Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bassisst90 on April 09, 2013, 04:02:27 pm
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Hey guys. I'm looking for a way to increase the clean headroom/increase the maximum amount of volume before distortion occurs in my 50w bassman 10. I already replaced the speakers with eminence bp102's and that really helped, but now when I practice with my band we get loud enough to the point where my bass starts to distort. I know some people will say sell it and get another amp, but I love the way this one sounds!!! Anyone have a way to help? I'd heard of getting a more efficient output transformer to get more volume out of the amp, as well as replace the 6l6gc's with 7581a's, rebiased of course. I also thought about jumpering the negative feedback resistor, but I don't know if that will get more clean volume out of it (as in decibel level), or just have less gain. Any suggestions are appreciated. Thanks.
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A bass amp needs to be more than 50 watts.. how about putting a mic on it ?
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That might work, I know it will be fine for mic'ed gigs, this is just for rehearsals
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A bigger output transformer may help but there isn't much room for a bigger one in that cabinet.
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Yea, that's true. How much bigger would it have to be to be noticeable and not need a bigger power transformer?
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The sensitivity of the BP 102s is pretty low.
I think they about 92 dB.
If they are series parrallel, for an 8 ohm load,
try another baffle for a single 15, say D,E or K 140 or EVM15B or L.
These will give you way more sound per watt.
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Well, the problem with that is that this amp is a front loading cabinet, and I don't see a way to open it without completely destroying it. I have another 15'' speaker in its own cab, also 8 ohms that I can use (its a black widow). I was just hoping for a better, more permanent, and less hassly (don't think this is a word :laugh:) way to fix all of this
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Try running to the BW and see what happens.
I think that design was somewhat inspired by the JBLs
and may be higher sensitivity.
I got by longer than I should have by running a 50W Bassman into a pair or Altec 421s.
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a bass guitar is a power hungry beast when you are with a group of guys who like the adrenaline rush of playing with gusto aka LOUD.
I have heard of techs using a large, 4 tube, hundred watt output transformer in a 2 tube amp and getting more clean headroom. I believe you have to run this arrangement at one-half the OT's original load? e.g. If the OT is set to run at 8 ohms, you run it at 4....
I don't know if that would change the sound of the amp a great deal or not, but different output tubes and a different speaker probably will change the sound somewhat? So, eventually you may change enough parts that you decide you want to put it back stock?
I tried several different ideas when I ran out of power with a loud group and I settled on running two amps with an ABY box. I haven't run out of power again but I had to experiment to find a sound I liked.
:icon_biggrin:
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Remove the negative feedback tap on the speaker out jack/ This will give you major bloom,fullness and bottom boost in clean headroom. What bassman 10 do you have? If you have the Bassman 10 with the ultra linear power transformer i would remove the ultalinear taps and wire the screens right from the power supply node as the bassman 10 with the standard power transformer. Ultra linear is real clean to me but something goes on where the sound is chocked off to me. Remove the NF tap first and hear the difference. You want to do this if you are using this for a bass guitar. Also you could change V1A or V2A cathode bypass from a 25uf cap to 250uf for more bottom end rumble
EDIT:
Leave the ultra linear taps alone for now. Try the other suggestions first
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I tried using one of these for bass in a loud band. My solution, finally, was to a buy a GK 800RB. Not us much fun, but pretty effective.
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I'll try to remove the negative feedback loop. I've been looking around for more solutions and found the symptoms that I've stated may not have been specific enough, as I've heard of this sort of distortion as blocking distortion or "farting". Maybe there are other solutions for this? Such as in the phase inverter?
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So I removed the feedback loop and there doesn't seem to be any farting anymore, so that's good. It does overdrive, but it doesn't sound bad anymore. I'll test it out with others tomorrow and hopefully this is all well and good!