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Roy Mottram

Kentley

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LeGrace

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Transformer noise db level question

LeGrace: Posts : 388
Join date : 2016-08-07
Location : Ontario, Canada

Post n°1

Transformer noise db level question

by LeGrace Tue Nov 15, 2016 11:14 am

Power transformers typically generate some noise. The ones on my M125's are no exception. But normally I have to place my ear right up against the transformer to actually be able to hear anything. And even then its faint. Moving away just an inch or so and I cant hear it anymore.

Until last night. After an extended listening session when I went to turn off the amps I could clearly hear the transformer on one of my units from 2-3 feet away. Classic transformer buzz type noise, just much louder then normal. Turn it back on this morning and everything is back to normal, no audible buzz. Anyone else ever experience anything like this? Could it be somehow related to recently switching over to the 4 ohm taps after getting new speakers? I'm also running on only 2 power tubes now.

Wondering now if I should switch back to the 8 ohm taps? (fyi impedance on my speakers can drop down as low as 3 ohms) ie wondering if this is the transformers way of telling me it doesn't like the way things are currently set up confused

confused

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°2

Re: Transformer noise db level question

by Peter W. Tue Nov 15, 2016 12:26 pm

I would be quicker to suspect some level of heat-related vibration before suspecting the transformer of not liking the set-up. Try, for giggles, checking the hold-down screws and other hardware to see if anything is loose. I have been known to put a small bit of high-temp silicon sheeting (soft cookie sheet material) under a transformer if it continuously has a 'buzz' on that does not go away with conventional treatments. Not on Dynaco products, however.

As to impedance taps, generally, I run at 16 ohms when feeding nominal 8-ohm speakers, and the 8 ohm tap for everything else. My main speakers are 6 (Maggies) & 4 (AR3a) ohms (nominal) respectively, and both are very inefficient. Everything else is nominal 8 ohms.

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°3

Re: Transformer noise db level question

by deepee99 Tue Nov 15, 2016 3:37 pm

Try the bolt-screw tightening loosening thing first, as Peter W. suggests. If the torque ain't just right on all four bolts, you're going to get some noise, not all of it mechanical.

Bob Latino: Admin; Posts : 3263
Join date : 2008-11-26
Location : Massachusetts

Post n°4

Re: Transformer noise db level question

by Bob Latino Tue Nov 15, 2016 4:11 pm

What Deepee99 has said is good advice. The M-125 power transformer sits on 4 neoprene "isolation washers" to reduce the amount of mechanical vibration being transmitted to the chassis. If the 4 nuts that hold the transformer are too loose, too tight or as Deepee99 has said > have uneven tightness sometimes you can get some mechanical hum. This can be more noticeable after the amp has warmed up but should not be noticeable from your listening position 6+ feet away. If you only notice it from 2 to 3 feet away, I would just ignore it as it can't be heard from your listening position. If you want to play with the torque of the 4 nuts that hold the power transformer to the chassis, then you are welcome to try ..

Bob

LeGrace: Posts : 388
Join date : 2016-08-07
Location : Ontario, Canada

Post n°5

Re: Transformer noise db level question

by LeGrace Tue Nov 15, 2016 4:46 pm

They were a little loose. Amp has been on a few hours now, quiet again. Thanks! Main worry was that the recent changes had something to do with it, relieved that's not the case.

Still confused over which taps would be better with my 6 ohm speakers. Googling the topic returned recommendations for both. Perhaps the best approach is simply to try both then decide.

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°6

Re: Transformer noise db level question

by Peter W. Tue Nov 15, 2016 5:35 pm

LeGrace wrote:They were a little loose. Amp has been on a few hours now, quiet again. Thanks! Main worry was that the recent changes had something to do with it, relieved that's not the case.

Still confused over which taps would be better with my 6 ohm speakers. Googling the topic returned recommendations for both. Perhaps the best approach is simply to try both then decide.

