need help with cathode follower circuit

[REGNAD]

he folks, i want to build a cathode follower to use in my fx chain. im a tube noob so i have a few questions.
1: will resistor values differ based on the impedances both in front of and after the circuit?
2: if so, how do i determin the impedance/capasitance <- spelling of my rig?
3: is there a schematic of this circuit out there or a calculator to help with these values?
assuming i am right in aplication, i want to add a cathode follower inbetween my guitar and each effect all the way to my tube amp.
thanks in advance!

[JKowalski]

i want to add a cathode follower inbetween my guitar and each effect all the way to my tube amp.

That seems quite unnecessary and complicated. What are you trying to accomplish with this set-up?


http://www.freewebs.com/valvewizard/accf.html

[REGNAD]

i want a tube buffer between all my pedals.

[punkin]

Is there a particular reason why it has to be a tube type? There are a bunch of easier circuits that employ transistors. Smaller and simpler to make. Have you seen this? http://www.muzique.com/lab/buffers.htm

[Gus]

You could build a CF between each part of the signal chain.  You can find information on the web and in books to build CFs.

That said it might be a waste of time to do, because a CFs(cathode followers), SF(source followers FETs), EF(emitter followers)tend to have little to no added sound(distortion) at the levels in a guitar to amp path.

Two things you could try SFs or bootstrapped EFs(you can find a bootstrapped EF in "The Art of Electronics")

If you want CFs  google, tube cad, Radiotronics 4th edition, etc. or go to you library and look at tube books.

If you use a higher B+ voltage than 9VDC for the tubes you need to be aware of  safety issues.

Also a CF might affect the sound in a "bad" way if in front of a FF type circuit etc.

[REGNAD]

im not looking for any distortion fx from a cf circuit. to be honest, i didnt think i was going to get so much grief about this! Correct me if im wrong, but if Pete Cornish and David Gilmour feels theres a benefit to using tube circuits to isolate and impedance match fx chains then why not dable with them myself? does no one here have info other than "why would you do that" or "theres plenty of books out there"? i thought this was the place to get answers!

[Gus]

I posted you could do it.  I am not giving you grief.  Setting up a CF is not that hard.  Question what you read on the web.

Not knowing you B+ or tubes to be used and what you want to drive makes a difference.

With buffers too high or too low a input resistance can affect tone when connected to a guitar so do you want a 100K  or a 500K or a 1meg or a 100meg or even a 1 gig input resistance.  Google AKG C60 and look at the CF used.  Do you want a CF with a cathode resistor or one with an active load or a white follower or?

First state the design parameters and power supply voltages you want.  Then you could get an answer.

[JKowalski]

im not looking for any distortion fx from a cf circuit. to be honest, i didnt think i was going to get so much grief about this! Correct me if im wrong, but if Pete Cornish and David Gilmour feels theres a benefit to using tube circuits to isolate and impedance match fx chains then why not dable with them myself? does no one here have info other than "why would you do that" or "theres plenty of books out there"? i thought this was the place to get answers!

We gave you info. I gave you a link to a page that describes building CF in exquisite detail - that site is really all you would need. People suggested solid state instead. Gus gave you a chunk of good info.

I'll let you know something - most famous guitarists out there don't know squat about electronics. They often do ridiculous, stupid, or unecessary things to their rigs and everybody tends to copy them to get "that sound" - hence the chain of ignorance continues on. I don't want to appear too critical, but I am just saying you really have to do the research first. Sometimes, buffers are not necessary and will do absolutely nothing to your sound, and that's a fact.

I personally would be less critical if you were doing this solid state - it's alot less effort, which more closely matches the result I am expecting from this project - with so many tubes, it just seems like you are wasting expense and effort. You admit that you want the buffer to not change your sound, so why are you using tubes? Tube buffers are more likely to alter the sound of the signal (unless designed very well), and as stated before more bulky, troublesome, and expensive. Solid state will do the same exact thing, and can be done more precisely. (better quality buffering)

I can see the use that a big box o' buffers would be in a large pedal rig (I think having buffers available for use in certain situations would be a great tool). Having them between every effect is pointless, since some won't do anything and others will make some of your pedals sound worse.

