Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: blown240 on January 01, 2012, 02:13:13 pm

Title: Inpedance Mismatch Question
Post by: blown240 on January 01, 2012, 02:13:13 pm
I have a 1x12 4 ohm cabinet that I want to use for practice at home with my Fender 300PS.  The amp wants to see an 8ohm cab.  Is it going to be a problem using this 4 ohm cab?  I want to make sure I don't damage my head.

Thanks!
Title: Re: Inpedance Mismatch Question
Post by: PRR on January 01, 2012, 06:20:57 pm
> practice at home with my Fender 300PS

This is absurd. Get a smaller amp.

> problem using this 4 ohm cab?

For lesser amps, maybe not. However the _BIG_ amps are very high-strung, fussy, and much too costly to risk it.
Title: Re: Inpedance Mismatch Question
Post by: Tiny_Daddy on January 01, 2012, 06:25:15 pm
I have to wonder if the output transformer's dual secondary could be re-wired for a lower impedance. First thing to find out: Are the secondary windings identical?
Otherwise I agree with PRR
Title: Re: Inpedance Mismatch Question
Post by: Ritchie200 on January 01, 2012, 06:35:05 pm
> practice at home with my Fender 300PS

This is absurd. Get a smaller amp.


HEY!  Waddia got against big amps!!!! :icon_biggrin:

Jim
Title: Re: Inpedance Mismatch Question
Post by: Tiny_Daddy on January 01, 2012, 06:37:15 pm
300PS for practice at home??
Title: Re: Inpedance Mismatch Question
Post by: blown240 on January 01, 2012, 09:26:56 pm
Right now the 300ps is all I got for a bass amp.  Granted I have used it to play BIG clubs, but as it is, its all I got.  I will get a different cab to play it thru.  This thing has such an AMAZING tone with my upright bass going thru it!  I will look for a used 8ohm 1x15 or 1x18 with a tweeter.
Title: Re: Inpedance Mismatch Question
Post by: Dave on January 02, 2012, 10:01:37 am
One man's absurdity is another man's nunya. Its your amp, if you choose to use it as a feed trough for your hippo, that's your business.

Dave
Title: Re: Inpedance Mismatch Question
Post by: Ritchie200 on January 02, 2012, 02:37:08 pm
This thing has such an AMAZING tone with my upright bass going thru it! 

And I'll bet you can't get that tone with any other amp?  I can say the exact same thing.  Yes, it's like driving a Ferrari in a 15mph school zone, but it's still a Ferrari!  I can look/sound good at 15 as well as 150.

Jim
Title: Re: Impedance Mismatch Question
Post by: Willabe on January 02, 2012, 05:48:39 pm
Yes, it's like driving a Ferrari in a 15mph school zone, but it's still a Ferrari!  I can look/sound good at 15 as well as 150.

Yeah, but I bet you can't get that big, beautiful, 200w Marshall Major, 8x12 stack in the trunk of that Ferrari.      :w2:


               Brad            :laugh:
Title: Re: Inpedance Mismatch Question
Post by: Ritchie200 on January 02, 2012, 07:44:44 pm
It's a metaphor!  It's a METAPHOR!!!! :laugh:

Jim
Title: Re: Inpedance Mismatch Question
Post by: Colas LeGrippa on January 03, 2012, 08:30:55 am
at home, I practice with a small transistors Marshall combo. VERY GOOD voicing amplifier from 1985 or so. I guess a small PEAVEY would do a great job for bass. Use a compresser if you have one. Or use a SANSAMP bass processor ( small pedal preamp ) right into a  mixer with headphones, you'll get kick ass tone garanteed ! Even better than your beloved setup.

Colas
Title: Re: Inpedance Mismatch Question
Post by: Rev D on January 07, 2012, 08:29:59 am
 Haha, people used to laugh when they came in our Apt and saw my 100 watt Marshall full stack and I practiced with it. Course it had a master volume but still anything past about 1/2 of 1 or so and the neighbors were hearing it and feeling it.. haha..

Regards,

Don
Title: Re: Inpedance Mismatch Question
Post by: bobmegantz on January 08, 2012, 03:09:59 pm
I can't imagine any harm that could come by playing at low volumes through a 4 ohm cab.  High-power operation is where things would get ugly.  If you're really worried, just connect a 4 ohm resistor in series with the cab.
Title: Re: Inpedance Mismatch Question
Post by: Dave on January 08, 2012, 03:54:40 pm
A huge 4 ohm resistor.

Dave
Title: Re: Inpedance Mismatch Question
Post by: jojokeo on January 11, 2012, 02:59:49 pm
A huge 4 ohm resistor.

An old 4ohm blown speaker greater than 25watts or so to use instead of a large fuse. Cut away the cone & basket, save the voice coil/magnet assy and tinsel connections. Remove the spider and glue the voice coil down into the magnet w/ epoxy. Now you have a speaker motor. Wire it in series with your single 4ohm speaker and you are there w/out any worries. You effectively have two 4 ohm speakers but only one that you actually hear.