the transistor connected to the Vee pin of the CD4052 that I am unsure what it's purpose is.

Who carries those chips? Vintage Planet or any other suspect? Better look around... I've only given thought to the CEM3396 connected to the 83C53/54 timer IC before.

EDIT: Found 'em here: Analogue Renaissance

Questions I now need answered is can this be extended to multiple modules on a single core? I don't see why not but I could be wrong. Also can a core handle both the DCO and an AOUT module.

I guess one of the gurus like TK is best suited to answer the extendability question - but some performance measurements won't hurt once you get to that stage.

As for the DCO and AOUT I don't see why that shouldn't be possible. The issue here is rather which port to tie the AOUT to. I've seen both J10 and J7 been used in different applications.

Edited April 28, 2011 by olga42

[msi]

Very SID-modulesque choice of port. Either alternative should be fine.

Who carries those chips? Vintage Planet or any other suspect? Better look around... I've only given thought to the CEM3396 connected to the 83C53/54 timer IC before.

EDIT: Found 'em here: Analogue Renaissance

I guess one of the gurus like TK is best suited to answer the extendability question - but some performance measurements won't hurt once you get to that stage.

As for the DCO and AOUT I don't see why that shouldn't be possible. The issue here is rather which port to tie the AOUT to. I've seen both J10 and J7 been used in different applications.

http://www.analoguerenaissance.com/D5534A/ claims to carry replacements. I knew they had replacements for the filter chips but while doing research happened upon the vco replacements as well.

I just noticed your own edit......

Edited April 28, 2011 by msi