4 ohm vs. 8 ohm taps

Early B.

Can someone explain why there would be a sonic difference between the 4 ohm taps and the 8 ohms taps on my tube monos?

I unintentionally switched to the 4 ohm taps (I have 8 ohm speakers) and the sound is more pure and more detailed. It's a subtle difference; nevertheless, I wondered what changed in my system, and that's when I realized I switched taps when I hooked my amps back up.

Thanks.

ViperZ

I have the same switch in my HK Citation 24 amp, and the speakers do sound different/better in 4-Ohm mode. 8-Ohm mode is a "high voltage" mode, whereas 4-Ohm mode is "high voltage" / "high current" mode.

I would have to look at the schematics, but my guess is that the amp has more headroom since it expects much worse (i.e. 4-Ohm) load.

george daniel

Brad,, I've been doing the same thing with the anthem and the 7u's,, but I'm not sure which I prefer 8 vs. 4,,IIRC I think I finally settled on the 4 ohm tap.

I've been looking around and came up with this,, which for me, was a pretty good read.

http://www.symphonysound.com/articles/tubefriendly.html

Early B.

george daniel wrote: »

I've been looking around and came up with this,, which for me, was a pretty good read.

http://www.symphonysound.com/articles/tubefriendly.html

Thanks for the link. It's kinda technical, but it reinforces a couple of concepts:

1. synergy is supremely important

2. speaker specs are meaningless

3. due to specs and associated gear, price doesn't mean a damn thing in audio

4. the only way to determine if speakers are tube friendly is by listening to them

5. experimentation is important (I've had my amps for several months and hadn't tried the 4 ohm taps:()

6. tubes rule and solid state sucks!:p

fredv

When you use a 8 ohm speaker on the 4 ohm tap, the amp will see double the impedance of primary side of the output transformer. Tubez loves high impedance, and in general, higher impedance has lower distortion. I always put the vintage Polk speakers, which are 6ohm mostly, to the 4 ohm tap. So, what is the catch? The peak rated power is lowered because the voltage the power supply can swing is a constant. When the voltage is eaten up by the increased impedance, the output tubes will be cut-off and stop conducting, i.e. clipping. Unless you hear the amp running out of steam, keep using the 4 ohm tap if it pleases you the most.

reeltrouble1

excellent Fred, I have found this to be exactly the case with the Sound Labs which are amp killers, so I hooked the tube BAT's 4 ohm tap to a MF supercharger, then the supercharger to the speaks, I thought it might not matter, well, it does, the 4 ohm tap sounds oh so sweet, but even though its seeing a steady 50K input impedance the tube amp runs out faster than if I use the 8 ohm tap.

RT1

heiney9

fredv wrote: »

When you use a 8 ohm speaker on the 4 ohm tap, the amp will see double the impedance of primary side of the output transformer. Tubez loves high impedance, and in general, higher impedance has lower distortion. I always put the vintage Polk speakers, which are 6ohm mostly, to the 4 ohm tap. So, what is the catch? The peak rated power is lowered because the voltage the power supply can swing is a constant. When the voltage is eaten up by the increased impedance, the output tubes will be cut-off and stop conducting, i.e. clipping. Unless you hear the amp running out of steam, keep using the 4 ohm tap if it pleases you the most.

Excellent info.........that's going into my audio knowledge bank.

H9

mhardy6647

If the load is a perfect 8 ohm impedance, independent of frequency, mismatching to a 4 ohm output tap will give you some response contouring (assuming that the 8 ohm response is flat). Not unlike using interconnects or speaker cables as rather expensive tone controls! :-)

The fact is that most speakers are very complex, reactive impedance loads for an amplifier, and just may sound better on one tap than another. In general, higher-impedance speakers are preferred (e.g., 16 ohm), as they'll make better use of the OPT secondary.

A 100% mismatch will have no negative impact on either amp or speaker, so use what you like better.

Early B.

I've been listening to music for the past three days and there's definitely an improvement on the 4-ohm tap that is more noticeable on some CDs than on others. There's greater clarity, micro-detail, and a slightly wider soundstage. Vocals are a bit more recessed and you can "hear" more of the room. In addition, there's greater contrast between the low passages and the high ones in the same song, thus giving the appearance of increased dynamics. It's interesting.

Since the sound is different, my next "tweak" may be fooling around with placement again. It always amazes me how moving a speaker less than an inch can make a big difference.

zingo

george daniel wrote: »

I've been looking around and came up with this,, which for me, was a pretty good read.

http://www.symphonysound.com/articles/tubefriendly.html

This was a great read and I found it very helpful, yet pretty easy to understand. Thanks for posting it.