Tonal variations in output taps???? Can someone explain.

[jamison162]

I've owned my RV50 since I bought new in 2007. At home I mostly use a single 8 ohm speaker and always use the same tap. At gigs and rehearsal I use my 16 ohm cab (2 x 8 ohms in series). Same speakers....I just discovered that all 3 output taps sound different (RV50 has 2 x 8 ohm taps and 1 x 16 ohm tap).

First off, is this normal?? Can someone technically explain how/why this would be. One 8 ohm tap is somewhat harsh and has more headroom to the sound, I can hear it and feel it - the other 8 ohm tap is a littel sweeter sounding and has more compression, you can dig in a little more. When I checked the 16 ohm tap (briefly at low volume) I noticed it was the warmest and had the most compression, least headroom and was the least harsh.

I have been struggling with my sound at rehearsal. At home it sounds fine but I've noticed when running the 2x12 cab from the 16ohm tap my tone has been darker and not cutting through the mix as well. Yet, I like the compression and "less harsh" tone.

Anyway, is it normal to hear these differences? Different components the signal is traveling through, different windings used on the OT, different combination of the 4 x 6V6 power section??? What would cause this?

Oh, and it's the 8 ohm tap that I use the most (all the time really, I rarely use the other tap) that sounds the brightest/harsh compared to the others.

 

[Leonc]

Wow, interesting. First off, I would have assumed the two 8 ohm taps may be intended for use with two 16 ohm loads in parallel. But if they're in parallel, why would one sound different than the other? Hmmm. I've not tried this with my RV and I don't think I'm really set up to try.

As for 8 ohm sounding different than 16...there could be several things going on I think. First, have you eliminated the differences in cabs/speakers? I.e., have you tried using both with the very same cab and speaker type? Ideally like this: 2x12 cab with two 16 ohm V30 speakers, each one going into an 8 ohm output. Then trying the same cab with two 8 ohm V30s (wired in series) going into the 16 ohm output.

That would be about as close as you could get. But another thing going on could be the difference in sound/performance between speakers wired in series from speakers wired in parallel. I think you may wind up with a crisper, sound with a bit less grind with speakers in parallel and perhaps a bit more top end as there's less inductance in parallel. But when you put speakers in series, you may bet a bit more grind or compression and perhaps a bit less clarity / top end.

 

[Leonc]

But Eric...I could be wrong about the 8 ohm taps...maybe they are intended for two 8 ohm loads and are internally wired in series....? Hmmm...I may have a schematic somewhere...looking...

 

[jamison162]

Cab options are 1 x 16 ohm cab => 16 ohm tap, 1 x 8 ohm cab off either one of the 8 ohm taps, or 2 x 16 ohm cabs using both 8 ohm taps.

I'm using the same cab, same 8 ohm speaker plugging into each 8 ohm tap and listening, then into the 16 ohm (mismatch). So I don't know if the 16 ohm tonal difference is due to that tap itself or the impedance mismatch.

I can hear the changes as I switch though going from clearest/hard attack/more headroom off the 8 ohm tap I use the most; to a sweeter attack/more compressed tone off the other 8 ohm tap that never gets used; to the warmest, most compressed tone that really sings on single note lines using the 16 ohm tap.

I dunno...I've actually emailed Randall Aiken on this one.

 

['58Bassman]

I've owned my RV50 since I bought new in 2007. At home I mostly use a single 8 ohm speaker and always use the same tap. At gigs and rehearsal I use my 16 ohm cab (2 x 8 ohms in series). Same speakers....I just discovered that all 3 output taps sound different (RV50 has 2 x 8 ohm taps and 1 x 16 ohm tap).

First off, is this normal?? Can someone technically explain how/why this would be. One 8 ohm tap is somewhat harsh and has more headroom to the sound, I can hear it and feel it - the other 8 ohm tap is a littel sweeter sounding and has more compression, you can dig in a little more. When I checked the 16 ohm tap (briefly at low volume) I noticed it was the warmest and had the most compression, least headroom and was the least harsh.

I have been struggling with my sound at rehearsal. At home it sounds fine but I've noticed when running the 2x12 cab from the 16ohm tap my tone has been darker and not cutting through the mix as well. Yet, I like the compression and "less harsh" tone.

