EHX - Hot Tubes (original version)

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Bernardduur
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Post by Bernardduur »

Dunno if the unit was made before 75; if not, replace this post :)

This boxes has been one of my fav bass OD's for years. Once I was turned on to these babies by Sonic Youth; if you know the tone this pedal make and listen to ANY SY song, you'll hear the bass more clearly :)

I've had an original for some time and sold it because of the size. All online schematics I found were slightly wrong though.

Schematic
The 3n3 over the first inverter stage makes a HUGE difference.

Also, try the unit in a FX loop! Made the world for me between OK OD and SWEET OD!
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Post by sonicvi »

That cap says N3300 on it but it's actually only about 39pF, not 3300pF. I actually took it out and measured it.
I agree it is great with bass. A simple cool mod you can do to make it even better with bass use the useless direct out as an already buffered path for a clean blend knob.

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Bernardduur
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Post by Bernardduur »

sonicvi wrote:That cap says N3300 on it but it's actually only about 39pF, not 3300pF. I actually took it out and measured it.
I agree it is great with bass. A simple cool mod you can do to make it even better with bass use the useless direct out as an already buffered path for a clean blend knob.
OK, great to hear! I removed the cap once and hated the unit; luckily I found that cap back in my partsbin. It said N3300 like you said.........

I'll change the schematic!
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Fantabulousnoise
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Post by Fantabulousnoise »

hey, first post from a long time reader!

hope it's okay to bump this, I was wondering if anyone had sound clips of either an original or a clone

I'm a n00b to soldering (looking to start next month) and intending to put together a red llama for myself

The hot tubes interests me because it has the same chip, plus some easy to discern building blocks on the schematic such as the op-amp buffer and gain stage and the tonestack. If these building blocks are easy to discern it's my theory they are easy to replace in order to tailor the sound.

thanks :)

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slor
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Post by slor »

Hi there,

So great to find this info; I know next to nothing about pedals so it's great to have this resource. So if I'm gleaning this correctly, if there's not a 39pf cap across the 150K resistor between pins 9 + 10 of the larger IC, I should add one.

Any other mods / upgrades you can think of? For instance, could (should?) I do true bypass by subbing a DPDT stomp switch?

It seems that some folks feel that the Texas Instruments TL072 is a better (less noisy) replacement for the 4558. Any thoughts on this?

Thanks much!

-slor

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Post by mictester »

slor wrote:Hi there,

It seems that some folks feel that the Texas Instruments TL072 is a better (less noisy) replacement for the 4558. Any thoughts on this?
The TL072 is much lower noise than the 4558, but doesn't colour the sound in the same way. Believe it or not, there is a 4558 "sound" (just like you'll find in a Tubescreamer) and it has a number of other nice properties that make it a really good device for audio use!
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Post by sonicvi »


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Post by Fantabulousnoise »

Great clip, Sonicvi

certainly whets my appetite with regard to cloning

may need to do some more builds first, though (only 1 thus far)

questions: how does it react to boosters into the input? the clean blend knob mod: does it get a more tube screamer-esque sound with guitar? would it be much more effort to use the buffered path for a parallel effects loop that you could blend at the end of the circuit? I can see that being a fun way of blending distortion sounds :)

g

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Post by sonicvi »

Fantabulousnoise wrote:Great clip, Sonicvi

certainly whets my appetite with regard to cloning

may need to do some more builds first, though (only 1 thus far)

questions: how does it react to boosters into the input? the clean blend knob mod: does it get a more tube screamer-esque sound with guitar? would it be much more effort to use the buffered path for a parallel effects loop that you could blend at the end of the circuit? I can see that being a fun way of blending distortion sounds :)

g
I don't ever use it with a boost at the front. I've never found it to need it. This pedal and other 4049 based pedals I've heard don't really sound anything like tube screamers. They're much more edgy and saturated sounding, even with a little clean blend. As for the effects loop I think it would be about the same amount of work to make a loop rather than a clean blend. The only difference would be where you put the blend control. The blend would be before the send (clean output) and the loop would have it after the return. It wouldn't really be a real effects loop though, you'd just be blending in another pedal in parallel with the overdrive, unless you injected the return somewhere into the circuit, like before the tone control for example, rather than just at the end of the circuit.

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Post by voland83 »

4558 or tl072 or other opamps are just linear elements and cannot colour your sound, if they did, they were just a bad opamps ( really far from linear characteristic ). tone controll is realised by building integrator or differentiator circuit by means of opamps + capacitors+ resistors and/or inductors.

