What should I do with this Bassman?

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jmann
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What should I do with this Bassman?

Post by jmann » Sun Aug 27, 2017 2:46 pm

I have a used Fender Bassman 10. (It's a 4x10 combo).

These things were originally shipped with 4 32-Ohm speakers wired in parallel for an 8 Ohm load. But on this one, a previous owner swapped in some Eminence E-M10G speakers (#10609) which are 8 Ohm, and wired it all in series. So the amp, which generally sounds fine with both bass and guitar, is pushing a 32 Ohm load.

Should I fix it and wire these as series-parallel? What are the likely effects? (i.e. is it suddenly going to be much louder?) Am I damaging the amp running it like this? I haven't played it much but right now it sounds pretty decent for clean tones. I haven't cranked it up too high yet.

An added complication is that I finally got myself a bass (I'm mostly a guitar player) and want to be able to play that through the amp without tearing up the cones of these speakers.

Anyway have advice for me on how to handle this?

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Re: What should I do with this Bassman?

Post by Snarl 12/8 » Sun Aug 27, 2017 3:59 pm

I would rewire series/parallel to get back to 8 ohms. I'd rather blow those speakers, if that's a risk, than fuck up the amp itself. Tube amps are finicky about what load they drive. Bring the volume up slowly and judge for yourself. If you're just rockin' the amp solo you'll be able to hear if the speakers are crapping out.
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Re: What should I do with this Bassman?

Post by Drone » Sun Aug 27, 2017 4:00 pm

If you are sure it's wired wrongly, and the transformer is the original one, meant to push 8 ohms, then yes you should rewire it.

If you want to use it for bass-y bass, get an external cabinet, and wire in a speaker jack that allows you to turn off the internal speakers. A single 15" would be my preference.
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Re: What should I do with this Bassman?

Post by kslight » Sun Aug 27, 2017 4:51 pm

If it's wired as you say, shouldn't it have no clean headroom to speak of?

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Re: What should I do with this Bassman?

Post by jmann » Sun Aug 27, 2017 5:18 pm

Oh, it never occurred to me that the transformer could be a replacement. Better figure that out first, I guess. Thanks for the heads up.
Drone wrote:
Sun Aug 27, 2017 4:00 pm
If you are sure it's wired wrongly, and the transformer is the original one, meant to push 8 ohms, then yes you should rewire it.

If you want to use it for bass-y bass, get an external cabinet, and wire in a speaker jack that allows you to turn off the internal speakers. A single 15" would be my preference.

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Re: What should I do with this Bassman?

Post by jmann » Sun Aug 27, 2017 5:21 pm

I am a neophyte w/ regard to amps, but I assumed that any impedance mismatch this big would be instantly noticeable (if not catastrophic) so... yeah, I'm confused.

I just used this amp onstage (playing bass) with a small band a few weeks ago. Other than a slight buzzing in the speakers (which I think was loose wires rattling off the paper cones), it sounded pretty decent. And playing it solo at low volumes with either guitar or bass it doesn't sound half bad. But maybe it could be sounding much different and I just don't know what I'm missing?
kslight wrote:
Sun Aug 27, 2017 4:51 pm
If it's wired as you say, shouldn't it have no clean headroom to speak of?

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Re: What should I do with this Bassman?

Post by Drone » Mon Aug 28, 2017 8:39 am

Some of them had ultralinear transformers, which may explain why they would cope with a bad mismatch, but I wouldn't push my luck, y'know. :mrgreen:
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Re: What should I do with this Bassman?

Post by kslight » Mon Aug 28, 2017 9:38 am

jmann wrote:
Sun Aug 27, 2017 5:21 pm
I am a neophyte w/ regard to amps, but I assumed that any impedance mismatch this big would be instantly noticeable (if not catastrophic) so... yeah, I'm confused.

I just used this amp onstage (playing bass) with a small band a few weeks ago. Other than a slight buzzing in the speakers (which I think was loose wires rattling off the paper cones), it sounded pretty decent. And playing it solo at low volumes with either guitar or bass it doesn't sound half bad. But maybe it could be sounding much different and I just don't know what I'm missing?
kslight wrote:
Sun Aug 27, 2017 4:51 pm
If it's wired as you say, shouldn't it have no clean headroom to speak of?

That is my experience with the Bassman...a mismatch (depending on the severity) will cause your headroom to disappear. I haven't used the 10 though.


Did you measure your cab to see what the load is?

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Re: What should I do with this Bassman?

Post by jmann » Mon Aug 28, 2017 10:18 am

Thanks, folks. I measured the cab with a multimeter and it read just shy of 32 Ohms. (I don't have a true impedance tester, this was just DC resistance.) The individual speakers (disconnected from the cab) read around 8 Ohms.

To complicate things, a guy from Eminence wrote me back to say that bass frequencies would "destroy" this speaker. (It did survive a 45 minute live set the other night, but maybe the cumulative effect would be different.)

So now I'm thinking I'll re-wire it with these speakers in series-parallel, then build myself a small 1x12 or 1x15 cab to plug in to it when I want to use it for bass. (Don't know what I will do about live settings, but I'll worry about that later; there's nothing on the horizon).

Any strong recommendations for hookup wire for this cab? I was just gonna buy some 16 ga. lamp cord. (I do have a bunch of 14 ga. Romex lying around, but I figure that way be hard to work with...)

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Re: What should I do with this Bassman?

