Suitable Bass Guitar Speakers

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Suitable Bass Guitar Speakers

Postby SDS-PAGE » Tue Jul 31, 2007 1:52 pm

I just finished building a bass amp with a EF-86, a 12AX7, and 6V6s. I built it cheap (~150 bucks) with parts on hand and good deals on tubes off eBay. EF-86s ain't cheap! I was lucky to get a NOS Amperex, made in Holland for 7 bucks.
Ok, I need a speaker my amp. I can probably make a cab from the scratch for a 12-15" woofer, but I neither have time nor energy to mess with the wood. Is it possible to use a hometheater subwoofer for bass guitar? I can probably find one reasonably priced. I don't plan on performing on stage or anything, so it doesn't have to perfect. Just need one for practice. I would be interested in hearing any other ideas besides the bass amp one. Thanks!
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Postby gerryc » Sat Aug 04, 2007 7:56 pm

You could use a home theater subwoofer, but it probably wouldn't sound very good. Bass guitar needs a speaker that will give you a reasonable response to a few KHz to sound good. The subwoofer probably has little response above 200 Hz or so. You'd hear the fundamental fine, but it would sound kind of muddy.

If you really don't want to spend much, I'd look for a used full range speaker, i.e. a single hi-fi cabinet with at least a 10" woofer. Even if you hack it up and just use the woofer full range (disconnect the other speakers and crossover and directly connect the woofer), it should sound much better than a subwoofer.

Another idea is if you can find a cabinet without speakers (or blown speakers), get a bona-fide musical instrument speaker designed for bass guitar and just mount it in. You can get these (10, 12, or 15 in) from places like PartsExpress or MCM Electronics for $30 to $60. Then if you get the motivation to build a nice cabinet, you can pop the speaker in there.
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Postby erichayes » Sat Aug 04, 2007 9:56 pm

All but one of the bass players I know want higher fidelity than a typical guitar amp/speaker combo provides. They want to hear the harmonics that just don't come through on a woofer alone. That's why Ampeg and SWR, among others, are putting piezo tweeters in their bass speaker cabs.

I'd go with Gerry's full range cab idea, but don't disconnect the crossover and tweeter. Yard and estate sales can yield old '50s and '60s monaural systems for a song. Most of the woofers used treated paper or cloth for surround material, so you don't have to worry about rotten foam (look to be sure, though), and you probably won't fry the voice coil with 10 or so watts (use a battery; liisten for a well-defined click and look for uniform cone excursion).

Give me a holler if you have any questions.
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Postby SDS-PAGE » Mon Aug 06, 2007 4:43 pm

Thanks for those great suggestions, guys! I ran into some problems (typical!) with the amp concerning its output. I didn't try out hooking up the amp to a bass guitar until yesterday 'cos I didn't have a cord for it. The output is rather low. There is definitely amplification, but it's low. When I hook up my iPod to it, I get good sound w/ an ample volume. So, it's acting like a hi-fi monoblock. I am guessing it's a problem with impedance matching? I understand that guitar input has high impedance levels around 450k ~ 1M ohm and those of hi-fi audio are around 100 ~ 1k ohm. The schematic I used didn't call for a 1M resistor between the sleeve and ground. My first preamp tube is 12au7. Any ideas? Thanks a bunch.
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Postby SDS-PAGE » Tue Aug 07, 2007 8:33 am

Eric, I tried pluggin in 12AX7 in liew of 12AU7 and there is a marginal increase in volume. I guess 100x amp factor of 12AX7 is needed in my case. The reason for using EL34s for now was that I made a grave (actually stupid is more like it) mistake is hooking up filament supply with high volt supply. I am using one of those bulky militray spec power trans that has 12 leads and I got careless. $50 worth of tubes frying before your eyes....
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Anyway, I need to get a couple of 6v6s and see if that would make it even better. Thanks a lot for your call, Eirc. I really appreciate it. -Min
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Postby Uncle Ned » Fri Aug 10, 2007 2:01 am

SDS-PAGE wrote:Eric, I tried pluggin in 12AX7 in liew of 12AU7 and there is a marginal increase in volume. I guess 100x amp factor of 12AX7 is needed in my case.


