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need help with passive volume and tone
need help with passive volume and tone
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Old 11th January 2017, 05:14 PM   #1
melodicol is offline melodicol  United Kingdom
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Default need help with passive volume and tone

Hello

I am new to audio electronics as in wiring, been mostly playing instruments. with the odd like for like replacement on guitars. I am building a small travelling combo for a bass guitar. having built the small speaker cabinet I opted to use the 30W amplifier pictured. It will be fitted inside an aluminium case and I am very tight for space.

I want to fit a passive volume and tone at point A in the diagram attatched, to save battery life for the amplifier. I would be grateful of any help ensuring me that I am wiring things correctly. I have room for 3 mini pots and would prefer volume tone and bass, but only using 2 is still an option.
As far as I know the ground on the amplifier PCB (the one in the diagram) should be linked to the back of the pots and the ground from the guitar.
and that is my knowledge so far.

I am also a bit confused over the shut down to ground on the PCB. I had planned just a switch on the DC input+. is the shutdown a signal shutdown ?

The amp will be supplied by a 12-18V battery or DC power supply. I already checked with the company that the amp is ok with 8 Ohm at the output. the wattage of the speakers is for a cleaner tone from the bass. as I have no room for one larger speaker. and I understand each speaker will get half the output.

Thanks in advance for any help.
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File Type: jpg sure 30w.jpg (14.8 KB, 65 views)
File Type: bmp wiring schematic 2.bmp (141.8 KB, 16 views)
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Old 11th January 2017, 05:36 PM   #2
Pano is offline Pano  United States
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need help with passive volume and tone
Welcome to the forum.

Can't tell what the amp chip is from the photo, but it does have an RCA input, which would indicate it wants line level in, somewhere around 1 volt. An passive guitar output is nowhere near that, and generally needs a preamp and/or a high input impedance. Do you have a preamp or booster, or an active pickup?

Also, don't count on that 30W. The amp will probably be just fine for a practice rig, but don't expect to get more than 18 clean watts running from an 18V battery or about 8 watts from a 12V battery.
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Old 11th January 2017, 05:44 PM   #3
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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I don't know anything about music and musical instruments, but a single opamp with 3 pots and some passive components (Capacitors and resistors) will do the job, both amplifying and tone correction.
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Old 11th January 2017, 07:57 PM   #4
melodicol is offline melodicol  United Kingdom
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Thanks for the replies, heres the info on the amp.

Sure Electronics' webstore 1 x 30 Watt Class D Audio Amplifier Board - TPA3110

the RCA is the output, and the block with the screws is the input. my problem is I don't know how to wire the pots, with some internet info telling me to link one or two of the pins to the ground. and if my grounding would be ok linking all the pots to the PCB and the guitar ground. also which capacitor to use on the tone though I know a bass guitar goes from 40Hz to 400Hz without harmonics and 400Hz to 4KHz when you start using popping technique. so if a capacitor works as a high or low pass filter, which one(s) to use and where lol.
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Old 12th January 2017, 12:02 AM   #5
melodicol is offline melodicol  United Kingdom
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heres my attempt at a wiring diagram
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File Type: bmp wiring schematic 2.bmp (141.8 KB, 10 views)
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Old 12th January 2017, 01:12 AM   #6
melodicol is offline melodicol  United Kingdom
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sorry Pano your right about RCA beimg input, just checked again
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Old 17th January 2017, 01:24 AM   #7
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by melodicol View Post
I want to fit a passive volume and tone at point A in the diagram attatched, to save battery life for the amplifier.
Passive is a big, big ask straight off the bass. The simplest answer is an EQ pedal. Or one of the various 'sans amp' bass DI boxes.

If you've got some soldering licks then a simple JFET circuit can act as a buffer to drive either a traditional (vox/fender/marshall) tone stack, or a bandaxall (see Duncan's explanation) or a big muff tonestack.

You can mount the zener & fet on the input jack and everything else on the pots.

There's a good thread on diystopboxes you should look at.

Or you can buy a 2 x NE5532 bass/mid/treb/volume premade board from ebay for a few bucks and hack it to run off your battery by faking a Vref at half your battery voltage.

Last edited by thoglette; 17th January 2017 at 01:32 AM. Reason: Add link to J. Donald Tillman's FET preamp
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Old 17th January 2017, 09:07 PM   #8
melodicol is offline melodicol  United Kingdom
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Many thanks thoglette. the Jfet circuit looks like it draws very little power. brain food for me for the next few days lol.
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