Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: GLFSHNT on January 19, 2018, 10:31:38 am
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In my opinion Attenuators all sound like crud what you dial them back to quiet practice volume. You always loose the "twinkley" highs and upper end clarity that makes tube amps so superior. You also loose the "back off the guitar volume a bit and things clean right up" so I was thinking....
Has anyone ever built a small tube amp (Deluxe 5E3?) with this idea of setting it up to perform best when attenuated. This would require a tone that would be far to bright for normal use. I am thinking about tweaking my 5e3. I am not a real experienced amp building guru but I like to play with things..... Thoughts??
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Have you tried a VVR?
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LOTS of VVR and cathode biased amp info here in ARCHIVES: http://el34world.com/Forum/index.php?topic=6899.0
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Would this be for home? Recording? Stage? Another option might be an isolation cabinet. That way you could crank away and not lose any of those fine features.
Jim
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A lot depends on the attenuator-- what types have you tried, and/or plan to use with this amp?
Guitar speaker impedance is not constant and usually higher than the rated value, one graph here shows an example: https://www.eminence.com/pdf/Legend_1275.pdf
I believe the way the amp interacts with speaker impedance is one of the most important factors in tube amp sound. A pentode "should" drive high impedance more readily than a constant-voltage source like modern transistor amps. Of course, things change as you turn up the volume... the pentode can't indefinitely push equal or greater power into "higher than ideal" loads, so this is one of the factors that shapes the frequency response and character of a cranked vs quiet tube amp.
Simple resistors won't preserve this amp/speaker interaction. Inductors can be used to simulate high-frequency behavior-- since inductance is listed on speaker datasheets that's relatively simple. Low-frequency impedance spikes (caused by resonance) are tricky. That's why attenuators like the Weber Mass "cheat" by containing an actual speaker mechanism.
This doesn't mean you can't make an amp sound good with a simple resistor attenuator for example, but your design would depend on the type you're using.
Another option is a low-watt amp. I've tried the AX84 Firefly, wasn't quite the sound I was looking for. It is after all a self-split triode stage. But you could drive smaller pentodes with a traditional phase inverter, for example use 90% of the 5E3 circuit, but use 6AU6 pentodes as output tubes. Aim for maybe 22k load impedance and similarly low voltage as a Firefly.
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A guitar speaker typically has as SPL of 90 - 105dB: 1 lousy Watt into the speaker is as loud as a NYC subway train, at 3' from the speaker.
An active crossover could boost highs in the system to overcome the hi-killing effects of an attenuator.
You could buy or build a firefly type amp. Or use headphones for quiet practice alone.
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line 6 pod with headphones. you're own rockin' utopia.
--pete