I was looking for a small practice amp like the Ruby Amp. I realized that I could make it a litlle more on the dark side of the gain by using the fet as an amplifier not as a buffer. I added some leds and voilà:
(http://www.geocities.com/guitarfxs/images/jade_1w_practice_amp.gif)
Not a Vox AC30 but it kicks the 12" HH of my LC30 decently. Hope you like it.
mac
Looks cool, I'll have to look at it closer....
Thanks for posting.
If you get a sound clip I'd like to hear it!
John
working on the sound sample... :icon_cry:
mac
Nice! Do you think it will work fine also as a stompbox? I know the smashdrive also uses a 386.
There are a couple of LM386 based pedals at ROG. Maybe replacing everything after pin 5 and using a 0.1uf to 1uF and a volume pot of about 100k. I designed it to be a small practice amp so as not to disturb the whole building with LC30. To be honest, I did not consider the possiblity to use it as a stomp.
mac
A small input cap of about 10nF to 100nF can be placed.
mac
Thanks for sharing!
So, do you get a pretty nice clean sound as well? How does it sound with a booster or distortion/overdrive/fuzz in front of it?
Thanks,
EZ
Quote from: ezanker on February 20, 2007, 02:43:33 PM
Thanks for sharing!
So, do you get a pretty nice clean sound as well? How does it sound with a booster or distortion/overdrive/fuzz in front of it?
Thanks,
EZ
With the pots at min. Did not try pedals.
Sound sample here:
http://guitarfxs.tripod.com/mp3/jade.mp3
If tripod does not allow remote download copy the link to the address field of another browser window and hit return.
Full gas, crappy mic, uninspired, from the breadboard with some nice radio station on the back... the diodes, and some crt noise.
mac
Nice ;)
When trying to dload:
"This file is hosted by Tripod, a Lycos®Network Site, and is not available for download. Please check out Tripod's Help system for more information about Remote Loading and our Remote Loading policy. "
BTW, where are you from?
cheers
DAC
Quote
Nice
When trying to dload:
"This file is hosted by Tripod, a Lycos®Network Site, and is not available for download. Please check out Tripod's Help system for more information about Remote Loading and our Remote Loading policy. "
BTW, where are you from?
cheers
DAC
Copy the link in another browser window.
Argentina.
mac
That sounds nice!
It has a good growl to it.
Good job on this.
John
Do you have a layout available? My layout skills have ended me up with 2 unworking pedals so far.
Hi
It would be interesting to try different diodes and different biasing in the compression section.
BTW, the 386 is only good for half a watt from 9V, despite lots of references to it producing 1W. (the spec sheet quotes it at 0.7W at 10%THD, but it only produces about 0.4W at reasonable distortion levels).
cheers
iv been thinking about doing somethign similar, mosfet boost > ruby in one circuit inside an old practice combo. was thinking about running the ruby at 18 and the mosfet at 9vs so the power amp has a bit more headroom. i tried scoping out some alternative chips to give more power at low voltages/curent consumptyion but iv been pretty unsuccesful.
Nifty looking pre-amp-comp section !
Quote from: tjcombs on February 22, 2007, 02:40:23 AM
Do you have a layout available? My layout skills have ended me up with 2 unworking pedals so far.
Possible mods to the schematic: a big cap to ground, 47uf to 100uf, a switch to choose different diodes and a 4th 100k-B pot instead of the fixed R6.
Quote
Hi
It would be interesting to try different diodes and different biasing in the compression section.
BTW, the 386 is only good for half a watt from 9V, despite lots of references to it producing 1W. (the spec sheet quotes it at 0.7W at 10%THD, but it only produces about 0.4W at reasonable distortion levels).
cheers
I tried with 4148 and 1n60 but I prefer the leds. Also You can play with R5 and R7 from 2k2 to 22k and with R6 from 4k7 to 100k to get different textures. R5 and R7 need not be equal.
As is it sounds loud for what is intended. To get 1w or 2w from 18v maybe two bridged 386? I don't remember if National datasheet has a schem of a this.
BTW, chip is UTC LM386. I should buy a National to see if they work the same or not.
mac
Me c... en tripod!!!
Sound sample here:
http://geocities.com/guitarfxs/mp3/jade.mp3
For a bridged 386, see ROG's Little Gem MKII: http://www.runoffgroove.com/littlegem.html (http://www.runoffgroove.com/littlegem.html)
EZ
Quote from: ezanker on February 22, 2007, 11:34:21 AM
For a bridged 386, see ROG's Little Gem MKII: http://www.runoffgroove.com/littlegem.html (http://www.runoffgroove.com/littlegem.html)
EZ
I knew I have seen a bridged 386 somewhere... lol
mac
The clip sounds nice! :)
Could you explain what de diode's in the pre-amp section do (i know what the do but i haven't seen diode's used like you use em in your amp) and which 'path' the sound signal follows?
Quote from: mac on February 22, 2007, 11:20:02 PM
Quote from: ezanker on February 22, 2007, 11:34:21 AM
For a bridged 386, see ROG's Little Gem MKII: http://www.runoffgroove.com/littlegem.html (http://www.runoffgroove.com/littlegem.html)
EZ
I knew I have seen a bridged 386 somewhere... lol
mac
I have a TDA2822, I have thought about using for at practice amp. It's stereo, but the channels can be bridged in a Little GEM II type configuration. My hope is that it should give more headroom than the 386.
Regards
Carsten
Hi Mac.
Congratulations ! :) Your practice amp sounds very good, I´ve made a ruby to try and yours will be in my future list. I´m from Argentina too, I live in Buenos Aires but have family living in MDQ !
