Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

Tone Control
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Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« on: November 17, 2010, 04:11:16 AM »

Last week I tried a Fender Tonemaster (it's a late 90s custom shop model)
It had some very good sounds, but what surprised me was the Lo-Med-Hi switch on the back that completely changes the tonality of the amp

I got the manual online, and the switch is 4/8/16 ohm,
yet this is primarily INTENDED by Fender to be used to change the amp's sound, when used with the matching 16ohm cab, to get different saturation effects, the manual says:
"IMPEDANCE SWITCH - This is labeled LO, MED and HI. This switch serves two functions.
One, to set the output impedance of the amplifier to best match the speaker impedance for maximum
power. Second, to enable the amplifier to better achieve the cranked-up sound at a lower
volume."

Is this technique valid on other amps? Has some extra tolerance been built into the Tonemaster to allow this to be recommended usage?

thanks
Tone


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Dr Tone Control, Strats mostly, prefer saturated clean tones, a little OD sometimes
BM50, JTM45, 36w EF86, DZ30, Expression, + non-Ceriatones (Matchless, Victoria, Wienbrock)
Just started with pedals a little after a 10 year purist spell, but usually just delay

212Mavguy
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #1 on: November 22, 2010, 02:19:11 PM »

The thing to watch for is too LOW of a load for the output transformer, not too high. You are fine with 4 ohm setting going into that 16 ohm speaker.

I have an old Fender 160PS vocal amp running a pair of 6550's that is rated for 160 watts rms into a 2.3 ohm load. It's been modded in a couple of the six separate preamp sections for guitar use. The speaker outs on the back are rated 5.6 ohms. So when both speaker outs are parallelled the load drops to that 2.3 figure. Using one speaker out I run it into a 2/15 semi closed back with JBL g135's in series for 16 ohms. With that kind of loading, the amp is more compressed and easier to play. Because those speakers are so efficient, that rig is still VERY loud.

The best way to get great sounding breakup at lower volumes for me by FAR is my custom ordered Weber MASS attenuator. Because I ordered it with a TRS balanced line out, I will never have to mic an amp again at a gig, the line out puts out a very hot signal to go to the PA board, and there is a full tone stack only for that line out with volume, treble, mid, and bass controls. I can adjust those controls and send them to the board, which is something quite special. I recently used it to help a friend of mine in the recording studio and the results were spectacular in a good way, and easy to setup and use. www.tedweber.com


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cmoore
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #2 on: November 22, 2010, 04:36:17 PM »

Is that a Solid State amp?
If so, they are a bit different and only require a MINIMUM impedance. A tube amp with an Output Transformer is a different proposition. It is always best to match the impedance of the amp to the speaker. Just buy another speaker if you do not have the right one. A guitar player with only one speaker is kind of like a painter with only one color. If you are going to play, you need some stuff and speakers last a LONG time.
The worst scenario for a tube amp is for the impedance of the speaker to be Too High. A 4 ohm out tranny into a 16 ohm speaker is the worst possible set up. That is where amp builders (and owners) worry about fly back voltage and transformer failure. If you had to, it would be better to run a 16 ohm amp into a 4 ohm speaker. That is one reason amp builders short the speaker jack to the chassis and not leave it open. They would rather have a short than an open circuit if the speaker connection goes away.
But this is all theoretical, just buy the right speaker or maybe a Z Matcher from Weber.
Good Luck


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wyatt
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #3 on: November 22, 2010, 07:59:47 PM »

Here is the complete text of the manual...

IMPEDANCE SWITCH - This is labeled LO, MED and HI. This switch serves two functions.
One, to set the output impedance of the amplifier to best match the speaker impedance for maximum power. Second, to enable the amplifier to better achieve the cranked-up sound at a lower volume. On the B CHANNEL, with a single Tone-Master enclosure, this switch should be set according to the setting of the B CHANNEL volume knob: For volume settings of 3.5 and lower, LO would be the appropriate setting. For settings of 3.5 to 7, MED is best. For settings above 7, HI will produce full power and tone. This switch will not damage tubes or reduce tube life at these settings. What it does do is increase the gain in the LO and MED settings and thereby better approximate the Full volume sound at a lower level than by adjusting the VOLUME alone. With a single 16½ enclosure, LO will produce 30 watts, MED will Produce 60 watts, and HI will produce a full 100 watts. With two 16½ enclosures, (an 8½ load), LO will produce 60 watts, and MED will Produce 100 watts. In the A CHANNEL, the switch has the same function, although blues players may like running the switch on LO all the time to get that great crying tone. Conversely, a player looking for a New Wave Strat® tone might like the sound of the A CHANNEL on HI.

