Ruby for bass?

barret77 · September 20, 2005, 01:02:30 AM

Hello

I'm almost sure this topic has already been discussed, but I could not find it in the search.

I'm planning to build a small bass amp, and I would like to use the Ruby circuit; are there recommended changes to use it for a bass instead of a guitar?

Thanks!

birt · September 20, 2005, 06:31:40 AM

as far as i tested it a stock ruby sounds quite good on the right speaker for bassguitar :wink:

solarplexus · January 19, 2011, 05:50:35 PM

I'm having problems using the stock ruby with my P bass. It's always into distortion territory because of too much bass getting in. I had modded the Ruby with Bassman specs prior to trying it with bass. Would there be anything else I could do to help the distortion issues with bass? Probably changing the input cap would help, but is there anything else?

Thanks for the help.

panterafanatic · January 19, 2011, 07:46:03 PM

Try adding a simple bass control, a stupidly wonderful tone control 2 would work for this, or even design an active filter and a mixing system.

solarplexus · January 19, 2011, 07:49:26 PM

Problem is, a bass control IMO would do no good, since there is too much bass coming in in the first place...

solarplexus · January 20, 2011, 03:49:34 PM

anyone?

phector2004 · January 20, 2011, 04:10:17 PM

Smaller input cap?

Have you looked into filters at all? A bass control would cut the bass, not boost it.

solarplexus · January 20, 2011, 04:17:11 PM

mmm... I think I'm not explaining well enough or I just don't get it!

I think the distortion is from the circuit not being able to process all the bass coming through, like overdriving a tube with gain, but this time with either gain or bass frequencies. Does that makes sense? If yes... wouldn't changing the caps for higher values would let the bass come through?

Gurner · January 20, 2011, 04:17:26 PM

Quote from: solarplexus on January 19, 2011, 05:50:35 PM
I'm having problems using the stock ruby with my P bass. It's always into distortion territory because of too much bass getting in. I had modded the Ruby with Bassman specs prior to trying it with bass. Would there be anything else I could do to help the distortion issues with bass? Probably changing the input cap would help, but is there anything else?

Thanks for the help.

Your explanation of the symptom is still not explicit enough "It's always into distortion territory because of too much bass getting in. "

...geting in where?

The ruby has a volume pot midway through its circuit - are you are hearing distortion even with that particular control turned down?

It could be because your LM386 has too much gain....Or perhaps your bass guitar signal is too hot for the input fet? Are you running an active bass? If so - and if it's an active bass - put say a 47k pot in front of the fet...top lug connected to you input, wiper conneted to the fet gate, bottom lug connected top ground.

solarplexus · January 20, 2011, 04:30:46 PM

Ok thanks for the input. I am using a passive P bass. My hypothesis is that there is too much bass frequencies getting in the input stage and that the other caps in the circuit are of too small value to let those bass freqs out, thus causing fuzz. What do you think?

solarplexus · January 20, 2011, 04:33:13 PM

Also forgot to add that the the volume can't get high because it causes fuzz. So turned down it is kind of ok, but I have no output. I also have the gain pot turned down to zero.

phector2004 · January 20, 2011, 06:10:16 PM

I honestly don't get what the problem with tonestack/cap change is...

Have you actually tried swapping input caps? A lower frequency signal "fills up" a smaller capacitor and less bass gets through.

Likewise, a filter before the LM386 will cut lower frequencies out of what's going into the amp.
You can throw a tonestack in, as suggested by panterafanatic, but it would have to go before the chip.

Gurner · January 20, 2011, 06:31:10 PM

In my opinion, I wouldn't be dicking about with filters (or caps) in an attempt to attenuate the signal - this circuit is intended for his bass...presumably solarplexus wants all the frequency content in the signal from his guitar to be amplified!

This sounds as if it's a level/biasing problem (or possibly too much gain on the 386)

Is it just the one bass guitar that's affected? (do you have access to any other guitars you can put through it?)

What happens when your roll the guitar's volume pot down - does the ruby sound cleaner?

Do you have access to a meter? What's the quiescent DC voltage reading at the JFET drain?

petemoore · January 20, 2011, 06:55:01 PM

Connect to a higher voltage supply, 10% under max rating.
Heat sink, but not much room and a small one covers it.
Let less bass in.
More effecient lighter coned speaker.
9v happens to be easy and enough to vibrate a little speaker coil/cone, almost any speaker except the very small would have wider frequency range especially in the LF's where the speaker coil is not only moving the coil, cone and suspension weights +overcome suspension rigidity, it is then asked to move larger amounts of air longer distances, this loading may exceed what the PS and chip can deliver, the speaker controls the amp [more], the amp may even hit it's PS rails fairly hard, and struggle with clipping.

solarplexus · January 20, 2011, 07:07:33 PM

thanks guys I'll look into that. I play the Ruby with my guitar also and it sounds just fine. Less fuzz when the volume is down on my bass for sure.

