There's a faint whining noise in my EHX big box Holy Grail.
Throughout the years many other owners have complained about this issue with their HG as well.
I'd like to get to the bottom of it.
The factory schematic is linked below.
My 2 main questions:
- why does the whining noise completely disappear when there's a (buffered? Boss) pedal after it ?
- what can I do to the circuit to remove the whining noise when it's connected directly to my (tube) amp.
Additional information:
- I'm using a replacement, but sold as original, EHX power supply 9V 500mA. It supplies 15 volts DC unloaded- and 11,75 volts loaded. It drops 0.7volts over the reverse polarity diode that I added and 1 volt over the 4,7 ohm series resistor, so the circuit draws 212mA. The 7805 regulator gets 10 volts and puts out 5 volts.
- link to the psu I've bought and that I'm using: https://www.banzaimusic.com/EH-9V-DC-EU-500mA.html
- Better picture of the same PSU (but with a different plug): https://www.banzaimusic.com/images/D/50854_2.jpg Why does it say: "For I.T.E. use only" when it's clearly meant for audio???
- It's not daisy chained.
- In one pedal I replaced all 10µF and 1µF (smd) electrolytic capacitors as they had leaked and now read in the nF or pF range. This reduced the whining noise by 90% and also fixed the pedal as it had a very weak reverb signal due to a faulty C8 cap right at the input of the dsp chip.
- I have two of these pedals (rev A and rev C). Rev A still has a strong whine the first time I power it up, but after 2 minutes and 55 seconds it suddenly drops the whining noise by 90%.
- I can make the initial strong whine go away immediately by unplugging and replugging the power supply. But only when I unplug the jack from the back of the pedal, not when unplugging and replugging the wall wart. If I unplug the wall wart from wall and pedal and read the voltage it still says 15 volts. When un/re-plugging the jack from the back it's impossible to do so without hitting the sleeve(ground) with the posistive tip of the 1/8 jack.
- The frequency of the whine is 666 Hz and its harmonics: 1,33 kHz , 2 kHz, 2,66 kHz, 3,33 kHz, 4 kHz ...
- Not all harmonics are always present or as loud at every setting. I can introduce 'missing' harmonics or make some louder by touching the blend pot's casing (myself being ungrounded).
- When audio probing, the whining noise is every where, both on the ground as along the signal path. I cannot find where it starts.
- The entire pcb is microphonic. I cannot find the component (ceramic capacitor?) which causes it. Anywhere I tap, I hear the thump or click, Even when I tap the wooden table it's sitting on. I only hear this though with extremely high amplification and through headphones.
- I've tapped all the components individually, very, very softly with a wooden tooth pick to check if some produce a louder tap and it seems that the components around the first opamp (U3: c6, r5) may produce it a little louder than the rest.
- I've tried putting several buffered pedals after the circuit. The 'active' setting in my Zoom G3 works best at completely removing the whine. My Boss LS2 works very well too. My TS808 works but still leaves a fraction of the whine.
- Thinking I could never do any harm by putting a 2.2nF 630v box cap across any component in the circuit to see which or what affects the whine I found that:
* the cap parallel to r6 (at pin7 on the output of U3 input opamp) the whine is louder
* cap parallel to r31 (emitter resistor of the Q1 transistor before the blend pot) the whine is gone when connected to my Zoom G3 in passive mode but still there when connected to my tube amp. From what I read this was a stupid thing to do as bypassing the emitter resistor in an emitter follower config should have fried the cap or transistor. Both seem fine though.
- The whine is louder with the blend at 100% dry and slightly lower when turning towards 100% wet. At 100% wet there's so much loud white noise/hiss I can not say if there's still some whine buried beneath it.
- On the Hall setting there's a very strong high frequency roll off. From 4,66 kHz (7th harmonic of 666hz...) to 5.328 kHz (8 harmonic) it drops 12db. I don't see that ultra strong filtering on the other two settings: Spring and Bathroom/Short Spring (I replaced Flerb on both pedals) but the whine is also present on those two settings.
- The included schematic below is rev B. The only difference with rev C is that in rev C they added a reverse polarity diode and they added 100pF caps from tip to sleeve (signal to ground) at the input and output, before the true bypass switch, so, always in circuit. Rev A is not true bypass (connects input to intersection r34 and c29 in bypass). I've converted my Rev A circuit to rev C. The only remaining difference is some changes in layout.
- Input and output jack sleeves are connected to the chassis. Sleeves of input and output jacks are also connected together with a wire. Sleeve of power jack is connected to the sleeve of the input jack. Another wire goes from there to the ground on the pcb. Led ground comes from a spot on the pcb. During all the tests there was no connection to the chassis.
I've read countless forum posts on 'whine' issues. A big part of them are about klon/clone charge pump issues and clock whine in bbd delays, choruses etc.
I've run out of things to test or try. I've been at it for weeks now. I'm happy to hear your thoughts and suggestions.
(https://i.postimg.cc/mhB9QKht/Electro-Harmonix-EC-0060-Holy-Grail.png) (https://postimg.cc/mhB9QKht)
I don't have any helpful advice, but you've gotta admit it's funny for a "Holy Grail" to be cursed by that particular frequency... ;)
Does the frequency of the noise stay the same in the different modes? How are you measuring the frequency and reduction in the noise? It is possible you are getting power supply noise, and in some modes the power supply has to run at a different frequency, making it appear to be reduced. Do you have any opportunity to use it with a really high quality power supply?
The louder microphonics around the first chip might just be because it is the first chip, and its noise level is dominating.
Does the noise go away with a really short cable to your amp, or just with a buffered pedal?
When you say you converted it to rev C, do you mean you added 100pF caps? Was the noise there before that?
Quote from: r080 on June 02, 2021, 10:42:37 AM
Does the frequency of the noise stay the same in the different modes?
It does but the strength of the different harmonics changes a little so the overall 'tone', being the sum of the harmonics is slightly different. And if I recall correctly in one mode the 4 kHz was completely missing.
Quote from: r080 on June 02, 2021, 10:42:37 AM
How are you measuring the frequency and reduction in the noise?
I hooked it up to a DAW (Reaper) and I'm using a real time spectrum analyzer (SPAN Voxengo). I see the spikes at 666 Hz, 1,33 kHz , 2 kHz, 2,66 kHz, 3,33 kHz, 4 kHz etc.
When I say '90%' reduction it's just a way of saying but I could get the exact db. When I say 'gone' I no longer see the spikes.
Quote from: r080 on June 02, 2021, 10:42:37 AM
It is possible you are getting power supply noise, and in some modes the power supply has to run at a different frequency, making it appear to be reduced. Do you have any opportunity to use it with a really high quality power supply?
The whine is a well known problem described in many posts on many forums. The general agreed upon solution is to not daisychain and to only use the PSU that comes with the pedal. It makes the whine almost inaudible but it's still there.
I have no other really high quality power supply that delivers more than 200mA. I have a 1-spot switching power supply that can deliver 1700mA. There's also whine with that psu.
Quote from: r080 on June 02, 2021, 10:42:37 AM
Does the noise go away with a really short cable to your amp, or just with a buffered pedal?
I'm using a 3m (10ft) cable. I'll try with a patch cable tonight.
When using the Zoom or Boss pedal inbetween there was a 3m cable from the HG to the Boss and a patch cable after the Boss. So, the length of the cable and its capacitance didn't seem to be the reason the whine went away.
Quote from: r080 on June 02, 2021, 10:42:37 AM
When you say you converted it to rev C, do you mean you added 100pF caps? Was the noise there before that?
