acoustic 360 clone

[yo7604]

hello all,

recently i finished a almost stock clone of an acoustic 360 (minus etf, and regulated power supply replaced with 25 volt dc wall wart).

it sounds pretty good, verry high gain especially when used with my tobias (bartolini pickups).

fuzz is funky, could use some fine tuning though.

but my concern is this: eq controls do nothing at all, up or down.  the eq now sounds pretty much even but i have triple checked my work and i am suprised to find no response at all.

heres the schem: http://www.lynx.bc.ca/~jc/acoustic360piazza.gif

any ideas?

[Eb7+9]

... you mean the Bass and Treble controls do nothing ?? ... if so, maybe the tone stack isn't grounded ... the 360 should cut and boost treble and bass quite a bit when working properly ...

... in the fuzz, the ATTACK control mixes between half-clipped and full-clipped waveforms ... if you increase one or both of the feed caps it alters the overall sound quite a bit (in my personal units I use 0.01uF instead of 0.001uF in the first leg) ... selecting a 2n1306 Germanium NPN device with low leakage is crucial in avoiding a farty sound - using a high gain device (2n5089) as the first fuzz device seems to help focus things also

[yo7604]

i will open it and check that ground, maybe i put in a 680k resistor instead by accident.

the fuzz section cap values could use a little tweaking, i like your suggestion though.

other than that this thieng sounds great and looks cool to. (1u rack space with a pedal that switches bypass, fuzz and bright through opto couplers.)
wish i had a digital camera.

thanks for the help

[Eb7+9]

... through opto couplers

... nice !

[yo7604]

you were right, found a cold solder joint on the 680 ohm resistor.

i would like to try one of those geranium tranistors for the fuww.  i am using a nte100 right now.

thanks for your help.

[downweverything]

you get a lot of gain out of yours? i barely get past unity. is there a gain structure difference in the two different schematics, what transistors did you use? i noticed some of the values are different.  an nte 101 (germanium) works pretty well in the fuzz.

[yo7604]

well to clarify,

i really am refering to gain within the preamp.

i.e. its really easy to start getting distortion on the clean channel.  especially on the high end.  i was thinking of a lower gain 1st phase.

the final output stage drives my amps fine but is relatively tame.

i cant help but wonder if switching the mpsa09 with the last 2n3391 and there respective emitter resistors wouldent help.  or just make the last stage "inverting".

i also used mylar 1u caps through out instead of electolytic, i always got more gain with mylar?

[downweverything]

yeah that sounds more like what mine does too... ive tried a few different bipolars throughout the circuit.  really didnt change much.

[yo7604]

i have a few more questions about this circuit if any one has time:

first of all, i noticed removing the 2n1306 has little to no effect on the ammount of fuzz.  i.e. using no transistor at all here.(i used sockets for expirimental reasons).  I thought this was the fuzz transistor.

secondly, am i correct in guessing that the final result of the gain stages is a out of phase signal from the origional?  with and without fuzz

thanks all
mark

[Eb7+9]

... i noticed removing the 2n1306 has little to no effect on the ammount of fuzz.  i.e. using no transistor at all here.(i used sockets for expirimental reasons).  I thought this was the fuzz transistor.mark

it should make a huge difference ...

... secondly, am i correct in guessing that the final result of the gain stages is a out of phase signal from the origional?  with and without fuzzmark

yes it is ...

... that's why I like sticking an inverting variable-gain op-amp circuit at the output - it guarantees good fidelity over a wider range of loads, offers more gain in case you want to drive the power stage of an SVT or something like it, and the output signal is in phase with the input ...

IMO, the 680 emitter resistors in gain stages 2 and 4 should be replaced with 2k2 or 2k7, this lowers overall gain but increases signal headroom with altering spectral transfer - circuit now has tons of headroom and will not growl or distort like the stock circuit did, if you like that then keep those in ... the resultant gain loss can be compensated with the op-amp driver circuit - usually I try to avoid op-amps in preamp designs but here the high-drive NE5532 really shines ...

... jc

[yo7604]

jc, your right it does change the fuzz alot w/o the 1306, just not so much with the attack all the way up.  my bad dude!

so far as opamps go that sounds like it wold be perfect, but maybe ill just take the sinal off the colector instead (for now).  i was going to go with your kit at first but was afraid it was modded to much. now i am finding myself changing the origional more and more.  now i realize that your design isnt just tweaks but actual improvments to sound and stability.  i sometimes have to learn the hardway.

the emitter resistor change is great.  right now i have the second 3391 in the clean channel replaced with a 3.3k resistor (pin 1 to 3) to deal with the distorting and a little of the high end.

if it wasnt for jc's website i would have been lacking an easily readable schematic and alot of info.  

thanks again to all

[Eb7+9]

so far as opamps go that sounds like it wold be perfect, but maybe ill just take the sinal off the colector instead (for now).  i was going to go with your kit at first but was afraid it was modded to much. now i am finding myself changing the origional more and more.  now i realize that your design isnt just tweaks but actual improvments to sound and stability.  i sometimes have to learn the hardway.

... just so you know, I have two output feeds on some of my early 360 pedals - the original emitter follower and the op-amp ones - just in case ... from trying them out all over the place over the last three years I've concluded that the original output pretty much never sounds as good and clear as the buffered one ... yeah, sticking an op-amp stage at the output is trouble but worth it ... plus it allows to reduce the gain and increase headroom in stages 2 and 4 and then compensate for lost signal gain with the op-amp ... so it works well with the circuit for several reasons, tone fidelity being one of them ...

... btw, I appreciate the trouble of you guys go to trying out alternatives to the route I've taken because at least you also get to check out the two sides of the coin ... this stuff is so subjective that you can't guarantee good tone on analysis and equations alone ... the hard way has its rewards - thanx for the feedback ...

... jc

[downweverything]

hey jc have you tried inductors yet?... i bought all of the stuff but havent got around to winding them yet.

[Eb7+9]

nope, I wish I had the time ... it would be nice to get someone to wind these for us - not even sure if the "other" specs like leakage need to be tight or anything ...

... when I had a real 360 unit in my hands I didn't bother to yank out the coil and measure it for series resistance and the like, I assumed it didn't matter (actually from my sims it only results in slight level loss and no shifting) ... plus out of respect for the amp and its owner I didn't want to risk damaging it ...

I have an insane amount of work backlog right now, sitting for six hours in a rocking chair flipping a popsicle stick around an iron ring is not within my leasure - but then again the original coil didn't seem to be wound around a ring ... I obviously know very little about it, so that's why I came up with a GIC runaround based on simple modeling ...

However, you'll have to let me know how it turns out for you - maybe you can test the resulting circuit on one of those software FFT-based spectrum analysers through the sound card ... and send me a plot of the various Variamp responses ...

... jc

ps. I wonder if some of the signal coils found in Ampeg tube amps are any close in design to the Acoustic ones - maybe they could lead us in the right direction ... wish I had time for everything ...