Post by A.David.MacKinnon » Mon Aug 28, 2017 7:35 pm

The bassman 10 was my first amp. I bought it along with an 82 Squire p bass in 84. Wish is still had both. It was a great, great guitar amp but not a great, great bass amp. Not enough head room for clean bass with a drummer. Totally loud enough for guitar but it gets fuzzy ( in a good way). It's likely a good recording bass amp if volume isn't an issue. At lower volume the bass tone was really good.
If it was me I'd rewire it to 8 ohm and see what you think. Maybe you keep it for guitar duties, maybe you swap it for something else.

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Re: What should I do with this Bassman?

Post by Drone » Tue Aug 29, 2017 5:11 am

jmann wrote:
Mon Aug 28, 2017 10:18 am
So now I'm thinking I'll re-wire it with these speakers in series-parallel, then build myself a small 1x12 or 1x15 cab to plug in to it when I want to use it for bass. (Don't know what I will do about live settings, but I'll worry about that later; there's nothing on the horizon).

Any strong recommendations for hookup wire for this cab? I was just gonna buy some 16 ga. lamp cord. (I do have a bunch of 14 ga. Romex lying around, but I figure that way be hard to work with...)
Sounds like your doing exactly the right thing. 16ga lamp cord will be fine. The only thing you want to avoid in hookup wire is co-ax cable, like you might get in an instrument cable.

Don't make the external cab too small, remember, bass needs space :mrgreen:
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Re: What should I do with this Bassman?

Post by jmann » Thu Sep 07, 2017 11:44 am

UPDATE:

I am lazy, but finally wired the speakers correctly and... Ta-DA! it sounds better! I feel like it's slightly louder but not dramatically so. I think it's also a bit more open sounding, but I haven't cranked it up too high yet. (Neighbors....)

So, two questions:

1. If I were to connect only one speaker and leave the rest disconnected but installed, would that enable me to overdrive the amp at lower volumes? It seems like it would, but maybe the difference wouldn't be as great as I imagine. (If it did work, my next idea would be rigging some kind of switch that would enable me to quickly toggle between all four speakers in series-parallel and just one.)

2. For the bass cab I'm going to build to use with this amp, I'm struggling with finding a speaker and cabinet design. Most bass speakers I've found are rated for more than 150 watts and this amp is only 50. Will under-powering the speaker that drastically sound weak? Any advice on whether to go 10", 12", or 15" if my main goal is to play and record in my house, not gig with this thing? (i.e. trying not to vibrate my kids' beds while they're sleeping...)

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Re: What should I do with this Bassman?

Post by vvv » Thu Sep 07, 2017 11:55 am

1. one speaker will probably make it easier to overdrive and/or blow the speaker.

2. recording is, of course, a different aminal than jamming at home, what is different than playing with a live band. I use a Ampeg BA108 (20 w. or so, 8" speaker) what I think is awesome for recording. Jams and small gigs I am very happy with a ported 1x12" (300 w. JBL), and in fact prefer it to my 1x15". You won't hurt a 100 or 150 w. speaker with a 50w. amp, and may or may not like the sound, but it shouldn't sound bad.

When I played guitar thru a silverface bassman 50w., I used a 4x12" with 30w. Celestions, and loved it all except the weight.
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Re: What should I do with this Bassman?

Post by Snarl 12/8 » Thu Sep 07, 2017 11:59 am

Well, one speaker moves a hell of a lot less air than 4. The other 3 will vibrate sympathetically however. I think the effect will be less pronounced than you might imagine, but still be worthy of trying out and probably yield exponentially fewer noise complaints. Give it a try and see what you think. I think you're only a couple experiments away from getting yourself a versatile and good sounding setup.

As far as putting together a dedicated bass cab, if you're only going to run this thing quietly for bass I wouldn't worry so much about what the speaker guy said about bass frequencies "destroying" anything. If you're at a "not wake the kids" volume you're not going to blow anything up, IMO. You can really hear it when a speaker is dying if it's the only thing playing in the room. It sounds like shit. As long as the cone isn't over-excursioning or staying pinned at its limits for very long I think you'll be fine. I'm talking about "clean" bass sounds. Using fuzz or distortion or overdrive can obscure the picture. Once you bring it to a gig and you're trying to compete with other blaring sound sources all bets are off.

I should point out that I'm a total hack, not a professional and, as a kid, I blew up a hell of a lot of speakers. I haven't blown a speaker in a long time. I guess all those botched experiments paid off eventually.
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Re: What should I do with this Bassman?

Post by Snarl 12/8 » Thu Sep 07, 2017 12:10 pm

One thing to point out is that it's actually very easy to blow a speaker with an underpowered amp. This is the way I blew most of the speakers that I've blown. I thought my badass Hafler amp was killing the speakers by overpowering. Once I realized what was really happening, and started using more efficient, horn-loaded speakers, I basically stopped frying speakers.

What happens is that when you try to get as loud as possible with a low wattage amp you start clipping the signal which results in the speaker cone physically being pinned (both outwards and inwards) while electricity is flowing through the voice coil. This is essentially running DC electricity through the speaker when the speaker is designed for AC current. The speaker is usually designed so that the speaker cone acts as a fan, cooling the voice coil by moving air in and out of the voice coil. If you've got current flowing, but not air, the speaker isn't long for this world. This is why you've got to use your ears and/or visually inspect the movement of the speaker while you're experimenting. You wanna get your speaker breakup sound from something other than power stage clipping. Keep that speaker moving or in it's neutral state as much as possible. A pinned speaker cone isn't making any sound anyway.
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