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Old 9th January 2002, 01:30 PM   #1
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Default A few things....

This is my first post here, I'm a newbe at the electronics stuff, but very interested in learning. I'm mostly interested in music gear, being a musician, and recently built an active DI box from a scematic on the ESP site. and...It WORKS! However, it's still on a breadboard and now I have to mount it and stuff it into some kind of box. But, that's not my question...

The guitar player in the band I'm in (I play bass) has an old (68) Fender Twin. It sounds great when it's cranked up, but then it's way to loud for our small practice space. What I'm looking for is a way to crank the amp, but keep the output volume down. My first thought is to run the speaker output throught the DI box I just built, and then into the PA. But, this limits using it with a PA. Then I thought, there must be a way to just take the speaker output and run it thought some sort of attenuator to bring the level down, then out to the speaker. I'm not sure of the output of the amp when cranked, but it must be 100 watts or so. Any thoughts? In the end, what I'm looking for is the twin tube sound, but not so loud...

Also, my next project is a mic preamp. Any thoughts on a good schematic? I ordered a few samples from TI (after reading a post here, very cool) and received a few OPA627 opamps to play with. Any schematics using those would be great. It will be used, at this point, with Shure sm57/58s into a Tascam TSR8 multitrack.

Thanks....
Ziller
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Old 9th January 2002, 01:50 PM   #2
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there are effects units that you can build that will give you this distortion without having to overdrive the amp.
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Old 9th January 2002, 01:54 PM   #3
yeti is offline yeti  Germany
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Default Amp

Hi,Ziller
Probably you might use an L-Pad between the Amp`s output and
it`s speaker.
This provides a load to the amp and decreases volume.
But you should take hi-power resistors, min>100 Watts!

amp out ----------res1--------------------
! !
r s
e p
s k
2 r
! !
gnd--------------------------------------------

For calculations search the web.

regards,

Arne
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Old 9th January 2002, 01:56 PM   #4
yeti is offline yeti  Germany
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Default graphics

ooops!
got a problem with the graphics
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Old 9th January 2002, 01:57 PM   #5
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dont use an L-Pad cause it'll make too much heat.
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Old 9th January 2002, 02:06 PM   #6
yeti is offline yeti  Germany
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Default heat

The heat is a problem in fact, but no fuzz-box sounds like an overdriven tube-amp!
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Old 9th January 2002, 02:14 PM   #7
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Default OK...

Thanks for the quick responses. I did think of putting a resistor between the amp and speaker, but thought it would be toast. I didn't realize you could get such high wattage ones (remember...newbe...).

Why is it then I can run a speaker level output into the DI box and not fry that? I'm a little confused on this issue. The DI box is here

http://sound.westhost.com/project35.htm

and when plugging a speaker level in, the signal only runs thought a 22K and 1K pot before the coupling cap. These are just 1/2 watt resisters (I haven't actually tried the speaker input yet)
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Old 9th January 2002, 02:14 PM   #8
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there are a couple that come close.
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Old 9th January 2002, 02:20 PM   #9
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the speaker level input runs thru the 22k resistor which limits the current into the device to less than about 5mA which is safe with 1/2 watt resistors
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Old 9th January 2002, 02:54 PM   #10
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Default Ah...

I see. So, what is the problem with the heat? If the resistor is a high enough wattage, wouldn't it dissipate enough heat? The back of the amp is open.
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