Matchless Hot Box Questions...

[rsalinger]

Hi there, I'm new here... a total noobie.

Wow, lots of information... Great site.

While searching the net for a Tube Distortion pedal, I came accross a Matchless Hot Box schematic, designed by Frank Berend ... which seemed fine and dandy... until I found a layout that didn't correspond. Both of these are posted here: http://www.generalguitargadgets.com/content/view/96/26/

The more I studied the layout and schematic, the more questions I had.

1) I was wondering if anyone could tell me if this is the fabled "Sampson-era" pedal?

2) Has anyone successfully built this pedal? How was the noise-floor?

3) What are the specific tranformer requirements/ tap outputs?

4) Is the pedal 'hot' enough to be used directly into a power-amp? If so, what's the tone like?

5) Could someone please explain the reasons as to why the V1 input pin on some schematics is "pin 7"... while the same input pin is "pin 2" on others? Which is correct?
This has got me confused. Stumped. But, then again... I'm not the sharpest nail in the toolbox.

6) Does anyone know of any other layouts available for this pedal, for comparison?

7) And, last but not least... I don't require a 'clean boost', so... Would be possible to forego the switch and keep both channels on similtaniously? Like a Sparkle Drive Pedal. This is from the Voodoo Lab site: Voodoo Lab Sparkle Drive is an overdrive pedal featuring a unique "clean" control. Its overdrive circuit provides the same tone as a vintage '808. Then the clean control blends back in a boosted direct signal. This restores the attack and feel which is lost in a highly compressed overdrive circuit...

Keep up the good work... and God Bless.

Thank you, and feel free to e-mail me at: rob_salinger@msn.com

Rob

PS.: Sorry, for the ramble... Cheers.

[MikeH]

Hi there, I'm new here... a total noobie.

Welcome!  Not to kill your buzz right off the bat, but this isn't a project for beginners.  High voltage is dangerous, and high gain can be difficult to keep quiet and oscillation free.

1) I was wondering if anyone could tell me if this is the fabled "Sampson-era" pedal?

- Sorry, no idea

2) Has anyone successfully built this pedal? How was the noise-floor?

I have.  Lead dress and transformer placement are very important in keeping noise down.  Mounting the PT outside the enclosure will help, but isn't practical for stompboxes.  I ended up building a small shield around mine inside the enclosure.  Running the heaters DC instead of AC helps too, mine are AC, but it's still really quiet.  If I switched them to DC, I'm sure it would be dead-quiet.

3) What are the specific tranformer requirements/ tap outputs?

I do not know exactly; you do need a 6.3v secondary- not sure what the rating needs to be on the HV secondary.  I bought my PT from a guy in Lansing, MI, who had bought up the stock from Matchless when they stopped making the hotbox- supposedly.

4) Is the pedal 'hot' enough to be used directly into a power-amp? If so, what's the tone like?

It's basically the preamp section of an AC30ish amp, so it can be used directly with a power amp.  It has tons of output.  I found the tone to be waaaay too bright.  Actually it seemed to have 2 settings: too bright or too dark.  Needles or Mud; you choose.  I ended up totally replacing the tonestack with a more Marshally-Fendery type.  I honestly don't remember all the changes I made.  It's better now but I'm still tweaking it all of the time.

5)Could someone please explain the reasons as to why the V1 input pin on some schematics is "pin 7"... while the same input pin is "pin 2" on others? Which is correct?
This has got me confused. Stumped. But, then again... I'm not the sharpest nail in the toolbox.

A 12ax7 is a dual triode- it's like 2 tubes in one; they share the same heaters but they are interchangeable.  Pins 1,2 and 3 are analogous to pins 6,7 and 8, respectively.

6) Does anyone know of any other layouts available for this pedal, for comparison?

I used the GGG layout, but forum member banicka has a great page on it on his website- http://diy-fever.com/amps/tube-reactor-pre/  Although I think this is a hotbox variant, not an exact clone.  Which probably means it sounds way better.  Ha ha ha.

7) And, last but not least... I don't require a 'clean boost', so... Would be possible to forego the switch and keep both channels on similtaniously? Like a Sparkle Drive Pedal. This is from the Voodoo Lab site: Voodoo Lab Sparkle Drive is an overdrive pedal featuring a unique "clean" control. Its overdrive circuit provides the same tone as a vintage '808. Then the clean control blends back in a boosted direct signal. This restores the attack and feel which is lost in a highly compressed overdrive circuit...

The "clean" setting on the hotbox just bypasses all of the gain stages after the first.  So they arent independent mixable channels.  There is no 'clean' mix on the hotbox.  And if you don't need the clean side, then you can wire it up without the switch; just hardwire the connections the switch would have created.

