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DIY Stompboxes => Building your own stompbox => Topic started by: merlinb on January 19, 2011, 12:12:31 PM

Title: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on January 19, 2011, 12:12:31 PM
My most recent completed pedal. (I have actually been working on this since the summer, but it takes me ages to complete anything)

It is essentially a "real" Tubescreamer, since it used feedback clipping diodes, except they're replaced with EB91 / 6AL5 valve diodes. I discovered that by operating the heaters at reduced voltage (between 4V and 4.5V) you get much more favourable diode characteristics and true soft clipping.

The first clipping stage is voiced for treble and the second for bass/mids, so I named the knobs "bright" and "fat". This gives you control over what bands of frequencies and boosted / distorted, rather than simply distorting everything and then adding a tone control afterwards.

The sound varies from mild tone fattening at the lowest setting (a rather nice booster pedal) to medium overdrive, to medium/heavy distortion at max, but with a 'warmness' that a typical Tubescreamer can't muster. Clips to follow when possible.

Built-in voltage stabiliser and proper electronic bypass switching. And yes, the LEDs light up the valves when you hit the footswitch, so they act as a status indicator!
(http://i81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/SparkGapGlow.jpg)

(http://i81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/SparkGap2.jpg)

(http://i81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/SparkGapGuts2.jpg)

(http://i81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/EB91pedal.jpg)





Title: EB91 / 6AL5 characteristics
Post by: merlinb on January 19, 2011, 12:23:45 PM
Here are the measured characteristics of the EB91 at different heater voltages. Notice that above about Vh = 5V it actually doesn't act much like a diode as far as small signals are concerned, which is why simply subbing tube diodes into a tubescreamer circuit doesn't normally work. This valve is unusual though, because the whole characteristic can be shifted to the right by reducing the heater voltage- problem solved!
(http://i81.photobucket.com/albums/j207/merlinblencowe/EB91.jpg)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Govmnt_Lacky on January 19, 2011, 12:25:35 PM
Absolutely phenomenal work Merlin!  :o  :o  :o
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: ayayay! on January 19, 2011, 12:46:25 PM
I like your work!  For two reasons:

1)  The tube used.  I've never seen them before (in my limited knowledge of tubes) so it's great to see some tubes that work with such low voltage.

2)  The LEDs.  At first I thought, "Hey, he's not fooling anyone thinking they're 'glowing.' "  But then I saw that's the status indicator, which I think was a GREAT move.  

And thank you for sharing the schem, and the coming soundclips.  (<-- Hint hint) 

Is R1 one optional? 
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: thetragichero on January 19, 2011, 01:43:08 PM
hey, that's neat!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Renegadrian on January 19, 2011, 01:44:25 PM
Altough I am not particularly keen on hybrids, I see a great idea behind that pedal! I guess I have to build it sooner or later! Now I'll check those tubes, prices, availability...thx for sharing!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: thetragichero on January 19, 2011, 01:58:42 PM
Altough I am not particularly keen on hybrids, I see a great idea behind that pedal! I guess I have to build it sooner or later! Now I'll check those tubes, prices, availability...thx for sharing!
i agree that most pedals that run a tube are bleh, but i LOVE the ingenuity of using a tube diode in place of clipping diodes.

you should build a cage to protect the tubies, if you're anything like me (i have a feeling i would either stomp on or kick them)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Manny on January 19, 2011, 01:59:32 PM
Great work Merlin, this looks like a very interesting build.
Finally a screamer that's actually tube  :)

I'm looking forward to hearing the sound clips!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: amptramp on January 19, 2011, 02:51:53 PM
Nicely done!  Do you intend to add a filament voltage control so you  can adjust the clipping level?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: panterafanatic on January 19, 2011, 03:46:31 PM
Pretty sweet, a variable heater control would work cool for something like this (http://www.diystompboxes.com/smfforum/index.php?topic=86809.0).
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on January 19, 2011, 03:51:27 PM
Is R1 one optional? 
Yep.


Quote
you should build a cage to protect the tubies,
There was supposed to be a metal bar that ran over the tubes, but my friend (trainee metalwork teacher) made them the wrong size :icon_rolleyes:. I don't mind much though, as they're not easy to step on, all the way at the back and with the knobs in front.


Quote
  Do you intend to add a filament voltage control so you  can adjust the clipping level?
Right now I don't plan on doing anything. It took me long enough to get this far! However, it is designed to accept both regulated and unregulated power adapters, and you get slightly different heater voltage depending on what you use, and it does affect the sound, so it's definitely a possible mod!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: PRR on January 19, 2011, 11:01:42 PM
I don't see the sparks?

> it actually doesn't act much like a diode as far as small signals are concerned

What is "a diode"? Two bits in one bulb.

_I_ would say the vacuum diode is the better _rectifier_.

But when building a "clipper", you want an ideal diode PLUS a voltage. The fault of crystal diodes as rectifiers is a large built-in voltage. If this voltage is suitable for your clipper, the fault is a feature.

Cooling the cathode works (I'm sure you know) by lowering the average emitted electron velocity below zero. The high-tail of the gaussian curve can be urged to leave the cathode surface by some "large" positive voltage on the other electrode.

This is also the cause of DC error in tube DC amplifiers. Diff-pairs tend to cancel, certainly good enough for 1.5V VTVMs. More sensitive tube DC amps often sport regulated heater supplies (an awful expense in those days).

> The tube used.  I've never seen them before

Small twin-diode. THE way to demodulate FM. The standard AC-DC converter for VTVMs. Sometimes used in AM/SSB for detection and AVC or for (duh) clippers to tame ignition hash and other impulse noise. I have seen it used for B+ power supply for very-very small gear.

But the exact tube used is NOT a key detail. Take any isolated-cathode twin-triode. Tie each grid to its plate. It is now a twin-diode. Obviously it should cost more; in today's world you can buy 12AX7 on a rainy saturday night in a distant town, or may have a stash of odd-sounding 12AU7es which just might be groovy diodes.

