Analog delay high frequency noise

[Vsat]

Here's a thought - if the clock trim has been re-adjusted and the clock freq is too low, the filter won't be doing much filtering any more. The compander will hide most of it, but only when there is no input signal.
Cheers, Mike
(no problem Rob! Nice to see this schematic comes in handy after... err... 5 years)

[Eb7+9]

what`s that about changing the 220µF: d`ya think it`s spoiled? (spikes on the rails?) [an extra 100n across the power-pins at the chip never hurts]

yep ... if you look at the supply circuit in flanger, chorus and delay units you'll notice that the clock chip isn't fed directly from the main supply as the rest of the audio path - there's a PI filter circuit with a low (100 ohm) resistor and a second filter cap ... there's two supply feeds in a sense ... in Boss schematics you'll notice a white upwards arrow for one and a black upwards arrow for the other ... usually the lone feed goes to the clock chip ... if you undersatned anything about ground bounce you'll understand why ... it's a standard problem in mixed signal chip design ...

Obviously this is done to prevent clock feedthrough into the audio part (noisy digital living alongside sensitive analog = mixed signal) - if this cap gets weak and doesn't regulate that segment of the feed then you'll have feedthroug obviously ...

... an extra 100n across the power-pins at the chip won't do F'all if the main cap is lossy ...

[space_ryerson]

I'm having a hard time finding the 100K resistor in series with a 0.0022 uF cap that I need to connect to the 10k resistor connected to the wiper on the 'null' trimpot in order to make the filter like the DM-3; that is after I swap the 100k with a 10k resistor. Maybe it's sunspots, but I can't seem to find the suckers.

I haven't had a chance to swap out the 220uF cap yet either, since I seem to have a bit of a cap shortage here. Anyway, I got tired of flipping the PCB over and over, so I scanned it in and composited it in photoshop for ease of use.

[Vsat]

S.R.,
I sent you a private message today asking for your email address so I can send a revised jpg of your TDL, with arrows pointing to the 100K and 2n2.
Cheers, Mike

[Eb7+9]

If you can re-scan at slightly higher rez the trace side (without the parts super-imposed) that would help ... I think the two psu caps are at the top LEFT next to the 3205 - but it's hard to tell ...

[bwanasonic]

Prompted by this thread, I replaced the filter caps in my 80s era KMD analog delay. It did help the clock whine a bit. If I max out the clock trim and the delay time I can still hear a bit, but I think it would take a redesign to remove this. I mainly use the pedal as a *thickening agent* in conjunction with other delays, so I don't rely on it for longer delay times anyway. Curious if clock whine is typical of the *name brand* pedals of this era (Boss DM2/DM3, Ibanez AD9) ? The KMD was allegedly made at the same plant as the Boss pedals, and resembles those circuits. Though the trace side of the board looks pretty damn crude compared to the Boss stuff (or even the Tokai pictured here).

Kerry M

[space_ryerson]

If you can re-scan at slightly higher rez the trace side (without the parts super-imposed) that would help ... I think the two psu caps are at the top LEFT next to the 3205 - but it's hard to tell ...

You are right. The one you mentioned changing is on the top left. VSAT sent me photo with other components highlighted for the 'island', which I'm looking at now. I actually have higher res. scans without the superimposing, if you want it for reference.

[space_ryerson]

Thanks VSAT and eb7+9! I found the 100k and cap, and wired them as you had directed. I think it does sound better. I'll put it through some serious testing tomorrow; but thanks for all of the help. The clock noise isn't quite as apparent, and I think changing that other cap might help that one out even more. I also tried my stratocaster out, as opposed to the les paul; and since the treble knob is much lower on my amp when I use the strat, the clock noise is practically invisible.

[Eb7+9]

The clock noise isn't quite as apparent, and I think changing that other cap might help that one out even more. I also tried my stratocaster out, as opposed to the les paul; and since the treble knob is much lower on my amp when I use the strat, the clock noise is practically invisible.

If either cap was lossy you'd hear an improvement - if there's room for a 470uF on the pin5 connection then I'd use one ... you should be able to crank the treble on your amp and hear no clock at all following nulling adjustments ... good luck !

[Vsat]

Congrats on the re-wire S.R.!
I liked the sound of my unit better after doing this mod. Also, thanks for posting the Tokai phaser photos on the other thread!
Regards, Mike