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Old 12-19-2013, 01:16 PM   #1
pinkjimiphoton
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hi, re:Jim's Kay 704 distortion/tremolo

man... was hard to find out where i found it mindlessly surfing the net...

turns out it was here in what appears to be a deleted thread.

first off, hi, i'm pink jimi, some peeps may already know me (hey!! keep yo hatred!! lol)

nice place, look forward to lookin around some more!

anyways, i'm a fuzz monger and am always building weird stuff to sooth the fire, and a ways back i came across this schematic during a google search for an old kay guitar amp i was restoring, and i found this thread where some kind gentleman named jim
had built hisself a fuzzboxular unit out of the circuit of an old kay 704 guitar amp.
it also appeared he had a prob getting it working again after the breadboard stage from the thread.

sometimes poo happens. it gets us all.

anyways, if he/you/jim sees this, i just wanted to say thanks man, i built your project minus the tremolo, cuz that would have led to me abusing it...one of my earliest forays into electronic noise was taking the courtesy speaker out of my kay 707 and feeding it into the tremolo side. the tremolo of course is an oscillator, and you could get some very theremin-like but extremely loud sounds out of it by manipulating the tremolo/volume and tone. do NOT try this at home please. i digressed. again.

anyways, jim, thanks man, i built your project, even went so far as to buy a mess of the proper transistors for it NOS.

built it last nite to your exact values, my vero matches each node point to point.. tho i did make a couple mistakes i rectified on building...

and this little bitch ROCKS dude. yes, it sounds like poo, but in a very good way... it sounds just like these things did when dimed. it's kinda like an overdrive thru a cocked wah, very warm and kinda... not quite brown, more like...tan? bronze-ish?
i dunno.

i left off the trem circuit cuz i didn't really need it. i may add it on later.

used a bog standard 3904 for the third q. may go all ge like the original.

i reccomend going up to a 100k gain, 50k tone and 50k volume... opens it up a little more, makes it scream.

it only really sounds good close to dimed... just like the real thing.

anyways here's a verified vero of it if invader jim is still around, and my thanks man.




peace out. if anyone builds it let me know. jim...thanks man, whomever you are.. i still have the schematic and thread archived if you don't mind it being shared if you do, i'll delete this man.

peace.
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Old 12-19-2013, 02:36 PM   #2
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Hey, dude. I'm glad you got some use out of it. Man I did this a long time ago indeed. I still have the thread and all of my old pics archived, as well as the stuff I found while researching the original amps, including a sound clip. I even made a Sketchup drawing of the cab based on measurements and my firsthand experience of an actual amp. I went nuts trying to clone one of these. Still haven't found one for a good price, though...

I had this thing on the breadboard and it sounded pretty damn good. By the time I got onto perf it didn't sound quite the same. Could be that breadboards are sloppy with stray capacitances, could just be me. I don't know. I was just never fully happy with it. I actually still have my prototype. I didn't have a proper enclosure so it is housed in a cardboard box. I did some mods later on it to try to convert it back to an amp, as was my original intention. Never got it working though. Eventually I plan to try it again and start fresh.

BTW, I used 2N1302 transistors, not 2N3102. Q3 was a plain 2N3904 because Ge distorted in a bad way as it got warm. I found that Q2 does most of the distorting and that if I tried to use a Si as Q1 then it wouldn't work at all because, I'm assuming, the bias was too low.

In the interest of full disclosure, I kinda winged the trimmers. I never used them (probably should have) so I had no way to adjust the bias of the transistors. I wasn't even sure they would be effective when I drew them into the diagram.

If you decide to build the trem, you'll need a 20k pot for the Strength control. Any lower and the trem is too subtle. Any higher and the trem sound is only controlled over part of the pot's rotation.

Any chance you could post pics of your build?

Here's my original diagram, albeit I have re-drawn it. The circuit is the same, just re-arranged. Again, I winged the trimmers.