I feel like I am being redundant. So here's what I have to say summed up:

Make a box of a bunch of solid state buffers that you can use in specialized cases, when necessary.

Of course, it's your final decision. 

[REGNAD]

thanks gus, your last response was getting me closer to asking the right questions. but jkowalski, where do i start...

"im a tube noob so i have a few questions"
as originally posted. the questions that i asked in the first place where not answered at all. anyone can pass out canned aswers, hell i can do that! i have read the info in the links but i didnt get the aswers i needed. at least not in a form i could understand, so i came here. 

"I personally would be less critical if you were doing this solid state - it's alot less effort, which more closely matches the result I am expecting from this project - with so many tubes, it just seems like you are wasting expense and effort. You admit that you want the buffer to not change your sound, so why are you using tubes? Tube buffers are more likely to alter the sound of the signal (unless designed very well), and as stated before more bulky, troublesome, and expensive. Solid state will do the same exact thing, and can be done more precisely. (better quality buffering)"

i guess you think cd's and digital fx sound better than analog!


"I'll let you know something - most famous guitarists out there don't know squat about electronics. They often do ridiculous, stupid, or unecessary things to their rigs and everybody tends to copy them to get "that sound" - hence the chain of ignorance continues on."

wow, i guess i should of started my post with " assholes need not respond"  what started out with "go to the library" ended with "your ignorant if you emulate someone elses gear to get that sound"!!!
its like im having a conversation with radio shack employees. a transistor isnt the answer for everything.
i guess i wont bother you guys and your "circle". i'll go somewhere else for what im looking for.

to all that have been a great help in the past, thank you. everyone else, tell yoursef your doing a good job.

[punkin]

Wow...honestly, I was trying to help but after reading and re-reading my post, I guess I didn't realize just how big an ass hole I was   .  The one thing I might have going for me is that I too am a fan of analog (I'm too old to appreciate the digi-stuff). Check out my pepper-shredder...it's my "go-to" distortion pedal.

Wish you the best with your build...maybe you'll find some help here;

http://www.glass-ware.com/tubecircuits/Easy_Cathode_Followers.html
http://www.tubecad.com/2007/04/blog0104.htm (note the tools being offered on this site)
http://archive.ampage.org/threads/1/gagd/000205/Why_a_cathode_follower-1.html (another thread where someone posted the same question...interesting responses)
http://digilander.libero.it/paeng/cathode_follower_follows__audio.htm (some support with the math when designing your own...this is probably the most helpfull of the bunch)
http://diyaudioprojects.com/Schematics/12AU7-Cathode-Follower-Tube-Preamplifier.htm (here's an actual circuit you could build)
http://www.siteswithstyle.com/VoltSecond/Foreplay_Unity_gain/Unity_gain_Foreplay.html (This guy is doing quite a bit with a pre-amp)
http://home.comcast.net/~machrone/bjr/follower/cathodefoll.htm (and a guy modding a preamp using what you're trying to accomplish...i think).


oh...just found another which has a lot to offer. It makes some compelling arguements for the u-follower configuration.
http://books.google.com/books?id=b4Thv_rINKYC&pg=PA100&lpg=PA100&dq=cathode+follower+buffer&source=bl&ots=ybgufIhbfe&sig=VRkWKDLeHfLBXXIhrDB8AN-GGPQ&hl=en&ei=nyGbSqzVG4LCsQPxwdSTDg&sa=X&oi=book_result&ct=result&resnum=7#v=onepage&q=cathode%20follower%20buffer&f=false

Regretably, I'm not finding much for you in the low voltage areas. When you get down that low, sometimes its just plain simpler to look at a mosfet or JFET. I like JFET as they're something of a compromise...they behave rather similarly to the glass valves.





