Favorite NON Pedal Delay(s)

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MKULTRA
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Re: Favorite NON Pedal Delay(s)

Post by MKULTRA » Sun May 06, 2018 12:16 am

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Last edited by MKULTRA on Wed Aug 22, 2018 2:00 am, edited 1 time in total.

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Dyecap
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Re: Favorite NON Pedal Delay(s)

Post by Dyecap » Sun May 06, 2018 4:35 am

Ha! Didn't know there were so many variants.
Here's my crusty little fella -
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WhiteWarlock
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Re: Favorite NON Pedal Delay(s)

Post by WhiteWarlock » Sun May 06, 2018 7:30 am

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hmm those all remind me of Multivox MXD-5
(mine has HUGE reverb tank puled from Fender 180w stage amp)
stock max delay of about 250-300ms
Delay Time Modification: upgrade the "Delay" pot from the stock 10k 50k for 100k
100k Delay Time pot plus tweaking the 3 internal trim pots will get you easily 2+ seconds
first learned that little trick on my ancient abused & overused Digitech pds1002
drove myself nuts tweaking extending degrading delay using the internal trimpots
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Dyecap
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Re: Favorite NON Pedal Delay(s)

Post by Dyecap » Mon May 07, 2018 1:54 am

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MKULTRA
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Re: Favorite NON Pedal Delay(s)

Post by MKULTRA » Mon May 07, 2018 2:20 am

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Last edited by MKULTRA on Wed Aug 22, 2018 2:01 am, edited 1 time in total.

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WhiteWarlock
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Re: Favorite NON Pedal Delay(s)

Post by WhiteWarlock » Mon May 07, 2018 2:52 am

yeah have the 4 cards in MXR digital delay...
yet it smoked voltage regulator
have VR replacement for it around here somewhere
pulled from rack
should grab another parts machine off ebay
cheap one missing all the memory cards or something
hasn't been highest priority
on "the list" somewhere
sure you get how it is sometimes

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WhiteWarlock
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Digitech PDS1002 troubleshooting & schematic

Post by WhiteWarlock » Tue May 08, 2018 8:37 pm


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made reference to Digitech PDS1002 not working the other day
the original owner of this pedal was old chicago noise scene from 80s
one of my old friends at infamous arts building/studios in wicker park chicago
he started having serious health problems from way too much "smoking & drinking" insane artiste lifestyle
he ended up in coma at hospital with liver complications
when he got out he needed walking with cane and had serious damage
showed up for giving me some of his old gear
this pedal came with explicit conditions
"Use it for making noise"
so that's what have done with it for years since the 90s
obviously this pedal is not getting trashed sold DOA on ebay
therefore took some time focusing for bringing it back for more life & use
so despite this thread title making mention of recent events here
because mention it not working
need somewhere for documenting the process that used repairing this old pedal
someone said online it was cd4007 gone bad
ordered some today even though probably have them here somewhere
no signal passed & the repeat hold would not activate
plugged it in on for hours since it had been off for years
capacitors were getting flaky needing warming up
then had signal with no feedback
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so spent hours retweaking all the trimpots
extending the time range
(once again for getting the 4+ crunchy brutal seconds looping)
then getting feedback working
4 trim pots on that machine
obviously need putting in some new capacitors
PDS1002 is somewhat happily functional once more
time for recording some tracks with that old blue baby
here is the Digitech PDS 1002 Schematic
http://www.n01ze.com/synthwizards/ARKIVE/PDS1002.pdf
for anyone that needs it

figured it sort of half assed relates this category
plus wanted documenting for future reference
Dankes

next up is repairing the DOD DFX94 delay sampler pedal
it's sitting here with the guts out now
no effect signal symptom
time for troubleshooting that little blue delay
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searching for DFX94 schematic

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WhiteWarlock
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Re: Favorite NON Pedal Delay(s)

Post by WhiteWarlock » Tue May 08, 2018 11:38 pm

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Roland FS 3 Pedal original for Jazz Chorus 120
have one hiding around here somewhere
wondering if it can be used for triggering/controlling RDS TimeMachines
may have actually got it with RDS 3.6
thinking about experimenting with multitap looper rig using various various echos/delays/sample grabbers
that way can put RDS 7.6 at ends of delay tap chain
for sonique sculpting some textures
8 taps with 3 loopers?
was contemplating that while repairing PDS 1002 pedal
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seems that the pedal let's me do SOUND ON SOUND

SOUND ON SOUND is achieved with the INFINITE REPEAT foot switch. Put down a rhythm riff as explained above. Turn the FEEDBACK control all the way up. Press the INFINITE REPEAT foot switch, play a lick that fits the rhythm, and press the INFINITE REPEAT foot switch again. With this method, several tracks may be stored in memory, however, the earlier tracks will be attenuated (reduced) slightly.