And the PCB layout:
http://i40.tinypic.com/6hqnuv.jpg

To this day nobody has figured out what HT-704 Stampede means...
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Last edited by Invader Jim : 12-19-2013 at 02:39 PM. Reason: typos
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Old 12-19-2013, 03:41 PM   #3
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well, i assumed the 704 was the model of the amp. i figured stomped cuz you're stomping on it but the rest eludes me, i must admit.

i built a little amp in a lunchbox for dick wagner (yeah, THAT dick wagner) a year ago, and tho all the parts worked ace when apart, combined it made me CRAZY. sometimes stuff just happens.

so i spent 28 bux on the wrong transistors? ooops. npn ge's. they sound great. a couple duds (as expected) but 6 out of the 8 were ok.

i used 2n3904 in my build for q3. makes it a bit louder without making it too harsh.

i'll be glad to post some pics... it's not real pretty, but it works.

if you change the values of the three pots, you can get a little more signal out of it.

gimme a little bit bro.
i've got the first page of the thread as a pdf, but would love to see the second if possible.

thanks.
back shortly... will try and shoot a little video of it today so you can hear it.

peace out
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Old 12-19-2013, 03:45 PM   #4
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brain dEAd... i miss-spelled the names of the transistors. oy....

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Old 12-19-2013, 07:55 PM   #5
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i found a mistake on the vero. now it doesn't work at all. arrrrrgh...
well the vero wrong, it will work.

sorta..

gotta gig tonite, let me play with this some bro
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Old 12-20-2013, 03:40 AM   #6
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PM sent.

It is probably better that you used the 3102 transistors rather than the 1302. I used 1302's because they are the only NPN Ge's I had. I'm really glad it ended up sounding like the original amps. That is exactly what I was aiming for. That alone makes it seem worth a second go on my workbench. I think I'm getting the itch to build another one of these.
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Old 12-20-2013, 11:41 PM   #7
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hey jim,
been playing with this some more.. first stage works great.
second and third don't seem to be doing much.

gotta couple questions... the 4.7k at the node of q2c and q3b supposed to go to b+ or ground?

are you sure the 1m/10p rc network should go from q2b to the OUTSIDE of the output cap and not to b+?

shouldn't there be a resistor between q3b and ground?

onwards and upwards.. we'll figure this out eventually.
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Old 12-21-2013, 05:56 AM   #8
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1- The 4k7 (15k trimmer in my earlier diagram) goes to B+.

2- On the original amps, the RC went directly to the speaker. For the pedal version I put it directly on the output jack. I honestly don't think it has any effect in the pedal version.

3- The amps had a resistor on the base of Q3 going to the (negative) supply voltage, so in an NPN circuit this resistor would go to B+. The 100R trimmer takes the place of the driver transformer's primary coil.

Here is the schem of the amp.
http://i39.tinypic.com/2dtt6ic.jpg

Here it is drawn like my earlier diagram. This is the way I was planning to build my amp clone, sans mods.
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Old 12-21-2013, 09:20 PM   #9
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diggit.
i have now got it working on the original vero i posted, but i had to make a couple changes.
i had to (obviously) add a jumper from q2c to q3b, which i'd forgotten somehow...
also didn't like the way the 1m/10p rc was hooked to the output.. don't want dc on the output signal!! seemed to me the typical thing to do would be to connect it as a feedback shunt between q3 b and c instead, so that's what i did.
it worked.
we have fuzz and overdrive, and it's fairly loud.
i bumped up the fuzz pot to 100k, the tone pot to 50 k, and the output to 50k as well from the 10k it was.
changed the feedback resistor from q3 b to c to 470k, a bit more gain.
dropped the 3.3k resistor from e to ground of q1, made it 47r instead. bumped the gain up quite a bit. can still get the kay tone, but takes it beyond and up to a nice fuzzy distortion when dimed.
made all three trimmers 10k, also.

i will post a fixed vero and quick revision of the schematic once i get it done.

having a bit of a hum issue, but i didn't add any power supply filtering and it's not boxed yet, so hoping that adding both will cure it.