The pedal was broken when I bought it: it had a very weak reverb signal. (another well known problem)
Cause: dry signal going into the dsp chip too low or wet signal coming out too low or losing signal in the Butterworth filter just before the blend knob.
I had another working pedal so I could compare readings between the two.
I found the cause was a faulty C8 cap at the input of the dsp chip. I replaced that cap and then pedal worked again but had the whining noise. (a well known problem)
I found all electrolytic caps to be 'off' (dried out?, leaked?, capacitor plague?) so I replaced them and the whine reduced drastically. It has even less whine than my 'perfectly good' REV C pedal now.
I added the reverse polarity diode, the 100pf caps, made it true bypass and removed the circuitry that was used for the old bypass config to make it pretty much identical to my Rev C.
It's only at that point that I started testing the 'perefectly good' Rev C pedal for whine and noticed it had even more whine. I just never noticed it all those years because I had never used it without a Boss pedal after it. And also because I always used it 100% wet and mixed in the dry with a Boss LS-2 pedal.
Since my last post I also wired it for star ground by the way. Power ground, output jack ground, input jack ground all going to the same spot on the pcb. Only the LED ground I haven't touched but it's connected to the same big ground plane on the pcb.
The next thing I should try is adding a bigger e-cap parallel to those 10µF filter caps. They read 10µF (brand new caps) on the quieter RevA and 7-ish (older/original) on the slight whinier Rev C. None of that explains to me why a Boss pedal makes the whine go away though.
Here's a photo of the populated side of the board.
You can see the extra cap I soldered parallel to the faulty C8 cap. Just to see if that would fix the 'missing reverb' problem. Afterwards I removed the faulty smd cap and did the same for all the e-caps.
(https://i.postimg.cc/McJRRz6n/IMG-20210519-204819.jpg) (https://postimg.cc/McJRRz6n)
You do have a different power supply, anyway. Is the frequency of the noise the same with the 1Spot?
I see you mentioned noise on the ground. You may already be familiar with RG's "sewer ground" idea. I can't say I understand it very well myself, but is there any chance the changes you made to the grounding could have polluted your signal ground with sewer ground?
A 220 ohm dummy load is a good place to start for switching power supply noise.
Play with the value. The fact the whine shifts with load is a good indication it is the power supply.
A lot of switchmodes produce noise if they don't have enough load.
They might "work" with light loads but they are noisy.
Quote from: j_flanders on June 02, 2021, 12:16:50 PM
The next thing I should try is adding a bigger e-cap parallel to those 10µF filter caps.
That didn't help one bit.
Quote from: j_flanders on June 02, 2021, 12:16:50 PM
Since my last post I also wired it for star ground by the way. Power ground, output jack ground, input jack ground all going to the same spot on the pcb. Only the LED ground I haven't touched but it's connected to the same big ground plane on the pcb.
That seems to have made things worse. Now the noise reduction by using a Boss pedal after the Holy grail is less than before.
I moved the power ground/return back to the ground pin of the 7805. That seems to have made the most difference. Boss noise reduction is working again.
Moving the ground from the output jack sleeve back to the input jack sleeve doesn't seem to make a lot of difference.
Quote from: r080 on June 02, 2021, 01:18:36 PM
You do have a different power supply, anyway. Is the frequency of the noise the same with the 1Spot?
I checked and the frequency is the same. Good idea though.
Quote from: r080 on June 02, 2021, 01:18:36 PM
I see you mentioned noise on the ground. You may already be familiar with RG's "sewer ground" idea. I can't say I understand it very well myself, but is there any chance the changes you made to the grounding could have polluted your signal ground with sewer ground?
My rev C is still completely stock and has now (slightly) more whining noise than my currently modded rev A.
Also, a lot of people have this problem with their HG and I'm pretty sure very few have attempted to mod it (DSP, smd etc.)
Quote from: Rob Strand on June 02, 2021, 06:32:06 PM
A 220 ohm dummy load is a good place to start for switching power supply noise.
Do you mean the original PSU is of the switching type?
To me it looked too big and heavy to be of that type. Is there any way I can tell for sure?
(https://www.banzaimusic.com/images/D/50854_2.jpg)
QuoteDo you mean the original PSU is of the switching type?
To me it looked too big and heavy to be of that type. Is there any way I can tell for sure?
That type is unlikely to be a switchmode.
The weight is a tell tale sign that it is a transformer not a switchmode.
Actually, my apologies for not going through all your details. I just saw some posts about the power supply.
Switchmodes are common source for that type of noise but it's not the case here.
You have done a good job documenting a lot of details. I need to read over it in detail to see where the
cracks are.
This part is interesting,
Quote- why does the whining noise completely disappear when there's a (buffered? Boss) pedal after it ?
When you do that, is the Boss pedal powered from the same power supply as the EHX unit?
A couple of things,
It seems the EHX unit follows the CS4811 datasheet quite closely. I'm not sure how clean the buffered CMOUT on the
EHX since they didn't use any CMOUT filters (the filters in the datasheet can cause trouble with some opamps).
Also the filter cap C10 on the EHX looks pretty small. Not enough to filter out 600Hz signals.
They are just some initial observations I wouldn't read too much into it.
QuoteI can make the initial strong whine go away immediately by unplugging and replugging the power supply. But only when I unplug the jack from the back of the pedal, not when unplugging and replugging the wall wart. If I unplug the wall wart from wall and pedal and read the voltage it still says 15 volts. When un/re-plugging the jack from the back it's impossible to do so without hitting the sleeve(ground) with the posistive tip of the 1/8 jack.
So this one is interesting as well.
The input supply filter C1 on the EHX is very small. There will be a a big cap inside the wall-wart. When you pull the wall-wart at the mains power is still supplied by that big cap. However when you pull the DC jack at the pedal the big cap is removed and the power will drop quicker.
Any low frequency supply currents will not kept local to the PCB because of the small C1 value.
I'm not sure but it looks like the DC jack is not isolated from the chassis that means any low frequency currents have the potential to pass through the signal grounds.
Those points and your symptoms are strong evidence ground currents are the cause.
Some ways this can be reduced,
- increase C1 to prevent the low frequency current pulses on the PSU from going between the PCB and wall-wart via the DC jack
- Isolate the DC input jack and make sure the wiring from the jack connects close to C1's ground. (That might not be *the* best place as it depends on the ground layout on the PCB.)
As a test you could unscrew the DC jack so it is not grounded.
You probably need 100uF to 1000uF for C1. Use a big value as a test.
Not sure if the power is switched by the (6.5mm) input socket. The schem doesn't show it is but that assumes the schematic is correct.
EDIT:
I just noticed that board is smd. If the 4.7R ohm input resistor is a tiny SMD part you might not be able use 1000uF. What happens is the resistor can fry during power up.
Quote from: Rob Strand on June 02, 2021, 07:20:27 PM
So this one is interesting as well.
The input supply filter C1 on the EHX is very small. There will be a a big cap inside the wall-wart. When you pull the wall-wart at the mains power is still supplied by that big cap. However when you pull the DC jack at the pedal the big cap is removed and the power will drop quicker.
Any low frequency supply currents will not kept local to the PCB because of the small C1 value.
I'm not sure but it looks like the DC jack is not isolated from the chassis that means any low frequency currents have the potential to pass through the signal grounds.
Ok, thanks, that explains.
The DC jack is not isolated from the chassis, but during all these tests there's nothing connected to the chassis but the 3PDT switch. It's the only way I have access to the populated side of the board.
Quote from: Rob Strand on June 02, 2021, 07:20:27 PM
Those points and your symptoms are strong evidence ground currents are the cause.
