Ruby amp

newperson · February 05, 2006, 03:56:18 AM

Hi,
If I hook up the Ruby amp at ROffG as a preamp (running it into my amp) can it hurt my real amp? There has been no changes to the design. Just instead of using a speaker out, putting that output into my tube amp.

Thanks,
Paul.

bancika · February 05, 2006, 04:47:02 AM

I don't think it's ok, it's output is at speaker level. You shouldn't stick it where guitar level is expected
Just my .02

Joecool85 · February 05, 2006, 09:07:17 AM

eh, its up to you. I built the little gem and have been plugging its output straight into my line in on my laptop. Granted line in is substantially higher voltage etc than mic/guitar in.

d95err · February 05, 2006, 10:02:18 AM

Quote from: newperson on February 05, 2006, 03:56:18 AM
If I hook up the Ruby amp at ROffG as a preamp (running it into my amp) can it hurt my real amp? There has been no changes to the design. Just instead of using a speaker out, putting that output into my tube amp.

If you want a distortion pedal based on the LM386, check out the Grace Overdrive and Big Daddy from Runoffgroove.
http://www.runoffgroove.com/grace.html

newperson · February 05, 2006, 02:02:39 PM

Could it damage anything? What is the difference in the signal strength? I see the Ruby is 1/2 watt. What is a normal signal? Or is there something more to it than just the signal strength?

-Paul.

Joecool85 · February 05, 2006, 02:14:06 PM

From what I gather it mostly has to do with voltage. My little gem puts out around 6 volts or so max. Guitars put out something like .4 volts or something. Someone correct me if I'm wrong.

petemoore · February 05, 2006, 06:22:38 PM

I suppose i'td be cool if you like it and aren't blowing inputs..i certainly wouldn't recommend it though/

newperson · February 06, 2006, 12:38:33 AM

is there a way to mod it so the voltage could be cut down but still be able to switch back to using it as an amp? right now it is hooked up with a dpdt to switch between a speaker and an output jack.

thanks,
paul.

petemoore · February 06, 2006, 01:31:17 AM

A Voltage *Divider like two equal, make 'em say at least 100k resistors, series, [wired like a volume pot, or make it a volume pot, the seriesed pair go from signal path [to input of *divider circuit] to ground, with the junction of the resistors being output. This'll 1/2 it, or you can make the 'top one bigger and/or the bottom one smaller for a little more/little less output...or use a pot.
note i *think standard pots will handle an LM386's output @ 9v.

newperson · February 06, 2006, 02:07:21 AM

I have been looking at what you have said and this is what I have come up with. Please correct me because I am not 100% sure I follow what you are telling me. I am still new.

I have the 2 wires for the output: wires to speaker (jack) hot + and ground -
You are saying to put a 100K pot between these wires and the speaker output which will lower the voltage so that it would now be low enough to safely use as a preamp to plug into my amp.

100K pot has 3 legs:
1 to (ground -)
2 tied to leg 1
3 (hot +) to output tip of jack

Turning this pot in one direction will lower the voltage enough so that I can plug it into my amp and use it as a preamp. The other direction will raise it enough to drive a speaker?

Is this correct in any way?

Thank you for your responses,
Paul.

newperson · February 06, 2006, 05:20:43 PM

bump for petemoore
-p.

newperson · February 07, 2006, 12:54:30 PM

bump for petemoore
-p.

newperson · February 08, 2006, 12:35:16 AM

Maybe I am looking at this problem wrong. Since this is an amp, is there a preamp in this circuit? And should I not be able to take the output from this before it goes through the amp stage? And this would plug into the amp and still have the 386 distortion?

Also how does an attenuator work?

_paul.

newperson · February 08, 2006, 12:56:06 AM

I now see that the 386 is the power amp. Is this where the distortion is coming from then?
-p.

newperson · February 08, 2006, 02:47:38 AM

Ok,

I tried a couple different things. First I measured the output voltage on the speaker hot side and read around 4.+ volts. It trickled away as I held the meter to it until it went down to under 0.4 volts. It seems that it would still go lower if I held it longer.
Question one: Why did it do this?

Then I tried adding two 100K 1/2watt resistors in series together on the hot side before it hooks up to the speaker. With this I do not get any sound out of the speaker, but sounds fine when plugged into an amp. This took away the crazy hot input sound when it was plugged stright into the amp.

Then I tried adding a 500K pot (hot wire from board to legs 2/3 tied and then leg 1 out to the speaker output jack). This gave the ability to change the pot to one side that would allow a speaker to be driven. With the pot turned to the other side it could be plugged into an amp without the crazy hot signal sound.

Is this what you was trying to tell me to do? And will this be ok for the amp to ran as an effect now? It is too late to turn up to see if it is still holding onto the same distorted sound, but it seems to be.

The voltage with the 100+100k resistor mod or 500k pot mod is around .02 volts to no reading. I could not get a 4.0+ voltage reading from the output again after the first intial reading. Once it trickled down it stayed that way. I am going to measure again tomorrow after it sets without anything plugged in.

thanks,
-paul.

newperson · February 08, 2006, 02:10:44 PM

first, do the changes i made make any sense?
Also how does the
http://www.geocities.com/tpe123/folkurban/fuzz/snippets.html
Stupidity box work a speaker and as a preamp?
Is it just risking dammage?

thanks,
p.

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Ruby amp