PRR · January 21, 2011, 12:50:30 AM

The Ruby's zero-biased input stage will cover most guitars, but may get into some trouble with a hot bass.

"Turn-down the VOLume knob on bass" is an appropriate answer.

"Try another MPF102" may help some.

This mod should swallow anything that would go into a normal stage-amp:

Add 4.7Meg resistor to bias-up the JFET. Add blocking cap so that DC bias does not sneak back out to your bass.

Forget the "Gain" control, that's only for over-the-top distortion from soft-stroked gitars. Cut the wires.

More bass mods:

Cap on pin 7 does several things. Generally it should be more like 10uFd, polarity as shown.

The cap into the volume pot is blocking bass. With 10K pot, the stock 47nF gives 340Hz low-cut which is appropriate for guitar into 4-inch speaker. You don't want your precious one-Watt going into cone-slap. If you will be using 10"-12" guitar speaker, you should go to 100nFd and increase the speaker cap some. If you will use a LARGE bass cabinet, you could try 0.2uFd at the volume control and 470uFd or more at the speaker. (If you have a true bass-horn as big as a porta-potty, 0.5uFd and 2,200uFd may give audible 42Hz with a mere Watt; but any lesser speaker with one Watt won't make enough 42Hz to hear, and you should block the deep bass to put your power up where it will do some good.)

solarplexus · January 21, 2011, 04:05:29 PM

Quote from: PRR on January 21, 2011, 12:50:30 AM
The Ruby's zero-biased input stage will cover most guitars, but may get into some trouble with a hot bass.

"Turn-down the VOLume knob on bass" is an appropriate answer.

"Try another MPF102" may help some.

This mod should swallow anything that would go into a normal stage-amp:

Add 4.7Meg resistor to bias-up the JFET. Add blocking cap so that DC bias does not sneak back out to your bass.

Forget the "Gain" control, that's only for over-the-top distortion from soft-stroked gitars. Cut the wires.

More bass mods:

Cap on pin 7 does several things. Generally it should be more like 10uFd, polarity as shown.

The cap into the volume pot is blocking bass. With 10K pot, the stock 47nF gives 340Hz low-cut which is appropriate for guitar into 4-inch speaker. You don't want your precious one-Watt going into cone-slap. If you will be using 10"-12" guitar speaker, you should go to 100nFd and increase the speaker cap some. If you will use a LARGE bass cabinet, you could try 0.2uFd at the volume control and 470uFd or more at the speaker. (If you have a true bass-horn as big as a porta-potty, 0.5uFd and 2,200uFd may give audible 42Hz with a mere Watt; but any lesser speaker with one Watt won't make enough 42Hz to hear, and you should block the deep bass to put your power up where it will do some good.)

This is exactly what I need. Thank you soooo much!

Brymus · January 21, 2011, 04:25:51 PM

I would take PRR's mods and go a little further,bridge two 386's for more headroom,doing this you wont need the large cap at the spkr either.(look at the Little Gem MKII from ROG)
Definetly leave pins 1 and 8 open !
And try a 12V supply if you have the chips that will take it,but no higher.(most all will)
Also if using a wall wart be sure its not a 300ma one,you need about 700ma for the single 386 at max output.
Not enough current in the power supply will lead to distorted/farty/fuzz sound.

solarplexus · January 21, 2011, 04:41:59 PM

What was the Chip # for those that take 12V ? 386___ ?

PRR · January 22, 2011, 01:26:00 AM

> for more headroom

If you need headroom, MORE POWER, don't use LM386.

LM386 won't make more power in 8 ohms when over-volted or bridged because it can only flow 0.4A of current.

I was assuming Mondos -wanted- a one-Watt amp for very small sound. And 1 Watt isn't all that small: with any non-lame speaker, it can annoy neighbors.

If he's truly clipping the OUTput (not input), then he's gonna need something beefier than any LM386 amp. The car-sound chips are the next obvious choice. Bridge on 12V gives 8W in 8 ohms or 16W in 4 ohms, and as you say no large cap. CanaKits and others sell such projects, add the JFET buffer in front.

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Ruby for bass?