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Dyecap
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Re: Favorite NON Pedal Delay(s)

Post by Dyecap » Wed May 09, 2018 1:04 am

Interesting post up there re: PDS
Nice those chips are in sockets!
Be curious to hear if you can get the fabled 4sec delay from the dfx94 also.
Cheers.

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WhiteWarlock
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Re: Favorite NON Pedal Delay(s)

Post by WhiteWarlock » Wed May 09, 2018 10:16 am

DFX94 may end up on ebay DOA
spent couple hours on it last night
couldn't inject input for delay on PCB
plus the lights are both constantly on
it came to me for free fuct up after some noise show
if you owned one and you gave it away after it died during some show
then this one was yours
it's going back on WTF status so can get other things accomplished
that pedal doesn't have the same extreme personal value as my PDS1002

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WhiteWarlock
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Re: Favorite NON Pedal Delay(s)

Post by WhiteWarlock » Wed May 09, 2018 11:22 am

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eventide 1745M. Digital delay auction for consideration
https://www.ebay.com/itm/eventide-1745M ... SwcwVa8X0G
modified for parts glitchy with erratic noises as is condition
start replacing aging capacitors in power/audio path until it functionally is operational

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WhiteWarlock
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Re: Favorite NON Pedal Delay(s)

Post by WhiteWarlock » Wed May 09, 2018 11:43 am


"This box rules, but I have one complaint.... it has an automatic mute function that interrupts the flow of sound when buttons are pressed to change mode... bleh! pointless... but if you cut two leads this box is able to make a nice wall of sound.

Then plug an external LFO (5V) into the REPEAT/HOLD jack and freak out.

Digitech RDS 7.6, RDS 1900, RDS 3.6, RDS 2001 digital delay FX units all share the same PCB so this mod should work for any of them.


Digitech RDS 7.6

You’re about to download the schematics for Digitech RDS 7.6, RDS 1900, RDS 3.6, RDS 2001 digital delay effect processors (ca. 1987). Its just one document because all four models share a common PCB, with the RDS 7.6 as the most desirable flagship unit. The lesser models are potentially upgradeable as they share the same PCB and chassis, differing only in RAM chip type, a couple standard logic chips, jumper configuration, and chassis hole pattern. These are 8-bit effects with NE570 compressor/expander chip to enhance dynamic range. The Lexicon PCM-42 is a similarly featured unit but with a sweeter sound because of its 12-bit resolution (if I remember correctly) and a more sophisticated analog section, so it commands a much higher price.

Digitech RDS 123 REV E schematic https://web.archive.org/web/20120308054 ... matics.pdf

rds 7.6 top open



No warranty that any of this is correct…

Relationship of master clock to sample rate. Digitech RDS allows manual control over length of the delay by varying the sample rate of a constant-sized RAM buffer. It has roughly a 3-octave range. To achieve this, the maximum sample rate is about 8x the minimum. The master clock is generated with an interesting high-frequency VCO built from 2 opamps (U47 & U48), an NPN transitor, and a 74HC00 CMOS quad NAND gate (U41). I find that its temperature stability is very poor though. After a cold start, the delay time constantly decreases for about half an hour. Its really noticeable if you are sampling a sound and comparing its pitch to the original. The pitch will keep climbing upward steadily until the unit warms up fully. I would guess this is due to temperature effects in current-source transistor Q1. A nice mod would be to temperature-compensate the clock.

RDS master clock VCO

Master clock VCO. CV input goes to R121 (right side)

If you are familiar with the CD4069 CMOS VCO project you should see some similarities. I measured the frequency range of the VCO in an RDS 7.6 with an accurate frequency counter, while varying the front panel delay time control from minimum to maximum. Of course, the exact values aren’t important because there is an internal trimmer that sets the overall range of delay times. At its lowest sample rate, the sound is lo-fi but longer delay times are possible than advertised.

296kHz < master clock VCO < 2.35 MHz

Why are these frequencies so high? It has to do with the inner workings of the analog-to-digital converter (ADC). This is a successive approximation ADC made with the AM2502PC successive approximation register (U17), an 8-bit current switch DAC (U15), and an LM311 voltage comparator (U12):

RDS SAR ADC

Analog input is from a sample-and-hold circuit made with a CD4066 analog switch (U14), a 470pF capacitor (C45), and a JFET opamp (U13A). The master clock VCO output is applied to pin 9 of the AM2502, and its conversion complete output (pin 2, /CC) goes low 9 clock cycles later. This is an important fact, because /CC is used as the sample rate clock, after being re-synchronized to the master clock with a 74HC74 D-type flip-flop (U35). Thus the sample rate of the digital delay is 1/9th the frequency of the master clock.

