Hot Tubes Build Troubleshoot - New GM Layout

[mydementia]

A while ago I built the new Hot Tubes layout from gaussmarkov and stobiepole (http://gaussmarkov.net/index.php?page=layouts#hottubes).

Here are a couple of my questions:
1) I didn't have a 2M pot so I used a 1M... I notice when I put my DMM across the the lugs, the most distortion occurs when the pot is at 0-ohms resistance - at my max resistance (1M) it's clean... what's the benefit of the 2M pot?  Wider range of drive?

2) I think the tone of this beastie is good - but I have an underlying 'misbiased' sound through the range of the OD pot (unpleasent fuzz under all the notes).  Here are my voltages - I haven't built many CD4049 circuits - but I assume it should run at approximately half the supply voltage, right?


The opamp looks about right to me...

The 1M pot and JRC4558D (instead of the LM4558N) are the only subs I made on this build. 
If the CD4049 voltages look OK, do you have any other recommendations on where to look?  Anyone else built this?  Success?

Thanks.
Mike

[Barcode80]

bump for mydementia

[gaussmarkov]

well, i did some searching around on the forum.  aron once complained of gating in a 4049 circuit that he was playing with on his breadboard:  4049 gating.  i turned out that he had no coupling caps between stages and adding them fixed things up.  so one hypothesis that suggests is that there might be something wrong around one of your coupling caps.  a short maybe?  or a bad cap?

all the best, paul

[electrobuster]

Hi,

Just built this, thanks Gaussmarkov and Stobiepole for the layout, very cool sound on this one.
Only sub is RC4558P instead of LM4558N and I have the same results as mydementia

1. the 2m pot really only worked at 0 ohms and at any resistance stops passing sound altogether. I had a 100k pot so I put that in and it now works as a usable gain pot. I will most likely try a 500k when I get a chance to get one.

2. I also have the misbiased underlying fuzz which I don't really mind, It adds another dimension to the sound but what I don't like is that it gates at the end of the note destroying sustain. I read the 4049 gating thread, but don't really get it sorry. Any help on a fix for this would be greatly appreciated.

I did notice that there is a picture in the gallery of a hot tubes board which seems  to have a 10uf electro near the 4049

www.aronnelson.com/gallery/v/DRAGONFLY-LAYOUTS_0/album146/album64/EH_HOT_TUBES_GUTS.jpg.html

the scheme does not have it. is it likely that it was and after thought for this gatey bias issue?

thanks Simon

[gaussmarkov]

well, stobiepole says,

I put a 10uF tant instead of the 1uF at C10, and a 33nF cap from the 1.8M resistor to ground and it improved the sound quite a bit - made it smoother and more tubey...

i've had folks tell me that the original has the same sound.  all we did was follow the schem on amz-fx. 

cheers, gm

[electrobuster]

Thanks GM

I will try the 33nF cap from the 1.8M resistor to ground. I think i will bypass the tone most of the time so  I might leave c10.
Don't get me wrong I love the sound, the gating just spoils the sustain.

Simon

[gaussmarkov]

ok.  i did a little background reading.  the most important thing i found is a post from Bernardduur:

Hey all!

As I am quite fond of my Hot Tubes clones I decided to buy one......




Oh well, I found one cheap

It follows this schematic quite right with some small changes:

- all 150k resistors are 160k
- all 4,7 uF caps are 5 uF
- the 1 uF cap in the tone section is 10 uF
- across the first "gain" stage (1.8M to ground, 160k across inverter) is a small cap (N 3300)

Voltage is 8.3V, IC = RC4558NB, inverter = SCL4049UBE (socketed)

Just to share!

so that confirms stobiepole's fixes and your detective work about the 10uF cap.  unless "across the stage" means from input to output.  [Edit:  and that cap might be 3.3nF]

also, here's a picture of the underside of an original.  my, my, what is that cap doing there? 



that's from this post:  Re: Pictures! by jlullo

[gaussmarkov]

i also meant to point out this post:

I built an old model of EH Hot Tubes last week and I thought I could tweak the bias to get a smoother sound ...(it hisses and the sound is a bit "rough"), so I believe I have a problem with tbe bias.

