Wall voltage

[hywelg]

I've been a long time lurker and avid reader of the Dumble discussions, though my electronics knowledge is severly limited so I do feel unable to contribute much, to my own disappointment. However I think my recent observations might be of interest.

I have a Ceritone OTS which I have modded a little over the 5 years I've had it, and it has been a useful learning process for me. However I have for a long time felt that the amp has good days and less than good days, such that a couple of years back I bought a plug in voltmeter just to check whether it had an influence. Last night I proved it not only to my satisfaction but also other band members noticed it. Heres what happened.

I arrive at our rehearsal room at around 6:30, set up in anticipation of a new bass player coming for an audition. The volt meter read 242.7 (UK obviously!) The amp sounded great, three way bright switch was off. I had a play for a while until the others arrived then we ran through a couple of numbers and chatted waiting for the phone call to alert us the bass player was outside. It was then i noticed that the amp had lost a little brightness, no changes to how the amp was set, I checked the voltmeter and it read 240.7 and mentioned it to our drummer who said he thought it sounded different.

Anyway, played with the new bass player and the voltage was dropping alll the time (sure it wasn't our fault, though we do play loud!) and it ended around 238.2v with a very significant change in the tone. Normally I would have just flicked the bright switch but I wanted to be sure of what I was hearing.

Now, the question i have for the more knowledgeable amongst you, is this likely to be entirely down to bias drift? or is there more going on? Could it be ear fatigue? I doubt the latter because I have noticed it at home with much lower volumes.

Would it be instructive to check the bias at each and every noted tone change associated with a voltage drop? I might not be popular with the rest of the band causing such a hiatus but I'll live with that.

If this can be attributed to bias drift would there be any mileage in installing a small value pot on the rear panel that would give a very limted additional bias adjustment range, such that it would be safe no matter how it was set?

TIA

[mr_hankey]

(...)

[PaisleyTube]

very simple: that new bassplayer absorbs too many highs!



Besides humidity and different voltages the amount of "mess" on the mainsvoltage does also effect the sound/fee;l of an amp.

[ic-racer]

This (the red thing):
[IMG:500:369]http://img.photobucket.com/albums/v670/ ... /RFrig.jpg[/img]

[hywelg]

Please enlighten me, the red thing is what exactly.?

I have looked at regulators but the Furmans are expensive and seem to allow a bigger drift than I have experienced.

[hywelg]

The voltage at my house seems to fluctuate between 227v and 235v. That change will of course affect more than just the power tube bias, so I don't think it's worth worrying about. However, I do check the wall voltage every time I'm doing subtle tweaks, as I suppose an 8v difference is going to cause bigger changes than increasing a resistor value by 5%.

Do you notice a change of tone with those sorts of swings? I couldn't be sure until I started using the voltmeter regularly and paying attention to what it said, then trying to equate it to what i was hearing.

[ic-racer]

Please enlighten me, the red thing is what exactly.?

I have looked at regulators but the Furmans are expensive and seem to allow a bigger drift than I have experienced.

That picture is Robben Ford's rig. It appears he is plugged into a VARIAC (the red thing) so he can set the exact voltage he wants, irrespective of the stage's line voltage. It is not an AUTOMATIC VOLTAGE REGULATOR (although the label on it is printed "REGULATOR"). You would need to manually check it and re-adjust it if the stage's line voltage changes during the gig. Some VARIACS have a meter built in for that purpose. They are not very expensive, this one was only $65 new. https://taweber.powweb.com/amptechtools/variac.htm

[IMG768]http://img.photobucket.com/albums/v670/ ... ile-98.jpg[/img]

[hywelg]

Cheers IC, as you were writing I went off and found this http://www.ebay.co.uk/itm/Variable-Tran ... 43ac4e06c2

Seems I would want a decent easy to read voltmeter, plus output sockets. Not too difficult to sort I wouldn't think.

3A would be enough for running most amps wouldn't it? Or should I go a little bigger?

[ToneMerc]

I've been a long time lurker and avid reader of the Dumble discussions, though my electronics knowledge is severly limited so I do feel unable to contribute much, to my own disappointment. However I think my recent observations might be of interest.

I have a Ceritone OTS which I have modded a little over the 5 years I've had it, and it has been a useful learning process for me. However I have for a long time felt that the amp has good days and less than good days, such that a couple of years back I bought a plug in voltmeter just to check whether it had an influence. Last night I proved it not only to my satisfaction but also other band members noticed it. Heres what happened.

