Can I use my Impedance Switch with no ext cab

[shootingstarno]

Greetings. I bought a Bugera BC30. It has an impedance switch that switches from 4,8 and 16 ohms. IM not sure how my speakers are wired. Its a 2X12 combo. Its set on 8ohms. Can I switch it to 4 in order to get a cleaner sound or will that blow things up. Its has an extension cab output and I know thats really why the switch is really there. Although I also have a half power switch from 30 to 15 watts. I heard if you switch to half power your suppossed to switch its impedance as well and Im not sure what it would be switched to there either. Any help is appreciated. The Bugera forum hasnt got any info yet.Thanks. shootingstarno

[pdf64]

IM not sure how my speakers are wired. Its a 2X12 combo. Its set on 8ohms. Can I switch it to 4 in order to get a cleaner sound or will that blow things up.

Welcome to the forum!
Look at the terminals on the speakers; if like terminals are connected together, then they're in parallel.
Most likely the amp is fitted with 16 ohm speaker wired in parallel, to create a total load of 8 ohms.
If the amp output is switched to mismatch the speaker load, then the amp's max power output capability may be reduced, and if pushed to the extreme, there's a possibility that something may be damaged.
A mismatch may alter the amp's gain slightly, so different amp impedance settings (given the same speaker load) may seem slightly louder or quieter than the correct setting; the highest maximum sound output level will be achieved when set correctly.

I also have a half power switch from 30 to 15 watts. I heard if you switch to half power your suppossed to switch its impedance as well and Im not sure what it would be switched to there either

To keep the same load per power tube, the amp's impedance setting should be halved when set to half power.
The amp's quick start guide p27 (p14 of the pdf) indicates this https://media.music-group.com/media/...212_QSG_WW.pdf

[Jazz P Bass]

To keep the same load per power tube, the amp's impedance setting should be halved when set to half power.

I do not see this at all in the literature.
Most newer amps leave the plates connected when going to half power, thus avoiding the mismatch issue.

Note: The factory cabinet has two 8 ohm speakers wired in series, resulting in a 16 ohm load.

[Leo_Gnardo]

I do not see this at all in the literature.
Most newer amps leave the plates connected when going to half power, thus avoiding the mismatch issue.

Two ways of going about "half power." The ol' fashioned way, take 2 of 4 output tubes out of action, usually by disconnecting their cathode connections. In this instance you should correct the impedance, now driving an 8 ohm speaker from 4 ohm tap for instance.

There's been a trend towards switching output tubes into triode mode. First well known amp I saw that on was Marshall's 25th anniversary "silver" series, with an extra rocker switch labeled 50/25 or 100/50. Now lots of amps have "pentode/triode" switches, sometimes labeled differently, but if that's what your amp does, there's still an impedance change, but altering the OT tap selection generally isn't done. The idea being "tubes in triode are more forgiving of impedance mismatches." Perhaps one of our super experts can elaborate on that.

First you have to know what YOUR amp's "half power" switch is really doing. Then use a different OT tap if appropriate.

[shootingstarno]

I thank you for your post. It seems by further examination that the speakers are indeed two 8 ohm and wired in series for a resulting 16 ohm load. God bless you. The switch was on 8ohms and now Ive switched to its correct position. Hopefully it wasnt damaged and will sound better now that there is a match. shootingstarno

[Chuck H]

The amp will be loudest when the load is matched properly (as noted), but you may not even notice because it'll only be a couple or a few watts. If the amp seems to be working correctly then nothing was significantly damaged when the amp was set for the wrong impedance. Stressed a little maybe. Nothing to worry about if nothing is broken.

A great way to get a louder clean tone is to fit the amp with more efficient speakers. I don't imagine the stock speakers are all that (no offense). If they have an efficiency of, say 99dB, a pair of very efficient speakers at 102dB would increase volume on par with doubling the amps wattage. Another way to go would be to use an extension cabinet loaded with efficient speakers and leave the stock speakers disconnected. A closed cab will also have better lows. Do this for gigs to get the louder clean tone and then you can plug into the stock speakers at home for a lower practice volume.

[shootingstarno]

I just read about speaker efficiency ratings in db and my first thought was changing these stock speakers with ones with a higher efficiency. I heard in a post of a guy who contacted Bugera amps and found my amp has only a 92db efficiency rating. Thanks for the post. My amp just doesnt sound like a pro amp fully, it does sound usable. Its doesnt sound like a Fender twin or the other classic amps. Have a blessed day.