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71
Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by PRR on May 31, 2023, 09:47:31 PM »
A Ling ?

Chuck Berry - My Ding A Ling (1972)

The man refined and developed rhythm and blues for 70 years, and he is remembered for singing a dumb ditty about his wee-wee. (This was his only #1 hit, and next-to-last top 40.)

much much longer version
72
Building your own stompbox / Re: Intersound IVP gyrator circuit output
« Last post by PRR on May 31, 2023, 08:58:15 PM »
> Since this is a single supply

You are right, Tom. I already expressed my opinion about 'plans' with key details cut-off.
https://www.diystompboxes.com/smfforum/index.php?topic=130027.msg1259476#msg1259476
Draw the WHOLE circuit. None of it is unimportant.
73
Building your own stompbox / Re: NE555 tone generator variable frequency
« Last post by Rob Strand on May 31, 2023, 08:23:05 PM »
In the OP's schematic pin 2 of the NE555 should connect to pin 6 not to +V.  This error is not present in the Elektor schematic below.

wow. all that shaping of the square wave, you could just take the pin2/pin6 output and buffer it for a sawtooth-ish output.
I think the filter is intended to give a nicer sine output than just the exponential output across the cap.   The advantage of *starting* with the exponential output is the level is automatically set by the NE555 regardless of the frequency pot setting.

To me the circuit around C6 looks wrong.  I think there should be another 10k resistor between C4 and C6. Another options could also pull C6; which now seems more likely - see below.

The problem with making the frequency variable is the level of the sine output (and triangle and exponential outputs for that matter) will decrease with frequency.


Quote
Replaced R1 with a 1M pot and inlined the 10k resistor with that as without it would cut out if the frequency got too high, presumably outside the spec for the chip or something like that.
You would do better making R2 variable so the output remains more or less square when you adjust the frequency.   Making R1 variable means the shape of the waveform changes when the frequency is adjusted:  the output high time varies and the output low time is fixed.

For R1 variable, putting 10k in series with the pot is necessary to ensure the oscillator can oscillate.   For R2 variable you don't need the 10k but it is very desirable because without it the frequency will increase rapidly at the end in an impractical manner - 10k to 50k is a good choice.


Looks like the original Elektor circuit has the sine filter error as well:
(Need a resistor between C7 and C4, could also just pull C4.
 But oddly enough the kit PCB seems to have C4 loaded, like the schematic.)

https://worldradiohistory.com/hd2/IDX-UK/Technology/Technology-Modern/Archive-Elektor-IDX/IDX/00s/Elektor-2000-12-OCR-Page-0097.pdf


Seems like there's a few problems with that circuit.  Some tentative fixes.
The idea was to work out what the circuit was based on the sine output level in the Elektor (Dec 2000) article.



I'm seeing about 0.7V p-p on the square output, 2.5V p-p on the exponential output, 0.7Vp-p on the triangle output.

With the square output the buffer is being totally cut-off on the negative swing because the 1k on the divider is killing the bias on the output buffer.   The same thing isn't allowed to happen on the exponential and triangle waveforms as that would chop off the negative tips of the waveform.  Luckily as you progress down the 10ks it finds a new bias point which keeps the output buffer biased enough not to clip.
74
Building your own stompbox / Re: Aion Theseus (KoT) issues
« Last post by RickMcCarthy on May 31, 2023, 08:14:21 PM »
IC 1 reads:

IC1
Pin 1: 8.12v
Pin 2: 2.40v
Pin 3: 2.30v
Pin 4: 0v
Pin 5: 1.99v
Pin 6: 2.00v
Pin 7: 1.96v
Pin 8: 8.61v
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Building your own stompbox / Re: Aion Theseus (KoT) issues
« Last post by RickMcCarthy on May 31, 2023, 08:08:35 PM »
Ok, so I checked R12 and 13 - both are 47K and correct. I tested R12 and one lead is getting the full VA (8.61v) and the other side reads the same as the end of R13 that its tied to (4.25v), but the strange thing is that I read 0v on the + pad of C10. As a contrast, on the B side of the pedal I read the 4.25v on the + pad of C20.