> Do you intend to add a filament voltage control so you  can adjust the clipping level?

Just separate the 9V for the chippy stuff from the heaters, rig two supplies. Replace the heater regulation with a buffered potentiometer.

(http://i.imgur.com/ndSj6.gif)

This may "go too far", the lowest half or third of knob-turn may not do much. Or maybe it will. try it.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on January 20, 2011, 04:50:05 AM
But the exact tube used is NOT a key detail. Take any isolated-cathode twin-triode. Tie each grid to its plate. It is now a twin-diode.
Unfortunately, all the regular double triodes I tested would not work in an application like this, because lowering their heater voltage simply raised the anode resistance rather than 'shifting the characteristics to the right'. It seems you need a close cathode-anode spacing to make it work.

Quote
> Do you intend to add a filament voltage control so you  can adjust the clipping level?
Just separate the 9V for the chippy stuff from the heaters, rig two supplies. Replace the heater regulation with a buffered potentiometer.
You could use simple zener stabilisation for the TL074/LEDs and leave the transistor to handle the 250mA heater current.
Title: PCB files
Post by: merlinb on January 22, 2011, 06:15:54 AM
The PCB layout I used can be found here:
http://s81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/ (http://s81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/)

I use Evatron enclosures, but since it's 60mm wide I *think* it would fit in a Hammond 1590N.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on February 01, 2011, 02:43:57 PM
Provisional stripboard layout: I have added a 100n cap across the zener out of habit (Cnoise on the layout). The taller electrolytics & Q3 need to lay down if you want it to fit in the Evatron box. Don't miss the track breaks under C1 & C2.

(http://i255.photobucket.com/albums/hh143/werdnayarg/webstuf/th_sgapvero.jpg) (http://s255.photobucket.com/albums/hh143/werdnayarg/webstuf/sgapvero.jpg)

I have built from it, but I work from the schematic at the same time - use at your own risk!

The knobs are only stop-gaps - they're 1/4" bore knobs on a 6mm shaft, so they look even wonkier than they really are. For a bit of bling, I used rainbow colour changing LEDs to light the valves up when the effect is active :icon_twisted:


(http://i255.photobucket.com/albums/hh143/werdnayarg/DSC_9003.jpg)

(http://i255.photobucket.com/albums/hh143/werdnayarg/DSC_9001.jpg)

(http://i255.photobucket.com/albums/hh143/werdnayarg/DSC_9002.jpg)

(http://i255.photobucket.com/albums/hh143/werdnayarg/DSC_9007.jpg)

(http://i255.photobucket.com/albums/hh143/werdnayarg/DSC_9013.jpg)

(http://i255.photobucket.com/albums/hh143/werdnayarg/DSC_9021.jpg)

It sounds really smooth - a bit like a valve amp 'crunch' that moves seamlessly into a smooth distortion. I lent it to a friend who is a Proper Guitar Player (tm) who liked it. He had a quick go at recording it, but the recording sounded "like a bee in a bottle", despite sounding good in reality.

I have a PCB version on the bench, as well and it is no quieter or noisier than the veroboard version - it's a quiet pedal, noise wise.

If you fancy a great sounding  pedal with major mojo and no high voltage - give it a go!  ;D

Andy
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Joecool85 on February 01, 2011, 03:10:37 PM
Sound clips please!  That is one neat circuit.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Renegadrian on February 01, 2011, 03:15:35 PM
thx for the vero!!!  :icon_razz: Now I have no excuse!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Govmnt_Lacky on February 01, 2011, 03:18:42 PM
Keeping an eye on this one. Waiting for a PCB layout. I would try one myself but, I have 11 projects in work right now!  :icon_eek:
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on February 01, 2011, 04:01:22 PM
Keeping an eye on this one.Waiting for a PCB layout. I would try one myself but, I have 11 projects in work right now!  :icon_eek:

See the post above mine (http://www.diystompboxes.com/smfforum/index.php?topic=89363.msg757885#msg757885).

No excuses  :icon_wink:

Andy
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Brymus on February 01, 2011, 07:22:43 PM
IDK how I missed this one.
Splendid and superb looking pedal!
Thank you for sharing the design,Merlin !

Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: petemoore on February 01, 2011, 11:30:38 PM
   :icon_wink:
  Interesting application for a space charge device !
  Did you have to search for it or did you know what to look for ?
Title: Re: PCB files
Post by: Govmnt_Lacky on February 02, 2011, 08:56:16 AM
I use Evatron enclosures, but since it's 60mm wide I *think* it would fit in a Hammond 1590N.

Are you using PLASTIC cases from Evatron?
Title: Re: PCB files
Post by: merlinb on February 02, 2011, 03:55:04 PM
Are you using PLASTIC cases from Evatron?
No, they're aluminium.
Title: Re: PCB files
Post by: Govmnt_Lacky on February 02, 2011, 04:06:40 PM
No, they're aluminium.

If its not too much trouble, could you post a link to the enclosure because I could only find  that size in plastic.
Title: Evatron enclosures
Post by: merlinb on February 02, 2011, 04:21:14 PM
If its not too much trouble, could you post a link to the enclosure because I could only find  that size in plastic.

Direct from evatron:
http://www.evatron.com/index-pag-products-cid-13-sid-130-l-2.html
(The photo is incorrect; they don't have ribs inside).

Or from Rapid:
http://www.rapidonline.com/productinfo.aspx?tier1URL=Tools-Fasteners-Production-Equipment&tier2URL=Enclosures&tier3URL=Metal-Cases&tier4URL=Diecast-aluminium-enclosure-natural&moduleno=122722#
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 02, 2011, 04:25:13 PM
merlins layout will fit in a 125b hammond without much room to spare.
i would have another one done to post, but i think smallbear forgot about me...
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Govmnt_Lacky on February 02, 2011, 04:43:19 PM
merlins layout will fit in a 125b hammond without much room to spare.

