Do you think the OT tap you use makes a difference in tone?

[daz]

Before you answer, what i mean is if you use the SAME speaker model but each with a different ohm rating. In other words, say you have 3 celestions of the same model at 4, 8 and 16 ohms and you try each with it''s corresponding OT tap. Do you feel it makes a difference that u can hear or feel? If i recall i have seen this debate and i don't think theres a general consensus but i wanna see what youse guys think.

[Chuck H]

I haven't noticed any significant detriment for a given secondary tap using many different amps and transformers. That said, I have never done the apples to apples test you propose. That is, same speakers and cabinet. I mean, how many of us have a pair of identical cabinets but one is 8 ohms and the other is 16? (interestingly, if you consider something like a 2x12 you would use 16 ohm speakers for the 8 ohm cabinet and 8 ohm speakers for the 16) But my guess is that the speakers themselves would make a bigger difference in that scenario. Maybe Juan will comment (or correct me ) but I'll guess there are differences in inductance, coil weight, etc. that might make the 8 and 16 ohm models for the same speaker noticeably different.?.

[Helmholtz]

Probably no significant difference as long as the power amp is not clipping/distorting and uses global NFB.

But as a different OT tap means a different load to the tubes, the changed loadline will change clipping characteristics.

A tube power stage has an optimum load(-line) and that not only means max. output but also operating tubes within their limits.
A lower than optimum load increases plate dissipation, while a higher load increases screen dissipation. Both can lower tube life.

[daz]

Probably no significant difference as long as the power amp is not clipping/distorting and uses global NFB.

But as a different OT tap means a different load to the tubes, the changed loadline will change clipping characteristics.

A tube power stage has an optimum load(-line) and that not only means max. output but also operating tubes within their limits.
A lower than optimum load increases plate dissipation, while a higher load increases screen dissipation. Both can lower tube life.

So does this mean 8 would be likely optimal and therefore have the most clean headroom?

[Helmholtz]

So does this mean 8 would be likely optimal and therefore have the most clean headroom?

It it's a 6.6k:8 Ohm OT, yes.

[Chuck H]

So does this mean 8 would be likely optimal and therefore have the most clean headroom?

Actually I think regarding operating conditions Helmholtz was stating what would happen using different secondary taps while using the same speaker load. Your inquiry was about using different secondary options while keeping the load matched accordingly.

[daz]

Thanks. I was considering replacing my 4 ohm celestion with an 8 of the same model but i guess that won't matter so i'll just leave it. In the future if i decide to use a ext cab with the internal speaker i'd get and 8 for the combo and put a impedance selector in the amp.

[g1]

I got the same impression, that impedance would be correctly matched in each case. I think Helmholtz meant what happens with mis-match.

One of the factors that is sometimes pointed out is the weight of the voice-coil and the slight impact on tone and response.

[Helmholtz]

You're right.
I meant a load mismatch.
Seems I misunderstood the question and didn't see your post while composing my answer.

Some speaker manufactures (like Jensen) publish different frequency responses for different impedance versions of the same speaker model.
Not sure if there's a general answer, though.

[daz]

One of the factors that is sometimes pointed out is the weight of the voice-coil and the slight impact on tone and response.

I could see how that might make a difference, especially ate the extremes ex: 4 vs 16

[Gregg]

Assuming correct impedance match the OT tap used may and will affect the tone if secondaries are poorly or non interleaved. If this is the case the 4 Ohm secondary may have very high leakage inductance which will affect the high frequency response. Good news is in reality this is not such a problem and actually some iconic amps have very poorly made OTs that even a novice in this field wouldn't design that way. And no, they were not designed specifically to get that tone, they were just cheap.

[daz]

Assuming correct impedance match the OT tap used may and will affect the tone if secondaries are poorly or non interleaved. If this is the case the 4 Ohm secondary may have very high leakage inductance which will affect the high frequency response. Good news is in reality this is not such a problem and actually some iconic amps have very poorly made OTs that even a novice in this field wouldn't design that way. And no, they were not designed specifically to get that tone, they were just cheap.

I would think it's a good quality OT. It's a classictone which is pretty well regarded, so at least not some no name junk. Not sure if that matters with respect to that possibility but just FYI.

[Greg_L]

As long as your loads are matched to the OT, the rating of the speaker doesn't matter as far as how it sounds. An 8 ohm speaker does not sound better or worse than the same speaker made for 4 ohm. A 16 ohm Greenback is not a "better" speaker than an 8 ohm Greenback.

But if you mismatch to the OT, then you can get a difference in sound, but that's not the speaker. That's the tubes and OT. Some people intentionally go for a one step mismatch between cab and output tap.

[mozz]

Go to Jensens website and look at the the curves for the same speaker with different impedance. 4, 8, 16 are not going to be the same, may be subtle but they are different.

[Gregg]

It's a classictone which is pretty well regarded, so at least not some no name junk.

Depends on the OT type. The manufacturer may and would copy the original design in order to get to the original sound as close as possible (although the original iron and materials are not available anymore).
For example in some amps Fender have very cheap and simple OTs while in others you can see HiFi quality OTs.