Some ways this can be reduced,
- increase C1 to prevent the low frequency current pulses on the PSU from going between the PCB and wall-wart via the DC jack
- Isolate the DC input jack and make sure the wiring from the jack connects close to C1's ground. (That might not be *the* best place as it depends on the ground layout on the PCB.)
The original C1 electrolytic cap was bad, as were all the other e-caps.
I replaced it with a through-hole version and soldered it directly across the pins of the 7805 regulator.
The power ground/return I moved to the ground pin of the 7805 since the cap's ground is also there now.
In rev A the power ground/return was originally soldered to the sleeve of the input jack.
In rev C they did it as you suggest: smd e-cap on the pcb and power ground/return was brought to the pcb at the ground leg of that cap.
Quote from: Rob Strand on June 02, 2021, 07:20:27 PM
As a test you could unscrew the DC jack so it is not grounded.
see above (circuit and connections being out of the box)
Quote from: Rob Strand on June 02, 2021, 07:20:27 PM
You probably need 100uF to 1000uF for C1. Use a big value as a test.
EDIT:
I just noticed that board is smd. If the 4.7R ohm input resistor is a tiny SMD part you might not be able use 1000uF. What happens is the resistor can fry during power up.
It's funny you mention that as the number 1 problem with these pedals is a fried R1.
Rev A has a 4r7 smd resistor but it's bigger(1W smd?) than the rest of the 'regular' resistors.
Rev A had a 100µF C1. It was bad and read in the pF or nF range. I replaced it with a 10µF cap during the conversion to rev C.
Rev C has a big 1 or 2 W through-hole resistor for R1 and a 10µF C1.
Quote from: Rob Strand on June 02, 2021, 07:20:27 PM
Not sure if the power is switched by the (6.5mm) input socket. The schem doesn't show it is but that assumes the schematic is correct.
It's not. With a 500mA PSU and a circuit drawing over 200mA I guess it's not feasible or sensible to run it from a 9v battery
Since audio probing didn't tell me where the whine comes from (it was everywhere, signal and ground) I not only tried to reduce the whine but also tried to increase the whine.
When 'bypassing' R6 (150 Ohm resistor right after U3) I get more whine. So, I guess I'm having less resistance for higher frequencies going to the DSP chip.
Could that mean that the whine comes from U3 at the input?
That's also where it seems to be slightly more microphonic.
I once tried adding a cap parallel to the 39pF C6 to limit high end gain. But I was just holding it there (not soldered) and I got so much buzzzz (probably because of the interference coming from my body) that I didn't hear any difference.
Maybe I should try that again but solder the cap this time. I'm just a bit reluctant to experiment solder/unsolder too many times to those smd parts.
QuoteThe original C1 electrolytic cap was bad, as were all the other e-caps.
A larger cap is rarely worse but in the light of the R1 issue a compromise might be required.
QuoteIt's funny you mention that as the number 1 problem with these pedals is a fried R1.
Rev A has a 4r7 smd resistor but it's bigger(1W smd?) than the rest of the 'regular' resistors.
Rev A had a 100µF C1. It was bad and read in the pF or nF range. I replaced it with a 10µF cap during the conversion to rev C.
Rev C has a big 1 or 2 W through-hole resistor for R1 and a 10µF C1.
There seems to be two contributing factors. R1 dissipates quite a bit of power while running, 2W would be wise just for that. Then there's the turn-on issue. I doubt a 2W through-hole will blow. Clearly they have had problems in that area with all the mods!
QuoteWhen 'bypassing' R6 (150 Ohm resistor right after U3) I get more whine. So, I guess I'm having less resistance for higher frequencies going to the DSP chip.
Could that mean that the whine comes from U3 at the input?
That's also where it seems to be slightly more microphonic.
I once tried adding a cap parallel to the 39pF C6 to limit high end gain. But I was just holding it there (not soldered) and I got so much buzzzz (probably because of the interference coming from my body) that I didn't hear any difference.
Some good debugging work there.
The R6 bypass thing seems very significant. I can see some angles.
The first is the capacitive load on U3 is making it oscillate. That would happen if R6 is too low. R35 has the same value so maybe the capacitive load of the cable is causing that to oscillate. Adding the Boss pedal would buffer the HG from the cable capacitance. However, I would call this one a very weak theory since you are seeing a clean 666Hz whine and if the oscillation was from two places I doubt the frequency would be consistent.
High on the list is small values of C10 and C11. For debugging I would be trying some larger cap values in parallel maybe 10uF up. It's easy to do and would cut off a lot of crazy thoughts for debugging.
Something worth noticing is this device is digital. If you have strong high frequency components these can get frequency shifted by the sampling process. By bypassing R6 you would be letting more out of band highs and that would make such signals stronger. However, you have to ask whey are they there in the first place. The high frequencies no doubt originate from the digital circuits or power and they could get into analog signals from the power or the grounding on the PCB. The way they would get in on the power would be via the small C10 and C11 values.
[Of course, the 666Hz could be getting in directly via the power as well. Perhaps something to do with the software. It seems odd the 666Hz is stronger on power-up, like you mentioned before. That would seem more like a software related frequency.]
A way to get more filtering is to increase C9 or R6. The R6 value is show in the CS4811 datasheet. I'm not sure how much you could increase that.
As mentioned before R6 and R35 are on the low side anyway.
So the crack in all this thinking is why/how a buffered pedal after the HG also removes the whine. It's possible high frequencies are getting out of the unit perhaps because of the small C10 value but the fact the whine is complete removed by a post buffer seems like it's something else. The points to maybe R35 too small. Unfortunately the links between cause and effect aren't clear yet.
As for the microphonics I'd be thinking C5. If you temporarily replaced it with a through-hole poly cap it would soon answer the question.
This pedal refused to whine any longer, making further investigations impossible.
On a rare occasion it still does the whine on startup, but after a minute or so it also magically disappears.
So, there was nothing I could try and add to this thread.
I still wanted to get to the bottom of this and managed to find and buy another big box Holy Grail that had some whine. :)
Quote from: Rob Strand on June 03, 2021, 07:22:24 PM
The R6 bypass thing seems very significant. I can see some angles.
The first is the capacitive load on U3 is making it oscillate. That would happen if R6 is too low.
R35 has the same value so maybe the capacitive load of the cable is causing that to oscillate.
Adding the Boss pedal would buffer the HG from the cable capacitance.
However, I would call this one a very weak theory since you are seeing a clean 666Hz whine and if the oscillation was from two places I doubt the frequency would be consistent.
[...]
Quote from: Rob Strand on June 03, 2021, 07:22:24 PM
As mentioned before R6 and R35 are on the low side anyway.
Quote from: Rob Strand on June 03, 2021, 07:22:24 PM
So the crack in all this thinking is why/how a buffered pedal after the HG also removes the whine.
It's possible high frequencies are getting out of the unit perhaps because of the small C10 value
but the fact the whine is complete removed by a post buffer seems like it's something else.
The points to maybe R35 too small. Unfortunately the links between cause and effect aren't clear yet.
Thanks for all your help and suggestions Rob! The above was crucial in solving the whine in my last acquired HG.
I audio-probed the circuit again and found in this pedal that the whine occurred just after the output buffer (U5).
There's no whine at the middle lug of the blend pot which goes to the input of U5, but there's quite a lot of audible whine at the output of that opamp.
Similar to the other HG, the whine disappears when it is connected to my Zoom G3, but only when the input of that unit is in 'active mode' instead of 'passive mode'.
I went over all your suggestions and hints and googled what those 150 Ohm resistors are for, which lead me to this article:
https://www.analog.com/en/analog-dialogue/articles/techniques-to-avoid-instability-capacitive-loading.html
For now I tried the easiest solution: adding additional resistance in series with that 150 Ohm resistor at the output.