Apparently, that is a balance between active speaker impedance, amplifier loading and power delivered. Every source I have ever read will waffle and stand directly on the fence of which-is-better. With the exception of Magnepan speakers (I keep MG-IIIs), conventional speaker loads are NOT linear.

The one landing-on-one-side-of-the-fence-firmly suggestion I have ever seen was from some HH Scott literature that came with my LK-150. Which suggested strongly that (at least their) the tap used should be higher than the nominal speaker impedance, and that the 4-ohm tap should be avoided except under specific conditions. NOW and CAUTION: The tap that matches the actual impedance curve of the speaker will give the most efficient power transfer and widest bandwidth. BUT - if the actual impedance is significantly higher than the tap rating, the output transformers will work harder and could overheat. So, using a 4 ohm tap on an 8-ohm speaker is *generally* not a good idea. Conversely, using the 16 ohm tap on an 8-ohm speaker may de-rate the amp somewhat, but the OPT will run cooler.

A classic case of YMMV... .

Again, I am running my tube systems in rooms far smaller than my two main listening spaces - by 1/2 and 2/3 respectively, so I see no penalties for running at the higher tap levels.

In the interest of full disclosure, even my LK-150 cannot drive the Maggies in the main listening room, nor can two ST-70s in mono mode. For that, the big honking Citation 16 does the job. I have tried.

Kentley: Posts : 496
Join date : 2015-03-06
Age : 71
Location : Worcester, MA

Post n°7

Re: Transformer noise db level question

by Kentley Tue Nov 15, 2016 5:42 pm

"6 ohm" speaker impedance is, of course, an approximate value, as you probably know. Experimentation is the best way to find out.
PeterW and I have opposite philosophies here. Using taps that are "higher" in value than nominal speaker impedance will, indeed, give more power and often a noticeable increase in volume. BUT - you should be careful here - too much of a "good" thing can put a strain on the output stage by allowing a larger current draw than usual. Our beloved speaker-maker Tyler agrees that his speaks that are "8 ohm rated" often sound better and more controlled when plugged into 4 ohm taps. So I'd wager a modest sum that you will probably be better off using those speaks on the 4 ohm taps.
There is little chance of real damage to our well-made output trannies, thank Bob!

While I was composing this, another post went up concerning vintage Scott amps, which seems to contradict me. However, let it be noted that many older tube amps had major difficulty with designing output trannies which were stable from the 4 ohm taps. ARC is also in this camp. So the warning about taps here must be taken through a lens carefully.

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°8

Re: Transformer noise db level question

by Peter W. Tue Nov 15, 2016 5:55 pm

Using taps that are "higher" in value than nominal speaker impedance will, indeed, give more power and often a noticeable increase in volume.

I believe I wrote the opposite, or is this simply a typo?

Per my general philosophy-in-a-vacuum (pun intended), I would use a 16-ohm tap for 0-10 ohm nominal speakers, an 8-ohm tap for 0-6 ohms, and a 4-ohm tap for any speaker that drops, consistently below 3 ohms, such as my AR3as. The Maggies are pretty much a linear load at 6 ohms. This *de-rates* the amp somewhat, as it happens, but is easier on the OPTS.

What Kentley writes on the weakness of early OPTs, with specific reference to the 4-ohm tap and transformer stability may be the source of my opinion, formed in the dim-and-distant past.

Kentley: Posts : 496
Join date : 2015-03-06
Age : 71
Location : Worcester, MA

Post n°9

Re: Transformer noise db level question

by Kentley Tue Nov 15, 2016 6:20 pm

My own experience, with two tube amps and three different speaker sets is exactly as I have written. However, using first some B&Ws and then some Tylers with my ST-120 - off both the 4 and 8 ohm taps, I found that there is a greater FEELING of power, though the actual level is less, off the 4 ohm taps. More like the sensation that there's "more under the hood" than is actually being used. When I reverse the situation, my ears tell me that the energy is less-controlled. Does this make sense? I'd love to hear Bob's take on this....hint, hint.....

