New Looper Design

[robbiemcm]

Yay, new development on it. I havn't checked back here in a while, but it's good to see I came back not too long after your update. I think I'll make this raw version before trying to make an effects loop one, I've only ever built two pedals (one unsuccessful attempt, same problem twice.. most likely a grounding issue that I don't know how to fix). And for that reason aswell, and effects loop won't be particularly useful. I aim to get the bits for this project in 6 weeks when I have two weeks holidays, so I'll give it a shot

[The Tone God]

Since there is no schematic and I'm too lazy to trace it how are you doing the "vibrato" ? I put alittle thought into it and I think I came up with a nice clean solution but I wondering if you did something similar.

Andrew

[Jaicen_solo]

Good to hear you're still up for it Robbie

The vibrato effect is a bit of a dirty hack really. I'm basically using a variable voltage regulator, with an LDR modulating the output voltage. I'm sure there are easier ways to do it, but that's just the solution I came up with as the LDR will give the maximum swing from +4 to +6v. At values higher or lower the chip wont function, so at least this way it will never lock up.

[The Tone God]

The vibrato effect is a bit of a dirty hack really. I'm basically using a variable voltage regulator, with an LDR modulating the output voltage. I'm sure there are easier ways to do it, but that's just the solution I came up with as the LDR will give the maximum swing from +4 to +6v. At values higher or lower the chip wont function, so at least this way it will never lock up.

Hmm...I can see some advantages and disadvantages to that.

My idea was to use some clocked power regulator IC, probably a charge pump, that would take an external clock source like say the 7660/1044. I would clock the charge pump with a derivitive of the Vanishing Point v2.1's random mode. The HF clock would clock the charge pump set to the correct frequency. The HF clock would be modulated by the second clock only it's rate of modulation would be controlled with a pot. The depth of voltage modulation could be done several ways. It would get rid of the LDR and provide a fairly consistant voltage swing range through out the battery life. It would also be easy to reproduce once the part values were calibrate.

Just a few thoughts. I haven't looked at this circuit for some time.

Andrew

[robbiemcm]

I'm looking forward to building this, plus a vibrato would be a nice addition.. providing it had rate + depth pots, but I'm sure that's standard in this world

[Jaicen_solo]

Yes there are indeed rate and depth pots provided on the layout, i'm sure it wouldn't be much use otherwise!
With regards to the charge pump, I did consider that but decided against it for two reasons. Firstly, they have a tendency to introduce whine through the power rails, to which the ISD series is particularly sensitive. Secondly, it would require a more complicated & stable external oscillator.
In theory, regardless of the battery voltage, the regulator should always swing by the same amount though I understand that theory is not always the reality. To be honest, I only use external PSU's now so I find myself less and less concerned about battery life vs features. 

[robbiemcm]

Heh, my 9v PSU (old phone charger) died recently. I get nothing from it when it's plugged in, I assume it's because I just left it plugged in the whole time and due to the regulator that was across the rails it was trying to pump out power for about 3 months without ever beind turned off.

Would you mind pointing me to this thread with the other looper, I pwomise I'll build yours I'm just interested, and I couldn't find it in my short spammings around. Do you think this looper will be classed ready for the build in 6 weeks time

[Jaicen_solo]

I'd say it's probably ready to build now, I'm just a little busy this week so I won't be able to verify the layout till next monday probably.

The other thread is here: http://www.diystompboxes.com/smfforum/index.php?topic=45313.msg331710#msg331710
At the minute, i'd hold off on building it until it's been successfully prototyped. Dr Ron tells me that he's already modified the layout to use a new switching scheme also.
That said, it would be a relatively easy task to interface Dr Ron's loop selector control to the Lazarus layout i've made, perhaps using a seperate board containing all the switching. All that would then be needed is to cut two traces on my board, and replace them with jumpers to Ron's board. In all other respects, the loopers are going to be pretty much the same. However, I do believe that addressing the ISD chip introduces clicks into the start of the recordings due to the nature of the storage technology, so that could be problematic. Like I said before, best to hold off until a prototype is working.

