chongwui wrote: ↑21 Jul 2023, 22:14 Thanks for sharing this info. I fixed my unit by replacing C8.

That's great to hear. Thanks for posting.

Thank you for the help! My HG has no wet signal, but dry signal passes no problem. Every cap I measure, however, is reading much lower than it should, or they reading as overload. Do you know that might cause this issue? Thank you in advance! It probably means those electrolytic caps have dried out...

Hey! How did you test each cap? I'm assuming testing them in the circuit won't work. I did test them in circuit. Worst case scenario, you're reading additional caps in parallel. The values of parallel capacitors add up. If you measure a 10µF cap and it reads in the pF range, then you know there's s...

The regulator getting hot is 'normal'. I have several of these original Holy Grails, and they all run equally hot. On the surface of the 7805, I measure a temperature around 95° C (203° F). That's with the pedal open... I think the spec sheet somewhere lists 120° C as a limit. Most of these pedals h...

Maybe recheck your drawing of the HB Attenuator, my guess is that the NEG speaker output is also at Common/Ground to input, you can easy check with a meter to see if it is Common. Also the 10uF on the Bridge Rect is upside down. Thanks. Both correct. I've added a corrected version of the schematic ...

This post is mostly for documentation purposes and for future reference. Maybe it can help someone fix their broken Holy Grail. I recently got a used, older big box Holy Grail (pointer knob, Rev A, non true bypass) Though advertised as 'in good working order', there was very little reverb. Only with...

A100k seems like a good value for input resistance (impedance) and for the volume pot but it is completely useless for a gain/fuzz pot. I see there's a B1k pot in the picture of the actual pedal. That would make an excellent gain/fuzz pot. Maybe you can check and then update the schematic. Thanks fo...

I guess measuring the output voltages of any EHX PSU would prove useful then, and having these measurements clearly marked as well. Maybe it's more useful to find out which pedals use that 7809 chip. The pedals using the 7805 will work with any psu (9V, 12V, 24V, regulated or unregulated, all plent...

That's very close to the 14.95V I'm measuring for my 9V/500mA Holy Grail PSU.
(I was updating my post above while you replied.)

Excellent question. The Deluxe Memory Man says 24V on the enclosure but the power supply that comes with it delivers around 35V (unregulated/unloaded) and gets regulated down to 15V. (LM7915) The Holy Grail says 9V on the enclosure but internally it is regulated down to 5V (78M05). I never checked t...

Looks weird having a bridge rectifier as part of the speaker circuit Here's another project using a similar setup: https://i.screwtopdb.com/ftl274mqd.jpg https://arduino.openexpanse.com/en/arduino.openexpanse.com/article/id/330 I measured the AC voltage at the speaker output of my amplifier and it ...

Here's what I traced when I got the unit which is slightly different from the schematic posted above. I didn't trace the line out or the mic out btw.

Thanks for the reply phatt. Great post, highly informative! Love the load test smiley. :) I'll check out some of the references (UA, Guytron). Bottom line is that Mr. Benton did well making the resistive load higher and that I certainly shouldn't change that 16Ohm switching jack to get closer to 4 O...

Oh, and because the thermistor and pot values were missing in your schematic.

(where's the post edit button?)

I'm not seeing any difference between your schematic and mine (other than mine has all the header connections). Maybe I'm missing something. What makes it the "correct" one? You gave the impression having doubts about the one you posted so I posted one from a pedal I traced. Yours is nice...

Bside2234 wrote:

j_flanders wrote:Here's the correct schematic:
Which is what I have but the negative of C3 clearly goes to C5 on the PCB.

Correct, C3 neg to C5. Thanks.
Corrected my schematic:

Here's the correct schematic:

It's a Harley Benton Power Attenuator. In this web has a schmeatic: https://blog.brixit.nl/blog/2016/2/harley-benton-power-attenuator-measurement-and-teardown/ I measured all the amp inputs: 4Ohm: lpad min: 8.3R lpad max: 16.6R 8Ohm: lpad min: 12.3R lpad max: 20.6R 16Ohm: lpad min: 16.3R lpad max: ...

Frequency reponse of the delay / feedback signal. Level and mix set for unity gain, feedback at 50%. In real life the signal coming out of the bbd section has been filtered by the anti-alias filter and the reconstruction filter, but to see the effect of the differences between the DMM and VM1 feedba...

Some more frequency responses. The dry signal as it arrives after the compressor, just before the anti alias filter and the BBD section for the Deluxe memory man: (Level and mix is set for unity gain, feedback is at 50%) DMM_INPUT_TO_AAFILTER.jpg Same thing but for the VM1: The VM1 delivers a much m...