Roland System 700 709 sample and hold clone

Roland System 700 sample and hold PCB

It samples! It holds! Here’s an aggravating demo.

We’re into the area of circuits that I should have probably just built on stripboards, but anyway.

IC1 is a TA7504M in the service manual, I just used a 741. I even replicated the legs-in-the-air arrangement for the junction of Q3/C9/IC2 pin 3 as detailed in the service manual, presumably meant to minimise leakage.

S&H legs in the air

The schematic in the service manual didn’t need any corrections, it works fine as it is.

Just now looking at the service manuals I realise the 100m version looks more fun as it includes a slew – if you were looking for one to do, maybe try that one.

I included the 716 mixer as on the original, but I’ve not got round to making that up yet (probably ‘cos it’s not going to be very exciting).

Another board done, onto the next…

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3 comments

  1. 19th February 2021Mike FIction says:

    I got my 709A done and wanted to note to anyone thinking about building this, you DO need to replicate the legs in the air thing or you get pretty massive leakage, it becomes basically an LFO with some slight sample and hold, lol

    One issue I have is my LFO stalls at slow speeds – I’ve tried a Panasonic film cap and a NOS Mylar cap in the LFO section (C4) and either way my LFO stalls at the slowest speeds.

    I’m going to try multilayer ceramic and if that doesn’t help I’ll have to start tweaking some values.

    One other thing of note – My external clock input didn’t work at all (with any source) with the 100k input resistor, After some experimenting, I swapped it to a 10k and it works as expected with any clock source I throw at it. I have no idea why it wouldn’t work, as the impedance should have been no issue with the 100k resistor, but whatever, it works now.

  2. 20th February 2021ua726 says:

    Hah, I never tried anything but the legs-in-the-air setup for the 709, but it’s good to know.

    Do you mean that the LFO (706) or the S&H clock stops? If it’s the latter I feel like I’ve seen the S&H clock thing stalling at low speeds mentioned somewhere else, probably on Muffwiggler – mine seems to cycle at about one every three seconds at its lowest setting, which seems about right going off the markings on the panel. It’s a long shot but I’m wondering if maybe your pot measures more than 1M? (Or maybe mine’s a bit short..?).

    Just checked the external clock input and it triggers happily off my 100M clone S&H clock output, although I’m not sure what voltage level that is at, I haven’t measured it. The owners manual specifies +5V for the “external clock input sensitivity”, which I’m taking to mean that 5V is the threshold. If 10K works I’d go with that tho.

  3. 21st February 2021Mike Fiction says:

    Sorry, yes I did mean the Clock in the S&H module is stalling.

    Pot measures 0.996M so it’s close to perfectly 1Meg. It’s a reverse audio pot as the service manual specified.

    It’s so odd because the clock is such a simple circuit, it’s only 6 components! Maybe my LM301 is the issue, I used a NOS LM301AH metal can from eBay. I could always try a different one. They aren’t the cheapest component which is annoying.

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