Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: dude on July 15, 2011, 03:48:42 pm

Title: Which jack is four ohms ?
Post by: dude on July 15, 2011, 03:48:42 pm
Not sure if I'm posting in the proper place  but I picked up this Peavey Head.

I have a 8 ohm, 4 ten bass cab and not sure what speaker output jack I should use.

One is "ext" the other is "int" see pic. This is a 4 ohm Solid State head for 150 watts could someone explain the two speaker jacks?
If I'm using a 8 ohm cabinet into a 4 ohm tap, is the volume the only sacrifice or could I damage the transformer?
Title: Re: Which jack is four ohms ?
Post by: rafe on July 15, 2011, 08:04:29 pm
What ohms are the individual speakers? Can you rewire them into a four ohm configuration?
That is what I would do....
Title: Re: Which jack is four ohms ?
Post by: dude on July 15, 2011, 09:15:18 pm
It's four tens, each 8 ohms

They're wired Series, Parallel for a total of 8 ohms. Since all speakers are 8 ohms I can't get a 4 ohm load.

So I'm asking which speaker out put do I use for best performance.

I'm thinking the two output speaker jacks in the picture are wired at 4 ohms in parallel so it doesn't matter which I use as each jack alone wants to see 4 ohms. But can take as low as 2 ohms which would be two 4 ohm cabinets plugged into each jack.

I'd like to know what the ext. and int. mean? 

thanks,

al
Title: Re: Which jack is four ohms ?
Post by: LooseChange on July 16, 2011, 06:22:14 am
Post a schematic of the amp.
Title: Re: Which jack is four ohms ?
Post by: sluckey on July 16, 2011, 11:07:54 am
Quote
...I picked up this Peavey Head.
Pic is Crate???

Quote
I have a 8 ohm, 4 ten bass cab and not sure what speaker output jack I should use.
Use the ext jack. SS amps from that era are not fussy about output impedance. That amp can provide 150W into a 4Ω load, or about 75W into an 8Ω load. Don't go any lower than 2Ω total load.
Title: Re: Which jack is four ohms ?
Post by: dude on July 16, 2011, 11:16:45 am
Yeah, it's a Crate CR 285b solid state head, I'm showing my age.

Can't fine the schematic without buying it.

I figured the two jacks are both 4 ohms if used separately, jacks are wired parallel.

So I'm only getting 75 watts with an 8 ohm load, thanks.

I have a separate cab with a 12" bass speaker (200 watts) at 8 ohms. If I plug that in too (running two 8 0hms cabs in parallel for 4 ohm load) I'll get the total 150 watts out put.

Question how is the power divided?

Half to each cabinet, the four tens get 75watts and the single 12" gets 75 watts?

Thanks,

al
Title: Re: Which jack is four ohms ?
Post by: sluckey on July 16, 2011, 12:24:15 pm
Quote
Half to each cabinet, the four tens get 75watts and the single 12" gets 75 watts?
yes
Title: Re: Which jack is four ohms ?
Post by: dude on July 16, 2011, 12:51:07 pm
Thank you

Title: Re: Which jack is four ohms ?
Post by: PRR on July 17, 2011, 08:53:49 pm
Transistor stage-amps sag when loaded. And un-sag if lightly loaded. If it was 150W in 4 ohms, I would suspect 90+W in 8 ohms.

The difference 150 or 90 is no big deal.

A four-Ten cab should be mighty efficient. Our 60W 4-10 was Too Darn LOUD.

Use the 8 ohm load and stop worrying.