First DIY tube OD pedal... some advise please?

[hopkinWFG]

Hi there am trying to build a MODKIT Persuader Preamp tube pedal based on 12ax7... however i manage to get the parts list and diagram on how to wire up.. All thanks to ModKit for providing such details...

i have gotten my prefboard which have individual isolated soldering rings.. and i dont know if am i suppose to do a soldering connection point to point by using just the leads of the electronic component to connect?

[Greenmachine]

you can solder to the copper pads directly under the leads for support.  as many or as few as you want. 

[hopkinWFG]

thanks but I just did few connections of several leads together from various electronic components..

however just to ask because am doing a tube pedal 12ax7 is there a possible mods to do a stack of two 12ax7?
also have heard of the real tube usuage would runs at AC12V...but is a 9VDC based pedal was wondering if is possible to mod it as well in future?

last is this pedal is having a mosfet BS170 transistor does it require a transistor for gain since I thought 12ax7 already a gain tube? how about changing the transistor to a higher gain type would it inturn be a distortion pedal than an OD ?

thanks am new to it excited and far more ambitious please excuse me..

[Greenmachine]

hmm ... I don't know - but I'm sure someone around here will answer your questions. 

[pinkjimiphoton]

thanks but I just did few connections of several leads together from various electronic components..

however just to ask because am doing a tube pedal 12ax7 is there a possible mods to do a stack of two 12ax7?

maybe. i'd have to look at the circuit. a lot of it would depend on if the power supply could supply enough current for the two tubes. you'd probably need to run a bigger transformer than a 9v one. you'd need a good amp probably of current just for the heaters. one 12ax7 is two gain stages, you should be able to cascade them and get a fair amount of gain. google up cathode follower, it may or may not suit your needs. i'm not familiar with this circuit...do you have a schematic you can post?

also have heard of the real tube usuage would runs at AC12V...but is a 9VDC based pedal was wondering if is possible to mod it as well in future?

sure. when ya build it, if you wanna run on 12 or 18v or whatever, make sure you go to at least 1/4 watt resistors, better to be half watt, and make sure your caps are rated at least double your voltage. but... be extremely careful, you CAN hurt yourself even with a low voltage.

but...the higher the voltage you can hit the plates with, the more dynamic they will be..."cleaner", "louder". if you want distortion, you don't necessarily need that. the more you "starve" the b+ to the tube (the voltage going to the plate resistors) the more the tube is apt to distort. so if you want more distortion, at less headroom, take a couple of healthy pots, like, 1/2 or one watt, one plate probably a 50k and cathode maybe a 10k or so, and swap it in for the plate resistors and the cathode resistors...dial it in til it sounds good to you, then measure the resistances and use appropriate resistors. you can make a tube "fuzz"...but it may not sound that great. like, to start, take the plate and cathode resistors, and try doubling them to the next standard value...ie, if it's 100k plate/1k cathode, try 220k plate/2.2 or 2.7k cathode. you can also go for bigger cathode bypass caps, if you use them. i've even seen diodes in the cathode circuit, if memory serves, to help it distort.

last is this pedal is having a mosfet BS170 transistor does it require a transistor for gain since I thought 12ax7 already a gain tube? how about changing the transistor to a higher gain type would it inturn be a distortion pedal than an OD ?

depends where the bs170 is...if it's at the front of the circuit, it's probably there to wallop the tube and make the tube overdrive. if it's at the end, it's to buffer the tube signal i'd imagine. putting a higher gain transistor probably isn't necessary, just increase the available gain to the bs170 if it's at the front of the circuit... a SHO uses them, and them puppies are LOUD!

and of course, you can always add diode clippers at the tail end of the circuit, led's would probably work well and give a nice hard "edge" when ya lean on it. for easier distortion, use silicon diodes. or ge. like i said, i'm not familiar with the circuit at all, just musing about some of the stuff i've tried in tube amps over the years.

thanks am new to it excited and far more ambitious please excuse me..

hope this helps in some way, i bet there's some great ideas on this forum, and probably people will be able to give ya a lot more specific info if you can post the schematic.
peace!

