Acoustic 360 Fuzz

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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Solidhex
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Post by Solidhex »

I've noticed no one has mentioned that the original Acoustic 360 uses a NPN germanium for "Q2" in the fuzz section. The section resembling the Fuzzrite. It was a 2N1306. You can't always throw in a low gain silicon and expect the same results.


--Brad

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Dr.Pain-MD
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Post by Dr.Pain-MD »

Yeah, we did notice that, but we're trying our best with some silicon trannies in its place right now as far as I can tell. Cheers. :)

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Post by Barcode »

Solidhex wrote:I've noticed no one has mentioned that the original Acoustic 360 uses a NPN germanium for "Q2" in the fuzz section. The section resembling the Fuzzrite. It was a 2N1306. You can't always throw in a low gain silicon and expect the same results.


--Brad
Barcode wrote:... I'm guessing the biasing for the second stage 2n1306 replacement needs to be altered, 2n3904 not being suitable as having a much higher gain. The datasheet for the 2n1306 device shows a gain of about 20, so I'm guessing we need to find a better replacement than 2n3904, which has a much higher gain. Since 2n1306 is a Ge device, the biasing resistors for that stage probably need adjusting too....
:)

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Post by Barcode »

By the way, NTE shows a cross reference part number for that transistor of NTE101, which can be had fairly cheaply:

https://cgi.ebay.com/ECG101-NTE101-REPL ... 3cb0dab33b

But I'd still rather attempt to get it biased up with a Si...

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Post by Solidhex »

Ah

Sorry about that. I searched the page for the word "germanium" so I didn't see it...

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Post by Barcode »

A bit of good news! My buddy and I pulled the currently-not-passing-signal 360 out of my garage. I pulled the fuzz board (carefully so I can reattach...) and wired it up on my 25v charge pump and VOILA! it works and sounds AWESOME...

So... we now have a comparison unit for voltage purposes. Just an FYI, while both the source schematics we have looked at are identical in all other aspects, the piazza one lists the correct transistors. This thing sounds pretty damn good, but I actually think that once we get a Si working in there, it'll sound better to my ears. It's got a soft buzzy edge on the otherwise great fuzz that a lot of people like, but I like a little harder edge on my clipping. I'd box up the board from the preamp as is though, and love every minute of it!

So it looks like the voltages on the factory unit are as follows

q1=who cares, it can be omitted

q2 (Ge)=
C: .114
B: .048
E: 0

q3 (Si)=
C: 2.2
B: .561
E: 0

Q4 (Si)=
C: 25.33
B: 18.90
E: 19.68

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Dr.Pain-MD
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Post by Dr.Pain-MD »

That is so awesome, thanks for doing that! How awesome is it that you have an original 360? I'd love to build a full on 360 preamp someday and use it with my 300, but the fuzz will do for now. :twisted:
Any word on rebiasing the transistors? We should try to find a good replacement Si tranny for the germ original since I don't think there's a point in trying to replicate that 100% of the way. Any ideas at this point?

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Post by Barcode »

Dr.Pain-MD wrote:That is so awesome, thanks for doing that! How awesome is it that you have an original 360? I'd love to build a full on 360 preamp someday and use it with my 300, but the fuzz will do for now. :twisted:
Any word on rebiasing the transistors? We should try to find a good replacement Si tranny for the germ original since I don't think there's a point in trying to replicate that 100% of the way. Any ideas at this point?
Well, I don't really know which part numbers might match the gain, and I would need to throw it on my breadboard with some trimpots to rebias it, and I don't really have time. It was quicker for me to etch a board! I hate breadboarding....

Anyhow, I'll see if I can figure it out in the next couple of days. In the meantime, I'll also try to record a sample for comparison.

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Post by Dr.Pain-MD »

Barcode wrote:Well, I don't really know which part numbers might match the gain, and I would need to throw it on my breadboard with some trimpots to rebias it, and I don't really have time. It was quicker for me to etch a board! I hate breadboarding....

Anyhow, I'll see if I can figure it out in the next couple of days. In the meantime, I'll also try to record a sample for comparison.
So wait, I'm confused. Did you get your copy working already? :hmmm:
I realized that those original 360 values that you posted are the bias points we should be aiming for. I'll try looking for a good replacement for the Ge tranny when I have some time.

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Post by Barcode »

Dr.Pain-MD wrote:
Barcode wrote:Well, I don't really know which part numbers might match the gain, and I would need to throw it on my breadboard with some trimpots to rebias it, and I don't really have time. It was quicker for me to etch a board! I hate breadboarding....