[nelson]

I still have the chip for this in my collection.

I am waiting for a schematic to be published before I build it.

[robbiemcm]

It's good to see I'll have a nice 2 week holiday project to encourage me to rip my hair out.

[The Tone God]

I eventually get back to my design so I will give that feature another shot as I did not really play with it before. I still think the output section could be improved as well. Ah so little time.

Andrew

[robbiemcm]

Have you had the chance to make a prototype yet? I'd love to hear what it sounds like

[The Tone God]

Have you had the chance to make a prototype yet? I'd love to hear what it sounds like

Is that directed at me ? If so I did do some work but I never finished the output section as I spent most of my time with control section (i.e. using the address inputs for multiple loops and other things.) To me the output is the biggest issue with pretty much every looper I have seen. I have some ideas of how to solve it but need to find some time to play with it again. Before I ever release something to the public I always like to make sure it works by building it so to that end I will won't post anything until I'm confident of its performance.

Andrew

[slacker]

To me the output is the biggest issue with pretty much every looper I have seen.

I've seen you mention this before, I was just wondering exactly what the problem is with the output?
I'm only asking because I've put one together, based on Jaicen_solo's design, but with simplified input and output stages and I can't see a problem.

[The Tone God]

I've seen you mention this before, I was just wondering exactly what the problem is with the output?

I didn't experience any issues but I was using the IC to drive a speaker as per it's intended design since I was focusing on the control section. I have seen many reports of people complaining about the output quality being fuzzy, low, noisy, etc. I personally think this is because trying to drive an opamp input using a circuit that was designed to drive a speaker might not be the best way to do it. Just theory on my part. When I get back to the circuit I test this out and see if there is a solution if need be.

Andrew

[robbiemcm]

Have you had the chance to make a prototype yet? I'd love to hear what it sounds like

Is that directed at me ? If so I did do some work but I never finished the output section as I spent most of my time with control section (i.e. using the address inputs for multiple loops and other things.) To me the output is the biggest issue with pretty much every looper I have seen. I have some ideas of how to solve it but need to find some time to play with it again. Before I ever release something to the public I always like to make sure it works by building it so to that end I will won't post anything until I'm confident of its performance.

Andrew

Sorry for the confusion, it was originally intended for Jaicen but it was open for anyone else that was building it I look forward to hearing how it goes.

[slacker]

If anyone's interested here's a couple of soundclips of my looper prototype, it's based on Jaicen's design but with a simpler audio side that I put together to test my switching idea.
The first sample is a prerecorded loop with some frankly dodgy lead playing on top. The second loop starts with guitar, with a loop recorded and played back on the fly. There's a bit of switch click but this doesn't get recorded by the loop. The looper's on 2 boards with some pretty long leads and it's not boxed up, hopefully thats why the click's there.
prerecorded loop
on the fly recording

[The Tone God]

I have just started work on my own looper design. I'm designing from scratch not that I am saying anyone's design is bad just that this is usually what I like to do.

I don't know if it was my particular IC or something in the family (25xx) but the thing popped BADLY when entering and leaving power down. I have solved the power up/down output pop problem now and the IC output interface issue. I think I have a much better way to do the vibrato then I previously thought as well. I will hopefully be adding a number of new features too.

Andrew

[domenico]

tonegod says : "The IC does not respond instantly either so there would not a be a smooth time transistion processor to processor. It would eventually lead to weird time problems as oppossed to a smooth delay."

yes it's true and now is my problem ! I've built a looper with isd2564 with slacker design control and when I switch from record to play the chip cuts some notes at the begin of the sample , what's wrong???
thanks
domenico

[Jaicen_solo]

When you say it cuts some notes, do you mean it doesn't record the first bit of the loop?
There is a small (few millisecond) latency inherent in the design of the chip, but this shouldn't be audible.
Are you sure you've got the IC wired correctly?