simple delay circuit

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Hank Dussen

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Jan 30, 2009
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Antwerp, Belgium
I’m looking for a simple circuit that delays an audio signal with something like 10 to 20ms.
Fixed, no blend or feedback.
I've searched and found some info about BBD chips that need a clock signal but it’s still a little vague for me.
Anyone has any info about this?

thanks,
Pieter
 
Yes, I sold an audio delay line kit using BBD back in 1976.

Today it is probably cheaper (or close) and surely higher quality to use digital conversion and digital storage to make a 10-20 mSec delay.

BBDs were relatively short and noisy, so they didn't give great delay/bandwidth products, or good S/N without companding noise reduction.

Still probably used for guitar effects, but surely not a high performance audio path.

JR

PS: The BBD technology was developed by Phillips in Eindhoven during the late '60s, early '70s. 
 
What kind of audio resolutions/noise floor are you looking for?

If it's consumer grade audio, then I'd look at using a PCM3060 + TPA5052 (H/W Control)

TPA5052 can have it's delay set with a simple dip switch.

You'll need a 5V supply and a 3v3 supply, as well as a 24.567MHz Crystal and a sn74lvc1gx04 (to create a cmos grade clock).

You'll also need some opamps etc to make sure you don't clip the ADC inputs, and to scale the DAC outputs to what you need.

It's not incredibly complex, but not as simple as a BBD.
 
JohnRoberts said:
The BBD technology was developed by Phillips in Eindhoven during the late '60s, early '70s.  

Warning: Nit picking ahead: It's actually Philips with one L.  (Eindhoven local here, sorry for derailing the thread)
http://en.wikipedia.org/wiki/Philips
 
Oops...  I have a lot of respect for philips (?) engineering chops, but in this case they licensed the BBD technology to matshusita (aka panasonic) to manufacture. The OP can probably find more info about BBD apps by googling MN300x series panasonic parts.

Sorry, I was trying to add some local color to the BBD story...

JR

 
There is an all-in-one delay processor called the PT2399, made by Princeton Technology Corporation (I haven't heard of them, either).

http://www.datasheetcatalog.org/datasheet/PrincetonTechnologyCorporation/mXyzsyzt.pdf

René Schmitz has a schematic for a modular synth delay module here, which is probably overkill for your needs:

http://www.uni-bonn.de/~uzs159/pt2399.html

I can't comment on the suitability of this part for your application, but I had run across it recently and thought I'd mention it.
 
Well it's actually for some sort of guitar like effect I want to use live (on the PA) so I think the quality of BBD's will do.
The PT2399 doesn't seem to go lower the 30ms but there seems to be an PT2396 as well that goes to 12ms.
 
BBDs are still being used in pedals. 10-20 mSec is long (IMO) for flanging, and a little short for proper chorus/double track, but my guess is the latter (chorus/ADT) is your application.

Check out the MN300x series... I think the 3005 may be marginally too long to make your shorter delays, but will deliver cleaner, wider response thanks to the high clock frequency. Something like the shorter 3001 will be running into audible clock frequencies at longer end of your desired delay range.

BBD analog shift registers are simple in concept. They require a two phase clock, to step an analog input voltage one clock cycle at a time from input to output.

For the shorter BBDs I have used simple cmos flip flops as clock drivers, while the longer delay chips have too much capacitance for that. I believe Panasonic also sells a dedicated clock driver.

While these are analog in/analog out devices, the audio is time sampled, so you need to consider anti-alias and anti-imaging filters to prevent birdies, and reconstruct the waveforms. 

To modulate the clocks to provide texture to a chorus effect, you will need a simple voltage to frequency, or voltage to period convertor. It is generally simpler to generate a clock at 2x the needed clock, then divide that by 2 in a flip-flop to make perfect 50% duty cycle.

have fun... there are lots of guitar pedal schematics published on the WWW

JR

PS FWIW my old 1976 kit used MN3001, and one of my kit flangers was used on a popular recording (Heart's Barracuda).

 
Rochey said:
What kind of audio resolutions/noise floor are you looking for?

If it's consumer grade audio, then I'd look at using a PCM3060 + TPA5052 (H/W Control)

TPA5052 can have it's delay set with a simple dip switch.

I've been building all sorts of delays for longer than I care to remember and was rather chuffed
when I saw the TPA5052 arrive on the scene, so I ordered a couple of samples from TI (+ the
Codec). They arrived and....MERDE - the bloody things are about the size of a tealeaf and they
have NO LEADS. The package is totally unsuited to lash up prototypes.
They languish in my curiosities drawer.
M
 
Mobyd -

A 4mm x 4mm QFN package isn't always the easiest to hand work, I agree.

Its not impossible though! :)

You'll need to get some custome pcb's made (batch pcb), some solder paste (cheap from deal extreme) and an electric frying pan / skillet.

One of these days I'll start a rochey's guide to smt thread. :)
 
Rochey.. Put on your TI employee hat for a second.

I appreciate that TI doesn't want to get in the business of selling adapter PCBs, or offering parts in non-competitive packages, but it would be useful for small companies also, to be able to get QFN or BGA packages in something that can be hand prototyped without laying out a special PCB.

I believe (know) there are many parts like this, that could find a broader market, and perhaps win more design ins if they were easier/cheaper to check out.

I bet a strong secondary market could emerge for parts, attractive to DIY or old gear upgrades, if offered in more through-hole compatible packaging. 

I know that companies like TI sometime sell demo PCBs but these are too expensive and often unwieldy to prototype with.

If TI cultivated an informal distribution of re-sellers to market these "adapted" parts. large production runs of these adapters could be grouped together to reduce cost, and even some defacto standards could emerge for similar parts adapters.

This might even save TI the cost of offering their super audiophile opamps in expensive through hole packages, if the smaller modern packages could be cost effectively dealt with using adapters. 

Just my $0.02 If I was still in the kit business I would be tempted to pursue this, because some of the new parts are really cool... I love a new class D chip I am using to save battery consumption in a portable product, but it was a real PIA to prototype. I probably wouldn't have pursued it, if not for the obviously compelling benefit of class D efficiency.

JR
 

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