Earthquaker Devices - Acapulco Gold  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.

Re: Earthquaker Devices - Acapulco Gold

Postby EBRAddict » 14 Nov 2015, 16:31

When I look at the datasheets for this chip many times it has a 4.7nF cap in series with a 10 ohm resistor to ground at the output pin 5 before the output coupling cap. So I think the bleed to ground theory is sound.

I might monkey around with a pot as a voltage divider on the inputs and a pot in the gain loop of the first IC. I'm using a NS LM386N1.

Image

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Re: Earthquaker Devices - Acapulco Gold

Postby captain_tango » 14 Nov 2015, 20:20

Nocentelli wrote:Whereas in this proguitar shop demo, he has the level knob really high: I am guessing this is massively driving a nice tube amp, and contributes to the smoothing out of the slightly yucky decay (even though, if you watch carefully, he never allows the note to fade out to silence)




I have also noticed this, playing with the circuit in front of an amplifier. If you set the volume high out from the circuit, the ugly decay lessens a bit. Using the JRC386D or the LM386 N-1 also helps a little. I timed the sustain of the three chips I had and the the JRC seemed to consistently work the best. The N-1 is nice too, and the cheapest Tayda 386L ones are noticeably worse. I hate to put things down like that with magic numbers and out of production stuff winning in unscientific tests like this, but I don't think I'm biased here.

Thanks everyone for your work so far. I'm learning a lot
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Re: Earthquaker Devices - Acapulco Gold

Postby EBRAddict » 15 Nov 2015, 17:29

I had some success. The breadboard is still a little noisy but the splatty decay and fizzy artifacts are gone. The biggest improvements were using an isolated power supply instead of a battery and replacing the crap capacitors with good ones. The center section of the circuit still needs some work; both halves sound excellent on their own, it gets noisy connecting them, the 10k got it manageable but there is room for tweaking.

A well shielded enclosure and a ground pour would really help--if I move my hand near the center section of the circuit it picks up a conversation in Mandarin, it sounds like my neighbors using a wireless headset on Skype.

Most of the changes to the prior schems are pulled right from the NS and JRC datasheets.
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Re: Earthquaker Devices - Acapulco Gold

Postby EBRAddict » 15 Nov 2015, 17:40

C5 should be flipped so the positive side is towards IC1
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Re: Earthquaker Devices - Acapulco Gold

Postby danndubblewe » 16 Nov 2015, 01:40

Boom. About to make a quick crummy draw up of where the 4N7/1uf connect on the traces but here's some more detailed board shots
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Re: Earthquaker Devices - Acapulco Gold

Postby danndubblewe » 16 Nov 2015, 01:45

sweet photoshop skills in action!
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Re: Earthquaker Devices - Acapulco Gold

Postby Hexjibber » 16 Nov 2015, 16:01

So are we saying like this?

Image

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Re: Earthquaker Devices - Acapulco Gold

Postby EBRAddict » 19 Nov 2015, 03:19

In his 2006 book "Advanced DIY Effect Pedals" Brian Wampler (Indyguitarist here at FSB) had a very similar circuit to the Acapulco Gold called "386 Fuzz" using two LM386 chips in series like this. Members can find the download link in the Davidoff Library subforum on the #1 PDF file, pages 31-32. There's a ton of useful info in those books.

http://www.freestompboxes.org/viewtopic.php?f=70&t=16716#p185781

His circuit is somewhat different:

He suggests a variable 1M voltage divider between the two chips for controlling unruly noise
He leaves Pin 2 on each chip floating (???)
470pF to ground at the input (Pin 3) of each chip
Both chips have the Pin 1 & 8 connected (no cap or resistor)
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Re: Earthquaker Devices - Acapulco Gold

Postby jwhtn » 20 Nov 2015, 21:24

Hi, guys. I think this pedal sounds great in the clips I've heard. I've been messing around with 386 chips for a while and recently built a Noisy Cricket amp, which gets all of its half watt of oomph from a 386. With the talk of just how loud the Acapulco Gold is, I'm wondering if it will drive a cab. The Cricket will drive an 8ohm Swamp Thang to a reasonable bedroom level. Has anyone tried just skipping a separate amp entirely with this pedal? I'm out of 386s at the moment, or I'd give it a shot myself.
Thanks!
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Re: Earthquaker Devices - Acapulco Gold

Postby bigbonedstacks » 21 Nov 2015, 23:09

So what would I have to do to make this layout work? Just use the appropriate values for the caps? Is anything in the wrong orientation?

