Planning 386 amp - fetzer? bridged? line out?

[suprleed]

My current amp is a cheap POS 2 channel solid state practice amp.  The dirty channel just sucks, sounds like a metal file rubbing the edge of a rusty tin can.  The clean channel is OK but gets hissy when I turn the volume up.  I use the clean channel exclusively and often play using various amp "sims" from my digitech rp200 at the end of my chain to make it sound like I'm playing into a good amp.  But as you all know, amp sims just aren't like the real thing.  I don't need a huge amp as I primarily just need a small amp for home recording and jamming.  I'm trying to save up for a small tube amp but in the meantime I figure this is a perfect situation for building a 386 IC practice amp a la ruby/cricket/little gem that will probably sound better than what I'm currently using.

I've been researching these little amps thinking about various input stages and whether to use a single or bridged chip setup and have a couple of questions:

For those who have built the fetzer-ruby, are you still able to get nice clean tones?  I've read the fetzer stage gives the amp a little more gain/dirt, which is good, but I also want to be able to go clean as well.  What's your experience with the fetzer-ruby as far as the range from clean to dirty?

Is it possible to put a headphone jack on a bridged amp?  I suppose its possible, I'm just worried it would be complex.  The ROG FAQ shows how to set up a headphone jack on the single 386 designs, but I'm not sure how it would be done on a bridged amp like the little gem mkII.

Can I use the headphone out as a line out for recording as long as I run the signal thru a cab simulator to round out/smooth the tone?

Thanks all.

[mojo_hand]

As long as you're buying a power aupply and perfboard (or whatever) anyway, I don't think that putting a FET at the input could hurt anything, it might help the overall sound a bit, and using it with a gain control would make overdriving strictly an option.  And options are never a bad thing, especially when they only add about 50 cents to your project cost.

A bridged design just lets you drive a moderate impedance load to higher levels while using a low voltage power supply.  You need to be sure that your output devices have enough current capability for the job, but, other than that, they're just like any other amp.  They will easily drive almost any headphones.

[suprleed]

As long as you're buying a power aupply and perfboard (or whatever) anyway, I don't think that putting a FET at the input could hurt anything, it might help the overall sound a bit, and using it with a gain control would make overdriving strictly an option.  And options are never a bad thing, especially when they only add about 50 cents to your project cost.

I'm sure either the original JFET buffer in the ruby or the fetzer valve input stage will sound great.  I'm just worried that the fetzer will be too high in gain and limit the clean ability of the amp.

A bridged design just lets you drive a moderate impedance load to higher levels while using a low voltage power supply.  You need to be sure that your output devices have enough current capability for the job, but, other than that, they're just like any other amp.  They will easily drive almost any headphones.

I love how bridging the IC's will nearly double the wattage of the amp.  But I play thru headphones late at night all the time, and I don't even know where to start to try inserting a phone out on the push pull outputs of a bridged 386 design?!?

Has anyone done any recording (direct to pc soundcard) using a ruby, noisy cricket, little gem, etc.?  Good/bad experience?

[mojo_hand]

I wouldn't worry overmuch about too high gain from something like a fetzer.  In fact, using 9V, it's hard to get even unity gain out of most JFETs.  You can with J201s, but, given around average Vp and Idss, your gain will still be no more than 5.  When I run FET boosters off of batteries, I usually have to use 3 stages to get them to clip audibly, playing into them with a P-90 (pickup).  So I wouldn't worry about that at all.  Although I forgot that the amp you were considering already had a FET gain stage in front of the 386, I'm not sure that there'd be any huge advantage to a fetzer over the standard input stage.  It might not even be as good, since it wouldn't have been designed for that specific purpose.  It might be best to leave well enough alone.

[suprleed]

I'm not sure that there'd be any huge advantage to a fetzer over the standard input stage.  It might not even be as good, since it wouldn't have been designed for that specific purpose.  It might be best to leave well enough alone.

Looks like we're going back and forth on a couple threads mojo.  Thanks.

Your right, sometimes the simple answer is the best answer (the old keep it simple stupid principle)!  That being said, has anyone compared a fetzer-ruby vs. a stock ruby that can comment on the differences (if any)? 

[Ardric]

I think the whole big appeal of the 386 mini-amps came from the sound of driving the snot out of the 386.  It's said to sound nicer when clipping than many other chips.  If you're looking for a clean sound out of the power amp, not intending to overdrive the 386, then I think you should seriously consider using another chip.

For fun I've built little amps, speaker cabs and combos.  I've decided that in practical terms the speaker and cab is much more important than the amp itself.  Some little battery-powered amps sound just awesome (and loud!) through a good efficient 12" guitar speaker in a real cab... but no matter how great the tube amp, it'll sound like poo through a 4" speaker scrounged from some old TV set.  Consider putting the money into a good speaker cab now.  Use it for your diy amps and as an extention for your existing solid state combo, and when you get a tube head it'll be even better.

Plugging a guitar straight into a 386 doesn't work well because of the 50k input impedence... unless you have active pickups.  It needs an input buffer at the very least.  That's the Ruby.

A little more complicated is some sort of pre-amp.  Not only do they perform the buffer's job, but they can also provide gain, distortion and eq.  The Fetzer is a basic one-JFET version of that.  You could instead use one of the more complex ROG amp sims as a pre-amp into that 386 too.

My own opinion is... either go the Ruby approach and use an external preamp or pedal, or build a complete amp with a nice preamp and tonestack.

[mac]

http://www.diystompboxes.com/smfforum/index.php?topic=54524.0

sound samples at

http://guitarfxs.tripod.com

mac

[suprleed]

Mac, are those clips with your guitar straight into the amp (no pedals)?  Very nice!  If I can get a 386 amp to sound as good as yours I'll be in business!  Looks like I have more options to consider...

Another question Mac, what does the 10uf cap in the loop between pins 1 and 8 do?  Is it affecting the gain in some way?  Seems to large for tone shaping, but I could be way off here?

For fun I've built little amps, speaker cabs and combos.  I've decided that in practical terms the speaker and cab is much more important than the amp itself.  Some little battery-powered amps sound just awesome (and loud!) through a good efficient 12" guitar speaker in a real cab... but no matter how great the tube amp, it'll sound like poo through a 4" speaker scrounged from some old TV set.  Consider putting the money into a good speaker cab now.  Use it for your diy amps and as an extention for your existing solid state combo, and when you get a tube head it'll be even better.

Excellent point.  I'm planning on building a cab for this project.  Like you said, with a decent speaker and cab I think any of the 386 based amps will sound better than my current Korean cheapo special. 

[mac]

Guitar to jade amp to my laney LC30 HH 12" speaker. Sounds pretty loud for practice and bedroom use with a good  10"-12" speaker.
The 10uf and the 2k pot set the internal gain of the LM386 chip. 10uf is suggested by the LM386 National datasheet IIRC, but you can use a different value to shape freq response.

mac