Sarcasm...now that's my passion. That and my collection of KWM-2a's and 4CX1000's...which reminds me...I've got a PA grid to neutralize on a new final.  

[sean k]

Settle down Regnad, everythings gonna be fine. As people have said, most likely from experience, that tubes require alot of work and expense compared to what you get from them. They are really good in some situations but for run of the mill signal buffering... we're saying they aint worth the effort... but if you've got the money and the time then I'd suggest 12AU7's as a good tube to use. They are low impedance and don't mind sending a bunch of current out. The plate current is usually about 10mA and a 12AX7's about 1mA.

I'd go for the systen where you use both tube sections with one atop the other. I can't remember what its called  but the top tube is on B+, it's grid goes through a cap to it's cathode and both the output and the second tubes plate are joined at that point. I'd look at similar circuits that use jfets and mosfets doubled up and emulate them with tubes that push lots of current. My biggest concern, unless you could create the high voltage in house with neon tube inverters and suchlike, would be the multiple power cabbles running at a few hundred volts, not in the danger for shocks, but for the high impedance they'd be running at so you'd almost have like the inside of a tube amp spread out over a couple square metres. As long as they are at 90 degrees to your signal cables it could cause you all sorts of problems.

If you can make 9-15 12V powered, using inverters onboard, tube buffers I think the next step of small scale manufactering would be a very logical one to take. Good Luck!

[REGNAD]

thanks for the real answers guys, i check out the links a bit and cool off. as mentioned, im a rookie with the tubes. i just built the Matsumin ValveCaster and really like it. i have no issues reading schematics. i didnt finnish my electronics degree and we didnt mess around with tubes so i dont understand how they work yet. i was assuming that the circuit would be built and powered similarly to the valvecaster. am i wrong?

[aziltz]

reminds me of the "RG's TS Explanation is WRONG!" thread.

good luck with your projects.  If I may add my dollar fifty, start with one tube buffer, and see how your rig reacts.  The people trying to talk you out of it were doing so because its tedious and expensive, and much harder than solid state.

[JKowalski]

thanks gus, your last response was getting me closer to asking the right questions. but jkowalski, where do i start...

"im a tube noob so i have a few questions"
as originally posted. the questions that i asked in the first place where not answered at all. anyone can pass out canned aswers, hell i can do that! i have read the info in the links but i didnt get the aswers i needed. at least not in a form i could understand, so i came here.  

"I personally would be less critical if you were doing this solid state - it's alot less effort, which more closely matches the result I am expecting from this project - with so many tubes, it just seems like you are wasting expense and effort. You admit that you want the buffer to not change your sound, so why are you using tubes? Tube buffers are more likely to alter the sound of the signal (unless designed very well), and as stated before more bulky, troublesome, and expensive. Solid state will do the same exact thing, and can be done more precisely. (better quality buffering)"

i guess you think cd's and digital fx sound better than analog!


"I'll let you know something - most famous guitarists out there don't know squat about electronics. They often do ridiculous, stupid, or unecessary things to their rigs and everybody tends to copy them to get "that sound" - hence the chain of ignorance continues on."

wow, i guess i should of started my post with " assholes need not respond"  what started out with "go to the library" ended with "your ignorant if you emulate someone elses gear to get that sound"!!!
its like im having a conversation with radio shack employees. a transistor isnt the answer for everything.
i guess i wont bother you guys and your "circle". i'll go somewhere else for what im looking for.

to all that have been a great help in the past, thank you. everyone else, tell yoursef your doing a good job.

I really didn't mean to sound so condescending, but I was trying to give you honest advice.

I am not on the side of tubes or transistors - I go with the electronic theory. Tubes are useful in getting certain sounds, and sold state is useful for others. Based on what I know, I think solid state buffers are the way that you should go. I said the thing about guitarists because it is true - many many times it happens, and I have a pet peeve with the whole concept of "mojo" (which applies to it). I'm sorry that that was kind of like saying "you are an idiot for doing this" - I was just trying to encourage you to be open to other options that will get you to the same results in a much easier way. I was saying that sometimes these people do the things they do because they don't really research it enough, and that you shouldn't stick completely to what they do because most of the time you really can't know for sure how much experience they actually have on the matter.