That's how the original Hot Tubes I have sounds.
But if you want to tweak something other than the bias, you can adjust the 75k resistor between pins 6 & 7 of the 4558. Raise it to get more gain going into the 4049. Or put a 500k pot in series with the 75k (at minimum you have the stock setting).

elgorgon@yahoo.com

[electrobuster]

So does that 33nf or 3.3nf cap go from pin14 in series with the 1.8m resistor or in parallel to it? Thanks GM, Hopefully I can have a tweak with this later tonight and post results.

[SonicVI]

That photo above is my pedal and that ceramic cap is in parallel with the 1.8M resistor that connects to pin 9 on the 4049.  Also, I've never noticed any kind of gating sound.

[gaussmarkov]

sonic, do you remember the cap value?

[electrobuster]

Thanks Sonic, Just about to ask the same question as GM

[SonicVI]

It just says N3300, which I can only assume is 3300p (3.3.n).  I'll see if I can't get a measurement to confirm soon.

[stobiepole]

Ah, 3.3nF instead of 33nF...I'll give that a try. With 33nF it's pretty dark sounding...

Chris

[electrobuster]

Just put in a 2.2nf  (don't have 3.3nf at the moment) and the gating is gone. Thanks for all the help I am really happy to get it sorted!!!

[gaussmarkov]

Just put in a 2.2nf  (don't have 3.3nf at the moment) and the gating is gone. Thanks for all the help I am really happy to get it sorted!!!

and stobiepole wrote to say the 3.3nF sounds much better in his build.  ah, very satisfying.  i will make changes to the gaussmarkov.net project.

thanks everyone, gm 

[Bernardduur]

LOL

I just made a post about my HT; I find it quite bass heavy.... anyone else experienced this???

Else, I LOVE it through my FX loop!

[gaussmarkov]

LOL

I just made a post about my HT; I find it quite bass heavy.... anyone else experienced this???

Else, I LOVE it through my FX loop!

... and your earlier post in the same thread is already cited above.   

stobiepole says that changing the cap across the 1.8M resistor on the first gain stage inverter from 33nF to 3.3nF relieved the bassiness a lot.

but bernardduur (is that really a reference to Ruud Bernard?  ), you have an original right?  i am wondering whether you and sonicvi can double check the position of that cap?  is across the resistor or across the inverter.  in the red llama and other 4049 circuits, there is are often caps across several of the inverters (connected to input and output).  the amz-fx copy of the eh schem shows none of these caps and i just would like to check again whether this cap actually goes to the output rather than to ground. 

if it's not possible, i understand.

given that the 3.3nF cap is an order of magnitude bigger than feedback caps in the llama, hot harmonics, etc., it may well not be a feedback cap.  but here's the thing:  i would've thought that a cap to ground would increase bassiness, because that is an exit route for highs out of the signal path.   what stobiepole observes is consistent with this.  when he puts in a smaller valued cap, more highs appear.

cheers, gm

[SonicVI]

LOL

I just made a post about my HT; I find it quite bass heavy.... anyone else experienced this???

Else, I LOVE it through my FX loop!

I use it with bass with an Ampeg tube amp and it retains a good amount of low end. You'll note in that photo I replaced the direct out jack with a clean blend knob. 

[SonicVI]

stobiepole says that changing the cap across the 1.8M resistor on the first gain stage inverter from 33nF to 3.3nF relieved the bassiness a lot.

but bernardduur (is that really a reference to Ruud Bernard?  ), you have an original right?  i am wondering whether you and sonicvi can double check the position of that cap?  is across the resistor or across the inverter.  in the red llama and other 4049 circuits, there is are often caps across several of the inverters (connected to input and output).  the amz-fx copy of the eh schem shows none of these caps and i just would like to check again whether this cap actually goes to the output rather than to ground. 

Ok, I just double checked and I you are indeed correct, the cap is in parallel with the 150K resistor between pins 9 and 10 of the 4049.    The 1.8M and 150K are right next to each other on the board. Sorry about that, my mistake.  I measured the cap with my meter and it gave me .733uF. I don't want to desolder the cap as it looks kinda fragile so maybe someone can do some math to find out if that would actually be 3300p if it were in parallel with a 150K resistor.