Anyway, is it normal to hear these differences? Different components the signal is traveling through, different windings used on the OT, different combination of the 4 x 6V6 power section??? What would cause this?

Oh, and it's the 8 ohm tap that I use the most (all the time really, I rarely use the other tap) that sounds the brightest/harsh compared to the others.

Each tap has a different number of turns and coils of wire have inductance. More turns=more inductance and in series, inductance rolls off the highs so, whichever tap has more turns, you'll lose more highs. It's up to you as far as whether it's better or worse. You can generally go one step up or down in impedance safely. Two steps can and has been done but it's not usually recommended if the amp is run hard.

 

[jamison162]

Would it be safe to run the 16 ohm 2x12 (both speakers) off one of the 8 ohm taps?

 

[GearHeadFred]

"safe" is a relative term..

It's pretty 'safe' to try this out at low volume for a short time. I would not recommend cranking the amp with a 2:1 mismatch.

I did a quick google for the schematic of your amp but could not find anything.

If those 8 ohm taps are wired parallel, and they probably are, you're fooling yourself.. It's the exact same wire going to both jacks.

That said, different taps can sound different for the reason stated above.. The lower the output impedance, the more 'windings' you are using in the transformer..

Another thing to keep in mind: When you have a mismatch, the amp becomes LESS efficient.. So you have to crank it up (or strum harder, or both) to get the same output. There is also a frequency filtering that occurs in a mismatch.

 

[pdf64]

When you have a mismatch, the amp becomes LESS efficient

Yes, in that the max power output will likely reduce.

So you have to crank it up (or strum harder, or both) to get the same output

Not necessarily; a mismatch might result in the reflected primary impedance doubling, which will increase the gain of the power amp, eg 16 ohm speaker on 8 ohm output. So the amp will have more gain AND overdrive at a lower power output level; a double whammy on 'headroom'.
What seems to be the loudest tap when you're messing around at the back of the amp may not be the correct tap, you may not perceive a bigger, cleaner bottom end (provided by the correct tap) until a few feet away from the amp.
Pete.

 

[jamison162]

Schematics are here and both 8 ohm taps are wired in parallel. http://users.telenet.be/orangefg/OFG_SCHEM/RV50C_sheet3.jpg

I do understand how the 16 ohm would sound darker as the signal is traveling through more windings on the OT; much like a guitar pickup or an 8 ohm vs. 16 ohm voice coil in a speaker. The more windings generally, the more resistance/capacitance which affects your high end.

On the two 8 ohm taps, there is a VERY noticeable difference and I am 100% positive I could pick which is which every time. In fact, I may try to record both to see how noticable it comes across that way. I'll upload to You Tube and post a link at some point if it turns out to be worth while. I didn't just go plug into both 8 ohm taps and listen to see if I could hear a difference one day - I just happened upon this by plugging into the "other 8 ohm" tap that rarely gets used and I noticed the Gold was "less harsh" so I went back and forth between both taps and the tap 8 ohm I normally plug into is definitely brighter with seemingly more headroom - sounds a little harsh compared to the other.

Still, no explanation for how this could be?? Those taps are wired together, hmmmm.......

 

[Stu Blue]

Actually I would say that something is wired wrong in your amp... they should sound exactly the same. Personally I dislike the modern multiple outs with different ohms instead of just two out with a ohms selector. I'm sure loads of people plug two 8ohm cabs (8ll8=4ohms) into the two sockets marked 8ohm (meant for 16ll16=8ohms).

EDIT Could just be the "dull" socket needs cleaning.........

 

[jamison162]

Actually I would say that something is wired wrong in your amp... they should sound exactly the same. Personally I dislike the modern multiple outs with different ohms instead of just two out with a ohms selector. I'm sure loads of people plug two 8ohm cabs (8ll8=4ohms) into the two sockets marked 8ohm (meant for 16ll16=8ohms).

EDIT Could just be the "dull" socket needs cleaning.........

Good point I replied in the other thread. I think I have most of this figured out now and can adjust my overall tone (regardless of tap used) by adjusting my bias with the load I'm going to be using. I.E. I use my 16 ohm 2x12 at gigs and rehearsal but last time I biased by ear was using a single 8 ohm speaker. I need to bias using the exact setup I'm going to be using out live.