I would hope so because the Evatron that merlin uses is smaller!  :o

Hammond 1590N1 (125B) = 121 x 66 x 40
Evatron EVA60 = 114 x 64 x 30
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 02, 2011, 04:53:46 PM
got me by 2 mils! so close, yet so far away...

i looked briefly for evatrons, but none of the sites i usually buy from sell them. are they nice as far as enclosures go? they appear to have a different "stance"
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Joecool85 on February 02, 2011, 07:23:04 PM
I'm still looking forward to a sound and/or video clip.  I gotta hear this thing!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: BadIdeas on February 05, 2011, 11:33:44 PM
Very intriguing. I don't really understand tubes, so forgive this possibly stupid question, but...
Are the current/voltage characteristics really a function of filament voltage or filament current?

Clearly the tube diode acts differently from the silicon and germanium diodes. I will have to try them some day. What is the filament voltage on this graph?
(http://i81.photobucket.com/albums/j207/merlinblencowe/DiodesIV.jpg?t=1285249409)
(From your post on my thread some time back)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 06, 2011, 03:53:21 PM
Are the current/voltage characteristics really a function of filament voltage or filament current?
Strictly it's filament power (temperature) that counts, so you can use voltage or current as the variable. However, "E" series valve have heaters designed for voltage drive -the rated current being approximate- so I stick to voltage measurement in such cases.

Quote
What is the filament voltage on this graph?
6.3V (the rated value). Here's what happens when you alter it. These curves only show what happens at less than 500uA anode current, but that's the region that matters in pedal design.
(http://i81.photobucket.com/albums/j207/merlinblencowe/EB91.jpg)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: BadIdeas on February 06, 2011, 07:54:39 PM
Looking again, I'm not sure I like your bypass. Don't you lose treble through the volume pot? Could you use a second BC337 between the output buffer's +input and the 10n cap or just put the existing one there? I don't have the means to cook one up right now, but what do you think? Maybe it's just fine, but it looks like a possible improvement.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 06, 2011, 10:34:04 PM
hay merlin, are there any problems that you know of with your pcb layout? im not getting any voltage through pin 3 of transistor Q3.  ive checked everything like 5 times, no solder bridges, good joints, etc...
then i did one of those cardboard coca cola box layouts of up til the heaters and...

volla! voltage throughout.
either i got a bad diode or there's an error in that section of the pcb.
just wondered if you knew of an error..
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 07, 2011, 07:05:19 AM
Looking again, I'm not sure I like your bypass. Don't you lose treble through the volume pot?
No, there is no loss. The output impedance of the "ON" transistor is extremely small.

Quote
hay merlin, are there any problems that you know of with your pcb layout?
Nope, it's the layout I used! One thing perhaps; the polarity of D2 is not marked (anode to ground), but that should be obvious from the schem.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on February 07, 2011, 12:54:09 PM
hay merlin, are there any problems that you know of with your pcb layout?

...

just wondered if you knew of an error..


PCB worked for me.... (2nd build, not boxed up yet)

Sound clip of sorts

Here's some noises I recorded through the vero build. No tunes, just single note & chords:

First set clean, then I gradually increase the Fat control to max, back to clean, then increase the Mids control to max (Fat at min), clean again, then increase both together. I think it gives a fair representation of how my build sounds. I tried to be consistent from clip to clip -  Nothing was clipping except the pedal (Single coil neck pickup on a strat copy).

http://www.4shared.com/audio/JSxRgHCk/sg-ts.html



Andy
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 07, 2011, 07:10:44 PM
ok thanks guys!
there has to be a bad component on there somewhere. ive checked EVERYTHING like 7 times now. i mean, ive stared at this thing for hours now.

oh well. im just gonna make a new board, get some new components, and start again.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on February 08, 2011, 01:36:19 PM
there has to be a bad component on there somewhere. ive checked EVERYTHING like 7 times now. i mean, ive stared at this thing for hours now.

You've done THIS (http://www.diystompboxes.com/smfforum/index.php?topic=29816.0), right?

Post your readings & a high res, in-focus picture of the top & bottom of the board (taken with a CAMERA, not a f%&$??g telephone) and I'll have a look :)

I think the TL074 is somewhat static sensitive, so you might have zapped it if you didn't take precautions. Maybe try plugging a different one in if you're confident that everything else is OK. (You did socket it, didn't you??)

Andy
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: BadIdeas on February 08, 2011, 03:16:51 PM
Quote
No, there is no loss. The output impedance of the "ON" transistor is extremely small.
OK, I get it now. Never mind me. I'm still figuring these things out. Great design.
Through Google Shopping search, I found the 6AL5 available from Triode Electronics, as well as a bunch of eBay listings. Where did you get yours?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 08, 2011, 04:29:08 PM
yep did all of that.  i dont think its is the tl074(at least not yet) as there is NO voltage on any of the circuit past Q3, the bd435.

my power supply is a steady 9.48 volts
Q1
1, 8.87
2, 9.48
3, 0

D 1N4001
A, 0
C, 9.48

Z9V1
A, 0
C, 8.86

also, ive tried 2 different transistors for q3
i will post some pictures here in a couple hours.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 08, 2011, 04:36:29 PM
 :icon_exclaim:
what an idiot!
i believe ive gotten my transistor in backwards.
this is unbelievable. i spent the past 2 days staring at this thing angrily and checking and checking.
today, maybe 3 minutes.

jeeze... well now i can see if the rest of this is right...
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 08, 2011, 06:59:09 PM
let there be light!!!  i have power now.
let there be sound!!!  nope.

