A challenge

[Mark Hammer]

A buddy contacted me about his old 4-knob Deluxe Memory Man with a quartet of SAD-1024 chips (Model EH 1307, for those interested).  At least that's how it started out.  Right now, it has a single BBD chip.  Even if he could locate 3 more to fill the empty slots, it would be cheaper to buy a Memory Boy with a quartet of new Xvive MN3005s and even more delay time.

But, he'd like to use what he has.  So, from what is currently available, and not priced like unobtanium, what choices are available as substitutes to make use of the rest of the circuit?  He understands, and accepts that some sort of daughterboard  and mods would be required.  I'm almost set to tell him to simply connect the sole BBD to the end of the delay path and use it as a slapback, but you folks are brighter and inventive, so you may have some other better ideas.

[StephenGiles]

Mark, I'm thinking put it in the dry path of a flanger for some thru zero flanging??

[Mark Hammer]

I like your thinking, Stephen, but that's a rather "hefty" time stagger, compared to Thomeque's little MN3207 board! 

I Can't say I didn't ask for it, though. 

[StephenGiles]

Out of interest I found Mike's sound samples using his one BBD TZF the other day! Did we ever find out how he did it?

[Mark Hammer]

Mike Irwin, or a different Mike?

[StephenGiles]

Mike Irwin, I'd forgotten his surname.

[thetragichero]

I've got a bunch of tda* and tca* chips from organ pulls. if someone can figure out how to make them work I'd be more than happy to send your way

[StephenGiles]

Here are Mike Irwin's TZF samples of 1 BBD Thru Zero Flanger

https://www.dropbox.com/s/2xv2vfzqh5ma2a2/TZ-5.mp3?dl=0

https://www.dropbox.com/s/vv35c289cn71v37/TZ-6.mp3?dl=0

[Mark Hammer]

Now there's a mystery that demands solving!
I haven't heard from Mike in years.  I thought I knew his phone number, but was told it was not a valid number when I dialed it.

[Mark Hammer]

I've got a bunch of tda* and tca* chips from organ pulls. if someone can figure out how to make them work I'd be more than happy to send your way

The TDA chips use a negative supply voltage.  Trying to fit them into the DMM would be problematic.  Not impossible.  Just not easy.

[StephenGiles]

Now there's a mystery that demands solving!
I haven't heard from Mike in years.  I thought I knew his phone number, but was told it was not a valid number when I dialed it.

I bet there's either a serious dome filter in the dry signal path or a filter delay network of the kind suggested by STM a few years ago.

[Rob Strand]

Maybe a PT2399 on a daughter board is a simple way forward.
The minimum delay will be longer than the EH but given (IIRC) the four-knob is *only* a delay that's probably not a big issue.
You could add a switch for short and long,  keeping the existing MN3005 for short.
Trying to automatically switch over from short to long is probably going to be messy since the clocks aren't synchonized.

[Mark Hammer]

Maybe a PT2399 on a daughter board is a simple way forward.
The minimum delay will be longer than the EH but given (IIRC) the four-knob is *only* a delay that's probably not a big issue.
You could add a switch for short and long,  keeping the existing MN3005 for short.
Trying to automatically switch over from short to long is probably going to be messy since the clocks aren't synchonized.

I gather you meant to say SAD1024, but wrote MN3005 by accident.
In fact, I had suggested a PT2399 retrofit, as some folks have done for the MXR/Ross Analog Delay, but he'd prefer to go all analog if possible.

[Rob Strand]

he'd prefer to go all analog if possible

The only solution then is to find some analog chips.

The tda etc chips thetragichero offered don't seem too difficult to get to work on a positive supply; there are single supply schematics for these kicking around.   You just can't connect them to the existing chips using DC coupled signal connections.

Most of the devices available these days are going to need work with the power rails, bias voltages and clock voltages,
for example: some are Pmos, some are Nmos.  some are 5V some are 9V.  This type of thing.

The point being the work required for these isn't much less, or no less, than the tda chips.

Getting your mits on some SAD chips is obviously the easiest solution but that might require mining rubbish dumps or paying crazy prices for fakes.

To be honest if you use the same filtering as the analog circuits with the digital chip your would be very close in sound.   You might need to tweak one of the first order low-pass circuits to get a little bit more roll-off to emulate the "extra" sinc filtering which naturally occurs with an analog delay.

[Mark Hammer]

he'd prefer to go all analog if possible

The only solution then is to find some analog chips.

The tda etc chips thetragichero offered don't seem too difficult to get to work on a positive supply; there are single supply schematics for these kicking around.   You just can't connect them to the existing chips using DC coupled signal connections.

Most of the devices available these days are going to need work with the power rails, bias voltages and clock voltages,
for example: some are Pmos, some are Nmos.  some are 5V some are 9V.  This type of thing.

The point being the work required for these isn't much less, or no less, than the tda chips.

Getting your mits on some SAD chips is obviously the easiest solution but that might require mining rubbish dumps or paying crazy prices for fakes.

To be honest if you use the same filtering as the analog circuits with the digital chip your would be very close in sound.   You might need to tweak one of the first order low-pass circuits to get a little bit more roll-off to emulate the "extra" sinc filtering which naturally occurs with an analog delay.

My sentiments exactly.

[Scruffie]

I've thought about this the last couple of days and have to agree, the PT2399 is going to be the least invasive surgery and thankfully the circuit doesn't use any emphasis, its grittyness at longer delays is what these sound like anyway. You will need to include the make up gain stage to keep the signal in phase and make the output op amp of the PT2399 variable gain or else you have nowhere to balance the wet and dry. You can also remove the 4047 (which with the extra current of the PT2399 would be a good idea anyway for the transformers sake) and jumper the pins and use the original delay pot.

If you did use Panasonic chips you'd need to change the values of the gain trims/source resistors on those and at the moment the BBD's are powered through the LED but the clock isn't, the SAD doesn't mind that voltage difference so much but the panasonic chips do so that would need changing, it would mean a lot of hacking the board up.

The other option would be to find just one extra SAD1024 and accept it as a slap back delay.