An additional 1k to 2k makes the whine inaudible. :icon_razz:
I haven't checked on a scope if it's still there, but I can no longer hear it. Not through headphones, not through my amp with all controls on 10.
The Zoom's 'active input' as well as some of my Boss pedals must have some series resistance at the input.
Monitor the 5v line and see what changes once the oscillation starts.
QuoteI still wanted to get to the bottom of this and managed to find and buy another big box Holy Grail that had some whine. :)
Wow. Just wow. One station closer to Stomp Box Sainthood. To so love trouble-shooting pedals that, when a problem goes away, you seek out another broken specimen.
Quote from: mozz on August 25, 2021, 05:53:51 PM
Monitor the 5v line and see what changes once the oscillation starts.
Ok, will do. Can you be a little more specific. Where, how, what? There are two 5V lines (analog and digital)
Quote from: idy on August 25, 2021, 06:00:50 PM
QuoteI still wanted to get to the bottom of this and managed to find and buy another big box Holy Grail that had some whine. :)
Wow. Just wow. One station closer to Stomp Box Sainthood. To so love trouble-shooting pedals that, when a problem goes away, you seek out another broken specimen.
I know. :icon_redface: Just don't tell my wife.
QuoteI went over all your suggestions and hints and googled what those 150 Ohm resistors are for, which lead me to this article:
https://www.analog.com/en/analog-dialogue/articles/techniques-to-avoid-instability-capacitive-loading.html
For now I tried the easiest solution: adding additional resistance in series with that 150 Ohm resistor at the output.
An additional 1k to 2k makes the whine inaudible. :icon_razz:
I haven't checked on a scope if it's still there, but I can no longer hear it. Not through headphones, not through my amp with all controls on 10.
That's a good sign you are on the right track.
Quote
The Zoom's 'active input' as well as some of my Boss pedals must have some series resistance at the input.
The series resistance at the input of the next pedal might only be helping a small amount. The root cause is the opamp with the low output resistor driving the capacitance of the cable. The input resistor on the next stage pedal is after the capacitance of the cable so the opamp still sees the cable capacitance. The resistor at the opamp output is *between* the opamp and the cable capacitance, which effectively makes the opamp see less capacitive load.
The way I normally check this type of thing is to have no cable at the output of the device, that makes the capacitive load as low as possible, then add different value capacitors to ground on the output jack, say 10p, 100p, 470p, 1n, 10n, 100n. If there is a zone where it kicks into oscillation I might use finer grain steps. Especially in the sub 1n region as this would represent different lengths of cable. The idea is to choose an output resistor high enough where it never oscillates.
I'd say the low value of R6 is if equal concern. If you raised R6 to 1k it's probably going to have no effect on performance with the existing C9 value.
Interesting, looking at the datasheet you would expect it handle quite a bit of capacitance, figs 19 thru 21
https://www.ti.com/lit/gpn/lmv358a-q1
Quote from: Rob Strand on August 25, 2021, 07:06:20 PM
The root cause is the opamp with the low output resistor driving the capacitance of the cable. The input resistor on the next stage pedal is after the capacitance of the cable so the opamp still sees the cable capacitance. The resistor at the opamp output is *between* the opamp and the cable capacitance, which effectively makes the opamp see less capacitive load.
I get your point.
I'm testing with a patch cable though, which has between 20pF and 80pF capacitance. The 20pF is 10cm, the 80pF 40cm long.
I don't know the capacitance at the input of the next device.
Quote from: Rob Strand on August 25, 2021, 07:06:20 PM
The way I normally check this type of thing is to have no cable at the output of the device, that makes the capacitive load as low as possible, then add different value capacitors to ground on the output jack, say 10p, 100p, 470p, 1n, 10n, 100n. If there is a zone where it kicks into oscillation I might use finer grain steps. Especially in the sub 1n region as this would represent different lengths of cable. The idea is to choose an output resistor high enough where it never oscillates.
How do I test without a cable?
I used a 5k pot to find a resistor where the oscillation is no longer audible.
However, it's not a case of 'kicking in'. The larger the resistance, the lower the whine in volume.
At around 1,5k I could no longer hear the whine over the white noise this pedal has.
I don't seem to hear any difference in treble for dry and wet signal though.
Another thing I noticed is that when I touch the tip out the output jack in the pedal, the whine disappears as well.
Quote from: Rob Strand on August 25, 2021, 07:06:20 PM
I'd say the low value of R6 is if equal concern. If you raised R6 to 1k it's probably going to have no effect on performance with the existing C9 value.
It's harder to test as I have to add series resistance in the middle of a circuit. But it's definitely something to keep in mind.
For now, since I don't hear any whine at both sides of the blend pot, I'm not going to unsolder any of the smd parts in that area.
QuoteI'm testing with a patch cable though, which has between 20pF and 80pF capacitance. The 20pF is 10cm, the 80pF 40cm long.
I don't know the capacitance at the input of the next device.
How do I test without a cable?
10cm is pretty short and it's sure possible to kick some circuits off with small capacitance values like that. The next device might be around 5pF to 10pF, not much.
With your short lead you probably won't gain much by making the set-up less convenient. I use two methods clip parts onto the board directly or use a dummy plug that I can clip or solder parts to. Unless you have strong need to test very low capacitance just do whatever is convenient and it should be OK.
QuoteI used a 5k pot to find a resistor where the oscillation is no longer audible.
However, it's not a case of 'kicking in'. The larger the resistance, the lower the whine in volume.
At around 1,5k I could no longer hear the whine over the white noise this pedal has.
I don't seem to hear any difference in treble for dry and wet signal though.
That method is perfectly fine. The only thing worth doing is add a little bit more capacitance to see if you can get it to oscillate. Then use a resistor a little higher than that value. When you are right on the critical resistance value you might be able to control the level of the whine a bit. However when you set it to the slightly larger "safe" value it should not oscillate all. That's where you can dial up you amp to 10 and you cannot hear any oscillation. That's what you want - no oscillation at all regardless of what cap value you load the output jack with.
QuoteAnother thing I noticed is that when I touch the tip out the output jack in the pedal, the whine disappears as well.
That could mean only small capacitance values are affecting it, or, it could mean your resistance is damping the oscillation. These things can be very fussy. I often stick my fingers on the back of boards to kill oscillations - after that try to work out what that's doing.
QuoteIt's harder to test as I have to add series resistance in the middle of a circuit. But it's definitely something to keep in mind.
For now, since I don't hear any whine at both sides of the blend pot, I'm not going to unsolder any of the smd parts in that area.
Yes, it can be a pain. Since you have identified a problem at the output you know there's a possible issue using 150 ohm. A slightly less optimal way would be to load the output jack with 2.2nF then check out what R35 value stops the oscillation. That would give you an idea what value should be in R6. If you don't want to solder a new R6 that's fine. If you get problems down the track you know where to look and you know what value to change R6 to. You can just keep that up your sleeve for a rainy day.
The output amplifier does not have any capacitance across the 100K feedback resistor. 100pF would give you a rolloff at 15923 Hz, not enough to affect the audio but it may be enough to stabilize the output stage. Feedback lead is necessary to compensate for the lag caused by the capacitance to ground at the inverting input. The LM356 can supposedly drive a lot of capacitance but it still needs a feedback lead to do it. More isolation on the output is a good idea as the combination of output impedance and capacitance to ground creates a feedback lag that will cause oscillation.
QuoteThe output amplifier does not have any capacitance across the 100K feedback resistor
+1 That's going to help for sure (maybe even enough).
It's also a difference between U3 and U5.
