#1
Simple question

Apparently these two resistors cut the input signal in HALF!
I know R1 can be bypassed and many replace R2 with a 10k or 22k, but can they both be jumpered for more gain?

Thanks Lads.
#2
if you jumper R2, it will ground out the signal.

my knowledge of tube circuits isn't as good as it used to be but lowering R1 should increase the input level. it won't give you 'more gain' because this is all before the first gain stage. jumpering R1 may not be good for the tube or w/e. like i said, i'm quite rusty.
#3
Quote by Invader Jim
if you jumper R2, it will ground out the signal.

my knowledge of tube circuits isn't as good as it used to be but lowering R1 should increase the input level. it won't give you 'more gain' because this is all before the first gain stage. jumpering R1 may not be good for the tube or w/e. like i said, i'm quite rusty.


Okay thanks,
I've read multiple other articles that say jumpering R1 will allow the guitar's input to push the preamp tube harder, making the sound more distorted, I should have distinguished what I meant by 'gain', but you're right it will shorten the life of the tube.

Once again, it's Jim to the rescue!
#4
here's a little piece of info for you guys, compared to an epiphone valve junior head a Harley Benton ga5h's resistors R1 and R2 are actually reversed!

So as invaderJim says bypassing R2 would ground the signal on an Epi but on the Benton bypassing R2 increases the amount of signal that is allowed into the preamp and R1 bypassed grounds the signal completely
#5
the schematics im looking at show R2 in line with the input, and R1 going to ground. sounds like like your version of the schem has it the other way.

but to get more gain you want to lower the inline resistor, and increase the resistor to ground. it looks like people are dropping the inline resistor to about 22k and the resistor to ground is increasing to 1M.
so basicly, this:
#6
Quote by jof1029
the schematics im looking at show R2 in line with the input, and R1 going to ground. sounds like like your version of the schem has it the other way.

but to get more gain you want to lower the inline resistor, and increase the resistor to ground. it looks like people are dropping the inline resistor to about 22k and the resistor to ground is increasing to 1M.
so basicly, this:


So I snipped JP1, bypassed the first inline resistor (the one you reduced to 22k) and also bypassed R6 and R7 and removed the tone stack. The result? Well...it's verrry loud...bassy, almost farty and the attack is extremley harsh....I'm probably going to undo everything except the JP1...unless Anyone can suggest better tubes for overdrive because this sound is terrible, right now I have a Marshall 12AX7 (with black writing) and an EH EL84L
#7
Quote by Ma-hog!
So I snipped JP1, bypassed the first inline resistor (the one you reduced to 22k) and also bypassed R6 and R7 and removed the tone stack. The result? Well...it's verrry loud...bassy, almost farty and the attack is extremley harsh....I'm probably going to undo everything except the JP1...unless Anyone can suggest better tubes for overdrive because this sound is terrible, right now I have a Marshall 12AX7 (with black writing) and an EH EL84L



go back and do the things I told you to do.
Prs se Holcomb is the answer
#8
Quote by AcousticMirror
go back and do the things I told you to do.


I'm not trying to be a Dick or anything but what you've suggested can't be applied to the schematic, for example lifting the ground on r19, r19 is a fixed resistor lifting the ground side will create an open circuit, and lifting the ground on the bass pot is not going to bypass it (although it would on a normal tone pot)
The other suggestions I'm awaiting parts for.
I have bypassed the tone stack by connecting the positive and negative wires before they reach the tone circuit, and the volume increase through a 50w 12" speaker is monumental!
However, the schematic you provided was of great help, thanks again.
#9
what are you talking about. Of course it creates an open circuit.

it acts as a boost by bypassing parts of the tone stack.
Prs se Holcomb is the answer
#10
Quote by Ma-hog!
I'm not trying to be a Dick or anything but what you've suggested can't be applied to the schematic, for example lifting the ground on r19, r19 is a fixed resistor lifting the ground side will create an open circuit, and lifting the ground on the bass pot is not going to bypass it (although it would on a normal tone pot)
The other suggestions I'm awaiting parts for.
I have bypassed the tone stack by connecting the positive and negative wires before they reach the tone circuit, and the volume increase through a 50w 12" speaker is monumental!
However, the schematic you provided was of great help, thanks again.

i hope you didn't DC couple it.

what's R19? valve JR doesnt have an R19. o_O
Call me "Shot".

ShotRod Guitar Works

Custom Hand-wired Amplifiers and Effect Pedals.

Est. 2007


Source to everything I say about Guitars, Pedals, and Amplifiers: I make them.


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#11
Quote by ECistheBest
i hope you didn't DC couple it.

what's R19? valve JR doesnt have an R19. o_O


Harley benton ga5h its a valve junior clone with a bass control so the parts are slightly different
dc coupling?
why would letting ac and dc through be bad?
okay what I've done is the equivalent of bypassing r15 on a valve junior is that dc coupling? I think it is
Last edited by Ma-hog! at May 31, 2011,
#12
Quote by ECistheBest
i hope you didn't DC couple it.

what's R19? valve JR doesnt have an R19. o_O


the benton is a bit different then the vjr.

http://www.sewatt.com/files/sewatt/HB-GA5-Stock_0.pdf

c2 couples to the power tube so no worries of dc coupling.

i've actually done that before...the cathode resistor explodes on the power tube. was lols.
Prs se Holcomb is the answer
#13
yea dc coupling gives u awesome results that aren't so awesome.


so you're trying to maximize distortion. to do that, u can do few things. it won't lead to pleasant sound tho, but you can get more distortion out of it.

-jumper R6
-clip R7
-replace R3 with 220k
-replace R4 with 180k
-jumper the treble cap of the tonestack, clip R17 and R15
-for tonal properties, you might want to increase R18 to 270k, replace C4 and C3 with 2uF, 1uF respectively.


these are suggestions. doing all of the parts that increase gain will probably result in unpleasant sound.
Call me "Shot".

ShotRod Guitar Works

Custom Hand-wired Amplifiers and Effect Pedals.

Est. 2007


Source to everything I say about Guitars, Pedals, and Amplifiers: I make them.


UG's Best DIY PedalBoard
#14
Quote by ECistheBest
yea dc coupling gives u awesome results that aren't so awesome.


so you're trying to maximize distortion. to do that, u can do few things. it won't lead to pleasant sound tho, but you can get more distortion out of it.

-jumper R6
-clip R7
-replace R3 with 220k
-replace R4 with 180k
-jumper the treble cap of the tonestack, clip R17 and R15
-for tonal properties, you might want to increase R18 to 270k, replace C4 and C3 with 2uF, 1uF respectively.


these are suggestions. doing all of the parts that increase gain will probably result in unpleasant sound.


Oh no, maximising distortion is not my aim at all My board doesn't conform to the schematic in some areas, R1 and R2 is one of those areas, in my amp they're reversed which caused some confusion which is why I created the thread.

But now I've done some more eccentric mods using parts of old amps and moving the tone stack and the results are great I just have to solder it all in because right now its croc clipped and then it's done
Last edited by Ma-hog! at May 31, 2011,
#15
oh ok nvm. good thing u got good results from modifications to your own taste haha
Call me "Shot".

ShotRod Guitar Works

Custom Hand-wired Amplifiers and Effect Pedals.

Est. 2007


Source to everything I say about Guitars, Pedals, and Amplifiers: I make them.


UG's Best DIY PedalBoard
#16
Quote by ECistheBest
oh ok nvm. good thing u got good results from modifications to your own taste haha


Ah no you're grand, a miscommunication, thanks though!