So what happened to the EF86? That ought to have plenty of gain unless it's inside a feedback loop (which, BTW, you could disconnect, or try fiddling with the feedback resistor... note that'll affect the bass damping ie tone as well).

Some bass amps have input resistors as high as 5 megs.

You do need a relatively high efficiency speaker to get decent output with only 10 watts for bass, and (a) many home speakers aren't very efficient (look for 95 dB/W/M and up efficiency), and (b) crossovers tend to be power soaks (thus the piezo tweets seen on some bass cabs, they don't need crossovers).

The guitar pickups I've measured generally put out in the 100 mv range, about 1/10th typical input sensitivity for a tube power amp, with a 12AX7 preamp tube you should have plenty of gain unless you've got a really lossy tone control.

Last week I saw an itinerant (if you're British, read: buskers ) 3 piece Mexican ranchero band where the bass player (solid-body) was playing through a battery powered Peavey that couldn't have had more than an 8 inch speaker in it, and he was keeping up with the lead (and loud enough for a couple dozen patrons) , but the lead was playing an acoustic. So, yes, even a small bass amp can be useful. BTW, they collected about $100 (at $10 per song) in less than an hour, then moved onto another bar. Probably pays better than the average rock gig, I'd guess...
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Postby SDS-PAGE » Fri Aug 10, 2007 8:56 am

Uncle Ned wrote:So what happened to the EF86?


I saw it fry along with all other tubes that I bought brand new when I high-voltaged the filament tap. Didn't get to play with it, much to my vexation.

The guitar pickups I've measured generally put out in the 100 mv range, about 1/10th typical input sensitivity for a tube power amp, with a 12AX7 preamp tube you should have plenty of gain unless you've got a really lossy tone control.


I got the gain I needed. Now I need to work one getting the right speaker for it. The home speaker that I have been testing the amp with can't take the bass. BTW, what's the major difference between a regular guitar amp and a bass guitar amp? Can a regular guitar be used with my bass amp?
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Postby erichayes » Sat Aug 11, 2007 1:03 am

Absolutely, Min.

As I mentioned earlier, a bass amp will generally have higher fidelity than a guitar amp, which means it will reproduce the original signal more accurately.

The neat thing with a good amp is you can always louse it up after the fact. With a bad amp, you have a one trick pony.

I'll try to be in touch this weekend.
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Postby Uncle Ned » Sat Aug 11, 2007 1:45 pm

SDS-PAGE wrote: BTW, what's the major difference between a regular guitar amp and a bass guitar amp?


About the only hard rules I can think of are that for the same power, a tube bass amp would need a larger output transformer and a different style of speaker, since the lowest note on an electric bass is either 31 Hz or 40 Hz, vs a regular electric where the lowest note IIRC is about 80 Hz.

Usually bass players want a lot more power than lead players, since they usually don't want distortion, and in order to keep up volume-wise, but some well known bass amps (I'm thinking of the Ampeg B15) are only 50 watts.

Can a regular guitar be used with my bass amp?


Heck, some bass amps (I'm specifically thinking of the Fender Bassman) are better known as guitar amps than as bass amps! In other cases companies have made two versions of the same amp made and the "bass" version is more or less just lacking the reverb and tremolo..
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Postby SDS-PAGE » Sat Aug 11, 2007 5:11 pm

Excellent! I think I will use the amp as a regular electric guitar amp. The OPT seems small (approx. 20 watts) for bass duties anway. I went garage saling today and picked up a pair of speakers that were custom-made by someone in Sacramento. Got 'em for 10 bucks. I got 'em 'cos I liked all-wood construction and wanted to find out what DIY work went into it. I opened the cabinet and found that they actually have 12" Tempo Series 30 W woofers (full range?) by Oxford Transducer Corp. Illinois, USA. They also have horn tweeters. I hooked up my Darling then my bass guitar and both sounded pretty loud and nice. Could this be good for a regular guitar amp? Also, any guesses as to how efficient these speakers might be? Thanks!
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