[rutabaga bob]

The schematic is at modkits...9 volts to the heaters (!), and 8-something on the plates. 

[pinkjimiphoton]

gotta link bro?

9v to the heaters? yah, that's not cool. thats almost 1.5 what they should have. 6.3v ac is what they want. they're probably running the heaters at 4.5v instead. the tubes will last forever.

but not at 9v. that would smoke 'em....well, in time.

[rutabaga bob]

No, this is wired like the Valvecaster, 9 volts to pin 4, pin 5 to ground...no connection at pin 9.  You're thinking of standard amp wiring.  Wired this way, it is 3 volts low.  If you happen to be using a filament-sensitive tube, one where the emissions drop off unless using full rated voltage, this would be a bummer.
http://www.modkitsdiy.com/sites/default/files/product_files/the_persuader_schematic.pdf

[pinkjimiphoton]

whoa, weird.

i'll have to take a peek at it one of these days.

[rutabaga bob]

Just click on the link, my man... 

[pinkjimiphoton]

just looked...yep, slammin' the front end of the 12ax7 with the fet.

iffin' i was looking for more balls, i'd prolly use a 33k on plate 1, and a 10k on plate 2, but i don't know if it will still bias with the cathode directly grounded.
i'll have to play with it some.

thanks larry!

[rutabaga bob]

@hopkinWFG:  I re-looked at your first post, and I'm unclear whether you bought the modkit, or are just planning to use their design.  My 2 cents, which isn't worth what it used to be, says - if you haven't spent any money on a kit, do some searching on the forum and check into projects that will give you more toward a higher-gain pedal that you're looking for.  Several people have built dual Valvecasters, a pedal that uses a 12au7 tube.  (the dual uses 2 of them)      Larry

[pinkjimiphoton]

that said...looking at their projects, every single one is someone else's stuff. i've seen sho, fuzzface, etc etc...

i haven't seen an ORIGINAL idea there...not that i have any... seems to me they're kinda just taking other peep's designs, and selling them.

[hopkinWFG]

whoa, weird.

i'll have to take a peek at it one of these days.

yes larry has gotten the schemetic down...its gotta parts list and instructions down ... am from singapore so I just source out the needed electronics from my local stores..is my first attempt in building one..ill try to post pics of how I attempt to solder the leads... however I cannot attach pics here..

[hopkinWFG]

@hopkinWFG:  I re-looked at your first post, and I'm unclear whether you bought the modkit, or are just planning to use their design.  My 2 cents, which isn't worth what it used to be, says - if you haven't spent any money on a kit, do some searching on the forum and check into projects that will give you more toward a higher-gain pedal that you're looking for.  Several people have built dual Valvecasters, a pedal that uses a 12au7 tube.  (the dual uses 2 of them)      Larry

thanks alot for your profound knowledge jimi..but yeah it is using a mosfet bs170 to push the gain ? I dont know if its a real tube design? correct me if am wrong...thanks

[pinkjimiphoton]

@hopkinWFG:  I re-looked at your first post, and I'm unclear whether you bought the modkit, or are just planning to use their design.  My 2 cents, which isn't worth what it used to be, says - if you haven't spent any money on a kit, do some searching on the forum and check into projects that will give you more toward a higher-gain pedal that you're looking for.  Several people have built dual Valvecasters, a pedal that uses a 12au7 tube.  (the dual uses 2 of them)      Larry

thanks alot for your profound knowledge jimi..but yeah it is using a mosfet bs170 to push the gain ? I dont know if its a real tube design? correct me if am wrong...thanks

hey bro, greets from connecticut, usa...welcome to the forum!
yah, basically they're using the mosfet to make the first stage of the tube overdrive, and then using the second stage of the tube to make  it louder. the first stage is biased relatively clean, with the 68k....a standard tube amp usually uses 100k for the plate resistors. by using the second stage with a smaller resistor, it make it a bit cleaner so it can be a boost.
it's a hybrid design, should sound good. it's kinda like using a zvex super hard on overdrive into the first stage of a slightly overdriven amp. the mosfet is probably pumping about 30db into the first stage, which is pretty starved by the low supply voltage and the big resistor, making it distort a lot.