Anyhow, I'll see if I can figure it out in the next couple of days. In the meantime, I'll also try to record a sample for comparison.
So wait, I'm confused. Did you get your copy working already? :hmmm:
I realized that those original 360 values that you posted are the bias points we should be aiming for. I'll try looking for a good replacement for the Ge tranny when I have some time.
No, my copy isn't working yet, but my original fuzz board from the original unit is. Those bias points above are from the original. I have some 2n3133's that fall in a similar gain range to the original transistor, so if I can ever find the time to breadboard, I can try to bias it up with that.

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Post by RnFR »

wow, those voltages look rather low. did you measure the power rail after that 68k dropper resistor? also, can you double check c4(.15)? it seems like there is some discrepancy on ag's schematic.
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Post by Barcode »

RnFR wrote:wow, those voltages look rather low. did you measure the power rail after that 68k dropper resistor? also, can you double check c4(.15)? it seems like there is some discrepancy on ag's schematic.
Good eye. Looks like according to the piazza schem C4 should be 150pF (150mmF) which sounds more likely and matches the markings on my original upon closer inspection.

Those voltages were taken from the functional original right at the transistor legs, so they are pretty dead on. I've deleted all the other schematics of mine posted in this thread and have redrawn with the corrected value of R10, C4, and the transistor part numbers.

I just got a lot of 23 pieces of 2n3391 and some low gain Ge devices on ebay, so in a few days when they get here I'll try those and see what I can come up with.

I'm thinking a 100K trimpot in place of R8 might allow me to dial in a different Ge by ear? Thoughts?

https://i85.photobucket.com/albums/k42/ ... ematic.jpg
Acoustic360FuzzSchematic.png

Gutshots of the fuzz board from the original:

Image
Image
Image

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Post by Barcode »

SUCCESS!!! Okay, I've built up a unit using 2n3391A's and a GT404 in the Germanium position, running off 9v with R10 jumpered. It's very close. It sounds very good, however it's got a little less volume than th original, and the low end of the attack knob is a little muddy. SO I think it's probably because of the A suffix on the 2n3391's. Probably slightly different spec.

Anyone think the lack of volume could be the lower voltage going to the last stage?

I did this with a drop-in replacement with no tweaks (except removing R10), and it's pretty dead on, so I'm guessing devices in he Ge position just need to be of similar gain. Thoughts?

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Post by gus »

The output stage is an EF check the emitter voltage maybe adjust the base to 9VDC resistor for the bias. I don't like the biasing used for the EF

If you want to adjust the 2nd transistor C operating point adjust the C to B resistor not the 47K.

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Post by HydrozeenElectronics »

This is great. You should post a youtube vice of the original and yours for comparison. That would be sweet!

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Post by disorder »

I've been simulating this circuit.. have the 6.8k/zener trans omitted, 9v power, 150hfe on Q1 and Q3, and 20hfe Q2. Gain control 3/4 up, attack 1/2 up... I get the following voltages..

Q1c - 4V
Q1b - .625V

Q2c - 2.75V
Q2b - .562V

Q3c - 9V
Q3b - 4.42V

Q1 crushes the top swing of the signal, flattens it, and the bottom swing is greatly amplified.
At the collector of Q2 the signal is a jagged sine which I guess makes sense. Q3 has a gain of 1.

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Post by Pigyboy »

Thanks for all the info in this thread. I have a bunch of 2N1308 NPN Ge's here and want to get to this eventually.
Barcode...have you messed with this lately?
Cheers,
Chris

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Post by Barcode »

Pigyboy wrote:Thanks for all the info in this thread. I have a bunch of 2N1308 NPN Ge's here and want to get to this eventually.
Barcode...have you messed with this lately?
Cheers,
Chris
not lately, but the original circuit board is still laying on my bench for me to get back to developing a workalike. I have a functioning layout, but I'm still trying to tweak to find a way to use modern or common transistors to get the same sound.

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Post by Pigyboy »

Hi Barcode,
I am going to try this out over the next weeks and I will post regularly once I do. I have always wanted to have one of those amps and love the fuzz section. I need a bit of time here before I go into it but I will do my best to help it along.
Thanks for the response.
Chris

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Post by Barcode »

Pigyboy wrote:Hi Barcode,
I am going to try this out over the next weeks and I will post regularly once I do. I have always wanted to have one of those amps and love the fuzz section. I need a bit of time here before I go into it but I will do my best to help it along.
Thanks for the response.
Chris
Did you ever get around to building this? Also, Once I get this tweaked, I'll be doing a limited run of builds on it if anyone is interested (limited run because of the limited number of NOS transistors I have!)

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