cabinet voicing

[dbw]

Okay, so I built myself a 1/2 watt solid state "Little Gem" amp (http://runoffgroove.com/littlegem.html).  My goal was to get something I could plug headphones into and practice through in the middle of the night while being considerate to my neighbors.

So I wired it up and built it in a plastic box I got a pickup in.  It definitely works!  However I was astonished to hear the distortion when I plugged my headphones in... it's extremely harsh and unmusical, not at all like the sound clip on runoffgroove.  After rechecking the circuit to make sure I didn't screw up, I tried plugging it into my Mesa 4x12 (not expecting much to come out), and lo and behold, nice smooth distortion came out (at an incredible volume considering it's being powered by a 9V battery).  I also hooked it up to the line in on my Peavey 1x8 combo and that sounded quite nice too.

Okay, so how can make my headphones sound more like a real cab?  Doesn't need to be great, it's just for practice, but that distortion seriously gives me a headache!  I just need to mellow it up a bit.

The clean sounds are fine, by the way.

 

[Micahbell]

I have tried a couple cheap pocket amps, and I have found this to be true with all of them. Somebody may have had a different experience, but I think the only way to get a good distortion sound through headphones is with a POD, or the Behringer pod copy or something similar.

 

[Rab]

Maybe a loading issue?

Is there only one output?  If so, the cabinet will present a much greater load to the amp (4ohms, 8ohms etc) than the headphones (normally nearer 600ohms), maybe a loading resistor (8ohms or so) across the output would help.

Cheers - Rab.

 

[jimh]

You ever try one of these?
http://www.smokeyamps.com/

They are hilarious.  You can use it as a stand alone 0.5W amp, or you can run the output into your signal chain and it'll act as a fuzz box, or you can run the output into you speaker cab and use it to drive your extremely expensive beefy Mesa 4x12 cab.

I tried it with my Orange 2x12. Doesnt sound great as such, but its good fun........

 

[dbw]

Maybe a loading issue?

Is there only one output?  If so, the cabinet will present a much greater load to the amp (4ohms, 8ohms etc) than the headphones (normally nearer 600ohms), maybe a loading resistor (8ohms or so) across the output would help.

Cheers - Rab.

Hang on I'm confused... 600 ohms is way more than 4 ohms!  Anyway I measure my headphones at 30 ohms each channel, so that's 15 ohms mono.  My cab is 8 ohms.

 

[Rab]

Load's the opposite of impedance: low impedance = big current =  big load, high impedance = small current = small load.  Maybe the amplifier expects a minimum load, the circuit you linked to appears to be designed for a speaker, not headphones.

I take it your headphones are the portable type if they are measuring 30 ohms. 

Anyway, the circuit appears to be designed for an 8 ohm load and your headphones are double that, try the load resistor (a lot of the 386 circuits use a 10ohm resistor) or a capacitor on the output to cut some of the higher frequencies.

Cheers - Rab.

 

[dbw]

Thanks Rab.  I'll try this out later.  And Jim those amps are cool  :guitaristgif:  I might get one made in a box of reds.

 

[Rab]

Just had another thought, the drivers in your cabinet probably roll off at 6-7kHz, your headphones probably go all the way to 20kHz,  maybe capacitor filtering is the way to go.

I'll try and come up with something tonight.

(Edit)

Try this modified circuit:

The 2.2uF cap with the 10ohm resistor should act as a filter a 7kHz, you might need to tweak the value to get a sound you're happy with.  A bigger cap will move the cutoff lower, a smaller cap will move it higher.

Cheers - Rab.

Cheers - Rab.

 

[DiMitriR33]

there are no cliping diodes? :icon_scratch:

you must be driveing this thing into a true overdrive, i didn't think that worked well with solid state.

and yeah i agree that it's probably just too much treble, but might also be bottoming out the headphones or have some loading issue, i'd try his modified curcuit above first, then try a loading resistor which should solve the other 2 problems.

 

[neilium]

there are no cliping diodes? :icon_scratch:

The 386 opamp overdrives better than I ever thought it would. I would never mistake it for a tube or a germanium transistor, but it can sound pretty meaty. I've used it in a couple pedals, including a freaky octave distortion. Cheap fun for experimenting. It's at the heart of the previously mentioned Smokey amps.

 

[boogie2]

Yeah, what Rab said. 

A cab is a nice reactive load that acts like a lowpass
filter.  It's why the line-outs of most amps sound overly
bright and generally terrible.  I have yet to find a speaker
emulated direct box that was worth more that the parts
went into it...

Boogie2

 

[dbw]

All right, I'll go back to the breadboard and try some shit this weekend.  Thanks for the advice guys, I'll let you know what works and what doesn't.