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Post by dune2k »

voland83 wrote:4558 or tl072 or other opamps are just linear elements and cannot colour your sound, if they did, they were just a bad opamps ( really far from linear characteristic ). tone controll is realised by building integrator or differentiator circuit by means of opamps + capacitors+ resistors and/or inductors.
Usually if you turn the gain up enough the op amps produce distortion. Different op amps, different kinds of distortions.
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Post by Crumbchildz »

There's been discussions here about how different TL072s sound vs. TL082s, and they're different graded versions of the same chip. There's a bunch of mitigating factors with opamps like noise floor, slew rate, JFET vs. BJT vs. MOSFET topology, etc. I don't see how opamps can't color your sound. Especially since some folks think different resistors color your sound :D
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Post by gkoerselman »

I looked over the other two schematics of this pedal and noticed that they have C9 as 1u and not 10u. The schematics were found at: http://www.muzique.com/schem/hottube.gif and http://fuzzcentral.ssguitar.com/schematics/hottubes.gif. I think the fuzz central schematic was copied, with an error added, from the muzique one. It seems, in the beginning of the circuit, the 220k resistors, working as voltage divider, wrongly connect with the 120k resistor (connects to Vref in bernaduurs schematic).

Also it is stated that "pins 5 & 7 are held high to inactivate unused inverters". I assume this means connecting them to ground...?

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Post by Bernardduur »

gkoerselman wrote:I looked over the other two schematics of this pedal and noticed that they have C9 as 1u and not 10u. The schematics were found at: http://www.muzique.com/schem/hottube.gif and http://fuzzcentral.ssguitar.com/schematics/hottubes.gif. I think the fuzz central schematic was copied, with an error added, from the muzique one. It seems, in the beginning of the circuit, the 220k resistors, working as voltage divider, wrongly connect with the 120k resistor (connects to Vref in bernaduurs schematic).

Also it is stated that "pins 5 & 7 are held high to inactivate unused inverters". I assume this means connecting them to ground...?
The fuzzcentral is faulty! ignore that part!

I traced mine from my own unit and C9 = 10uF. Shouldn't make much of a difference for it's purpose is to block DC.

Pins 5 and 7 should be connected to V+ I guess
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Post by mictester »

voland83 wrote:4558 or tl072 or other opamps are just linear elements and cannot colour your sound, if they did, they were just a bad opamps ( really far from linear characteristic ). tone controll is realised by building integrator or differentiator circuit by means of opamps + capacitors+ resistors and/or inductors.
Op-amps will seriously alter the signal passed through them - they are certainly not "perfect" devices! You have to consider slew rate, noise, bandwidth, available voltage swing, input and output impedance, and several other parameters. The signal out of an op-amp can never be the same as the signal in!

The 4558 (for example) has a limited slew rate and quite a poor noise floor. However, it doesn't suffer from "latch-up" problems when the output approaches the supply rail, so it's good in the distortion stages of effects. The TL072 is much wider bandwidth and much lower noise. It also has a very high input impedance and very low output impedance. It's really good for buffers, hi-fi circuits, tone controls, buffers and balanced output stages. The two devices behave quite differently despite their both being "op-amps".

I suggest you build a simple 10X gain buffer with a socket for the IC. Try different devices in there, and you'll be surprised how different they sound!
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Post by Crumbchildz »

I couldn't agree more. It's like saying that different tube brands all sound the same. Or even better, that a tube rectifier will behave the same way as a solid state one. "Perfect" components only exist on paper. :D
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Post by blanik »

I'm very curious about this pedal but i can't find a single video of if on you tube ?!

i only get videos of the newer one with an actual tube in it... :-/

and a lot of Placebo guitar riffs with "EHX Hot Tubes" keyword..lol guess he used one

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Post by Bernardduur »

blanik wrote:I'm very curious about this pedal but i can't find a single video of if on you tube ?!

i only get videos of the newer one with an actual tube in it... :-/

and a lot of Placebo guitar riffs with "EHX Hot Tubes" keyword..lol guess he used one

Placebo used the newer one.......
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Post by marshmellow »

Some time ago somebody asked me to post some pictures of my pedal.

Here they finally are... next to some cold tubes :wink:.
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ehx-hottubes-2.jpg
ehx-hottubes-3.jpg

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Post by jimmyjimmytimmy »

thank you thank you thank you!!!

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