Quote from: amptramp on August 26, 2021, 12:19:06 PM
The output amplifier does not have any capacitance across the 100K feedback resistor. 100pF would give you a rolloff at 15923 Hz, not enough to affect the audio but it may be enough to stabilize the output stage.
I jumpered the additional series resistor at the output to get the whine back, then tried a capacitor in the feedback loop of U5.
I'm just pressing the through hole cap's leads to pin 1 and 2 and it doesn't take much to kill the whine/oscillation. The suggested 100pF works and 68pF, the smallest cap I had, worked as well.
There's some space around the 100k to tack on a through hole cap.
Maybe I could also simply solder an smd cap on top of the 100k.
It's a lot more fiddly operation than adding a resistor to the 3PDT switch (between the lead coming from the pcb output and the lug it connects to).
Quote from: j_flanders on August 27, 2021, 04:57:27 AM
Quote from: amptramp on August 26, 2021, 12:19:06 PM
The output amplifier does not have any capacitance across the 100K feedback resistor. 100pF would give you a rolloff at 15923 Hz, not enough to affect the audio but it may be enough to stabilize the output stage.
I jumpered the additional series resistor at the output to get the whine back, then tried a capacitor in the feedback loop of U5.
I'm just pressing the through hole cap's leads to pin 1 and 2 and it doesn't take much to kill the whine/oscillation. The suggested 100pF works and 68pF, the smallest cap I had, worked as well.
There's some space around the 100k to tack on a through hole cap.
Maybe I could also simply solder an smd cap on top of the 100k.
It's a lot more fiddly operation than adding a resistor to the 3PDT switch (between the lead coming from the pcb output and the lug it connects to).
Just think - all those manufacturers who paint or grind off the lettering on devices to attempt ot hide their circuit design and you have the ultimate means to do the same - put the cap on top of the resistor. It might be a fiddly operation but think of the concealment - no one can copy what you have done.
FWIW, I had a looks at some numbers for the opamp in the TI and (old) National Semiconductors data.
The 150 ohm output resistor should be OK. It's not great but it's shouldn't cause problems - 470 ohms to 1k would be better.
FWIW, the worse capacitive loading is in the 100pF to 470pF zone, which is in the same region as cables.
The TI data gives the input capacitances. With 100k feedback resistors it's going to do a lot more damage than the 150 ohm output resistor + capacitive loading. Adding a cap across the 100k is the right solution.
The fact you change the 150 ohm to removed oscillation means it's hanging on by a thread without the cap across the 100k.
Quote from: Rob Strand on August 26, 2021, 07:00:21 PM
It's also a difference between U3 and U5.
I opened up another one of these and it does have a whining noise at the output of U3.
I tried various caps parallel to that 39pF in the NFB of U3 but nothing helped, not even a 10nF cap.
The additional resistor at the output of U5 still makes the whine coming from U3 (?), entering U5, inaudible at the output of the pedal.
Another weird thing: adding the 10nF cap parallel to the 39pF cap gives whine at the output of U5 despite the extra resistor there.
There's no whine at the wet side of the blend pot.
EDIT: Some further audio-probing shows this whine is 'everywhere', similar to the rev A pedal in my opening post. It's both on the ground as on the signal path.
QuoteI opened up another one of these and it does have a whining noise at the output of U3.
I tried various caps parallel to that 39pF in the NFB of U3 but nothing helped, not even a 10nF cap.
Under normal circumstances the you only need enough feedback capacitance to overcome the input capacitance of the opamp. That will end-up a being a small value. However, there is a slight caveat, and that's if there a large resistor on the + input. It's possible adding a C4 like on this pic can help,
(https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/14/_EE5D06523575EF8D1F8DCD538899_.jpg)
A little after posting that snippet last night it occurred to me there might be something more going on. The "natural" oscillation frequency when things wrong regarding load capacitance and feed back caps should be about 100kHz to 1MHz, not 666Hz. Oscillation problems can produce some pretty weird output waveforms but even then on an oscilloscope you might expect to see some high frequency around 100kHz to 1MHz then on top of that some other complex behaviour perhaps with the 666Hz. You wouldn't expect to only see a 666Hz.
Low frequency oscillations type usually comes from much more tractable causes like design issues, component fails, circuit bugs which cause unintentional positive feedback. You can get positive feedback like this from high gain circuits. The circuit itself becomes the 666Hz oscillator. That's a much different cause to nitty-gritty electronics issues like capacitive loading and feedback caps.
As I mentioned earlier, we are dealing with a sample system so high-frequencies could be shifted down due to sampling/aliasing. It's something to keep in the back of you mind.
If an opamp is oscillating at 100kHz to 1MHz it could put a lot of junk on the supply and that could get into many parts of the circuit.
So I guess the best thing to do is to look at number of waveforms throughout the circuit with an oscilloscope and see if there is only a clean 666Hz oscillation or there is some evil 100kHz to 1MHz stuff in there.
QuoteThe additional resistor at the output of U5 still makes the whine coming from U3 (?), entering U5, inaudible at the output of the pedal.
Another weird thing: adding the 10nF cap parallel to the 39pF cap gives whine at the output of U5 despite the extra resistor there.
There's no whine at the wet side of the blend pot.
Yep, pretty weird behaviour. No oscillation on the Wet side is plausible since that comes from the processor and R6 + C filter could prevent high frequencies going into the processor. I wouldn't expect things at U3 to affect U5 and things at U5 to affect U3 unless it was coming from the supply.
If we keep an open mind we shouldn't write-off oscillations from the regulator U2. Those regulators can oscillate and it would create all sorts of weird behaviours if it did. C10 and C11 aren't big enough to do a good job of removing a strong 666Hz signal from the power rails.
Another thing which is kind of asking for trouble is the 100k resistor R25. You could try shorting it out or putting a 1k across it.
Thanks for the suggestions Rob.
Before I try them, I'd like to post one last find:
When audio probing, I hear whine on ground on the pcb but not on the sleeves of the jacks.
For example:
There is a wire coming from the sleeve of a jack.
It's about 2cm (1 inch) long and connects to the ground on the pcb.
At one end of this wire (at the jack) I hear no whine, at the other end (on the pcb) I hear whine. ???
The photo below is for illustration purpose. In my test setup all jacks are connected to the chassis. Chassis connected to mains earth.
(https://i.postimg.cc/4dpGCDwt/ground-whine.jpg)
> At one end of this wire (at the jack) I hear no whine, at the other end (on the pcb) I hear whine. ???
Bad joint? Wire broken internally?
PRR - what happened to the cube count over your avatar? Are you no longer a guru on this board?
The 666 Hz oscillation may be the symptom of an RF oscillation that develops a bias somewhere that cuts the oscillation off then allows it to start again. This is like a superregenerative radio receiver that regenerates but shuts itself off and starts again at some supersonic audio frequency except this time, the frequency is in the audio band.
Quote from: PRR on August 28, 2021, 01:06:21 PM
> At one end of this wire (at the jack) I hear no whine, at the other end (on the pcb) I hear whine. ???
Bad joint? Wire broken internally?
Nope, neither. I checked that before I posted. From solder pad to sleeve it reads 0,5 Ohm. That's as low as my DMM usually goes.
It's not radiating noise either because it stops as soon as if I lift the audio-probe from the ground solder pad.
Edit: Since the jack is connected to the chassis I cannot be sure I'm measuring the resistance of that cable. I'd have to disconnect the jack from the chassis and measure again.
However, I have another identical pedal that behaves the same. It'd be unlikely that both have the same bad joint or internal break.
Quote from: amptramp on August 28, 2021, 01:47:39 PM
The 666 Hz oscillation may be the symptom of an RF oscillation
With the pedal open, and using a high gain amp sim on the Zoom modeller and listening to headphones when audio probing for whine, I have heard a radio station on a rare occasion.
