# Add a 9V guitar tuner to at tube amp .

F

#### fffcj

Jan 1, 1970
0
I have a nice tube amp .
I'm modifying the case to lighten it etc ...
While I'm at it , I'd like to incorporate my guitar tuner into the amp .
Regarding the audio circuit , I'll probably just place the tuner into the
FX loop .

What I'm unclear on is how to find some 9V dc within the tube amp to
power the guitar tuner .
I guess I'll need maybe some more components to rectify / smooth the power
from the amps own power transformer .
I've not tested any ac voltages yet .

What circuit should I be using ?

Thanks

Chris

T

#### tempus fugit

Jan 1, 1970
0
What kind of tube amp is it?
Most people feel that a tuner in line degrades the signal, so if I were you
I'd take a parallel connection from the FX loop.
I doubt you'll find 9v in there, but if there are any opamps or other ICs,
you might be able to get 15v. Often the EQ stages are opamps or transistors.
I'd (very carefully) poke around there 1st. If you can get 15v, you could
just use a 7809 regulator to get the voltage down to 9v.

Always bear in mind that tube amps contain high voltages. Even when
unplugged, the caps can hold a considerable charge (enough to KILL you).
Make sure you know what you're doing before you go sticking probes around in
there.

F

#### fffcj

Jan 1, 1970
0
Thanks .
Especially the safety stuff .

Chris

S

#### Spajky

Jan 1, 1970
0
I have a nice tube amp .
I'd like to incorporate my guitar tuner into the amp .
Regarding the audio circuit , I'll probably just place the tuner into the
FX loop .
What I'm unclear on is how to find some 9V dc within the tube amp to
power the guitar tuner .
I guess I'll need maybe some more components to rectify / smooth the power
from the amps own power transformer .
I've not tested any ac voltages yet .
What circuit should I be using ?

lamps heating voltage ( ff ) is probably 6,3V AC coming from
power transformer, followed by a graetz type rectifier & a more than
1000uF/16V el.capacitor connected to rectifiers -/+ out properly;
you will get approx. 9V DC ...

But check first, that power ff source is not grounded; if is & the
other wire is 6,3V AC to ground, IMHO would be enough instead of
graetz rectifier to use just a diode ...

If is grounded in the middle (2x 3,2VAC), than you will have to find
another solution ...

C

#### CFoley1064

Jan 1, 1970
0
Subject: Add a 9V guitar tuner to at tube amp .
From: "fffcj" [email protected]
Date: 10/22/2004 8:51 PM Central Daylight Time
Message-id: <[email protected]>

I have a nice tube amp .
I'm modifying the case to lighten it etc ...
While I'm at it , I'd like to incorporate my guitar tuner into the amp .
Regarding the audio circuit , I'll probably just place the tuner into the
FX loop .

What I'm unclear on is how to find some 9V dc within the tube amp to
power the guitar tuner .
I guess I'll need maybe some more components to rectify / smooth the power
from the amps own power transformer .
I've not tested any ac voltages yet .

What circuit should I be using ?

