# impedance vs output



## ezcomes (Jul 28, 2008)

i didn't realize until just today that my amps output is measure at 4ohms...

the guy i bought my amp from found his manual (i had already printed one off the internet but didn't get to the spec's part)...

its supposed to be a 50W amp...but the specs show...
Power @ min Impedance - 50W
min Impedance - 4 ohm

so...i've been running an 8 ohm cab as the amp will run at 8 or 4ohm...so that means...by my understanding...that the power is cut roughly in half...so it'd be running actually between 25-30W...

the things you learn when you actually read the manual...

i just ordered a 2x12 cab at 8ohm to replace the one i have...maybe i should've just gotten a 4ohm...but then...i wouldn't be able to run two cabs at a time (in future)

just for reference...traynor YCS50


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## hollowbody (Jan 15, 2008)

The power output halving as impedance goes up applies to solid-state amps. Tubes don't work that way. Not sure why, but I heard this from Wild Bill and he seems to know his stuff. Maybe he'll pop by and explain


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## ezcomes (Jul 28, 2008)

hopefully we'll hear from this...this is rather interesting for me...


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## mrmatt1972 (Apr 3, 2008)

ezcomes said:


> hopefully we'll hear from this...this is rather interesting for me...


Yeah, it only applies to solid state because those amps use the resistance as part of the amp somehow?? With tube amps all that really changes is the frequency range the speaker sees.


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## dtsaudio (Apr 15, 2009)

> Yeah, it only applies to solid state because those amps use the resistance as part of the amp somehow?? With tube amps all that really changes is the frequency range the speaker sees.


Completely incorrect.

While you may experience frequency response changes it will be at the extreme ends and typically minor and not audible.

In both solid state and tube amps the actual maximum power will change with impedance. 
With solid state amps as speaker impedance drops, the available power increases. Theoretically doubling with halving of impedance. This is because with lower impedance more current is drawn from the amp to drive the load (speaker) with a given signal level. There are however limiting factors here. The voltage of the power supply will sag, the amp will reach a current limit where it can't give you any more. Also the temperature will rise on the output transistors and heat sinks, eventually causing damage (assuming the amp is under built). So it's tough to reach the doubling of power.

With tube amps it's a bit different. The output transformer is designed to work into a specific impedance 4, 8, 16 ohms. The further away from the impedance match you get, the lower the power. As an example - a 50 watt amp @ 8 ohms will deliver half it's power into 4 ohms or 16 ohms. Transformers are designed to match their load.


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## ezcomes (Jul 28, 2008)

i emailed Traynor and this is what they responded with (in less than 3 hrs no less too...amazing!!)



> Unlike solid-state amps, tube amps have a range of load impedance's over which they deliver roughly equal power. The YCV50's range is 4-8 Ohms.


so...hollowbody was right...each setting would provide the same approximate power...

i also asked about changing the tubes from EL34 to 6L6's and he said...



> swapping-in 6L6s, the performance changes aren't blatant and would probably not be favorable to the majority of users (otherwise we have built it with 6L6s) however you can do so without altering the bias which is as specified in the manual


so i kind of find it a little funny that they CAN be changed...but by the sounds of it...they don't recommend it


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## mhammer (Nov 30, 2007)

I changed the 6L6s in a blackface Tremolux head I used to own to EL34 workalikes (6CA7). As I recall, there were some small changes to make to accompany that, but they _were_ small. Sounded great, but I honestly couldn't tell you if it sounded different.

The discrepancy between what Traynor told you, and what you had thought is essentially the difference between amplifiers where there is a transformer between output devices and speaker, and amplifiers where there isn't. That's not saying much, though, is it?


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## mrmatt1972 (Apr 3, 2008)

dtsaudio said:


> Completely incorrect.
> 
> While you may experience frequency response changes it will be at the extreme ends and typically minor and not audible.



Looks like it's you who is "completely incorrect." And from past experience, I can say with absolute certainty that the frequency responce change _is _audible. This is particularily true of an amp (tube) hardwired for 4 ohms than is running at 16.


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## mrmatt1972 (Apr 3, 2008)

ezcomes said:


> i also asked about changing the tubes from EL34 to 6L6's
> 
> 
> > I tried that with a YCV40 i used to own. Since they are "self biasing" I figured what the hell. The difference is insignificant in that amp, but better with the stock tubes.


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## greco (Jul 15, 2007)

dtsaudio said:


> With tube amps it's a bit different. The output transformer is designed to work into a specific impedance 4, 8, 16 ohms. The further away from the impedance match you get, the lower the power. As an example - a 50 watt amp @ 8 ohms will deliver half it's power into 4 ohms or 16 ohms. Transformers are designed to match their load.


So...how does this influence volume..is the degree of influence audible? (not wanting to argue or anything....just looking for an answer).

Cheers

Dave


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## dtsaudio (Apr 15, 2009)

> I can say with absolute certainty that the frequency responce change is audible. This is particularily true of an amp (tube) hardwired for 4 ohms than is running at 16.


With that large a mismatch, you may get a frequency response chnge. However, what you most likely are experiencing is a rise in distortion, a loss of maximum power and there will most likely be a change in the feedback (not the howling kind, it's part of the circuit). All these things will change the sound of an amp. It's not just the frequency response that changes.



> Unlike solid-state amps, tube amps have a range of load impedance's over which they deliver roughly equal power. The YCV50's range is 4-8 Ohms


Theoretically that is incorrect. In practice though, it tends to be roughly right. However you do lose power the further away from a match. That said, a speakers impedance is far from flat. An 8 ohm speaker at say 100hz frequency, may be wildly different at higher or lower frequencies. So a mismatch, particularily in a transformer coupled amp may not be that big a deal.


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## dtsaudio (Apr 15, 2009)

> So...how does this influence volume..is the degree of influence audible?


Very little actually. Half (or double) the power is only a 3db difference in volume. That is barely audible to the human ear. Our hearing is not linear, it actually takes ten times the power to double volume at a given frequency. Where the difference is audible is in headroom. A 25 watt amp will distort quicker than a 50 watt etc.
What is significant is the efficiency of the speaker. That can vary quite a bit. The more efficient the speaker, the less power you need for a given volume. 
None of this has anything to do with the type of tone, or sound quality you want.


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## BrianA (Mar 1, 2009)

Regarding matching load impedance to tube:
1) With a properly constructed transformer, no special care is needed with regard to impedance selector settings. Some manufacturers realize this and suggest that the ohms switch should be used as a "tone" switch.
2) A transformer is like a window between the tubes and the speaker. If the load and source impedances are perfectly matched, you get the maximum transfer of power and bandwidth. Turn the window one way or the other, i.e. mismatch the impedance high or low, and part of the power is reflected back at the tube, resulting in reduced transfer of power and bandwidth.


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