Do pedals that feature a 12AX7/ECC83 tube really create preamp tube...

[petemoore]

  I was thinking of starting a thread for high gain all tube pedals. High or low voltage.
  Another approach might be to focus on internal/external appearances or just plunk some design into a box...
  I see it this way: For new tube design, getting messy and dangerous is either an accepted possibility or there may be an unseen limitation to how well the design meets the expectations or goals. This puts LV and recommended or even overvoltage in the picture.
  I would say for a complex and usable 'sound structure' [ie distortion stage/elements 'build' the sound], various [stepped] voltages and multiple stages might fit the bill.
  Suggested routine, one of any:
  Start with a triode stage to get signal to a 'workable' level.
  Then put it through a triode stage that has a ''touch of hifi trouble'', slightly distorts. Next stage distorts too, but the voltage of the signal having been stepped up is taken into consideration when choosing the supply voltage of 'this stage..some voicing [sprinkling of caps, other methods like perhaps for high-sheen or mid-cut], perhaps another stage before the tone control, sort of a BMP type thing with no diodes, perhaps even more stages to build the complex distortion [starts lookin' like a trainwreck or recto preamp].
  I think somewhere between hifi and well before a trainwreck would suit me.
 

[zambo]

here is my three tube six stage pedal running at 45 volts. It has a tone control every two stages. I had to put a few caps to ground in between stages to kill off some highs. It could use improvement as I was totaly guessing and am kind of hackish at best...   heres the vid link        http://www.youtube.com/watch?v=YhyyYjY5CgA     highest gain setting is near the end of the vid. 

[zambo]

Hi Zambo,

I quickly tried in a pedal the SRPP circuit (Shunted Regulated Push Pull - well known in tube Hi-Fi audio) on a 12AX7, which is a cascode variant.

It doesn't give much more gain than a 100K loaded 12AX7, but it's more linear and the Z output is lower. For a pedal I felt it had no real advantages, and some drawback : you need 2 triode section to have the gain of only one, the heater-cathode insulation fo the upper triode can induce ring noise or hum, so it's better to balance it between the lower and upper triode. Another unwanted complication !

But the real cascode circuit may be more interesting in gain performances.  (Note : I only use HV in tube design).

What is worth for audio is not always worth for pedals.

I just tried the cascode circuit and it was ringing and whining like crazy! The heater causes this? How do you fix it? The distortion was great, just that ringing in the back ground was insane!

[zambo]

Ok I obviousley cant post on here the right way. Anyway I built the cascode circuite and it sounds awesome except for the high ringing that wont go away. Anyone know how to cure that? I am using a smps bought from ebay putting out 200 volts. Its model 1363 ( in case anyone wants to look it up ) . I dont know if the nixie supply is causing the ringing or not. I copied the firefly circiute exactly. I have heard of a snubber on the smps being used sometimes??? Clue? Anyone?

[petemoore]

  Filter cap after the SMPS ?
  Filtercap>R>Filtercap?
  Gnd.                   Gnd.
  Ringing is a characteristic of SMPS's.
  ...and i've never built with one, perhaps someone else can shed more light.

[tubelectron]

Hi petemoore,

Ringing is a characteristic of SMPS's.

interesting info, as I was thinking about trying some...

Hi zambo,

I dont know if the nixie supply is causing the ringing or not. I copied the firefly circiute exactly

In a SRPP the ringing MAY occur if improperly H/K balanced, it's not compulsory. I do not already know the firefly circuit : can you send a link to the schematic for analysis ?

A+!

[zambo]

here is a link to the firefly        http://ax84.com/media/ax84_m276.gif     Once again, I am using a smps at 200volts ( more or less ) bought on ebay for 13 bucks! I have used it in other designs where it didnt ring like this. I have powered a 6k6 and a 12au7 simultaneousley ( and at the same time! ). I am wondering since both gain circuits i built using it yesterday only have one tube each if maybe the smps isnt loaded enough and therefore the switching is in the audible range? It switches faster under more load??? here is a link to the smps    http://www.tayloredge.com/storefront/SmartNixie/DataSheets/Datasheet_1363-1364.pdf     I would love to get these working on these smps or one like them as they are a small, cheap hv supply. here is the 6k6 amp running on the same smps.  http://www.youtube.com/watch?v=pAc2FTzLwbk  no ringing on this. Sorry for my electronic ignorance, I do apreciate the help!

[BarnyardBill]

I was wondering if someone could post a schematic of before and after the voltage multiplier.  How do you separate the voltage from pin 5.  Maybe run 12V to pin 5, then run through the multiplier, then run that into the resistors that go to pin 1 and pin 6.  This is assuming a valve-caster type scheme.  Thanks for the help.

-Bill

[zambo]

yep. You run a 12 volt lead to pin 5. run a seperate wire to voltage multiplier then from that to the plate resistors ( pin 1 and 6 ).

[BarnyardBill]

here is a link to the firefly        http://ax84.com/media/ax84_m276.gif     Once again, I am using a smps at 200volts ( more or less ) bought on ebay for 13 bucks! I have used it in other designs where it didnt ring like this. I have powered a 6k6 and a 12au7 simultaneousley ( and at the same time! ). I am wondering since both gain circuits i built using it yesterday only have one tube each if maybe the smps isnt loaded enough and therefore the switching is in the audible range? It switches faster under more load??? here is a link to the smps    http://www.tayloredge.com/storefront/SmartNixie/DataSheets/Datasheet_1363-1364.pdf     I would love to get these working on these smps or one like them as they are a small, cheap hv supply. here is the 6k6 amp running on the same smps.  http://www.youtube.com/watch?v=pAc2FTzLwbk  no ringing on this. Sorry for my electronic ignorance, I do apreciate the help!

Zambo,

Did you ever get the nixie supply to stop the high ringing with your valvecaster?  I started reading about these nixie supplies and it looks like many of them have that problem, but some of them can be adjusted to a "sweet sopt".  Apparently they aren't meant for audio tubes, but I am dying to try a higher voltage.  Did you ever try the 'voltage pump' that has the 10 caps and 10 diodes going to the IC?  I am also considering going amp style and trying to build something with a transformer. 

Also, my pal of Linux IRC showed me this link.  Maybe you already know of it.   http://www.shine7.com/audio/12au7_pre.htm

A very fancy circuit board on the pic in that link 

-Bill

[zambo]

I got the nixie to stop ringing by adjusting the load on it. It was tricky and I dont recommend it. The voltage pump works great. I think i eneded up with 16 caps and diodes one time. Pretty big for a pedal. Frequency Central was or is building the best voltage pump. I havent tried one yet but i here they work well if adjusted right. My real feeling is to just get a transformer from antique electronics or some such placem and build a power supply from that with about 200 - 250 volts using 2 12ax7's and 100k plate load resistors and 1.5k 22uf bypassed cathodes. Pretty standard construction and could be made smallish and good. I would also use about a 20k cold clipping stage on stage 3. Just my thoughts. the  P-T261C6  at antique electronic supply tubes and more is a real good choice and more than adequate for 2 or three tubes i believe. Should give about 150 volts of rectified power. More than enough to ovedrive those ax7's nicley. Just be careful building the higher voltage stuff. If you are new to this you can really get hurt or burn up lots of expensive stuff. Read the valve wizard page. http://www.freewebs.com/valvewizard/  It can only make you smarter. I know its helped me a bunch. Merlin is a smart guy! Good luck. Greg

[Renegadrian]

May I suggest you the 40106 multiplier!? It gives out 6.5 times the incoming voltage and it works good with the valvy. and it's quite small!!! Layout and schem in the voltage multiplier topic!