stay tuned man!! peace!
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Old 12-21-2013, 10:38 PM   #10
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ok, here's the slightly tweaked schematic.
original values do work, this has slightly more balls.
i changed where the 1m/10p connect... to the junction of the q3c and b+.
seems to work well!!
didn't add power supply filtering etc to the vero, just the basic circuit.

first, schematic:



here's a vero, i'd check it first, as i didn't build this yet, i adapted the previous one:



will try to post audio soon...
peace out!
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Old 12-22-2013, 01:53 AM   #11
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it's built, it's running, and it freakin' screams.

i toyed with paralleling the input cap with a 220n cap... dude. it's pretty sick. may be worth a switch.

with the gain down low, it sounds surprisingly like the amp did, or i think it did, it's been like... how long ago is 77?

as you juice it, it gets a little dirty thru crunch to overdrive to distortion to fuzz.

plenty of output baalz, too. i ended up going all GE in the end.

by putting the rc to b+ if doesn't seem to change the tone, but it does seem to stabilize it. i'm always leary about letting any signal out that doesn't pass thru a coupling cap. q3 doesn't seem to get as heated up... negative feedback or something? i dunno..

should have some video soon... and i did get the right transistors, i just can't type.

thanks brother jim <<nice name, that.
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Old 12-22-2013, 10:46 AM   #12
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That's it, I'm going to revisit this one. Sounds like a killer little circuit. Glad you got it working using the same transistors I used; now I don't have to buy any. I had thought about doing this again, without the trem this time. The trem was a hassle and seemed to cause problems. Plus omitting it lowers the parts count.

Part of the noise issue could be that you built it on vero. Lots of excess conductor length there. If it were me, I'd cut off the ends of the traces after the first and last solder joint where they aren't used. I've never built on vero, though. I always use perf.

I forgot to mention, my prototype has a switch to bypass the second and third stages, so that only the Q1 circuit is used as a booster. The output level was unusably low, however. Hopefully I have enough good 1302's to make this circuit with your mods.
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Old 12-22-2013, 11:32 AM   #13
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i looked at the schematic of the amp (wondering if this is the one i uploaded years ago... i had to pay for one, so i figured if i paid for it from some schmuck, i owned it so up it went.

the rc on the original is a hardwired presence control. if you want it to be effective in this situation, put it before the output cap. you need to block the dc from the output, and this is allowing feedback between amplifier and pre-driver stage in the original like a tube amp,

tie it to b+ and it still works. makes the circuit more stable.

the bigger cap on the input can sound great, but had a tendency to motorboating with the gain cranked.

definitely sounds more like the amp did without it.

by changing the gain of the first stage from 47k to 470k the output of stage one should be fine. make sure you take the time to tinker with whether the switch sounds better before, or after the gain control.

i recently re-engineered the classic t-rex shatterbox fuzz by moving one component in the circuit, and completely changing it. some peeps won't talk to me anymore cuz of it.

not my fault they made a mistake 50 years ago!! lol

the increases in the pot values will help bring this up to more modern standards, too. i hope once peeps wake up here i can shoot a little video today.
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Old 12-22-2013, 01:19 PM   #14
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and jim, you don't need to use the 1302's. any npn ge's in the right gain ranges should be fine. if ya get a lot of "hisssssssshhhhhhhhhhhhhh" the ge is too leaky, try another.
may sound BANGIN with a j or mosfet for q3, but may need some revisiting.

i agree on the tremolo... better to do it as an add on imho.

do you mind if i share this with freestompboxes.org and diystompboxes.com?

if ya end up needing a couple transistors, pm me bro, i can send ya a couple.

really digging this little circuit. it really freekin' screams!! you MAY be able to get away with the 47k resistor instead of the 470k... depends on how loud ya want it to be.

it's funny, the original 704 cct is set up and wired a lot like a tube amp. these were the original solid state amps, and looking at how they do some of it... it's like... wtf were they thinking>?!>!>!>!>>! lol
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Old 12-22-2013, 07:07 PM   #15
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Go ahead and post it anywhere you want. You did all the mods. All I did was basically copy the original circuit. I would prefer if you used my re-drawn diagrams; they look a lot better and are easier to follow than the older one you posted.