Ultimately, Bruce Zinky is using the impedance mismatches to attenuate the signal. The the OT is built robust enough to handle the mismatches. This is key, it's all about have the OT and the power amp is deigned. Most major brand, tour-worthy equipment can safely handle a mismatch of 1:2 or 2:1...that means any good Fender, Marshall, Mesa etc. should be able to handle a 4-ohm or 16-ohm load on their 8-ohm tap. It's not OPTIMAL, but a good amp should be built to handle it (do not try this with a vintage amp).

So, yes, your guess that the Tonemaster was designed to do this better than some other amps is true.

As for the attenuation, that's going to seem like a drop in the bucket, the amp isn't going to seem much quieter, it'll just loose some clean headroom. Mathematically, to get halve the output of a 100-watt amp, you need a 10-watt amp (in reality, it's more like a 20-watt amp)

Generally though, I wouldn't recommend using a 4:1 or 1:4 mismatch on any amp that isn't designed to handle it. That means don't go around driving a 4-ohm load with a 16-ohm tap or vice-versa.

You are going to hear people say that it's safer, or okay, to drive a larger load with a impedance mismatch than other mismatches. That's a myth. People hear it, it seems to gel with common sense, and they repeat it. "For every problem there is a simple and erroneous solution." But none of these people know jack about how tube amps work. It is NOT any safer to run a bigger load (is is not safer to drive a 16-ohm cabinet with a 8- or 4-ohm tap than is is to drive a 4-ohm cabinet with a 8- or 16-ohm tap), in fact quite the opposite. What you have to be wary of is "flyback" which is signal that bounces back and can damage the power amp.


« Last Edit: November 22, 2010, 08:01:35 PM by wyatt »	Logged

Tone Control
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #4 on: November 22, 2010, 09:39:28 PM »

on the Fender Tonemaster (which is an all-tube PTP amp, for the info of the earlier poster) did sound much quieter when using the switch, with the controls untouched, when the amp was mismatched.

It's unusual enough for me to mention it here, but I too assumed the OT was bullet-proofed to allow this


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212Mavguy
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #5 on: November 22, 2010, 11:34:20 PM »

Still sticking by my previous post. Have never seen any ill effects from flyback voltages EVER with low OT to high speaker mismatched impedance, and have spent lots of hours doing just that where the speakers had very big magnets and flattened ribbon wire VC's, and the amp was also powerful. Think that the "flyback hypothesis" is exaggerated in it's ill effect from my experiences. Maybe if the amp was dimed it would be slightly more of an issue, but in my experience that has not been a problem.

With that said, yes, I'd much rather run a matched impedance setup and use an attenuator instead to reduce volume of a cranked up amp, by far. It's true that you will lose surprisingly little volume with lower value impedance OT going into higher impedance speaker(s). A lot depends on the speakers used. The previously mentioned Weber MASS is available in different wattage capacities, MASS wattage rating should be double the wattage rating of your tube amp. Mine was worth every penny. Tones are better, particularly dirty ones than without using it at a given reduced volume if properly used. Overdoing the attenuation thang on a clean and dirty channel selectable 2 channel amp will cost you clean headroom on the clean channel, though.


« Last Edit: November 22, 2010, 11:37:24 PM by 212Mavguy »	Logged

Tone Control
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #6 on: November 22, 2010, 11:39:02 PM »

is the weber mass way better than the THD hotplate?


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212Mavguy
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #7 on: November 23, 2010, 03:25:45 AM »

Have not owned a hotplate, but the Weber unit offers more than just attenuation, much better feature set. Rather than just a network or resistors, the Weber uses an actual speaker motor to provide some of that (flyback voltage) feedback to the OT like a real speaker, mine has footswitch to turn attenuation on/off, headphone jack, TRS balanced out, hi or lo rate of attenuation, 4/8/16 ohm impedance matching, treble boost switch (more like presence) 0, +3, or +6db, plus a full tone stack (volume treb, mid, bass) controlling only the line out signal. That gives the user better control over his tone through the mixer, no more micing ever. About the only option I didn't get with mine was the rackmount ears. I get some amazing "cranked up" amp tones at small room regular gig volume levels. Better sustain and girth in the tone for sure. No loss of treble unless wanted due to treb boost switch.