Ok, as soon as I disconnect the DC-jack from the chassis, I no longer hear whining on the ground traces on the pcb.
It's one of these jacks:
(http://www.banzaimusic.com/images/P/17614_th.jpg)
It does not solve the whine at the output opamp though, I still need an additional resistor there or a cap in the NFB loop.
QuoteOk, as soon as I disconnect the DC-jack from the chassis, I no longer hear whining on the ground traces on the pcb.
It's one of these jacks:
When you probe a single point on a ground you are measuring voltage across two points on the ground. The first point is the probe point. The second point is the wherever the probe ground is connected. If your probe goes to a grounded amplifier the ground point can be ill-defined and the probe is not actually measuring what the eye sees as the ground point of the probe.
QuoteIt does not solve the whine at the output opamp though, I still need an additional resistor there or a cap in the NFB loop.
So that suggests there might be a probing issue. You are allowing the probe to see the issue or not but the basic problem is still present on the board.
On a board with digital parts you can get 666Hz noise due to noise on the ground which is caused by the processor activity.
The fact you can solve the problem with parts that relate to oscillation keeps making me think the issue is an oscillation issue and probably not a PSU/ground issue. The 666Hz is a complex side effect of the RF.
One way you can probe for high frequencies without an oscilloscope is to use a peak detector. The idea is the oscillation is usually fairly strong and at high frequencies. Point in the circuit which are normally DC or have moderate audio AC signals will actually have strong HF swings which are anything upto the full supply rail. You see the strong swings with one of the following circuits,
(http://techlib.com/electronics/graphics/wpbbxhr0.gif)
It might be a good idea to reduce the input cap value to 1nF (or even 100pF) as this help block any audio AC, including hum, and only detect RF AC. The shortcoming of the probe is you need some intuition to interpret the measurement. It will measure both audio signal, audio noise, and RF. You also need to make a good choice for the probe ground. Keep the multimeter and multimeter leads away from the chassis to prevent RF signal paths through the DMM.
Thanks for the replies and for coming up with new ideas Rob. They sure may come in handy further down the line.
I have a whine-free pedal at the moment, at least there's no whine at the output.
But not having found the root cause, for now, I'm still gathering some more 'data':
With the whine now removed from ground I probed further to see where there was still some whine.
There's a lot of whine on the +5A and +5D lines. For example on R28 and R26 (voltage divider to supply 2.5V for U3 and U5)
There's a huge loud whine on the input of the 78M05.
I tried several power supplies, both unregulated and regulated, no difference.
The mode switch affects the amount of whine.
I get the most whine around the 78M05 in the Flerb setting, slight less on Spring and much less on Hall.
In open air (not boxed up) the 78M05 measures around 80 to 90° C.
QuoteWith the whine now removed from ground I probed further to see where there was still some whine.
There's a lot of whine on the +5A and +5D lines. For example on R28 and R26 (voltage divider to supply 2.5V for U3 and U5)
There's a huge loud whine on the input of the 78M05.
I tried several power supplies, both unregulated and regulated, no difference.
The mode switch affects the amount of whine.
I get the most whine around the 78M05 in the Flerb setting, slight less on Spring and much less on Hall.
In open air (not boxed up) the 78M05 measures around 80 to 90° C.
There are a few causes of whine on the PSU rails:
1) The simplest is the circuit is working normally and the rails aren't "stiff" enough to prevent rapid load changes from affecting the voltage. The way you would handle that is with bigger supply caps and perhaps sometimes resistors in the supply rails to isolate noisy rails from quite rails.
That would also mean the frequency of the whine is a result of what the processor is doing. The fact the whine changes with different modes could mean it's from this cause.
A noisy supply rail could also affect U3 and U5 as the Vref caps are only 100nF and then supply noise will find its way to Vref and then into the audio. That would also explain whine at both U3 and U5.
2) The opamps are oscillating. When that happens it's not uncommon for the high frequency junk to get onto the supply rails. If the supply isn't "stiff" enough at high frequencies it makes things worse.
3) The regulator is oscillating. That can be because the input or output caps aren't large enough or located too far from the regulator.
The way I normal check this is to solder some 10uF tantalum caps at the input and output of the regulator. Solder the caps right on the regulator pins. Another test, perhaps not as good, is to do the same with known good 100uF electros. There's no intention that the 10uF caps are a fix since tantalums cause problems in the field. They are only used as a strong test to see if the oscillation can be turned off. If it works then a solution using more normal caps is sort.
IMHO, it's an easy test and worthwhile doing.
However trying to fit the problem to your observations isn't so clean-cut.
If you did have an oscilloscope the waveforms you get in case (1) are very different to cases (2) and (3). Case (1) will have some sort of pattern or perhaps you see bursts of activity. These patterns might be embedded in other mess which comes of normal operation of the processor. Cases (2) and (3) will have some sort of 100kHz to 1MHz waveform.
I still don't understand how playing with the feedback-cap or the output resistor could *help* cause (1), that's pretty much only going to happen in case (2). At a very long stretch it might work in case (3).
Bad grounds and poor layout can make any of the above worse than they need to be.
An oscilloscope would help narrow down some of the unknowns. Nonetheless it seems a tricky problem. If it were easy I doubt the problem would exist in the first place, or, it would have been solved after reply #5 or so.
You need a scope. The 7805 needs 0.1uf besides any larger caps. It should be easy enough to tack one on if there are none. I would even swap out the 7805 for another brand if possible.
This is what's on there now: (In the rev C circuits they also put a reverse polarity protection diode before the 4.7 Ohm resistor)
The 10µF at the input reads around 10 µF. The two 10µF's at the output read around 18µF (guessing 2 x 9µF in parallel)
Should I put two extra 10µF tantalum at input and output and also two 100nF (film? tantalum?) caps?
(https://i.postimg.cc/vmKVp63c/Screenshot-2021-08-31-011701.jpg)
QuoteShould I put two extra 10µF tantalum at input and output and also two 100nF (film? tantalum?) caps?
If I want to stop those regulators from oscillating I start with 10uFs tantalums because I've never seen that combination fail. However, I really hate tantalums across power rails as a commercial solution because they end-up failing and shorting out the supply rails. They are great for a test if you suspect regulator oscillations. Get rid of the oscillations first then shoe-horn in a practical solution later.
According to the datasheets you need at least 330nF on the input and 100nF at the output, both located right at the regulator. The claim is those parts should prevent oscillation even when the regulator is far from the main input and output caps. I'd probably go for those plus at least 47uF on the input and at least 10uF on the output.
Where things get fuzzy is when you put an electrolytic on the input side close to the regulator and ditch the "inconvenient" 330n. Sometimes you see 100nF at the input but it's technically not correct, it's a half-way skimp. There's 1000's of circuits out there like that and i'm sure not all are problem free when the electrolytics age. If you use 220uF to 1000uF maybe it will have more success.
What's clear is the existing 2x47n's aren't the way to ensure success.
Quote from: j_flanders on August 30, 2021, 07:19:12 PM
This is what's on there now: (In the rev C circuits they also put a reverse polarity protection diode before the 4.7 Ohm resistor)
The 10µF at the input reads around 10 µF. The two 10µF's at the output read around 18µF (guessing 2 x 9µF in parallel)
Should I put two extra 10µF tantalum at input and output and also two 100nF (film? tantalum?) caps?
(https://i.postimg.cc/vmKVp63c/Screenshot-2021-08-31-011701.jpg)
There are three kinds of tantalum capacitors you can run into, especially if you are getting old tantalums from military surplus gear.