hay, im just happy for power at this point.  sitll could you check these numbers over for me?
here are the voltages on tl072.
1    7.83
2    7.83
3    7.83
4    0
5    7.82
6    7.84
7    7.84
8    7.81
9    7.84
10  7.84
11  8.30
12  7.83
13  7.83
14  7.78
 
thanks
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on February 08, 2011, 08:25:53 PM
let there be light!!!  i have power now.
let there be sound!!!  nope.

hay, im just happy for power at this point.  sitll could you check these numbers over for me?
here are the voltages on tl072.
1    7.83
2    7.83
3    7.83
4    0
5    7.82
6    7.84
7    7.84
8    7.81
9    7.84
10  7.84
11  8.30
12  7.83
13  7.83
14  7.78
 
thanks

Nope. Something very wrong. Where is the -ve lead of your volt meter? Pin 4 should be ~9V (8.xx would be OK), Pin 11 should be 0V - these are the supply to the TL074. Either you've installed the chip backwards, your meter is backwards, or your power supply is  :o (It should be centre -ve for this circuit.)

The large areas of copper on the PCB should be 0V.

Pics??

Andy
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 09, 2011, 06:01:29 PM
you've installed the chip backwards

yep. i must have been drunk when i assembled this one :icon_biggrin:
i installed the f...ng socket backwards!!! so....i installed the chip backwards. glad that i usually order 2 of things like that.  feeling like a moron, but i really appreciate the help in making me realize these little blunders!
one question though...
what effect do the caps C4 and C6 have on the circuit?
i have tons of volume. as in unity volume is about a quarter of a turn, and C4 is the only sub i made.
although it does overdrive the crap out of my amp...
anyway, thanks



Through Google Shopping search, I found the 6AL5 available from Triode Electronics, as well as a bunch of eBay listings. Where did you get yours?
thats where i got mine. it was something like 16 bones shipped for 2 tubes and sockets. if you get the pc mount sockets(maybe the others too), you will have to CAREFULLY drill the center out and CAREFULLY glue/epoxy the two piecs together to get the cool led thing. also you may have to dremel the pins or make large holes.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on February 09, 2011, 07:05:10 PM
i must have been drunk when i assembled this one :icon_biggrin:

Glad you sorted it  ;D

Quote
what effect do the caps C4 and C6 have on the circuit?
i have tons of volume. as in unity volume is about a quarter of a turn, and C4 is the only sub i made.
although it does overdrive the crap out of my amp...


C4 & C6 (& other components) mainly determine the frequency reponse of each clipping section, rather than overall gain (what did you sub C4 with?) . There is plenty of gain available - unity gain on mine is about 2:00 with a log pot in the P3 position - that could well correspond to 10:00 or 11:00 if you have a lin pot for P3. If your gain seems hgher than this, check the connections to the valves, as they're supposed to limit the gain by clipping.

Andy
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: majornoob on February 10, 2011, 12:12:37 AM
Could someone post easy to find equivalent transistors? I found relatively good ones for the two bc's but I'm stumped as to the bd 437.
Thanks
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: PRR on February 10, 2011, 12:49:42 AM
The BC327 and BC337 may be any PNP NPN pair, such as 2N3906 2N3904.

The BD437 may be "any NPN" except it MUST be physically large.

The BD437 is TO-126, the plastic body is 0.3" by 0.4". That's just about big enough, but Merlin added a bolt to spread the heat. DigiKey has thousands of BD437 under a buck each.

An alternate which may be at Radio Shed is PN3055 (plastic 2N3055). This is in the larger TO-220 package, does not need any heatsink in this use, but you may have to squeeze the outer legs to fit the holes.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 10, 2011, 06:45:13 AM
I'm stumped as to the bd 437.
The BD433 and BD435 are the same as the 437( except for voltage ratings, but they're way beyond pedal requirements), so you can also look up those numbers.

In my first prototype I actually used a BC337! It worked, but it got pretty hot, so I swapped it for a larger package transistor just for peace of mind. As PRR said, any NPN in a big package should work.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 12, 2011, 08:04:06 AM
Here's a very dirty sound clip. LP into a home made 18watt and 4x8 cab, SM58 into sound card. Practice volume. No processing.

First is the bypassed sound, then with gain pots at about 3/10. Then with both gains close to max.
Then I switch two of them in series at max gain (but unity volume), just for fun!

www.freewebs.com/valvewizard2/SparlGapMixdown.mp3

(If it tries to redirect you back to this page, just cut and paste the URL into the browser instead)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: joelap on February 12, 2011, 12:39:19 PM
Amazingly cool pedal and refreshingly original idea.  LOVE the blue LED backlit tubes!  So cool.  If only I can get around to putting my bench together at my new place so I have a space to build things these days...

Joe
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Joecool85 on February 12, 2011, 05:04:22 PM
Here's a very dirty sound clip. LP into a home made 18watt and 4x8 cab, SM58 into sound card. Practice volume. No processing.

First is the bypassed sound, then with gain pots at about 3/10. Then with both gains close to max.
Then I switch two of them in series at max gain (but unity volume), just for fun!

www.freewebs.com/valvewizard2/SparlGapMixdown.mp3

(If it tries to redirect you back to this page, just cut and paste the URL into the browser instead)

You should have finished the intro to "Sweet Child O' Mine" !
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: benl560 on February 14, 2011, 07:14:05 PM
what did you sub C4 with?
Quote
100pf.

i used log pots throughout. unity gain on mine is about 9 oclock. i guess the tolerance difference could account for some of this... either way it sounds good.
i guess it dosnt really matter to me too much because i can always turn it up  ::)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: danielzink on February 27, 2011, 10:37:48 PM
My Spark Gap - an homage to the designer.....

I did modify the layout a bit - I used off board pots so I elminated the dummy pad for the pots.

Definitely have a bit of hum...using a Voodoo power supply - so it should be clean power...not sure where to start tracking it down at. Please take a look and be kind..

Thanks !

