Hello guys. I've seen Ruby on runoffgroove.com and was quite interested. You can look it up here Ruby
Could this amp be connected to another amplifier (used as preamp for more power and that nice overdrive) instead of speaker? Have any of you tried it? If not, what adjustments should be made (if even possible) ?
Thanks
Could this amp be connected to another amplifier (used as preamp for more power and that nice overdrive) instead of speaker? Have any of you tried it? If not, what adjustments should be made (if even possible) ?
Thanks
You can simply attenuate the output of any power amplifier to feed the input of another amp (two resistors).
But it seems pretty pointless doing so, if you want a preamp, then just use a real opamp.
But it seems pretty pointless doing so, if you want a preamp, then just use a real opamp.
I know that i could use an opamp, but i fell in love with this amplifier and would really love to have this nice overdrive and some more power. Maybe you could tell me how to connect those resistors and how to calculate the values? Will it be something like power sink?
Look up "voltage divider".
The two resistors go in series with each other, from your 386's output to ground, and you take the new (attenuated) output signal from between the resistors, i.e. the voltage across the resistor connected to ground.
The original output voltage gets divided between the two resistors in proportion to their values.
To get 1/4th as much voltage as the original signal, you could use 3k and 1k, or 30k and 10k, or 6k and 2k, or any pair with a 3-to-1 ratio of resistances. Note that 3 + 1 = 4, so taking the voltage across the "1" is 1/4th of the total.
You get to and have to choose in what range the R values should be. Too large and you pick up more noise. Too small and they overheat and start on fire, or the previous amp can't drive them well.
A potentiometer is a ready-made variable version of a voltage divider.
You might need an opamp configured as a unity-gain buffer (i.e. output tied to negative input), after the voltage divider, if you're powering another amp with the new output. But you can try it without one, first.
The two resistors go in series with each other, from your 386's output to ground, and you take the new (attenuated) output signal from between the resistors, i.e. the voltage across the resistor connected to ground.
The original output voltage gets divided between the two resistors in proportion to their values.
To get 1/4th as much voltage as the original signal, you could use 3k and 1k, or 30k and 10k, or 6k and 2k, or any pair with a 3-to-1 ratio of resistances. Note that 3 + 1 = 4, so taking the voltage across the "1" is 1/4th of the total.
You get to and have to choose in what range the R values should be. Too large and you pick up more noise. Too small and they overheat and start on fire, or the previous amp can't drive them well.
A potentiometer is a ready-made variable version of a voltage divider.
You might need an opamp configured as a unity-gain buffer (i.e. output tied to negative input), after the voltage divider, if you're powering another amp with the new output. But you can try it without one, first.
QUOTE Maybe you could tell me how to connect those resistors and how to calculate the values? Will it be something like power sink?
.....you can add a (trim)pot at the output as a volumecontrol.......as shown in the other examples/schematics. perhaps you try out 1k......10k
.....you can add a (trim)pot at the output as a volumecontrol.......as shown in the other examples/schematics. perhaps you try out 1k......10k
I picked 4k and 10k for the voltage divider, connected them properly (wikipedia) and for testing i plugged in 9V battery. Checked the voltage of 9V battery - 9,12V, the voltage after divider was 8,85V What's wrong? According to calculations (both mine and the ones I found in internet Circuit Design Tutor) i should get about 2,5V.
mjf,
If tried adding pot how would i need to set up properly? Should I just set it at some value (to give like 0,15W instead of 0,9W(which I get from lm386)).
mjf,
If tried adding pot how would i need to set up properly? Should I just set it at some value (to give like 0,15W instead of 0,9W(which I get from lm386)).
have you built this amp and does it work?
there should be no dc - volts at the output.........
suggestion: build in a res at the output (1k.......10k or so ) so that the dc - path is closed.
if the output of the ruby is too big for the power amp,change to a trimpot at the output...
there should be no dc - volts at the output.........
suggestion: build in a res at the output (1k.......10k or so ) so that the dc - path is closed.
if the output of the ruby is too big for the power amp,change to a trimpot at the output...
I've built it, tweaked it a bit. Now the only thing I want is a line out (which I would also use as headphone output)
You should put the two resistors in series, from your voltage source to ground. The output is the voltage from BETWEEN the resistors to ground, NOT the voltage across both resistors.
The ORDER you put them in matters, also.
With the 4k first then the 10 k between the 4k and ground (and 9.12 V connected across the whole thing), the output should be 9.12 * (10k/(4k+10k)) = 6.5V, across the 10k resistor.
With the 10k first them the 4k from there to ground, the output should 9.12 * (4k/(4k+10k)) = 2.6V, across the 4k resistor.
It sounds like you measured across BOTH resistors, to get 8.85 V. That would mean you were just measuring across the battery terminals. The resistors being connected probably just caused the battery voltage to sag from 9.12V to 8.85 V. You might also have had the resistors connected in parallel, instead of series.
The "output" is ONLY across the SECOND resistor (the one connected to ground).
Note, too, that you would need to measure the actual resistances, and THEN calculate what the output should be.
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Thank you guys. I simply connected 500 ohm resistor in series with ground to headphone ground. If i connected any less i had it too loud and too risky( my headphones can take up to 500mw and when i connected 10 ohm (as suggested) i measured about 300mw at about half power. Also, it was impossible to use as headphones cause it was damn too loud.
But, when i connected it to another amp it was very noisy, maybe oscillating.
But, when i connected it to another amp it was very noisy, maybe oscillating.
so...... if the headphones are way too loud..........try to leave out the 1k pot (between pin1 and pin8).this should bring down the gain to 20x(26db).
No way i'm gonna do that! This is where i get my overdrive! And even if i took it away, it would still deliver enough power to blow my ears and my headphones as well.
The 500 ohm resistor does a great job. But now I am trying to figure out why is there so much noise when i connect the amp to another amplifier? I cant describe that noise, but maybe I could record it 😉
The 500 ohm resistor does a great job. But now I am trying to figure out why is there so much noise when i connect the amp to another amplifier? I cant describe that noise, but maybe I could record it 😉
Q:No way i'm gonna do that! This is where i get my overdrive!
........yes,it is only a question to get some hints what could be wrong.
bigger gain gives more noise, so try to keep the gain low. the lm386 is a cheap and a little bit noisy opamp........
can you measure the voltage drop across the source res 3,9k?
........yes,it is only a question to get some hints what could be wrong.
bigger gain gives more noise, so try to keep the gain low. the lm386 is a cheap and a little bit noisy opamp........
can you measure the voltage drop across the source res 3,9k?
I will measure a little bit later because i have amplifier put in box and etc. The weird thing is that when I connect it directly to a speaker there is little noise (very audible, but it is caused by guitar pickups). The problem arises if I try to use it as preamp to another amplifier.
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