i'm gonna try and build this and play with it a little bit. it's not necessarily an "all tube" design...but overdriven mosfets sound great, and the tube stages should warm it up really nicely.

peace!

[hopkinWFG]

@hopkinWFG:  I re-looked at your first post, and I'm unclear whether you bought the modkit, or are just planning to use their design.  My 2 cents, which isn't worth what it used to be, says - if you haven't spent any money on a kit, do some searching on the forum and check into projects that will give you more toward a higher-gain pedal that you're looking for.  Several people have built dual Valvecasters, a pedal that uses a 12au7 tube.  (the dual uses 2 of them)      Larry

thanks alot for your profound knowledge jimi..but yeah it is using a mosfet bs170 to push the gain ? I dont know if its a real tube design? correct me if am wrong...thanks

hey bro, greets from connecticut, usa...welcome to the forum!
yah, basically they're using the mosfet to make the first stage of the tube overdrive, and then using the second stage of the tube to make  it louder. the first stage is biased relatively clean, with the 68k....a standard tube amp usually uses 100k for the plate resistors. by using the second stage with a smaller resistor, it make it a bit cleaner so it can be a boost.
it's a hybrid design, should sound good. it's kinda like using a zvex super hard on overdrive into the first stage of a slightly overdriven amp. the mosfet is probably pumping about 30db into the first stage, which is pretty starved by the low supply voltage and the big resistor, making it distort a lot.

i'm gonna try and build this and play with it a little bit. it's not necessarily an "all tube" design...but overdriven mosfets sound great, and the tube stages should warm it up really nicely.

peace!

Thanks there ! really appreciate this much time of yours to write and explain the functionality of each resistor and component.. well if your doing yours that would be great ! least ill have someone to check with and give details advise too in future if were to mod it for the better...

Well actually i am very interested in doing a DIY tube amp i wonder if you do yours too.. but without any experience in electronics i then try to DIY a simple tube pedal .. as this is a transistor boosted tube type of circuit... i wonder if you could introduce me to any good sounding real tube OD  schemetic pedal where i could work on? Thanks and i hope we could discuss thru having to complete mine and yours on this tread as time to come ...take care

[hopkinWFG]

Hi there guys this is how i connect up my electronic parts on the perfboard as is my first attempt again would my connection like it shown on the link below have any impact on the tone? i basically solder the component up and using the protruding leads to connect to another leads of the others..
will a perf board have any downsides or inferior to using a PCB?

or perhaps if you guys could suggest me few idea to have good connection in apperance and tone wise.. i know and i have heard probably a "horizontally/vertically" connected pref board but my silly mind didnt came to that point at that instance of purchase lol...

http://imageshack.us/photo/my-images/585/20121217005547.jpg/

another picture below shows the components i got.. not really high grade but am cutting cost just to see how the project works... have gotten a preamp tube socket but i wonder why are the soldering pins on the tube socket so loose? so i have to fix them up before soldering it and inserting the 12ax7 tube? or if its loose would it have any impact on the preamp tube when powered?

http://imageshack.us/photo/my-images/805/20121216195339.jpg/

[rutabaga bob]

Regarding your post about a simple tube overdrive pedal, search the forum for 'tube boost + overdrive' running on a 9 volt battery.  This is the monster Valvecaster thread.
The socket soldering lugs are normally a little wobbly.  (as are many forum members!) 

[Renegadrian]

A SHO before an uncommon tube gain stages pair...WTF! 
no cathode resistors, nothing...meh...