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Old 29th August 2006, 07:07 PM   #41
Brion55 is offline Brion55  United States
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Haven't been around much due to surgery and other health problems.

Glad to see the schematics were useful.

Hum and noise problems can usually be eliminated by single point (star) grounding and keeping the wires to the tone control pots as short as possible, or even shielding them. Sticky back copper foil can be used to shield the wiring cavity if necessary. It can be found at most hobby stores. I remember seeing shielding kits for guitars someplace, but I donít remember where. Maybe someone here knows.
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Old 29th August 2006, 08:10 PM   #42
DolbyR is offline DolbyR  Finland
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www.stewmac.com provides several types of shielding material from adhesive copper tape to conductive paint
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Old 29th August 2006, 08:28 PM   #43
Scummer is offline Scummer  United Kingdom
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I use baking foil and cheap glue for shielding on all my guitars, and it works fine (though it can be fiddly to get in to odd shaped spaces).

You can also buy shielding kits from any decent luthier supplier (am I allowed to mention names on this forum? Not sure, but typing "Luthier Supplies" into Google will probably work as well as anything....)

But then again, if we were the type to just go out and buy stuff, we probably would not be on this forum. Both the above sites will furnish you with an manner of pre-amps, but where is the fun in that?

Incidentally, the three band EQ with boost on my cheap Les Paul copy can make it sound almost as good as the real thing, but also gives it a tonal range way wider than any Les Paul I have ever played.
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Old 22nd December 2006, 09:09 AM   #44
aklz is offline aklz  Brazil
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I have some 100k pots, how can i use then in 3 band eq,(in place of original 50k)?
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Old 28th December 2006, 05:35 PM   #45
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Hello all! New here. Saw the original post (and admit I haven't had time to read all pages) so please excuse me if this has been referenced. Try Duncan Amps Tone stack calculator. I am sorry I don't have the link. (try Duncanamps.com) The calculator is very handy. Furthermore, I spoke with a friend who builds beautiful bass guitars and discussed the very same issue I will pass your information along to him. Glad to find this forum.
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Old 28th September 2007, 11:12 PM   #46
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Question OPA2134 volume pot problem

Hi, I built Brion55's 3 band eq (with modified center freqs) for one of my 5 string bass guitars as a replacement for the original cheap preamp like a year ago.

It worked fine with the original op-amps (old TL-072's), however they sound synthetic and harsh to my musical tastes and I replaced them with NE5532's... after hearing a loud bang everytime I engaged the boost switch I realized that a bipolar op-amp was not a good choice for that task so I swapped it for the old TL072, and I run it that way until I was able to purchase a bunch of great OPA2134's. The sound is incredible! Brighter, fuller, the bass turned itself into a different instrument! It is much more responsive, low notes sound gutural high notes sound brilliant and not muddy.

The preamp was a little bit noisy with the high knob turned a little bit. So after extensive simulations I decided to change the resistor values for the first gain stage, it had 10k and 4.7k (I left the 1 Meg resistors untouched) and I swapped them to 2.2k and 1k metal film. Noise was reduced to half the original noise floor level with the boost switch engaged, and it is hardly heard without it.

The only problem I noticed is that when I turn the volume pot I hear a scratch noise as if having a dirty pot, I swapped the output op-amp for the NE5532 and this is not heard, any idea of what can be causing this?
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Old 29th September 2007, 05:56 AM   #47
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I can't answer why the scratchy pot noise went away, but you should note that the NE5532 has a minimum operating voltage of 10 volts.

Very interesting thread.
Thanks for reviving it since I must have missed it the first time around. As if I don't have enough unfinished projects!!!

P.S. Thanks also for the heads-up on the TLE2426 rail splitter by TI.
I never knew they made such a thing. I've always made my own with resistors and an opamp, but this single T0-92 will really simplify things for me. Kudos my friend !
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Old 29th September 2007, 08:01 PM   #48
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Hi head_spaz, I forgot to mention that I play funk mainly with that bass so 9V was not enough headroom for me I'm running it with 2 batteries, I've made some modifications to the circuit to get a more gutural sounding bass since its a cheap 5 string Peavey.

I've shifted the bass center frequency to 15 Hz for example, I changed some resistor values to lower noise levels a lot, obviously the batteries last less than the original circuit but its fine for me since I'm using high quality rechargeable batteries.

The original circuit works fine, you should try it first to find out if it suits your needs and maybe you would want to tweak it a little bit later.

And yes the TI rail splitter is great!
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Old 29th September 2007, 10:03 PM   #49
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Default Re: OPA2134 volume pot problem

Quote:
Originally posted by frickecello

The only problem I noticed is that when I turn the volume pot I hear a scratch noise as if having a dirty pot, I swapped the output op-amp for the NE5532 and this is not heard, any idea of what can be causing this?
It's a well known occurance - it's because you have a DC voltage across the volume control, you need a blocking capacitor feeding it.
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Old 29th September 2007, 11:50 PM   #50
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Question Re: Re: OPA2134 volume pot problem

Quote:
Originally posted by Nigel Goodwin


It's a well known occurance - it's because you have a DC voltage across the volume control, you need a blocking capacitor feeding it.

Do you mean another one? The original schematic has a 4.7 uF cap before the volume pot, the scratch noise is not heard when a TL072 or NE5532 are used for the middle eq and output section that's the weird thing. Any suggestions?

Thanks in advance.
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