Dan


(http://pws.cablespeed.com/danielzink/musical/spark/spark1.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark2.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark3.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark4.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark5.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark6.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark7.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark8.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark9.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark10.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark11.jpg)
(http://pws.cablespeed.com/danielzink/musical/spark/spark12.jpg)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Ben N on February 28, 2011, 05:00:48 AM
Hmmm... I seem to recall having seen a mess of submini diodes out there for cheap. Some of them might go nicely with this project.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: amptramp on February 28, 2011, 10:24:35 AM
If you are getting hum, are you running DC on the heaters?  The 6AL5 takes 6.3 volts at 0.3 amps and you appear (from the view of the printed circuit board) to be running them in series.  This is a bigger load than most pedals require, so make sure the filtering is good.  If you are running AC on the heaters, lift the connections off the board.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 28, 2011, 04:10:33 PM
My Spark Gap - an homage to the designer.....

Definitely have a bit of hum...using a Voodoo power supply - so it should be clean power...not sure where to start tracking it down at. Please take a look and be kind..
That looks smegging amazing!

The Voodoo supply appears to be rated for 250mA max, and this pedal needs 250 to 260mA, so your PSU may be struggling.  Suggest trying a 300 - 500mA power supply.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: CynicalMan on March 17, 2011, 04:11:32 PM
Just posting here to confirm that 6BJ7 (http://www.radiomuseum.org/tubes/tube_6bj7.html) tubes work as clipping diodes. I used a 16 ohm 10W resistor in series with the heater for 3.7V at the heater, and I got clipping at 0.6-0.8V. Since they are triple diodes, you could use two of them here and have assymetrical clipping, or you could double up the diodes in the second stage like the Crank.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Steben on March 17, 2011, 04:59:17 PM
This needs to be tested in a clippeer to ground !!!  :icon_eek:

Would make a true OCD - killer.....
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: juansolo on April 16, 2011, 01:22:38 PM
Wizard's Sleeve

Continuing the wizard theme ;)

(http://juansolo.demon.co.uk/stompage/images/sleeve-o.jpg)

(http://juansolo.demon.co.uk/stompage/images/sleeve-i.jpg)

Untidy insides galore... I seem to be going through a scruffy phase in that respect.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: sgmezei on April 16, 2011, 02:49:14 PM
Man that thing looks Great. That picture is really creepy to me hahaha. I wanna hear it!!

Scott
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on April 16, 2011, 03:16:10 PM
Wizard's Sleeve
Continuing the wizard theme ;)
Amazing! I'm even reading Unseen Academicals at the moment! Is that just printed onto transparency and then lacquered on?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: juansolo on April 17, 2011, 02:39:43 AM
Wizard's Sleeve
Continuing the wizard theme ;)
Amazing! I'm even reading Unseen Academicals at the moment! Is that just printed onto transparency and then lacquered on?

Haven't read that yet, though it is the next on the list :)

Stonking pedal BTW. Love it!

The transparency is actually clear adhesive inkjet paper (but yes, basically a sticky transparency lacquered over on a painted box). I get asked about it a lot so did a guide: clicky (http://juansolo.demon.co.uk/stompage/decaling.html) (yeah, there was a mistake on the first Sleeve label, I did another with the right voltage). Very much my prefered method of decaling.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: misterg on May 07, 2011, 09:11:40 AM
Wizard's Sleeve

Continuing the wizard theme ;)

...


That looks fantastic!

Here's my #2 - built for a friend who is going to paint / finish it himself. It's a PCB build which I have to say I found much harder to put together than the vero one  :o

He requested 'protection' and this is the best I could come up with.

(http://i255.photobucket.com/albums/hh143/werdnayarg/newsg/DSC_9100.jpg)

(http://i255.photobucket.com/albums/hh143/werdnayarg/newsg/DSC_9123.jpg)

Thanks again Merlin.

Andy

Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: MichelP on September 06, 2011, 10:51:49 AM
Merlin, wow ! Interesting pedal to build !!  1 question : the Russian 6H2P tube is listed as an equivalent of the EB91, could I use them ? 
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on September 06, 2011, 11:05:42 AM
the Russian 6H2P tube is listed as an equivalent of the EB91, could I use them ? 
Yes, I don't see a problem with that.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: jaapie on November 28, 2011, 05:43:54 PM
I have a couple of 3AL5s. Would I need to adjust the heater voltage to compensate for the different heater voltage rating? It looks like the heater voltage is lowered by 25% for the 6AL5s, so should I run the two 3AL5s at about 4.5V in order to get them to work properly?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on November 29, 2011, 05:26:16 PM
I have a couple of 3AL5s. Would I need to adjust the heater voltage to compensate for the different heater voltage rating? It looks like the heater voltage is lowered by 25% for the 6AL5s, so should I run the two 3AL5s at about 4.5V in order to get them to work properly?
Yes I would expect that to work. However, the transistor regulator in my design won't be able to handle the power dissipation (your heaters will demand close to 500mA), so you'll have to find an appropriate way to do it.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: stevie1556 on February 18, 2012, 03:55:15 PM
Just started building this on strip board until I get a PCB sorted out.

A few questions though:
- What value are the diodes? I can see one on the schematic is 1N4001, is it the same for both?
- Is the transistor BC327-16 ok?
- Is the transistor BC337-25 ok?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 19, 2012, 07:52:29 AM
- What value are the diodes? I can see one on the schematic is 1N4001, is it the same for both?
There is:
One 1N4001
One 9.1V zener diode (e.g., BZX55C9V1)
One LED  of your choice.

Quote
- Is the transistor BC327-16 ok?
- Is the transistor BC337-25 ok?
Yes.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: stevie1556 on February 20, 2012, 12:32:17 PM
Thanks for the quick reply. Just ordered the extra transistors, and a couple of values of resistors that I seem to be missing.

