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DIY Guitar Amp Attenuator
DIY Guitar Amp Attenuator
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Old 2nd June 2019, 04:43 AM   #1
Moss Driver is offline Moss Driver  Australia
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Join Date: Nov 2014
Location: South Australia
Default DIY Guitar Amp Attenuator

Hi to all,

I'm having a go at building this 100W 8 ohm attenuator here for my Son:
DIY Workshop: How to build your own attenuator - Guitar.com | All Things Guitar
I've got a 16 ohm speaker load to drive but have already sourced all the parts on the BOM for this build.
(Speakers are 2 X 12" 8 Ohm speakers wired in series for 16 Ohm operation)

Does anyone know of a way one could move the 8 ohm resistor into series with the L-Pad to achieve 16 Ohm load being 'seen' by the amp? (My best guess)

I've got a DPST switch and figure I could add the 8 Ohm 100w resistor in series right at the attenuator's output to 'add' it to the L-Pad's already 8 ohm load. If that makes sense?

I've attempted a schematic with a proposed change for 8 and 16 ohm switching, but I'm unsure if I build this, if it will fry something.

Any thoughts welcome!

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File Type: jpg Attenuator 8-16 query.jpg (76.9 KB, 29 views)

Last edited by Moss Driver; 2nd June 2019 at 04:44 AM. Reason: Switch type incorrect
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Old 2nd June 2019, 05:24 AM   #2
PRR is offline PRR  United States
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Join Date: Jun 2003
Location: Maine USA
Do you need the *amplifier* to see 16 Ohms?

Then your plan is not right.

Here's a hasty hack. A "drawback" is it won't turn all the way up, only to "half" loudness. However full loudness is on the bypass;, when you want "less!" then half is probably the most you would need.

EDIT- it may be "safer" to not even offer an 8r choice, if the amplifier is normally used on 16. Leave the big 8r resistor in circuit.
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Last edited by PRR; 2nd June 2019 at 05:27 AM.
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Old 2nd June 2019, 09:48 AM   #3
Moss Driver is offline Moss Driver  Australia
diyAudio Member
Join Date: Nov 2014
Location: South Australia
Edit: Hey thanks for the drawings dude.
I think I see what you mean, but have several questions, so I better go read up.

Hope this helps.

I have three valve guitar amplifiers.
All three amplifiers have 8 and 16 ohm speaker sockets/outputs.
One particular speaker cabinet is a 2X12" and is 16 Ohm.
The other speaker cab I use is 8 Ohm.
I don't use them at the same time.

I would like an attenuator to be able to handle both the 8 and 16 ohm cabinets, (not at at the same time, of course).

So, in answer to your question, I am unsure.
I use the 16 ohm cabinet into 16 ohm sockets on my amps, likewise for 8 ohm speakers into 8 ohm sockets.
I guess I am trying to make the amplifier 'see' 16 ohms, for when I am using the 16 ohm cab and the 16 ohm socket on my amp.
But I know I am missing something...
Maybe it is simple to revise my speaker impedance values to a uniform 8 ohms.

Thanks, much appreciated.

Last edited by Moss Driver; 2nd June 2019 at 09:54 AM. Reason: Thanks for drawings!
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