What you can buy readily are dry-slug tantalums. The problem there is that the dielectric is tantalum pentoxide and if it is subjected to steady power line stress and any part of the pentoxide breaks down, it turns into tantalum dioxide, which is a conductor. This creates a blaze at that point which quickly sweeps around the capacitor like a firestorm as the pentoxide is converted to dioxide. Tantalum pentoxide is usually pinhole-free, so you get very small amounts of leakage current but any defect can result in a fire, so it is not rated for use across a power line where current can be fed continuously in it. Its reliability is determined by the number of ohms per volt in series with it. Dry slug caps have excellent high-frequency capability to the point where you do not need to parallel them with ceramic caps. Tantalum caps are smaller than aluminum caps because the dielectric constant of tantalum pentoxide is 27 whereas the dielectric constant for aluminum oxide is about 10.
Wet slug tantalum does not have the fire mechanism of dry slug but it cannot tolerate more than 0.3 volts of reverse bias or it will short out. They are usually seen as silver-cased devices with a red rubber insulator at the positive end. The reverse bias failure mode is silver dendrites going across the space from cathode to anode.
Tantalum foil capacitors are rare but they are also used across power lines and do not have the extreme sensitivity to reverse voltage the wet-slug devices have. If you find CLR69 capacitors, look no further - they are the holy grail of filter caps and I used them on a power converter for the Space Shuttle. With a specific gravity of 16.69 for tantalum, you have to use the minimum amount you can get away with for a space launch because these things are heavy.
I should mention that tantalum is a conflict metal that comes complete with bloodshed in the areas of central Africa where it is mined and you may have customers who don't like it for that reason.
QuoteThere are three kinds of tantalum capacitors you can run into
There's also modern-day "fusible" tantalums which attempt to address the shorting tantalum issue. IIRC these are targeted at automotive (and maybe medical) where you don't want hazards after a component failure.
Thanks for the valuable information concerning those tantalum caps.
Apart from the ethical aspects I didn't any of that.
It got me confused and somewhat weary to try them though, even for a very short test.
Here's what I found in the mean time:
There's a loud whine on all the +V lines.
From loudest to least loud:
- input of the 7805 (around 0.650 mV rms measured with my DMM)
- output of the 7805 +5 Digital line
- output of the 7805 +5V Analog line
I cannot hear it on any of the + 2.3V bias lines
Depending on whether the sleeve of the DC-jack is connected to sleeve of the output jack (through the chassis) I hear a faint whine on ground.
The whine on the input of the 7805 is a lot louder with the EHX unregulated adapter than with a regulated OneSpot.
Between those two I don't hear a difference in whine at the output of the 7805 though.
With the unregulated psu (around 12V unloaded) the 7805 runs around 90° C, while with the regulated Onespot around 70°C.
Since there's a 4,7Ohm voltage dropping resistor before the regulator I could try a cap there to filter out the ripple.
I tried a 1000µF cap and it drastically reduced the whine at the input of the 7805.
It did however make very little difference to the whine at the output. At least through headphones I could not tell if it was quieter.
I checked all the e-caps in this particular pedal. I thought I had done it before but apparently not, because I found that C12 (1µF) reads 100nF (being the C7 0.1µF cap parallel next to it).
All the other filter e-caps measure within spec.
I replaced the cap but it made no difference.
Trying to rule out transformer/ switching PSU related issues I tried an all battery setup:
Zoom G3 amp modeler powered by 4 AA cells + headphones.
Holy grail powered by 6 D cells.
It made zero difference. There's still a huge whine (666Hz and all its multiples going to 20kHz and beyond) on the 7805 input, output and finally on the output of the pedal.
Although I tried various filter caps in the past, I used them with leads that were clearly too long. The additional cap + long leads either didn't help or made things worse.
This time I held caps straight to the pcb.
What has helped is adding a 470µF cap at the output of the 7805 (from +out to gnd).
It doesn't need to be directly on the output pins. Anywhere there's access to a +5V Analog or Digital point, I can hold that cap, going to a ground spot nearby and it makes the whine at the output of the pedal inaudible.
But that's all it does. There's still the same whine on the 7805 input and on all the +5V A and D lines and on ground.
So far, to remove the whine on the output of the pedal I can:
- add a small cap in the NFB loop of the output opamp
- add a 1 to 2 k resistor at the output of the output opamp
- add a big e-cap from +5V A or +5V D to ground anywhere on the pcb.
I haven't isolated the sleeve of the DC-jack from the chassis yet.
Only when I crank a JCM800 type amp I can hear a very faint high pitch whine among the deafening white noise. And only when I hold my head/ears in a particular position towards the cab so the tiny whine can beam straight into my ear.
However, that whine is only there in Spring mode and on Flerb. It's gone when set to Hall mode.
Hall mode happens to be the only mode where none of the PIO (0,1,2) pins are connected to ground.
I would have to further investigate if isolating the DC-jack sleeve from chassis would help or if the wire from the mode-switch to ground is better off to another ground spot on the pcb.
Can the 666Hz be caused by ripple current? 'Pulsed drawn' by the dsp chip at 666Hz or other related frequency? Just guessing here as I cannot think of anything else, now that I've tried the all battery setup.
Would it explain why a big e-cap on the input of the 7805 doesn't not help because the source of the whine is after the 7805? But then why is it louder at the input of the 7805 than at its output?
I also wonder if the huge amounts of white noise in this pedal is related to the whine. I'll start another thread to cover cures for the white noise.
I suppose the CPU in that is surface mount? Those flat packages can become moisture traps, but also hide flux residue. There could be spots of low resistance causing higher current pulses.
Was there a version with program keys and a display? That might explain the unused pins that are not grounded and they could be handing out digital hash to nowhere.
Anyway, I'd give it a good soaking with a solvent cleaner in the hope of washing out any crap.
Something that popped into my head a while back. Is there is any correlation between the power supply revision (size of caps and resistors) and the units that oscillate (if that's the problem) ?
Quote from: anotherjim on September 14, 2021, 11:02:43 AM
I suppose the CPU in that is surface mount? Those flat packages can become moisture traps, but also hide flux residue. There could be spots of low resistance causing higher current pulses.
Was there a version with program keys and a display? That might explain the unused pins that are not grounded and they could be handing out digital hash to nowhere.
Anyway, I'd give it a good soaking with a solvent cleaner in the hope of washing out any crap.
It's surface mount.
There's no version with program keys and a display that I'm aware of. The more elaborate versions (Holier Grail, Holiest Grail) don't have any of that.
They're following the datasheet/ app notes as far as NC and GND pins. As well as all the other implementations aspects. The only thing I cannot judge is their implementation of power supply distribution and separation of digital and analog ground. Some important information wrt that is underneath the big chip.
By solvent cleaner you mean IPA?
Quote from: Rob Strand on September 14, 2021, 06:01:46 PM
Something that popped into my head a while back. Is there is any correlation between the power supply revision (size of caps and resistors) and the units that oscillate (if that's the problem) ?
I think I have to come to the conclusion that all of them have whine. If an affordable one comes along I'll buy a 4th and/or 5th pedal just to confirm.
The ones I have where it was actually a problem, those had bad e-caps which were either dried out or had leaked.
I can only guess what caused one or more e-caps to fail in every pedal. Age? Heat from that 90° 7805 regulator inside an unvented box? The oscillation/ripple itself?
Anyway, after replacing those dead caps the whine was still there but no longer objectionable, kinda hard to hear over the massive amounts of white noise this pedal has.
After I added the 470µF cap It became inaudible.
During my probing I was listening through headphones and no audio signal input.
I was just curious to find out what caused it in the first place as people have been whining about this whine for the past 20 years and not a single solution or explanation has been found.