Will post an update when it's done!  ;D
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: danamoose on February 29, 2012, 12:28:49 PM
Hey guys, I am starting to plan this out for my next build. I am writing out a parts list and have a few questions on some of the values. May be my screen but some are unclear so i wanted to ask. I have gone through all the posts on this several times to see what answers I could find there but here is what i still have pending:

R11 looks to say 220R on my screen....is that supposed to be 220K?
Same with R16/17...they look like 100R on my screen is that 100K?
What is "Link 2-zero"?

Thats all for now.
Thanks in advance!
-Dana
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on February 29, 2012, 12:46:37 PM
R11 looks to say 220R on my screen....is that supposed to be 220K?
Same with R16/17...they look like 100R on my screen is that 100K?
No, they're 220R and 100R. R means ohms.

Quote
What is "Link 2-zero"?
Means a wire link. Zero ohms.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: danamoose on February 29, 2012, 10:53:24 PM
Thanks Merlin, sorry for the noob questions  :-[
-Dana
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: wesman26 on March 01, 2012, 03:03:09 AM
This is completely awesome; I can't wait to get some tubes and build one.  I have some questions though, mostly because I'm new and don't necessarily understand.  :icon_redface:

I don't see how the voltage regulation on the heaters works, what voltage does it set them to?  What would I do to set it up such that I can change the heater voltage?

I saw PRR's post and recommendation, but I'm afraid I still don't understand quite how it works.  Any help would be much appreciated.

Thanks in advance,
--Wes
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: armstrom on March 01, 2012, 10:08:02 AM
wow, nice design and some great looking builds here! While this is an old thread it seems to have been brought back to life so I would like to take the opportunity to ask a question :)

Some time ago I penned this design:
(http://www.mr2-power.com/clipper.jpg)

But have not yet gotten around to building it. My plan is to use a 6AG11 compactron for the tube (it has two high-mu triodes and two diodes with discrete cathodes all in the same envelope) and a nixie SMPS for the HV (Will probably run closer to 180-200V than the indicated 300).

My question is, did you only need to mess around with the heater voltage on your design because you were dealing with the smaller voltage swings inherent in a 9V pedal design? As my chosen tube has a single 6.3V heater for all three elements within the envelope I don't really have the ability to change my heater voltage on the tube section without going to a separate tube for the diodes. I'm also considering adding a pot to the shared ground connection for the diodes so that I can lift them slightly and tame the clipping. I'm not sure how well that will work though. Your thoughts? I don't think I will have the same issue you did with your diodes (too sharp of a transfer function) If you look at the datasheet for the 6AG11 http://tubedata.tubes.se/sheets/093/6/6AG11.pdf you can see that the plate voltage to plate current curve is much less severe. We'll see though :) I have the tubes I just need to set aside some time to build the thing.

-Matt
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: danamoose on March 01, 2012, 10:11:01 AM
I thought sharing a parts list might help others save time on future builds. Here is what I came up with. Anyone want to give this another look to verify the values are accurate?
Thanks, and hope this helps others!

V1 - EB91 (6AL5), V2 - EB91 (6AL5)
IC - TL074, SW1 - SPDT, LINK 2 - JUMPER WIRE
D1 - 1N4001, D2 - Z9V1, D3 - LED, D4 - LED
Q1 - BC337, Q2 - BC327, Q3 - BD435, P1 - B10K, P2 - B10K,P3 - B10K
R1 - 10M,R2 - 1M,R3 - 1K,R4 - 2.7K,R5 - 1K,R6 - 2.7K,R7 - 10K,R8 - 100K,R9 - 10K,R10 - 10K,R11 - 200OHM,R12 - 10K,R13 - 10K,R14 - 1K,R15 - 470,R16 - 100OHM,R17 - 100OHM,R18 - 10K,R19 - 1M
C1 - 100n,C2 - 10u,C3 - 1u,C4 - 470p,C5 - 10u,C6 - 10n,C7 - 10u,C8 - 10u,C9 - 10u,C10 - 10u,C11 - 10u,C12 - 10n,C13 - 10n

-Dana
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: wesman26 on March 01, 2012, 12:46:32 PM
I thought sharing a parts list might help others save time on future builds. Here is what I came up with. Anyone want to give this another look to verify the values are accurate?
Thanks, and hope this helps others!

V1 - EB91 (6AL5), V2 - EB91 (6AL5)
IC - TL074, SW1 - SPDT, LINK 2 - JUMPER WIRE
D1 - 1N4001, D2 - Z9V1, D3 - LED, D4 - LED
Q1 - BC337, Q2 - BC327, Q3 - BD435, P1 - B10K, P2 - B10K,P3 - B10K
R1 - 10M,R2 - 1M,R3 - 1K,R4 - 2.7K,R5 - 1K,R6 - 2.7K,R7 - 10K,R8 - 100K,R9 - 10K,R10 - 10K,R11 - 200OHM,R12 - 10K,R13 - 10K,R14 - 1K,R15 - 470,R16 - 100OHM,R17 - 100OHM,R18 - 10K,R19 - 1M
C1 - 100n,C2 - 10u,C3 - 1u,C4 - 470p,C5 - 10u,C6 - 10n,C7 - 10u,C8 - 10u,C9 - 10u,C10 - 10u,C11 - 10u,C12 - 10n,C13 - 10n

-Dana

I think Q3 should be a BD437.  Also, Merlin, where did you get those tube sockets?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on March 01, 2012, 12:51:25 PM
I think Q3 should be a BD437. 
The BD433 and BD435 will also work.

