Use 4ohm tube amp to run 8ohm speakers ?

oris98 · « **on:** 28 Aug 2004, 09:57 am »

Hi all,

Can I use 4ohm tube amp to run 8ohm speakers ? What are the pros and cons ? Any protential damage to the amp ? or speakers ? Thanks..

mcgsxr · « **Reply #1 on:** 28 Aug 2004, 11:07 am »

As far as I know, a load that is of higher impedance than designed for, is not a problem - so the 8 ohm load off the 4 ohm pots should be fine - no possibility of damage to the speakers, that I am sure of - I am almost certain no possibility of damage to the amp...

I recall reading in HIFI+ that the review preferred the sound of the 4 ohm pots on a tube amp being reviewed (with 8 ohm speakers), something about the number of transformer windings?

I am sure someone with the definitive answer will chime in, but I would have a clear conscience doing it.

Mark

oris98 · « **Reply #2 on:** 28 Aug 2004, 04:35 pm »

Someone told me that when using 4 ohm pots, the amp will work harder to provide more power to the 8 ohm speakers as it has less resistance considered in the speaker side. The amp will work hotter for pumping out
extra WPC for inefficient speakers sort of like overclocking your computer..

Any comment on that ?

Thanks.

dado5 · « **Reply #3 on:** 30 Aug 2004, 03:53 pm »

Audio output transformer impedance is a confusing issue. The numbers given do not describe actual electrical impedance seen by the speaker(this is often less than one ohm in most PP amps, SETs may be higher), rather they describe the impedance relationship between the primary and secondary windings of the transformer.

In practical terms this means that a transformer spec'ed with a 10K ohm primary and an 8 ohm secondary will have a primary winding impedance of 10K when there is an 8 ohm load on its secondary. Taps for 4 ohm, 16 ohm etc., just utilize differing numbers of turns of wire in the secondary winding to meet the primary winding specification when loaded accordingly.

What all this translates to is that connecting an 8 ohm load load on a 4 ohm tap would theoretically double the primary winding impedance. The effects on the circuit performance, broadly speaking, are this: reduction in output stage distortion and reduction in the available output power. This may be good or bad listening wise but it is not likely to damage the amp or the speaker unless the reduction in power puts you into a constant clipping condition, which would be pretty audible. So don't be afraid to try it and see which you prefer.

Thanks,
Rob

Red Dragon Audio · « **Reply #4 on:** 30 Aug 2004, 05:07 pm »

I 2nd what DADO said.

The Killer Piglet · « **Reply #5 on:** 31 Aug 2004, 04:13 am »

Hello, Rob.

Hadn't seen you around in a while. Good to see you.

KP
(now dado1)

dado5 · « **Reply #6 on:** 31 Aug 2004, 06:26 pm »

Hey KP,

You still over at the asylum? I don't post much there anymore....haven't seen much to pique my interest...still lurk around the digital, tube, cable and prophead forums 1x or 2x a week.

I pop in here about once a day as well as my other haunt www.puritanboard.com (dado6 there-Renee and I have been busy!). Job hunting takes up most of computer time nowadays. Spare time is now devoted to DIY 100%...I am building a slightly modified version of Morgan Jones' EL84 amp at the moment.

Congrats! So how are the missus and the little'un?

Rob

MarkM · « **Reply #7 on:** 31 Aug 2004, 06:40 pm »

Damping factor will be increased running 8ohm load into 4ohm taps. Load line may be shifted, making it easier for amp. If your 8ohm speakers have low dips(below 8 ohm) in impedance, this should yield better sound.

If it sounds better, go with it. I run 8ohm speakers off the 4ohm taps.

The Killer Piglet · « **Reply #8 on:** 1 Sep 2004, 10:37 pm »

Wow, Rob, congrats! Six!

It's been great around Piglandia with the Third Little Pig.

Like yourself, I only hang around a few board there nowadays. Digital, Tubes, Speakers.

The place has lost its charm. General is as interesting as cold oat meal, but with less personality. I admit once in a while I will peek into the new Jerry Springer Show. I think they call it Critic's Corner.

KP

dado5 · « **Reply #9 on:** 2 Sep 2004, 01:04 am »

Yeah 6! 5 chicks and a stud. And the boy got the curly hair! We may go for one or two more, but honestly the diaper thing has got to end before I retire or I will go round the bend!

I am with ya brother, AA has deflated majorly over the last year. Very little cheery discussion over there (the tube boards are not bad though). Just don't get me started on the Toshiba 3960, I.....I....oh no! I brought the beast over here! Now it will take root and spread its undying evil throughout the 'Circle....May God have mercy on our souls!

Rob

Jon L · « **Reply #10 on:** 2 Sep 2004, 04:44 am »

Given all the variables in amps and speakers, only way to know is to try a particular combo. A "8 ohm speaker" often ranges from 2-16 ohms easy.

My amp has 2, 4, 8 ohms outputs, and with Every speaker I've tried, I prefer the 8 ohm output. As I move to 4, and more so to 2 ohm, I hear drying up of harmonic structure, loss of bloom, more distant/detached sound, and diminished magic.

The lower impedance output does sound like they control the drivers with tighter grip and higher damping factor, but results in less involving sound.

Of course, if your speakers regularly dip into 1 ohms, the 8 ohm tap will have no hope of controlling the speakers...