Hot Tubes Clone question...

[Barcode80]

So, I love GaussMarkov's layouts! the pads are good and large but somehow he doesn't seem to add a lot of size. however, he seems to use box caps and i can't get them readily here. so, for the 1uF caps, what would polarity be if you subbed in electrolytics?

http://www.gaussmarkov.net/layouts/hottubes/schem.png

[Barcode80]

bump

[gaussmarkov]

i'm glad you like the most recent layouts with the big pads.  i learned to do that from john/basicaudio and dave/pushtone when we worked on the dr. boogey together.  i agree that they are easier to use.

it's true, i like box caps.  and that probably limits the usefulness of my layouts.  the source of my schematic was on jack orman's site: http://www.muzique.com/schem/hottube.gif.  you can see the polarity of the 1uF caps there.

for future reference, i always cite my source.  it's the first piece of information for each project on gaussmarkov.net. 

[gaussmarkov]

lol.  you bumped while i was writing.

[Barcode80]

COOL! Don't know why i didn't think to check the schem...  also, where on earth do you get a 2M pot?!?!?! any ill effect from using a 1M?

[gaussmarkov]

COOL! Don't know why i didn't think to check the schem...  also, where on earth do you get a 2M pot?!?!?! any ill effect from using a 1M?

stobiepole (chris) used a 1M also.  because maximum drive occurs when the pot gives no resistance, it won't make any difference for high gain, just low gain levels.  if you find you have more gain than you need, you could add a resistor in series (you could do this at pot lug 1 or 3) after you have built it to get more in the low gain range while sacrificing some gain.  and there's plenty of gain, so this will be fine for some folks.  the value of the resistor would have to be chosen to taste.

[gaussmarkov]

COOL! Don't know why i didn't think to check the schem...  also, where on earth do you get a 2M pot?!?!?! any ill effect from using a 1M?

i should have marked the polarity on the schem.  i'll try to remember to change that.  there's a lot of places where that comes up.

[soulsonic]

You could always use non-polar 1uF electrolytics. If they're used for signal coupling, they usually sound much better than a polarized one.

[Barcode80]

yes, but i have none and i have plenty of electros

[Barcode80]

okay, built and working, but i'm not sure if something may be wrong. i really don't get any clipping until the gain pot is at about 8 (of 10). It's a linear pot, so i don't think that's the problem. i used a tl072 in the dual spot, my 4558 sounded like doodoo. any thoughts?

[mydementia]

Patrick, what do your voltages look like?  I built this circuit in May.  Mine sounds great while playing, but when a note sustains, it farts out ('misbiased tranny' gated sound). 
Here's my troubleshooting post with my voltages:
http://www.diystompboxes.com/smfforum/index.php?topic=58294.msg453949#msg453949

Anyone else built this circuit?  Voltages to share?

Also, don't forget places like alliedelec.com for AVX caps.
1uF box caps - 63V - small footprint (24-cents apiece):
http://www.alliedelec.com/Search/ProductDetail.asp?SKU=995-0185&SEARCH=&MPN=BF074D0105J%2D%2D&DESC=BF074D0105J%2D%2D&R=995%2D0185&sid=468D860048FB617F
0.1uF box caps - 63V - small footprint (6-cents apiece):
http://www.alliedelec.com/Search/ProductDetail.asp?SKU=995-0149&SEARCH=&MPN=BF014D0104J%2D%2D&DESC=BF014D0104J%2D%2D&R=995%2D0149&sid=468D86002CDD617F

My new discovery this order was their Vactrol's:
VTL5C2 - $2.53
http://www.alliedelec.com/Search/ProductDetail.asp?SKU=980-0705&SEARCH=&MPN=VTL5C2&DESC=VTL5C2&R=980%2D0705&sid=468D8600579F617F
VTL5C4/2 - $2.51
http://www.alliedelec.com/Search/ProductDetail.asp?SKU=980-0725&SEARCH=&MPN=VTL5C4%2F2&DESC=VTL5C4%2F2&R=980%2D0725&sid=468D8600C37617F

Now... if futurlec.com would just get the 35-cent jacks back in that I like, all would be well.

Mike

[Barcode80]

i occasionally get some misbias sounding sputter when the gain is at minimum. but it remains almost totally unaffected until i get way up there. i'll check voltages when i get home. thanks for the heads up on the caps!

[SonicVI]

Anyone else built this circuit?  Voltages to share?

I have an original in the mail on the way to me right now as well as a Snarling Dogs Blue Doo which is a copy of it.  I can take some readings from if anyone needs anything in particular. 

[stobiepole]

I'm still recovering from a lumbar discectomy so I can't strap on the guitar for very long periods. But I just had another play with my build of the Hot Tubes from the gaussmarkov layout.

I can get it to be farty, somewhere between clean and raunchy - just on the verge of raunch. It's a little hard to do, in fact. I kinda think that might just be the design - at higher gain there's no sustain problems. The gain pot does seem to be clean until quite a ways through the rotation - I'm using a 1M pot instead of the 2M specified. And at zero gain there's no volume.

So I'd suggest that, if the taper bothers you, replace R9 with a larger value resistor to get rid of some of the clean zone (probably a good idea anyway - you want some volume at zero gain). Personally, I'm going to grab a 2M pot and see how that sounds. Otherwise, maybe try a different taper. I think you'd need a reverse log...but maybe just try a bigger value for R9 and see how that goes.

Chris

[gaussmarkov]

wait a sec ... now i'm confused.  full clockwise rotation of the gain pot removes the resistance of the pot and makes the signal its hottest.  as you back off the gain, you add resistance.  so the value of the pot only matters for low gain settings.  if there is no signal at full counter clockwise with a 1M pot, there is no need to step up to a 2M pot, right?  or?

[stobiepole]

Hmm. I've got to think...

You're right, of course. In which case, would a smaller pot be better?

An audio pot?

Urggh. Now everyone knows that I am on lots of painkillers right now, right?

I'll have a bit of a tinker today, and maybe measure some voltages. After another cup of coffee.

Chris

[gaussmarkov]

yes, that's it.  patrick, check R9 and make sure it's 8.2K.  maybe you put something higher in there?

[Barcode80]

will do

[gaussmarkov]

yes, that's it.  patrick, check R9 and make sure it's 8.2K.  maybe you put something higher in there?

  it dawned on me on the way to work this morning that this is a great opportunity for using the infamous audio probe.    check before and after the pot/resistor combo for signal strength.  if that seems o.k. then continue on down the signal path looking for the location of a volume drop.