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°10

Re: Transformer noise db level question

by deepee99 Tue Nov 15, 2016 6:55 pm

Kentley wrote:My own experience, with two tube amps and three different speaker sets is exactly as I have written. However, using first some B&Ws and then some Tylers with my ST-120 - off both the 4 and 8 ohm taps, I found that there is a greater FEELING of power, though the actual level is less, off the 4 ohm taps. More like the sensation that there's "more under the hood" than is actually being used. When I reverse the situation, my ears tell me that the energy is less-controlled. Does this make sense? I'd love to hear Bob's take on this....hint, hint.....

I would, too. Some Forum members have (and use) thermometers to detect hot spots on their amps. One of those is on my shopping list, if anyone can recommend a fave. Now I just use the palm of my right hand but can detect noticeable temp differences between the 4- and 8-ohm taps depending on speaker loads. I operate under the assUmption that cooler is better. Please correct me if I'm wrong here.
Another esoteric consideration is the actual speaker load. As Kentley notes, it's not linear, and if you're stacking or running more than a single pair of speaks, the impedance drops like a new bride's dress on wedding night. I.e., strapping two 8-ohm speakers in parallel does not lead to a 16-ohm or a 4 ohm load, especially given the wobbly behaviour of speakers. You could end up with a half-ohm load, which ain't no fun for the pwr supply or the output xformer iron and both will get damn hot.

Again, I assUme that high heat is Not A Good Thing. Tube amps reputedly can tolerate a dead short but I'm not gonna try it. Do that with a sand amp and kiss your house good-bye.

Bob Latino: Admin; Posts : 3263
Join date : 2008-11-26
Location : Massachusetts

Post n°11

Re: Transformer noise db level question

by Bob Latino Tue Nov 15, 2016 7:08 pm

I paid about $25 shipped for the Cason CA380 back in 2010 but these little instruments have come way down in price. Less than $10 shipped from some USA sellers .. Link below to one on Ebay ..

Infrared thermometer on Ebay

Bob

Roy Mottram: Admin; Posts : 1837
Join date : 2008-11-30

Post n°12

Re: Transformer noise db level question

by Roy Mottram Tue Nov 15, 2016 11:19 pm

speaker impedance . . . . exact quote from the last time this topic was discussed . . .

also keep in mind that speaker "impedance" such as a rating of 6 or 8 ohms is a "nominal" value, not even an average value.
99% of all speakers have their lowest impedance below 300Hz, and it raises gradually at all higher frequencies.
Also 99% of all speakers have a very large bump in the low end, usually somewhere between 30 to 70Hz where the impedance is typically around 25 to 45 ohms.
Here's an example . . .
Transformer noise db level question Speaker impedance

Transformer noise db level question Speaker impedance

j beede: Posts : 473
Join date : 2011-02-07
Location : California

Post n°13

Re: Transformer noise db level question

by j beede Tue Nov 15, 2016 11:21 pm

LeGrace wrote:Power transformers typically generate some noise. The ones on my M125's are no exception. But normally I have to place my ear right up against the transformer to actually be able to hear anything. And even then its faint. Moving away just an inch or so and I cant hear it anymore.

Until last night. After an extended listening session when I went to turn off the amps I could clearly hear the transformer on one of my units from 2-3 feet away. Classic transformer buzz type noise, just much louder then normal. Turn it back on this morning and everything is back to normal, no audible buzz. Anyone else ever experience anything like this? Could it be somehow related to recently switching over to the 4 ohm taps after getting new speakers? I'm also running on only 2 power tubes now.