Thanks

Chris

Hi, Chris. If you don't need a lot of current, find a couple of small 6.3 VAC
secondary transformers and do something like this (view in fixed font or M$Notepad): .------. 120VAC 120VAC 6.3VAC | | + o---. ,-o-----------o-. ,------o--o~ +o-----o-----o 6.3VAC )|( )|( | | | )|( )|( | | +| o---' '-o-----------o-' '------o--o~ -o-. --- 8VDC | | | --- '------' | | | | - '---o-----o created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de Pick off your 6.3VAC to the tube heaters (which will almost always be grounded -- you can't use that) and use it to backfeed the first transformer, and then use that output to feed the second transformer. You can take the output of the second and rectify/filter that to give you a little over 8VDC. Use schottky diodes instead of a standard bridge rectifier for a slightly higher voltage. First, you have to oversize the first transformer if you're backfeeding -- It should be rated at least 4X the VA you are using at the DC side. So, if you've got two 3VA transformers ([email protected]), you shouldn't expect to get more than 80mA or so out of your DC without getting the first transformer really hot. And you do have to be careful about the heater power -- don't take too much, or you'll smoke the main xfmr. I like the concept of borrowing a couple of VA -- that's about 1 extra tube's worth of current -- it's usually safe. Second, you'll have to use a brute force cap to reduce ripple on the output. The 120 Hz ripple might not be too good for your application, so you might want to use a 12VAC secondary transformer for the second one, and then feed that to a standard rectifier/filter/linear regulator like the LM317. .------. ____ 120VAC 12 VAC | | | | --o-. ,------o--o~ +o-----o---| 317|--o----o )|( | | | |____| | | )|( | | +| | .-. | --o-' '------o--o~ -o-. --- |240 | | | | | | --- | | | | 2nd Transformer '------' | | | '-' +| | | | | --- | | o-----' --- | | | | | | .-. | | | | |1800 | | | | | | | | '-' | | | | | '---o-----o ---------o created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de Be sure to have a second transformer of less than or equal VA rating to the first. Also, be extremely careful here to avoid a situation where you connect a higher potential in to this circuit. It'll kill the LM317, and potentially cause a lot of other damage inside the amp. Good luck Chris K #### Kevin Aylward Jan 1, 1970 0 CFoley1064 said: Hi, Chris. If you don't need a lot of current, find a couple of small 6.3 VAC secondary transformers and do something like this (view in fixed font or M$ Notepad):

.------.
120VAC 120VAC 6.3VAC | | +
o---. ,-o-----------o-. ,------o--o~ +o-----o-----o
6.3VAC )|( )|( | | |
)|( )|( | | +|
o---' '-o-----------o-' '------o--o~ -o-. --- 8VDC
| | | ---
'------' | |
| | -
'---o-----o
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Pick off your 6.3VAC to the tube heaters (which will almost always be
grounded

Way to complicated and not necessary. Why wont people realise that DC
offsets are of no consequence for audio. Capacitors exist. The Tuner can
float at any voltage, so just use the bridge directly off the heater AC
to power the Tuner.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

K

#### Kevin Aylward

Jan 1, 1970
0
Spajky said:
lamps heating voltage ( ff ) is probably 6,3V AC coming from
power transformer, followed by a graetz type rectifier & a more than
1000uF/16V el.capacitor connected to rectifiers -/+ out properly;
you will get approx. 9V DC ...

But check first, that power ff source is not grounded; if is & the
other wire is 6,3V AC to ground, IMHO would be enough instead of
graetz rectifier to use just a diode ...

If is grounded in the middle (2x 3,2VAC), than you will have to find
another solution ...

Not really. The tuner can float at any voltage. It just needs capacitor
coupling. Just slap a bridge etc across the 6.3 heater supply.

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

C

#### CFoley1064

Jan 1, 1970
0
Subject: Re: Add a 9V guitar tuner to at tube amp .
From: "Kevin Aylward" [email protected]
Date: 10/23/2004 12:04 PM Central Daylight Time
Message-id: <[email protected]>
Way to complicated and not necessary. Why wont people realise that DC
offsets are of no consequence for audio. Capacitors exist. The Tuner can
float at any voltage, so just use the bridge directly off the heater AC
to power the Tuner.

Kevin Aylward

First principle -- "Do No Harm". You're right, it is too complicated. For
someone who knows what they're doing, like you (or possibly even me -- that's
your call, I guess). But, the isolation makes it relatively difficult for a
newbie to connect different potential commons by accident and let out the
smoke.

As the Guru Don once said,

"Sometimes the technical solution and the people solution are wildly
different."

I'm hoping the OP has a couple of small transformers in his junkbox and saves
himself grief if he makes a newbie mistake.

Thanks for the spot -- you're right, of course.
Chris

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