During my research I learned that the 700 series were the first mass-produced solid-state amps (but the 703 was a tube amp). If you are into funky old adverts, there's this:
http://www.tonegems.com/wp-content/...k700s-1965c.jpg

The 704A, 705, and 805 are all basically the same circuit, with a few component value changes and tweaks here and there. The 700 is basically a 704 sans the tremolo effect. Note that the 704 and 704A are very different circuits (their power amps are the same).

I've gathered the parts and am now ready to get this back on the breadboard. Hope my transistors are good enough. The 1302's are my only NPN Ge types.
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Old 12-22-2013, 07:43 PM   #16
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yeah i saw that before. i was actually searching for info when i came across your circuit and saw that page.

the pic i'd used for the schematic was just something i'd pasted your comments in to make my life easier. no prob posting the refined ones.

thanks for being so generous!! some peeps may wanna build one someday for themselves.

i put up a quick demo (stupid pedal tricks) at my youtube full of shitty outta sync video

stupid pedal tricks with pink jimi photon

here ya go:

https://www.youtube.com/watch?v=_d03JIuNnqQ
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Old 12-22-2013, 10:04 PM   #17
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ha!! the 708 galaxie II was my first "real" amp. it screamed!
thanks for the pic.
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Old 12-23-2013, 02:20 AM   #18
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dangit, found another mistake on the vero. revised.

here's my schematic, with the mods i made to jim's circuit (what i actually built):



i didn't bother with the vibrato.

here's jim's schematic. he has the presence circuit going to the outside of the output cap, seems risky to me.
i just tied it to b+ at the node of the q2 collector and the resistor feeding it from b+, seems to work still, and no dc on the output.



this is the original amp for comparison. all germanium. these were really warm sounding, tho not particularly loud til ya hit the 35 watters.



here's a pcb of jim's original circuit, this isn't what is in the video tho. i had to tweak it some, as original it just needed more cojones.

this also has the presence circuit tied to the output. i don't reccomend it. caveat emptor. you can omit it if you want, or tie it to ground. seems to work that way too.




here's the vero i cobbled together. check the nodes first if you wanna build it just to be sure, as the original vero i'd worked up had two mistakes on it that required a little judicious jumper action. the mistakes should be rectified on this, but ya never know....




thanks Invader Jim for a really cool idea and project!! this was fun and sounds really good, too.

let me know how ya make out if ya revisit it.

rock on!!
th th that's all, folks...
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Old 12-23-2013, 06:37 PM   #19
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Ah, I knew I recognized your name. I saw your Lardacious Phat Bastard demo a few weeks ago.

This little circuit is pretty wicked. I got it built but I'm having problems tracking down the cause of trouble. I skipped the breadboard and just built it. I never do that but I was bored and didn't want to take the time to screw with breadboarding. I also winged the layout. Another thing I never do...

First stage sounds great and has plenty of usable output level this time around. There's a nice grit and it cleans up well. It'd make a great dirty booster/mild overdrive.

The problem is with the second transistor. It gets hot within seconds of applying power and the only sound through the amp is power supply hum. The signal doesn't seem to be getting to the base either.

I hate troubeshooting...
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Old 12-23-2013, 08:17 PM   #20
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tie the 1m/10p rc to the node at the q2 collector and the resistor that connects there.
this was a "presence" control for feedback that was being isolated by an output transformer.
the second transistor is probably oscillating. it needs the feedback resistor to set it's gain. so tie that 1m/10p between b and c of q2, and i bet your problem will go away.

also, looking at your schematic, get that 47k between the c's of q2/3 outta there. it needs to go to b+ for q2 first of all, and should be 4.7k not 47k.

you had it almost right the first time.

the q3 c resistor should be a 1-10k trimmer. 100r is too small there.

you wanna fix your presence control.

i will download your schematic and try and fix it up and re-upload it bro.

you're close, but ya need to tweak some things from the guitar amp deal.

the feedback/presence works great but it's gotta be on the collector side of the output cap.

can you post pics of your build? i'll try and help ya debug.
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