Quote
Also, Merlin, where did you get those tube sockets?
ebay:
http://www.ebay.co.uk/itm/2-NEW-B7G-7-PIN-MINIATURE-PCB-MOUNT-TUBE-SOCKETS-/350515876687?pt=Vintage_Electronics_R2&hash=item519c5fd34f#ht_947wt_1344

http://www.ebay.co.uk/itm/40-7-pin-PCB-Mount-Mini-Tube-Socket-12AE6-3AV6-/270491239967?pt=UK_Consumer_VintageAudio_RL&hash=item3efa88c61f#ht_2555wt_1297
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: juansolo on March 01, 2012, 02:43:48 PM
Don't think I ever posted this. This is Merlin's Spark Gap feeding into Rick's (Frequency Central) Promiscuous Girlfriend. Pretty much a pedal of mass destruction. Absolutely epic thing :)

(http://juansolo.demon.co.uk/stompage/images/aod1-o.jpg)

(http://juansolo.demon.co.uk/stompage/images/aod2-o.jpg)

(http://juansolo.demon.co.uk/stompage/images/aod-i.jpg)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: blackcorvo on March 01, 2012, 09:41:05 PM
...what if one used a diode tube in the Diode Compression Op-Amp?

And what do you guys think of the 6H6? It's a tiny twin-diode in an octal base (looks like a midget 6L6 lol), that I happened to find on the site I usually buy tubes from. They have a nice stock of brands like General Electric and RCA.

I guess if you used these little guys for a distortion/overdrive pedal, you could even get some octal bases, each with different diodes types/combinations, and you could change them like you change tubes in an amp! OR you could have a single octal base, and a small board connected to it with lots of diodes, LEDs, transistors... and switches to change between them, make different combos... and an orange or amber LED connected to the heater pins...

Doesn't sound very practical, I know. But I bet that would be lots of fun to play with!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: iccaros on March 01, 2012, 10:49:31 PM
Don't think I ever posted this. This is Merlin's Spark Gap feeding into Rick's (Frequency Central) Promiscuous Girlfriend. Pretty much a pedal of mass destruction. Absolutely epic thing :)


nice, but crap, I have another project on the list now.....
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: PRR on March 02, 2012, 01:55:58 AM
I don't see how the voltage regulation on the heaters works, what voltage does it set them to?

http://www.ee.nmt.edu/~thomas/ee322_s06/labs/volt_reg/ee322_lab1.html
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on March 02, 2012, 04:18:15 AM
My question is, did you only need to mess around with the heater voltage on your design because you were dealing with the smaller voltage swings inherent in a 9V pedal design?
Yes, exactly. With larger signal levels like you get in a high voltage design, 6.3V heaters will work fine.

Quote
I'm also considering adding a pot to the shared ground connection for the diodes so that I can lift them slightly and tame the clipping. I'm not sure how well that will work though. Your thoughts?
Should work great! I did almost the same thing in an 18Watt once, but with the diodes+pot strung between the grids of the push-pull output valves. Got some nice distortion down to whisper levels!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: blackcorvo on March 02, 2012, 09:53:35 PM
Should work great! I did almost the same thing in an 18Watt once, but with the diodes+pot strung between the grids of the push-pull output valves. Got some nice distortion down to whisper levels!

Wow... now THAT sounds interesting! Care to share a scribble of that, oh mighty wizard of the glowy toobs?  :icon_cool:
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: bcalder on April 01, 2012, 04:11:48 PM
Hi all, I'm at the home stretch with my SparkGap, but have a newbie question.

I'm confused about what goes where on the three center bottom points - I see them on the schematic & layout, but not sure which lugs on the switch correspond to them.

I will probably use a 3PDT instead of DPDT switch. I understand I only use three lugs (thanks Merlin), but not sure which will go to the point that connects to R14 & which to the one that connects to Link2.


Thanks in advance,
Bruce
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on April 02, 2012, 04:29:52 AM

I'm confused about what goes where on the three center bottom points - I see them on the schematic & layout, but not sure which lugs on the switch correspond to them.

Here you go:
(http://i81.photobucket.com/albums/j207/merlinblencowe/Spark%20Gap%20EB91%20PEdal/switchwiring.jpg)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: bcalder on April 02, 2012, 09:15:07 AM
Got it now - thank you.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: bcalder on April 07, 2012, 08:46:18 AM
Hi all -

I inexplicably don't have any BC327's - I think Banzai sent me two orders of BC337's. Is it possible to sub in a BC337 at Q2?

Thanks very much for the help!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: bcalder on April 07, 2012, 10:30:02 AM
Ha, the bottom of my parts box yielded a BC327 ... I've been in Billy Gibbons land for the past hour and a half.

Thanks to Merlin for a wicked pedal & being an all-around great gent!!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Mustachio on April 07, 2012, 06:28:37 PM
Just seen this thread the other day for the first time! So I ordered eight 6AL5's before I was done reading this thread  :icon_lol:

Cant wait to get started this looks like a really fun build! thanks merlin!

Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on April 08, 2012, 10:23:10 AM
Thanks! Actually I'm thinking of redesigning, but keeping everything in the same position on the PCB so I can just drop it into the existing enclosure...
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: stevie1556 on May 21, 2012, 04:01:23 PM
What are you thinking about doing for the redesign?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Mustachio on May 21, 2012, 08:35:18 PM
Well I got all my parts and dove into making my own boards for the first time this weekend! This is my first build making my own pcb's , I used the positive photo process with mg chemicals products and it went really well!

I will post pics of the build process soon! I'm at the soldering components stage now. When printing the artwork for the pcb I couldn't find info for the dpi , so I just copied to clipboard and played with photoshop settings a few times to get it right. And I found it was right at 254 dpi. Now strangely I found this to be the case with a bunch of other pcb artwork I found in pdf's and gifs etc. and I'm wondering if it has something to do with a standard in one of the formats as to which these are shared(Copy/Paste/Monitor-dpi/Webformats?) , I thought for some reason we where supposed to be using 300-600dpi for pcb artwork.

But it works fine at 254dpi and maybe that will help some one else, I just set to mm or cm to what i could find on the pcb this one 60x80mm and when you change dpi when creating a new file from clipboard you can see the change in work area size. And I did a few test prints on reg paper to double check the sizing for ic socket and it was dead on!

