PaiA Axe Grinder problem

[Tony Forestiere]

The interchange and comradery of this forum has truly inspired me. I have recently cracked open my long ago banished trove of pedals, and have started to mess with them. (I've been playin sans effects for about 10 years.) Came across my favorite distortion/overdrive pedal- a PaiA Axe Grinder built in 1984! Now I remember why I ditched it...by itself it grinds, sings, and is so easy to dial to an infinite variation of TONE...but it won't play nice with others  :cry:  For some reason, any other effect plugged in before or after the AG loads the output down to nothing, but off mode works! I have checked and re-checked input and output buffer wiring and component placement (as I did 10+ years ago) to no avail. :x  Anyone run into this type of scenario? I would really like to play this disto/od with my Electric Mistress and soon-to-be modded Small Stone (actually sounds cool through a Rockman Soloist!) Thanks for this AWESOME platform all of you pedalheads.

Regards,
Tony

[J.Nadge]

Hmmmm.... You can sort of see where voodoo labs may have gotten their idea, when you look at the Axe Grindger...

Anyway, I know you have triple checked your wiring, but I don' see how it could be the circuit design itself.  The input impedance is very high, while the output impedance is very low.  

Did you use any other resistors as pulldown resistors around the switch?  The switch itself could have problems.  Or, (hate to say this) it could be a wiring problem.  Last, might be worth the effort to check the jacks and chords.

When you say loaded down, one would assume you mean less signal and less high end.  The fact that this occurs at the input AND output seems strange.  Makes me wonder what other circuits/effects you are using in conjunction.

Also, as a stab in the dark it might be worth double checking the values in your tone section.


Sorry, for the "buck shot" response.  Good luck!

[Mark Hammer]

The Axe Grinder output stage is a strange one, largely because of the switching scheme.  One of the things PAiA/Anderton tried to do with all their effects pedals was to retain SPST footswitching.  I gather this had something to do with keeping costs low for them and consumer, and probably had something to do with being able to add on remote footswitching capability.  SPST footswitches can be hived off to another assembly with a simple mono or stereo phone jack.

The output stage consists of an inverting op-amp set up as a mixer.  10k feedback resistor, 4k7 input resistors, non-inverting pin set to Vref, and a mere 1k resistor between the output pin and the output jack.  That particular "hasty exit" may be the source of your difficulties....or maybe not.

The effect always remains in circuit, and the switching scheme I have in front of me simply reverts back to something near unity gain by shunting some specific resistors...more or less.  This is why I am perplexed.  If what the switching scheme does is essentially change the "settings" internally to produce a clean signal, without doing a damn thing to the input stage or output stage, why should it matter if the pedal is in engage or bypass mode?

Having said that, I'm going to take a really wild guess and suggest that maybe you either have a) a mixing cap flipped around the wrong way, or b) the 4066 used for switching is partly fried.  

Why the cap? Bear in mind that one of the things the switching scheme does is flip between two versions (boosted and non-boosted) of the clean signal, with each having their own path to the mixer.  The polarized caps are oriented (at least in the schematic I have) with the "+" side towards the mixing stage and the "-" side towards the mix-level pots.

That may explain the weirdness about bypass, but it doesn't explain why the poor interaction between pedals.  There, I'm guessing the 1k resistor may be the culprit, especially since it has no DC-blocking cap on the output.  On the other hand, since just about every sensibly-designed pedal has a DC-blocking cap on its input, I can see why PAiA thought to shave a few cents off product cost in that manner.

[Tony Forestiere]

Thanks for the input guys. Mark, I may try to circumvent the entire switching setup, keeping the effect "hot" all of the time. This should clarify if the 4066 is the culprit, or if the loading occurs in the effect stage itself. thanks for the quick feedback (pun not intended  :wink: )

By the way, in which time zone are you guys? Europe I think...

Appreciate all new thought, and will keep you posted.

Regards,
Tony

[Tony Forestiere]

Replaced the output jack. Original was a generic Taiwan that the housing was able to twist. I don't understand how it was able to pass a signal in "off" mode, unless the circuit load pulled more current (go figure) :oops: .

Thanks to Mark and J.Nage for your responses.

All of you guys are a great resource!

BTW... if you bust open an old Canon copier (NP 400,500,250,270,350) and look at the potential control PCB, you might find the elusive gennie JRC4558 with the silver printing. They were used as comparator circuits.

Best to all the pedalheads,
Tony

[kevin_taylor]

2004->2022 I had an identical issue. I pulled my kit built Paia Axe Grinder out of the closet. It played well by itself, I really like the clean boost, but did not like to be in a pedal chain no matter the order. I found Tony's post and that he fixed it by replacing the jack. I replaced the output jack and resoldered the input jack and sure enough it fixed the issue. It's been a long time since 2004 and don't know if the original poster will see this, but thanks for the tip!