As said before it also depends on what comes after the pedal. It could explain why some people don't have/hear the whine.
I have been using one for years without noticing the issue because I either had a Boss pedal after it or because I used a mixer with the Holy grail set for 100% wet and mixing in the dry signal. And since the wet signal has no whine I never heard it.
QuoteI think I have to come to the conclusion that all of them have whine. If an affordable one comes along I'll buy a 4th and/or 5th pedal just to confirm.
So it's only a matter of degree.
Quote
The ones I have where it was actually a problem, those had bad e-caps which were either dried out or had leaked.
I can only guess what caused one or more e-caps to fail in every pedal. Age? Heat from that 90° 7805 regulator inside an unvented box? The oscillation/ripple itself?
Anyway, after replacing those dead caps the whine was still there but no longer objectionable, kinda hard to hear over the massive amounts of white noise this pedal has.
After I added the 470µF cap It became inaudible.
The interesting thing is there is a degree of whine which depends on the size of the cap. I'm assuming the cap at the input of the regulator. Worst case is stuffed caps which don't work at all.
Oscillation tends to be present then when you put on the means to stop it it stops entirely. The "dialing down" type problems usually mean current pulses along tracks and the bigger caps buffer the current pulse essential preventing the pulse going down certain track. The tracks of concern are usually ground traces.
So maybe the processor is producing the current pulses and the layout has a problem.
QuoteAs said before it also depends on what comes after the pedal. It could explain why some people don't have/hear the whine.
I have been using one for years without noticing the issue because I either had a Boss pedal after it or because I used a mixer with the Holy grail set for 100% wet and mixing in the dry signal. And since the wet signal has no whine I never heard it.
I don't get how following a effects pedal or changing the output resistors can help a grounding issue. If the Boss pedal and the HG shared the same power supply then, yes, you can get cancellations or reductions on noisy grounds. With separate power supplies on each very doubtful it would fix a ground issue.
So at the end of the day I still don't understand what's going on!
QuoteI was just curious to find out what caused it in the first place as people have been whining about this whine for the past 20 years and not a single solution or explanation has been found.
No doubt it's a tricky problem. One obscure detail setting it all off.
The reason for the fizz on the Boss SD-1 was never really identified. That went around for years. The solutions avoid the issue instead of identifying the cause but they do it an good way.
I think you made a good effort - best so far by anyone.
For the moment I've given up. Maybe some day I'll remove all the wiring and try to find out where or how the ground connections have an impact.
On all of the pedals I have managed to bring down the whine to an inaudible level with either (or combined):
- 470 µF cap across the output of the 7805, or anywhere on the pcb from +5V analog or digital to ground.
- 2k2 resistor at the output, soldered on the 3PDT switch, between pcb output wire and the 3PDT switch lug
- smallish cap (100-200pF) in the NFB loop of the output op amp
- isolating the DC-jack sleeve/ground from the chassis. With its shoulder, this jack is already set up for this, just increase the hole and use an insulating washer on the outside.
In the mean time I wrote EHX about the problem. This was their reply:
QuoteWe don't have a solution yet on the Holy Grail but we did find a Holy Grail making the noise plus a Holier Grail and Holy Grail Plus that do not make the noise. We will study all three when we can and hopefully find a solution. This is not a high priority for us at the moment so we're not sure when we'll actually get around to doing this study.
Next up is finding a good solution for the rather large amounts of white noise/hiss these pedals have.
I have a crude solution (boosting the input, attenuating the output) that works really well to increase the signal to noise ratio, but I have to incorporate it into the circuit.
I'll start another thread for that. :)
Big thanks to all who have tried to help and give input, feedback and suggestions.
QuoteOn all of the pedals I have managed to bring down the whine to an inaudible level with either (or combined):
That's pretty good going. A repeatable recipe as well.
QuoteNext up is finding a good solution for the rather large amounts of white noise/hiss these pedals have.
Another can of worms.
Start at the input stage. All bad: inverting stage, large resistor values, noisy opamp (most low power opamps are). However, that goes against the fact you can remove the noise by boosting the input gain. So what do I know!
Who knows, perhaps the way the whine is getting in is also letting in other more random junk from the power supply.
I often disconnect input to stages and connect them to Vref or ground (assuming DC is OK). Sometime you need to add an input cap. If the noise goes away it's a sign something before that point is causing the noise. Can be messy to do on a build board. Not to mention an SMD build.
Sorry to bring this topic back up.
Along with my quest for less white noise I have also been hunting down that 666hz whine again for the past few months.
Although I had previously found solutions to prevent it from finding a way to my amp, internally it's still there.
Quote from: Rob Strand on September 30, 2021, 05:49:33 AM
QuoteNext up is finding a good solution for the rather large amounts of white noise/hiss these pedals have.
Another can of worms.
Start at the input stage. All bad: inverting stage, large resistor values, noisy opamp (most low power opamps are). However, that goes against the fact you can remove the noise by boosting the input gain.
So what do I know!
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...
Back to the whine...
Although reluctant to revive a multipage, years old thread I still think it's best to have all info in one thread.
(Forum software should simply alert users they're about to enter an old thread. I get a warning for replying to an old thread. Users should get that warning when opening a revived multipage year old thread. ;))
Maybe years on, someone comes across this thread and finds it useful to have it all in one place.
As for the high pitched whining noise. Here's an update.
I've bought even more of these Holy Grails. :)
I've also bought other versions of this pedal that use the same DSP chip:
A couple of Holier Grails (using CS4811) a Holy Grail Plus (CS4812) and some V1 Holy Grails (CS4811)
Internally they all have the high pitched whining noise!
It's loud on the 5V lines (analog and digital) and less loud on ground and some ground parts have none.
During one of my tests where I was adding additional caps to ground I accidentally put a charged cap with the wrong voltage on CMFILT. I assumed Everything was 5V or 2.3V (bias) but CMFILT has 3.64V.
Doing this 'stopped' the DSP chip and the whine was gone. After a reset/repower it was back there.
So my conclusion is that it's the DSP chip (or some clock or switching inside it) or the way it draws power that is causing the whining noise.
The way ground paths are set up seems to determine whether the whine makes it into the audio path.
After all these years I think I'm willing to let this issue rest.
I haven't found a way to prevent the whining. I don't think there is one.
The solutions previously posted to prevent it from being heard through an amp still work:
Quote from: myself
- 470 µF cap across the output of the 7805, or anywhere on the pcb from +5V analog or digital to ground.
- 2k2 resistor at the output, soldered on the 3PDT switch, between pcb output wire and the 3PDT switch lug
- smallish cap (100-200pF) in the NFB loop of the output op amp
- isolating the DC-jack sleeve/ground from the chassis. With its shoulder, this jack is already set up for this, just increase the hole and use an insulating washer on the outside.
The two most important ones being:
-replacing dried out electrolytic caps (C8, C12, C15, C20)
-isolating the DC-jack sleeve from the chassis.
I have also traced the PCB, front and back.
*This is still a work in progress. I'll update the pictures the coming days with component numbering and some small changes to the digital parts around the pull up resistors and the off board wiring, and some 'heat maps' where most of the whine is located.
But for now:
Hi-res originals:
https://i.postimg.cc/kJPSY7HF/hg-traced1.jpg
https://i.postimg.cc/pWv9Yq9s/hg-traced2.jpg
(https://i.postimg.cc/7GGqWcCk/hg-traced1.jpg) (https://postimg.cc/7GGqWcCk)
(https://i.postimg.cc/jw7rX79q/hg-traced2.jpg) (https://postimg.cc/jw7rX79q)
QuoteYou 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.