I even tried installing another 100uf/25v cap I have here and same thing - no 4.25v on the + pad. When I install a small jumper from the C12/13 junction to + of C10 still nothing.

This has got me stumped. Considering starting over, though Id really like to see this through.
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Thanks Rob. You are a wealth of knowledge!

In the mean time I went to my local electronics store and they ordered some OPA1678's for me.
It could take two to three weeks for them to arrive.

I'll get back when I have installed them. We'll see how much it helps or doesn't and then we'll continue with mods for smaller resistors where possible.

I'll keep you updated.
Good luck with it all.   I admire your perseverance.  It's really what it takes to weed out these types of issues.  There's no short cuts.   In effect you have done what Electroharmonix have not!
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Building your own stompbox / Re: Yellow humper correct schematic
« Last post by Rob Strand on May 31, 2023, 07:52:14 PM »
Interesting they swapped the order of the Low and High EQ sections on the YH and the PP.  Presumably so the same PCB can be used to get treble boost on the PP and bass boost on the YH in the lone EQ setting.

Probably good idea to do a NPN version.  Seems like a good idea to keep the gains >= 200.
[FYI: The generic 2SA666 has a typical gain of 250.   However these devices come in
gain sorted -P, -Q, -R, -S, -T versions.  For those -R is hFE 180 to 360, and -S is hFE 260 to 520.
I don't know what the original used.  Need PCB pics.
I found a Red Ranger pic (Musitronics era) which had a 2SA666-R.]

Here's some more info:



Oh, it seems flat isn't flat.  I checked the sim and it seems to be the case.   It's the 470k resistors.  They are not large compared to the 2x82k =164k.   If you want flat in the flat position use a bypass switch or change the 470k's to something much larger.

78
Thanks Rob. You are a wealth of knowledge!

In the mean time I went to my local electronics store and they ordered some OPA1678's for me.
It could take two to three weeks for them to arrive.

I'll get back when I have installed them. We'll see how much it helps or doesn't and then we'll continue with mods for smaller resistors where possible.

I'll keep you updated.
79
Building your own stompbox / Re: Old telephone ringer stompbox
« Last post by Rob Strand on May 31, 2023, 07:25:57 PM »
Quote
I used phone's own case because I thought it was just neat.
Cool idea.
80
Building your own stompbox / Re: 666 hz whine in the Holy Grail
« Last post by Rob Strand on May 31, 2023, 07:25:18 PM »
Quote
You know a lot. :) Just not the reasoning behind this idea.
To avoid the white noise accompanying the dry signal I was using a Boss LS-2 as a splitter + mixer back then.
Although not exactly free from white noise itself the Boss LS-2 is much quieter than the dry signal path in the Holy grail.
So what I did was: mix dry signal through Boss LS-2 with 100% wet signal from Holy Grail.
The problem with the 100% wet signal is that it has a ton of white noise from the DAC outputs.
The 'good' thing about it is that the white noise is constant in amplitude regardless of the input level.
So by boosting the input and attenuating the output by the same amount, I got the same level of reverberated guitar signal out but with attenuated hiss from the DAC outputs. The key being that the DAC noise does not increase by boosting the input signal.
A poor man's compander...
Sometimes you just have to weed through all the possible sources until you get a hit.

You debugging trick with the external mixer was a really cool way to isolate the digital audio stuff.

Like you suspect already, the whine and some noise could well be layout.  So that's getting outside of what you can fix (without doing silly things like finding the noise source cancelling it at the output mixer!).

You can get extra hiss from poor anti-aliasing filters at the input of the ADC.  The current filter C6 and R5 are pretty weak.   You need at least a second order filter to keep the noise down.  The cut-off for the second filter R6 and C9 are very high.   I can't remember if you already tried playing with the filters early on in the thread.

You could only check noise from DAC's, with the ADC noise as well, if you can block the input inside the DSP chip and only output zeros on the DAC.  That's so easy to do when you don't have control of the chip/code.
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