Tube Amps / Music Electronics
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|5/12/2003 4:26 AM|
||PowerMan (2x6021) samples are up...|
For those playing around with ideas for amps using the sub-miniature 6021 tubes (and I know both of you are out there somewhere!), I've finally posted sound samples of my PowerMan amp. They're not great recordings, but they'll give you the idea. I didn't bother using the 4-inch speaker (my guitar playing is humiliating enough!), so it's all done with my 1x12 (Weber C12Q) cab.
|5/12/2003 6:10 AM|
Sounds really good to me, I could definitely see jammin' away at home with that tone!
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|5/13/2003 3:05 AM|
I think I've got me a pretty good practice amp here, but I'd be really excited if it sounded anywhere near that good with the 4-inch speaker – then it'd be a really portable practice amp!
|5/13/2003 4:19 AM|
Mark, your audio samples sound great. Even on my PC headphones I can hear that cool tube tone. By the way, I've been admiring the schematics for some of your other amps for quite a while now, especially the Decimator. I'd really like to take a shot at building that one. Anyway, nice work on the Powerman.
|5/13/2003 10:39 PM|
I like those samples too Mark.
Maybe you need to build a 4x4 slant-top closed back cabinet so you can have a desktop half-stack
That's the direction I'm going to try, just found four NOS 4inch alnicos.
|5/14/2003 1:02 AM|
I'm a bit surprised that you guys are liking those samples, but I guess that's because I compare them to what I actually hear in the room...
|5/15/2003 12:14 AM|
Working in the small scale I'm beginning to get an idea about balancing the iron in the *speaker loop* between the driver and the motor.
In a tube amp without NFB, the final output circuit is really the simplest most isolated loop of copper wire in the whole amp. Just the OPT secondary with its terminals connected by the speaker's voice coil, one big circle of copper. In theory the copper could be held constant, then the iron in the OPT secondary could be changed as well as the magnet size or strength at the speaker.
Imagine a full-size amp playing through a tiny speaker, it always sounds bad.
OTOH, everybody knows ohms are ohms but does it really make no difference if you try and drive a vast array of large inefficient speakers compared to a single fairly efficient one, just because they are wired to give the same load ohms? Large hifi speakers do have a minimum wattage rating, below which they sound bad, if you tried to drive them with a micropower amp no damage may be done if the impedance is matched, but I wouldn't expect it to sound good, some cones probably would not move at all. With enough speakers there could be significant mass that needs to be put in motion, if the power amp is too small there will not be enough energy to accomplish the work regardless if the impedance is optimally matched. Aside from the actual power output, maybe if the OPT iron is too small there will also be a type of difficulty getting the OPT to control the speaker.
When a small amp sounds better through a larger speaker, it's probably usually because its a better speaker. maybe there is some contribution just due to relative magnet size compared to OPT iron though. There might be a chance that a large mismatch in ferric strength allows either the OPT or speaker magnet's behavior to dominate the loop, and maybe a more balanced combination yields the character that we have conventionally come to appreciate as more desirable.
maybe the Powerman has a big enough OPT already to be out of ideal range for the 4inch speaker, not much differently than a bigger amp. It might be worthwhile to change to a smaller OPT to see if it improves the small speaker performance, I expect it would be at the expense of good tone when driving 12inch speakers.
Experiments along these lines would probably give good data using the Hammond 125 series of universal OPT's available in various sizes with the same ratios, in combination with various speakers which could be built using different magnets but having identical voice coils.
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