32.9kHz < sample rate < 261.1kHz

This reflects the manufacturers claim of 15kHz bandwidth, because bandwidth is limited to half the sample rate as described by the Nyquist-Shannon sampling theorem. So even at the longest delay time setting, Digitech gives us a generous 15kHz bandwidth. Although, as the delay time is shortened by increasing the sample rate, bandwidth doesn’t climb to the theoretical max of 130kHz because the unit has a fixed-frequency antialiasing filter (built around op amp U4B) on the input side, and another fixed-frequency lowpass filter on the output (U2B, U1B).

The delay time is directly proportional to the sample rate. In the owner’s manual we see that 262144 bytes of RAM are used when the unit is in Echo mode. At 32.9kHz, the delay time is 262144 / 32900 = 7.96 seconds. At the other end of the delay time dial, the sample rate is 261.1 kHz. 262144 / 261100 = 1.004 seconds.

Okay, so thats how the sample rate, master clock, and delay time are related. How is the CV generated to control the master clock VCO? The unit has a built in LFO with Speed and Width controls. This LFO is built with half of a LM324 quad op-amp (U40).

RDS LFO and CV

The delay time knob on the front of the unit is set up as a voltage divider with +5V at the top and 0V at the bottom, so its output is a steady bias between 0 and 5V. Plugging in to the unit’s rear VCO Control jack interrupts the signal from this potentiometer. (Some people would rather have these signals mixed together?) The Width control is set up as a voltage divider that ‘crossfades’ between the LFO and VCO Control signal. When width is at its minimum setting, its output is a steady CV that tells the VCO to oscillate at a constant frequency, i.e. no modulation (provided you aren’t doing something with the rear panel CV input).


The Digitech RDS 3.6 and 7.6 delay time modification

(non-professional way without any measuring instruments)
by Leander Reininghaus LEALOOP@compuserve.com

Needed tools:
screwdrivers PH No.2 and small slot-type ( 2-3 mm );
inbus (x ", sorry, I don't Know ) for the frontplate/bottomplate connection
or, lacking this, pliers

Before opening the unit pull out the wallplug

Remove the bottom plate of the unit

You'll see four trimpots on the board

The pot for adjusting the bias of the unit ( which changes the delay time ) is the one most right, when you look at the board with the frontplate next to you and the jacks away from you. It builds the top of a triangle with the 'feedback' and 'width' pots on the frontplate and is the only trimpot that 'lies down' (the other three 'stand upright')

Before changing anything MARK THE CURRENT POSITION OF THE POT !

Replug the unit to the wall, switch it on and connect input and output to soundsource and amp/mixer o.sth.

Crank the ' delay time ' all up and loop something

Now, carefully turn the trimpot clockwise and the delaytime will increase (pitch of the loop goes down). Do so until the sound of the loop gets distorted ( or to an amount of distortion you can bear ), then make another loop and listen again. Try also different delay time and feedback levels. Like I said before, changing the bias will cut down the frequency range, so, you have to experiment a little bit to find out what's okay for you ( depends i.e. on the instruments and amplifications used ... )

After you've found the best result for you switch off, pull out all plugs and put on the bottom plate again.

PS: The two pots up left are finetuners for the modulation. You may experiment with them, too ... The mid left pots function I don't remember, but it may also have to do with the bias/delaytime or feedback level ...

But before you try, MARK THE CURRENT POSITIONS !
I think I needn't to say, why ...
Last edited by WhiteWarlock on Wed May 09, 2018 2:42 pm, edited 1 time in total.

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xdugef
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Re: Favorite NON Pedal Delay(s)

Post by xdugef » Wed May 09, 2018 2:10 pm

WhiteWarlock wrote:
Tue May 08, 2018 11:38 pm
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seems that the pedal let's me do SOUND ON SOUND
The first piece of rack gear I ever bought was a Time Machine.. still have the original one I bought and a bunch of various models I've collected more recently.. they are also good circuit bending targets. I've always liked it's controls for on the fly sampling.. still haven't really found a good substitute for it in a system with higher sampling resolution.

I also have a pile of Lexicon Super Prime Times in various states of disrepair.

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Re: Favorite NON Pedal Delay(s)

Post by s.p.i.n. » Wed May 09, 2018 4:43 pm

The echo on a Barbie Karaoke

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