Image

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Re: Earthquaker Devices - Acapulco Gold

Postby albru80 » 22 Nov 2015, 19:51

This is the latest verified layout.
You can find more infos here:
http://tagboardeffects.blogspot.it/2015 ... -gold.html
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Re: Earthquaker Devices - Acapulco Gold

Postby FiveseveN » 22 Nov 2015, 20:51

jwhtn wrote:I'm wondering if it will drive a cab.

Only with the volume control full on, and even then there will probably still be too much residual resistance compared to the speaker load. Also the 1 uF output cap forms a 20 KHz high-pass filter with an 8 Ω speaker.
Of course there is little you need to modify in order to add a proper speaker output.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)
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Re: Earthquaker Devices - Acapulco Gold

Postby jwhtn » 24 Nov 2015, 01:19

An update: I picked up some 386s to experiment with this circuit. As laid out, it drives an 8 ohm Swamp Thang, but barely. Just for the hell of it, I stuck another 386 on the end of it, basically just doubling the second stage in the schematic, and it absolutely roars. Right now it's super high gain and oscillates when you stop playing -- which may just be due to my sloppy test rig -- but there is a pretty great raging amp tone in there. I need to lay it out properly with shielded cable and a gain control, but I think this might be a cool alternative to the tame Cricket/Ruby/Smokey practice amp circuit.
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Re: Earthquaker Devices - Acapulco Gold

Postby johnk » 01 Dec 2015, 03:31

I just finished mine. it's in a 1590A & I added a gain control. IMO, it's 1000X better with it and it sounds MASSIVE!:

Image

Image

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Re: Earthquaker Devices - Acapulco Gold

Postby gigelmargel » 01 Dec 2015, 08:34

johnk wrote:I just finished mine. it's in a 1590A & I added a gain control. IMO, it's 1000X better with it and it sounds MASSIVE!:



Nice work John, as usually :)

Can you tell me how you wired the gain pot?

Thx!
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Re: Earthquaker Devices - Acapulco Gold

Postby johnk » 01 Dec 2015, 09:53

I just used a C1M at the input.
input to lug 3 and lug 2 to the input of the circuit.
it's basically like rolling you guitar (or bass) volume down.
with it full up, it's like a stock Acapulco gold.

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Re: Earthquaker Devices - Acapulco Gold

Postby Hexjibber » 01 Dec 2015, 12:03

[quote="johnk"]I just finished mine. it's in a 1590A & I added a gain control. IMO, it's 1000X better with it and it sounds MASSIVE!:

Image

That looks great! I'm thinking about doing a board for this, is the schematic I drew verified as correct now then presumably?

Will probably add the gain control pot option as well.

Cheers!
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Re: Earthquaker Devices - Acapulco Gold

Postby johnk » 01 Dec 2015, 17:25

yours is the schematic that I used to make & etch my PCB, so yes.

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Re: Earthquaker Devices - Acapulco Gold

Postby Hexjibber » 01 Dec 2015, 17:37

johnk wrote:yours is the schematic that I used to make & etch my PCB, so yes.


Perfect, thanks John, I appreciate it! :)
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Re: Earthquaker Devices - Acapulco Gold

Postby Hexjibber » 01 Dec 2015, 17:45

johnk wrote:yours is the schematic that I used to make & etch my PCB, so yes.


Just noticed you have an extra cap on your layout, was that some extra power filtering at a guess?
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