Another layout and a dsign for those like it heavy by Chris at CDC Fx. No blurb from me, Chris does it better:
Things are rainy and depressing here in California. And also depressing
in the world, in general. So I've been drawing more layouts.
I was inspired by both the Dead Air Sawzall, and the layout another
Dirtbox user submitted to you under the name "Glass Jaw" - with a Bax EQ
in the middle of the two LM386 stages of the Acapulco Gold.
So I came up with a modified Acapulco Gold circuit with a better gain
control (instead of the common mod of a 1m pot on the input, this one
adds up to 10k of resistance between pins 1 & 8 of the 1st LM386)
and "sandwiched" (hence the name, hah) an HM-2-style EQ in the middle of
the two stages. I'm also running this at just under 18v with the
onboard charge pump. The result (I just built it, so it is verified!) is
a a pretty versatile amp-in-a-box with Sunn tonality and a switchable 3
band EQ! Not at all "chainsaw" but really cool sounding nonetheless!
The TO-92 18v regulator is probably unnecessary, since the TL082 can
handle more than that easily, but the LM386-4 is rated to max 18v and I
didn't want to risk damaging them.
Please add the schematics
ReplyDeleteSchematics? Damn (scratches head) I guess I'd have to actually DRAW one in order to do that, then, huh? I used the schematic from the pedalpcb El Sol and added the C10k gain pot between pin one of the IC and the anode of the 10uF cap on pin 8. Then pin five of that IC goes into Ander's drawing of the HM-2 EQ that is on here (there's a schematic for that on his post). I added the 82k resistor going in after the 1m pulldown on that circuit's input and then eliminated the 10uF at the output and just used the 1uF that is just after pin 5 of the aforementioned LM386. Kind of did this all in my head while I was drawing the design and... it worked! It's all extremely scientific over here at CDCE HQ, let me tell you...
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ReplyDeleteIf anyone out there is, in fact, interested in building this monstrosity, I've since made a few changes that are beneficial to the circuit.
ReplyDelete1) removing the link + 1uF cap before lug 5 of the DPDT Eq switch and having lug 5 just connect right to the 68k resistor that goes into lug 3 of the LM386. You can solder that 1uF electrolytic cap directly to lugs 3 (+) and 6 (-) of the DPDT.
2) replace the link that goes from the HM2 EQ section to lug 4 of the DPDT with a 10uF electrolytic with the cathode (-) on the lug 4 row. That way you get a stronger output from HM2 EQ going into the 2nd LM386. When this section is bypassed, you still get the stock Acapulco Gold value with the 1uF cap on lugs 3 and 6.
3) reducing the 82k resistor just after lug 1 of the DPDT to 47k. This keeps the gain level going into the EQ section high, actually teetering on the edge of "too high" but it sounds more brutal and appropriate to my ears.
4) reducing the value of the 220uF filter cap on the EQ section to 100uF - no audible difference but the higher value was not really necessary since there is a another 100uF filter cap on the power supply all ready going to the LM386 chips.