Un abrazo.
julián
Quote
Could you explain what de diode's in the pre-amp section do (i know what the do but i haven't seen diode's used like you use em in your amp) and which 'path' the sound signal follows?
The ac signal passes through the diodes, which are turned on by r5,r6 and r7. At first sight it seems that they are blocking the signal, but this is ac... I guess lol
Quote
Hi Mac.
Congratulations ! Your practice amp sounds very good, I´ve made a ruby to try and yours will be in my future list. I´m from Argentina too, I live in Buenos Aires but have family living in MDQ !
Un abrazo.
Voy seguido, nos juntamos y hacemos un poco de ruido jaja
mac
A new clean demo clip, copy the link and paste it on a new browser window since tripod.com does not allow remote hosting:
http://guitarfxs.tripod.com/mp3/jade_clean.mp3
http://guitarfxs.tripod.com/mp3/jade_clean.mp3 (http://guitarfxs.tripod.com/mp3/jade_clean.mp3)
mac
I still don't get the Led part in your circuit, you said AC will pass trough the diodes, I don't see why. I thought that the positive part of the AC signal will pass through a diode that's 'pointing the same way' as the signal (if it is over the threshold of the diode but in this circuit that's already taken care of by the V+ and teh resistors) and that the negative part will go through a 'reversed' diode (this is the way diode's work in distortion circuits with anti-parallel diodes to ground right?). I would really like to understand whats going on in this circuit, I hope that someone could explain this.
Btw, if the ac signal is completely passing through the diode's, what's the effect on it to the sound?
Clean sounds nice, although not completely clean, what settings did you use for that clip?
nice sounds mac ... :icon_cool:
... the diodes are being used for their non-linear resistance ... if you look at both diodes as a combined resistance you'll see it's part of a voltage divider acting between the Drain and the equivalent resistance seen at the volume pot ... the diodes are biased weakly so that minute variations in current through them cause a relative increase or decrease around their idle resistance value ...
you have to argue on a half-cycle basis, take a sine wave input for argument's sake ... when the Drain voltage goes high the first diode gets slightly less biased and the second one gets slightly more biased ... the incremental resistance, what the signal sees, is increased in the first and reduced in the second ... during the second half cycle the reverse happens ...
because of the logarithmic current-to-voltage nature of diodes the increase in resistance on the weaker biased diode is greater than the decrease in resistance on the stronger biased diode ... this means that the incremental sum resistance of both is greater than the idling sum value, and the increase is monotonic with signal amplitude ... to a point at least ... if the diodes and their biasing are well enough matched then the two half cycles will be attenuated through the divider in an equal way ...
at least this is what happens when the stage is operating in class-A ... with stronger signal levels you get to onset of clipping, and then into class-B fuzz and hard limiting ...
Marty/John - maybe something to explore in the Tornado dividers ...
Quote.. the diodes are being used for their non-linear resistance ... if you look at both diodes as a combined resistance you'll see it's part of a voltage divider acting between the Drain and the equivalent resistance seen at the volume pot ... the diodes are biased weakly so that minute variations in current through them cause a relative increase or decrease around their idle resistance value ...
you have to argue on a half-cycle basis, take a sine wave input for argument's sake ... when the Drain voltage goes high the first diode gets slightly less biased and the second one gets slightly more biased ... the incremental resistance, what the signal sees, is increased in the first and reduced in the second ... during the second half cycle the reverse happens ...
because of the logarithmic current-to-voltage nature of diodes the increase in resistance on the weaker biased diode is greater than the decrease in resistance on the stronger biased diode ... this means that the incremental sum resistance of both is greater than the idling sum value, and the increase is monotonic with signal amplitude ... to a point at least ... if the diodes and their biasing are well enough matched then the two half cycles will be attenuated through the divider in an equal way ...
at least this is what happens when the stage is operating in class-A ... with stronger signal levels you get to onset of clipping, and then into class-B fuzz and hard limiting ...
Marty/John - maybe something to explore in the Tornado dividers ...
The LEDs I used when I was testing were different, both red but one with the red case and the other transparent. 1.65V and 1.5V resp. Since the 1.65V were conducting less I replaced the 10K to gnd with a 8.2K. Also I used a 100K-B pot instead of the fixed 47K (R6). I'm using 100K now. As I wrote in the schem, play with the diode network resistors.
To be honest, I included the diode network because I had oscillations problems above certain gain, and a big resistor or shunting signal to gnd was not atractive and sounded horrible. When I read about the diode network (Joe Davisson maybe?) I said 'why not?'. It reduced the oscillations a lot but not completely. Then I realized that I was tweaking ROG version so the fet drain was going to the 386 (-) input, pin 2. I changed to (+), pin 3 and eureka! No more oscillations. I was too lazy to remove the diodes... :icon_redface:
mac
Quote
I have a TDA2822, I have thought about using for at practice amp. It's stereo, but the channels can be bridged in a Little GEM II type configuration. My hope is that it should give more headroom than the 386.
Regards
Carsten
Success! I used two bridged LM386-N, this ones have more power the the one I used first. I connected the 386s almost exactly as in the Little GEM MKII, after the 0.22uf. I only added a 0.022uf cap from (+) pin 3 to gnd, and a dual 10K pot to control both chips gain at the same time. And the caps are not 10uf but 2.2uf polyester. The bad news that the 386s, the 2.2uf and the 10 resistor get hot. Maybe a fan or small heatsink for the chips.
As soon as I draw the new schem I'll post it. MAybe a new thread.
mac