The only reason that I am posting on this forum, and this topic, is to help people. I am not trying to tout myself over the internet as a guru that must be worshiped by all (and a guru I am definitely not). I gave you my advice, and you can take it or leave it, but please remember that I am spending my time to offer it, with the goal of making your project easier and more successful.

I gave you a link to a site that I find helpful. I did not give you precise instructions as answers to your questions because I am not highly experienced with tube electronics yet and I would not want to have given you bad information which may confuse you. I simply gave you advice, because that is what I felt comfortable offering you, and I felt that it was worth hearing.

[frequencycentral]

Using the Valvecaster as a starting point I'd try this:



Reading for top to bottom the tube's pins would be 1, 2, 3 or 6, 7, 8 depending on which side of the dual triode you use. You might want to put a low value resistor between the tube's cathode (pin 3 or 8 ), say 1K for starters. You can make two of these from each 12AU7. The output will be almost unity with the input, about 99% of it anyway. +v to pin 5 should be a 12 volt filtered/regulated supply. B+ to the plates (pin 1 or pin 6, via the 100K resistor) could be 12 volts, or higher if you wish. A higher B+ could be derived from a charge pump. At 12 volts you may find a 'softening' of the waveform, higher B+ will give more claen headroom. Depends what works for you, but IMO something around 35 volts would be decent enough if you find 12 volts unacceptable.

Charge pump: http://www.diystompboxes.com/smfforum/index.php?topic=74729.0

[Gus]

I googled and found this link
http://home.comcast.net/~jroscoe/CornishQnA.html

Note the placement of the buffers at the input and the send and returns and the outputs if I am understanding the mark 2 setup.

I wonder if the buffers are tubes just to be tubes?

A well make follower should not have a sound.  All that should matter is defining the input Z and output Z and drive needed and stability into a load(long cables for example) and the level of the signal the stage should buffer without clipping and max distortion.

there are
CFs with a CC BJT in the cathode leg
White followers
CFs with resistor(s) in the cathode leg
bootstrapped CFs
Anode followers
SFs with another CC fet etc in the source leg
SFs with a resistor(s) in the source leg
Fet circuits like in the National Semiconductor notes Fet BJT?
bootstrapped fet circuits
BJT EF
bootstrapped BJT EF
IC based buffers
Opamp buffer
etc


frequencycentral why the 100k to the plate for a CF?

[frequencycentral]

frequencycentral why the 100k to the plate for a CF?

I figured the OP is looking for a non-inverting tube unity gain buffer, and the circuit I posted has worked to me in the past. I education is however incomplete.

[JKowalski]

I wonder if the buffers are tubes just to be tubes?

See, that's what my line of thinking is. I can't see any possible reason otherwise why someone would use tubes instead of SS for a simple buffer. I think that he did it because:

A: He already had a tube power supply set up and enclosed in his large board which makes it alot safer and easier
B: He wanted to give it the title of "all tube pedalboard", so he had to stick with tubes all the way through



I did not know the history of Cornish, and I admit that he does appear to be knowledgeable on the subject. But that does not change my opinion that you should use SS. I don't think he did it for any reason save the ones I listed above.

[REGNAD]

thanks freq, i assume we are talking about 12-35 volts dc? i'll get my hands on another 12au7 tube and try this out. is there any need for any adjustments on this circuit? and i didnt understand your comment about maybe adding a low value resistor between the tubes cathode. can you put that in the schematic?

[Salvatore]

Here is the valvecaster thread this buffer is based on.
http://www.diystompboxes.com/smfforum/index.php?topic=63479.0

It will typically run on 12 volts (although you can choose for higher voltage on the plate).