I arrive at our rehearsal room at around 6:30, set up in anticipation of a new bass player coming for an audition. The volt meter read 242.7 (UK obviously!) The amp sounded great, three way bright switch was off. I had a play for a while until the others arrived then we ran through a couple of numbers and chatted waiting for the phone call to alert us the bass player was outside. It was then i noticed that the amp had lost a little brightness, no changes to how the amp was set, I checked the voltmeter and it read 240.7 and mentioned it to our drummer who said he thought it sounded different.

Anyway, played with the new bass player and the voltage was dropping alll the time (sure it wasn't our fault, though we do play loud!) and it ended around 238.2v with a very significant change in the tone. Normally I would have just flicked the bright switch but I wanted to be sure of what I was hearing.

Now, the question i have for the more knowledgeable amongst you, is this likely to be entirely down to bias drift? or is there more going on? Could it be ear fatigue? I doubt the latter because I have noticed it at home with much lower volumes.

Would it be instructive to check the bias at each and every noted tone change associated with a voltage drop? I might not be popular with the rest of the band causing such a hiatus but I'll live with that.

If this can be attributed to bias drift would there be any mileage in installing a small value pot on the rear panel that would give a very limted additional bias adjustment range, such that it would be safe no matter how it was set?

TIA

All else being equal, your total AC mains voltage swing results in about a 8.6VDC decrease in B+ voltage at the plates and about a 1.5VDC decrease at the bias grids. Since your B+ is lower, other voltage nodes such as the PI and preamp will naturally be lower as well.

Now if you do determine that its not tired tubes, ear fatique, etc. and there is a tagible correlation between the lower mains voltage and a less positive favor of your amp, the best solution most likely is some type voltage regulation type device, only you can make that call.

good luck

TM

[vibratoking]

You talking about a change of about 1.5%. That is good IME. I think the spec is +/-10%. In the UK. I don't think you can hear 1.5%. Perhaps the supply voltage is changing in some other way that you didn't measure? I bought one of the these about 5 years ago and never looked back.

http://www.sweetwater.com/store/detail/AR15

You can find similar units on the used market for fairly cheap. This stuff is expensive new.

[NickC]

You talking about a change of about 1.5%. That is good IME. I think the spec is +/-10%. In the UK. I don't think you can hear 1.5%. Perhaps the supply voltage is changing in some other way that you didn't measure? I bought one of the these about 5 years ago and never looked back.

http://www.sweetwater.com/store/detail/AR15

You can find similar units on the used market for fairly cheap. This stuff is expensive new.

I've used the AR15 too, for several years now. I got tired of playing dive bars with lousy, dirty AC prone to brown-outs every time the beer cooler compressor kicked on. The AR15 solved that problem, but at a high cost and a LOT of weight to cart around. It's good stuff though, and it will clamp down power spikes so they don't damage your rig.

[vibratoking]

It's not that heavy. C'mon man...it's worth it's weight in gold.

[NickC]

It's not that heavy. C'mon man...it's worth it's weight in gold.

I had it in an 8-space rack with PA processors (EQs, compressors, FX) and that rack was a bear to tote around.

I looked it up, the AR-15 is around 15 pounds. Yes, worth the cartage indeed!

[mr_hankey]

(...)

[aflynt]

I use a Variac on my amp on occasion when I'm not plugged into our bands Furman regulator. I can definitely hear the difference either way tonally beyond 3 or 4 volts up or down. I bought a little panel mount voltmeter/led readout from Mouser to check the voltage and I set the Variac for 120VAC (US). I don't go too crazy checking it every few seconds or anything, but I do check it a couple times per set while we're playing and sometimes readjust it between songs. If we're playing a place that seems to be putting out pretty close to 120VAC I'll just leave the Variac in the car, though. It's more important for me at places where the voltage just seems to be consistently high or low.

IIRC Robben Ford used one to raise the mains voltage to 125VAC. I think Larry Carlton was using one too in a similar way. The Furman regulators are +- a certain percentage and they'll regularly put out anything from 117 to 124 volts in my experience when switching taps. Personally I've found there's not a huge difference in tonality through that range if you get your amp tweaked to sound good at 120VAC.

-Aaron