[rsalinger]

Thanks, MikeH...

Thank you for the in-depth answer and link. I'm going to digest what you've said and study the layout further.

How could I mod the circuit so that the 'Clean Channel' could function as 'Clean Bleed'... like a Sparkle Drive or a multi-amp set-up? ...Initially, I thought that this might be simple, since at first glass the 'channels' seemed to be in parallel and not cascading into one another. Perhaps, I'm wrong, though... There are Jello Brand Pudding Pops out there with a higher IQ than me.

Secondly, does your Hot Box sound/perform like a standard amp when plugged directly into a power amp... or, does it sound better in front of a guitar amp?

Thanks,
Rob

[rsalinger]

I'd like to upgrade the components, where ever possible... any brand recomendations for caps and resistors?

Thanks.

[MikeH]

Thanks, MikeH...

Thank you for the in-depth answer and link. I'm going to digest what you've said and study the layout further.

How could I mod the circuit so that the 'Clean Channel' could function as 'Clean Bleed'... like a Sparkle Drive or a multi-amp set-up? ...Initially, I thought that this might be simple, since at first glass the 'channels' seemed to be in parallel and not cascading into one another. Perhaps, I'm wrong, though... There are Jello Brand Pudding Pops out there with a higher IQ than me.

Secondly, does your Hot Box sound/perform like a standard amp when plugged directly into a power amp... or, does it sound better in front of a guitar amp?

Thanks,
Rob

I don't think you could modify the Hotbox to operate like a sparkle drive.  As you already stated, the 'clean' and 'dirty' channels aren't independent; they both share the same first gain stage.  You'd have to build another gain stage all together, which would mean another tube, and some other tinkering on your part.  I can't tell you exactly how. Projects like the buff n' blend and the splitter/blend at ROG will allow you a transistor/IC based solution to a clean blend, and work pretty well.  But they aren't HV tube solutions.

I haven't tried my Hotbox directly into a power amp; but it is essentially the front end of a tube amp, so it really should work fine.  Keep in mind, a lot of the distortion sound of an AC30 type amp is going to be breakup in the power section and speakers as well.  So although this looks a lot like the preamp section of an AC30, if you put it into a 300w QSC power amp, or something like that, it's not going to sound anything like an AC30.  I think the hot box works best when used in conjunction with a guitar amp.  If you're thinking you can just bring a hotbox to a gig and run it into the PA, you're going to be disappointed.

As far as components go- higher wattage resistors will provide less hiss- I used 1W all throughout mine.  Brand isn't really important.  I'd stay away from carbon-comp, as they are noisy.  Go with carbon film or metal film.  As far as caps go, Orange drops and Mallory caps are good and would suit this project just fine.  If you want to spend more money than necessary you could go with Sozo or something like that.  Don't even think about using paper oil caps.  In this project, it would be like feeding Kobe beef to a four year old.  I wouldn't worry about going crazy with the tubes you select either; something like JJs or EHX (although I have had bad results with EHX tubes) will do fine.

[rsalinger]

I built a Dr. Z Stangray Clone, with ALOT of help from Pop... I've been considering using the Matchless Hot Box circuit for a 'dirty channel'.

[MikeH]

That's a really cool amp- and it is based on Bristish style single ended design, so a hotbox might work really well with it.

Of course, so would a sparkle drive.

[Paul Marossy]

Re: transformer

Calculating the heater filament current is easy. It's 300mA per tube at 6.3VAC (or 150mA per tube at 12.6VAC), so with two preamp tubes, your heater winding would need to be 600mA. The HV winding won't need that much current. It's about 4mA per tube, so maybe 10mA is all that is really required for just two 12AX7 preamp tubes operating at 250V. I'm guessing that the transformer was probably designed for around 175VAC before rectification.

I imagine that whatever transformer you end up getting will require you to mess with the values of the voltage dropping resistors until you get approx. the same voltages as what is shown on the schematic.

[MikeH]

This is where I got mine:

http://www.westlabs.com/Trannys.HTML#Foot%20Pedal

[Paul Marossy]

This is where I got mine:

http://www.westlabs.com/Trannys.HTML#Foot%20Pedal

Yeah, they are the ones that make/made the transformers for Matchless amps.

[rsalinger]

Re: transformer

...I imagine that whatever transformer you end up getting will require you to mess with the values of the voltage dropping resistors until you get approx. the same voltages as what is shown on the schematic.

THAT'S where I'll get "fried"... and go live with baby Jesus.