I have been trimming the pcb with some large industrial snips and now filing down the sides and its just a hair away from the copper on both sides and still doesn't fit into a Hammond 1590N1. I mean its a Razor thin margin for fitting but I think ill get it :D just a lil more to file down, but it will be a very tight fit.

I could not find any tube sockets without a solid metal plug in the center so I drilled these out with my press. The center metal plugs actually hold them together and I figured so before I removed them. I used some super glue for now to keep them together. but I'm wondering if I should do something else maybe some Large shrink tubing.

Anyway this has been a really fun project for my first self made pcb build! I love tubes! and if this sounds in the ball park of a tube screamer I know ill love it!

Ill post more pics soon! Thanks again merlin! I love your circuits , I may build your engineers thumb on vero, I was itching to do it on pcb but I seen Harald at sabrotone made a vero of your engie thumb with all 5 knobs and a bright switch ! I would love to do it on pcb but Im not good enough yet to modify the pcb and make it ready to go with all controls.

(http://lh6.googleusercontent.com/8t-QM3pUe9mZnSX1afrt4PKkFY6FqbgPH_f_5yNta2d6bwHRX87fuy-aojKuo5d1mLHP_Gompww)

:::::::::::::My pics keep disappearing was trying to use googles picasa or even the G+ photos to host and it seems to be given a lil issue. ill toss some up on a diff host later::::::::::::
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: Mustachio on May 21, 2012, 09:58:09 PM
ok maybe this will work

(http://i1053.photobucket.com/albums/s479/MCMustachio/IMAG1858.jpg?t=1337651110)

(http://i1053.photobucket.com/albums/s479/MCMustachio/IMAG1860.jpg?t=1337651136)

(http://i1053.photobucket.com/albums/s479/MCMustachio/IMAG1847.jpg?t=1337651097)

(http://i1053.photobucket.com/albums/s479/MCMustachio/IMAG1848.jpg?t=1337651124)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on May 22, 2012, 05:25:30 AM
What are you thinking about doing for the redesign?
The problem with the Tubescreamer/feedback diode approach is that it has no compression, it's just a fixed clipper. Personally I think this approach sounds dry and gets boring after a while.

More 'creamy' and touch responsive distortion circuits such as real valve amps and discrete OD pedals use AC coupling, and this leads to self rectifications effects that work a lot like a compressor.

I want to redisgn the spark gap to produce these effects, and get closer to a real valve amp sound. Possibly incorporate some SS clipping just to increase the available grind, with valve OD for colour...
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: stevie1556 on June 02, 2012, 12:12:49 PM
Sounds like a fair amount of work fitting all that into the box! Good luck with it :)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: dukie on June 08, 2012, 12:47:37 PM
Wow..I think i've been away from this forum waay too long..i was searching for the old "12ax7 in DS-1 mod" when stumbled upon this thread.
I think spark gap is even better than the 12ax7 DS-1 mod! because i can't get any explanation of how it done and nor any schematic of the DS-1 mod.  :icon_mrgreen:
This baby will be in my next build list for sure.. ;D

But Merlin, is it possible 12ax7 be used intstead of EB91? if it possible then what components must be added or changed?
Great build Merlin!

Cheers! ;)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: iccaros on June 08, 2012, 01:15:54 PM
the EB91 is a dual Diode, while the 12ax7 is a dual triode (has a control grid). so the pin out is different
to turn a triode into a diode, I believe you attach the grid to the plate you will have a diode.. But I believe Merlin did not have very much luck at these voltages with that.. see bottom of page 1 where Paul brought this up using 12au7.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: asbrooks on September 19, 2013, 12:36:47 PM
Hi Merlin,
I realise that this thread is over a year old, I'm interested in how your redesign is going.
I use a solid state amp and would like to add some of that valve amp driven creaminess to it.
Sounds like it could be a great little pedal!
Looking forward to seeing the results  ;D
 
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on September 19, 2013, 05:32:45 PM
I haven't even touched this project again :(   Don't hold your breath people, I may never get round to it! (I am always surprised at the interest this design gets. It's not nearly as good, original or unusual as some of my other pedals! :icon_rolleyes: :icon_lol:)

A 12AX7 will almost certainly not work. It's reverse current and dynamic resistance are both probably too high. I suspect that's why you can't find any schematics for a DS-1 mod, i.e it probably doesn't work!
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: rankot on February 15, 2019, 09:07:54 AM
Merlin, why did you use NPN/PNP bypass circuit, and not switch?
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: rankot on May 17, 2019, 08:34:14 AM
Just built this one, but used true bypass switch instead of transistor switching.


(https://i.postimg.cc/4n5brn8P/Spar-Gap-Ranko-s-Build.jpg) (https://postimg.cc/4n5brn8P)
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: rankot on May 18, 2019, 07:30:48 AM
Also added simple voltage control for filaments (potentiometer + BC337). Works fine and the results are clearly visible on an o-scope, but not too audible. Also tried to add a tone control pot in series with C12 (10n), but it wasn't much useful.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: merlinb on May 18, 2019, 10:28:10 AM
Love it! Always gives me a warm fuzzy feeling inside when I see people adapting my circuits.
I never saw your previous question. Simple answer is, I'd never tried BJT switching before and wanted to see how well it worked, since you hardly ever see it mentioned in the textbooks. I'm going to revisit it at some point, purely for my own continued learnings.
Title: Re: Spark Gap: Unusual 9V Hybrid Valve Overdrive
Post by: rankot on May 18, 2019, 11:36:38 AM
I have also compared those tube diodes to Si and Schottky, and noticed that Schottky (1N5819) have big loss of volume, while Si (1N4148) sound a little bit brighter than tubes. Also tried to remove tubes, and sound was similarly distorted as with them!

What is the purpose of C12 (10n)? Some kind of low pass filter?