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Tone Control
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #8 on: November 23, 2010, 09:07:48 PM »

Quote from: 212Mavguy on November 23, 2010, 03:25:45 AM

I found a comparison at http://www.legendarytones.com/weberma.html:

Quote

Now the question is undoubtedly going to come up later if I don’t address it here first – quite simply, “How does the Weber MASS’ tone compare to the THD Hot Plate?”

I did some A/B tests using all amps and cab types and found that when set for little to moderate attenuation (-8 dB max on the Hot Plate and tuned to a similar output level with the MASS), the tone of both units was very similar, though the Hot Plate was a hair brighter (which could be viewed as a benefit or a disadvantage depending on your perspective!). When going to –12 dB or more on the Hot Plate, the Hot Plate won out on versatility because that’s when its frequency compensation switches really assisted in making the tone seem more natural with extra low and high end reinforcement. The MASS’ treble boost switch serves it well at those settings as well, but overall it is more of an extreme adjustment, whereas the Hot Plate tone network is a bit more subtle and therefore more useful in a wider range of applications.

Sonically for my personal uses, which involve attenuation typically no more than –8 dB, I would be happy with either unit. Any further than that in attenuation and the Hot Plate is my favored choice simply due to the frequency compensation switches which I feel are very well tuned.

Now for direct out use or in a “wet-dry” combined setup, the versatility of having the tone network on the MASS to compensate and correct the tone of the DI signal makes it an easy pick as the winner over the Hot Plate. Direct out signals from amplifiers can typically sound atrocious in general, so being able to e.q. and set the level for them prior to going out to another amplifier, mixer, or effects, is a tremendous benefit.

All together the Weber MASS is an excellent unit and is also a tremendous value for those looking for a quality attenuator today. I label it as a “tremendous value” because there are various models available for different power handling characteristics and you can order the options you’d like as needed. Ours was a nearly fully-equipped model and at a price of 180.00, still makes it a very compelling buy.

The THD Hot Plate had previously earned a score of 10 out of 10 when I tested it last year as it ran circles around it’s well-known competitor, the Marshall Power Brake. The Weber MASS definitely does the same and you could do no wrong with it as well. With its features, solid build quality, and overall value, I’m also awarding the Weber MASS a score of 10. For more information about the Weber MASS, visit www.webervst.com.

I had 3 Hotplates.
Personally I think beyond -4dB the tone is lost. Beyond -4dB, worth getting if you want a dummy load.
I now try to use iso cabs for recording. If I was less lazy, and played out of my house, I'd pick an amp for the occasion I think. I'm not convinced that the speaker driver sound colouring for Celestion Blues, V30s, etc is possible to dial in with EQ though.
Some software does a fair job, but just into the desk? must be harder to get right surely?

Cheers
Tone


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212Mavguy
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Re: Mismatching impedances OK? Like fender Tonemaster (16ohm speaker, 4 ohm tap)

« Reply #9 on: November 24, 2010, 03:42:26 PM »

Honestly, your last thread input is tough for me to answer. But here is my best try...

I had major success in the studio helping a friend out. The improvement in sound quality using a Mass into the board compared to using a Shure sm58 in front of the speaker cab was more than substantial. YMMV with other mics, though. The miced setup in this instance did not accurately reproduce the speaker tone at all. What works for me might not work for you, though. The review comparing the Weber and the hotplate says it pretty well.

I enjoy the changes in tone that using the Weber MASS brings. In my own use practicing or playing out I crank the amp of choice's master up just enough to get the basic tonal character I'm looking for and attenuate with the MASS just enough to make the volume manageable. Most changes in tone due to the MASS are compensated for in the main amp's tone stack fairly easily, so no tone is lost for me if I squash the volume down a lot. I don't have a way of measuring numerically how many decibels the reduction in volume is.

If what comes in and out of the sound board sounds good, then it sounds good, period.

Peace.


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