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Vanishing Bass

B

Birray

Nov 19, 2004
6
0
#1
I just got 2 Electric Amp non-master volume 200W KT88 units (What they call the 'Power Unit'). I use one of them to power a 2x15 and a 1x18 cab. I send it a clean signal, and it gives massive bass until about volume: 11 o' clock. After this point, the bass begins to disappear, and the signal starts to distort. By the time I get to 2 o'clock, a lot of the bass seems to be gone.

What I want is to be able to crank the amp and still get a clean, bassy signal. I was reading about lower gain factor preamp tubes, but I really don't want the amp to have drastically less output volume as a result. The amp has 3 12ax7s, and I tune very low (A standard). Any suggestions?
 
#2
At a point you'll stop getting more bass and just get more distortion, when the valves are outputting all they can. If you want huge clean low at huge volume, valves aren't really the way. More efficient speakers will help you some. Old dub rigs were all valve powered, and used huge horn subs to get the lows to volume. But really, big solid state power amp for the real lows, valves for the flavour.

Also, get a real Matamp

matamp001.jpg


Mmmm
 
#4
I'm a little confused, though. Which 'valves are outputting all they can'? The power tubes, or the pre tubes? In other words, is the problem that the signal I'm trying to amplify requires more power than the power amp is capable of giving, or that it has maxed out the preamp?

Also, I forgot to add: The amp has a 4-position 'Bass' knob that seems to be a kind of high-pass filter. With the knob set to the most bass, it sounds the most massive, but will function as described above. Higher settings have less bass but will retain what bass they have at higher volume.
 
#5
Mr. Foxen said:
At a point you'll stop getting more bass and just get more distortion, when the valves are outputting all they can.
Click to expand...
Speakers will do the same. When xmax is reached in the low end additional power applied gives more mids but not more lows. With enough power thermal power compression sets in and additional power applied can result in less output across the board.
 
#7
Most older tube amps ran out of gas by noon on the master. after that it is just compression and distortion. Great for guitar but for clean sound thats it folks. Makes you feel good to be really loud at 11:00 but much more and you are done (at the limits of the output tubes).
 
#8
Birray said:
The speakers are definitely not the problem. All 3 are high-wattage eminence, matched to the enclosures. I used to run a coliseum lead & a slave to those 2 and a 4x10; the bass was huge.
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yeah, well you had a 410, too. you apparently don't use it in this rig, so naturally it would be less earth shaking. physics tells you that. a 215 generally has about as much air movement as a 410, maybe slightly more.

anyway, yeah, you're just reaching the outer limits of your gear and trying to get more than what it's capable of. i personally think it's in the speakers. real world power handling is often grossly overestimated by manufacturers. a driver rated for 400w means that the voice coil will burn up past 400w for any length of time. but in a cab, even a lot of really good cabs, it'll reach its physical limit far below that rating. if you want loud and massive you need bigger cabs. i would at least consider replacing the 118 with your 410 or another 215. if you could swing two 810's, even better ;)

EDIT: after re-reading your initial post, it's also that your amp just cuts low end when you get into distortion. but that'll happen on most any tube amp, not just yours. i think if you had bigger cabs with more speakers, you would have more acoustic coupling to rely on making up for the low end loss from your head. any time you double your driver count, you get a pretty sizable boost in low end response as well.
 
#10
Well, as far as I know, that's kinda the point of Electric Amps. They can get stupid loud, and have wicked distortion when full cranked. They aren't really intended for big clean tone. You could try putting in lower gain pre-amp tubes, maybe a 12AU7, but it would be quieter, and you'd probably still be getting distorted after a certain point without much additional Bass.
 
#11
I'm still using the 4x10 with the 2nd Electric Amp, which I use for fuzz. I've tried various cabinet configurations; 8x10s have no low bass, and IMHO don't sound meaty enough for me. (I know lots of people play 10s, it's just an opinion, don't jump down my throat) and 4x15 was not clear enough. I haven't gone 8x12 yet, which has been recommended to me by others. So far, this has been the best combo I've tried. I still have a Coliseum Slave, maybe I should just run 3 amps, Zoroaster-style?
 
#12
Try a 12AY7 in the first preamp tube position. You might find that you get some more clean headroom out of it.

The loss in overall volume by doing this will not be substantial.

Give it a try. It's an easy swap, and 12AY7s aren't too expensive so you have little to lose.
 
#13
Birray said:
I'm still using the 4x10 with the 2nd Electric Amp, which I use for fuzz. I've tried various cabinet configurations; 8x10s have no low bass, and IMHO don't sound meaty enough for me. (I know lots of people play 10s, it's just an opinion, don't jump down my throat) and 4x15 was not clear enough. I haven't gone 8x12 yet, which has been recommended to me by others. So far, this has been the best combo I've tried. I still have a Coliseum Slave, maybe I should just run 3 amps, Zoroaster-style?
Click to expand...

Bear in mind Electric amps, and most valves amps for that matter, are build to power cabinets that are only expected to put out the lows of an 8x10, or maybe an oldschool 2x15. Low bass in the heyday of valve amplifiers required huge horn cabinets. Nowadays we have very much better speakers, and very much better cabinet design (as much as they are often ignored), but we also have high powered solid state amplifiers, which most low bass cabinets are designed for, to keep the size sensible, you sacrifice sensitivity, so it needs a lot of power to get up to volume, but power is cheap.

You might also get a small but expensive benefit for fitting higher quality KT88s and rebiasing it.
 
#16
12au7, 5751, o even a 6np2(military soviet spec) Preamp tubes to replace those 12ax7's.

The voltage on the 6np2 is dfferent, but it works in place of 12ax7. Also takes a slight mod if you choose it.

Also, you can try adjusting for more bias to relieve excess voltage, this can clean up quite a bit.

The 5751's have agod wide bias range, can be used for clean or ever so slightly overdriven for warmth.

The kt88 is a strong tube, and can be more hi-fi than the 6550 at lower output. A well desiged pair if kt's in the 60-80 watt range is very dynamic and powerful/clean. It appears your amp has 4, with an output of 200 Rms. That should make a good warm sound, but slight loss in dynamics.

The 12ay7 suggested above is a good choice as well.
 
#17
D.M.N. said:
Well, as far as I know, that's kinda the point of Electric Amps. They can get stupid loud, and have wicked distortion when full cranked. They aren't really intended for big clean tone. You could try putting in lower gain pre-amp tubes, maybe a 12AU7, but it would be quieter, and you'd probably still be getting distorted after a certain point without much additional Bass.
Click to expand...

Yeah, they're not really known so much for high clean volume. I thought they were SUPPOSED to get dirty fast.
 

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