Wondering now if I should switch back to the 8 ohm taps? (fyi impedance on my speakers can drop down as low as 3 ohms) ie wondering if this is the transformers way of telling me it doesn't like the way things are currently set up

FYI: The tiny transformers in the DC bias supply in my electrostatic speakers would keep me awake at night due to hum. Inserting rubber washers between the transformers and chassis had zero effect on the hum. I used a reamer to enlarge the mounting holes in the transformer and chassis. I inserted rubber grommets in the transformers and chassis and replaced the mounting hardware with the next smaller size to eliminate all metal-to-metal contact. Decoupling the transformers this way resulted in utter silence.

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°14

Re: Transformer noise db level question

by deepee99 Wed Nov 16, 2016 1:48 am

I'm still curious how mechanical hum from the iron translates into electronic hum. I just know that it does, but no clue why . . .

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°15

Re: Transformer noise db level question

by Peter W. Wed Nov 16, 2016 8:02 am

deepee99 wrote:I'm still curious how mechanical hum from the iron translates into electronic hum. I just know that it does, but no clue why . . .

Actually, it doesn't. Well - OK, if the power supply filtering is inadequate there will be noise.

However, the transformer *magnetic* hum is will be 60 (50) HZ, and electronic hum will be 120 (100) HZ. But a buzzy transformer will typically not be manifest elsewhere assuming proper filtering.

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°16

Re: Transformer noise db level question

by Peter W. Wed Nov 16, 2016 10:00 am

[quote="deepee99" >>Massive Snippage<<

Again, I assUme that high heat is Not A Good Thing. Tube amps reputedly can tolerate a dead short but I'm not gonna try it. Do that with a sand amp and kiss your house good-bye.
[/quote]

Heat is never a good thing outside of a cooking appliance, heating appliance or fireplace. And uncontrolled/unanticipated heat can do a great dea of harm in a rather short time. Further, even a bit of extra heat will contribute to early failure of many things.

I also keep a small 'heat gun', it is one of my work tools, and I have had it for almost 20 years now. Even then, it was less than $20 to purchase, and today is probably half of that. Other than checking discharge temperatures at HVAC diffusers, one of its best uses is detecting *differences* in temperature from one part to another. Keep in mind that if one has no effective basis on which to judge what is the proper temperature, a difference between two otherwise identical parts or locations may be significant.

So, what is the correct operating temperature of an OPT on the typical ST70?

Betcha it is going to be a range!

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°17

Re: Transformer noise db level question

by deepee99 Wed Nov 16, 2016 12:50 pm

Peter W. wrote:[quote="deepee99" >>Massive Snippage<<

Again, I assUme that high heat is Not A Good Thing. Tube amps reputedly can tolerate a dead short but I'm not gonna try it. Do that with a sand amp and kiss your house good-bye.

Heat is never a good thing outside of a cooking appliance, heating appliance or fireplace. And uncontrolled/unanticipated heat can do a great dea of harm in a rather short time. Further, even a bit of extra heat will contribute to early failure of many things.

I also keep a small 'heat gun', it is one of my work tools, and I have had it for almost 20 years now. Even then, it was less than $20 to purchase, and today is probably half of that. Other than checking discharge temperatures at HVAC diffusers, one of its best uses is detecting *differences* in temperature from one part to another. Keep in mind that if one has no effective basis on which to judge what is the proper temperature, a difference between two otherwise identical parts or locations may be significant.

So, what is the correct operating temperature of an OPT on the typical ST70?

Betcha it is going to be a range![/quote]

Peter W, massive snippage of my garrulous posts is frequently salutary. I used to have editors who did that for me, but newspapers have died.
While I cannot give you specifics on the heat generated by the OPTs on the ST70,my experience with tube gear is that it takes several hours to settle into what tug-boaters used to call the "company notch" -- that ideal balance between power and fuel efficiency. You can hear it when it gets there. I regard any measurements taken before she hits that notch as irrelevant. The exceptions of course are when you're checking out a new build or new tube/rectifier installation to expose any obvious wiring or equipment flukes (pun intended). Otherwise, I wouldn't take any measurements seriously until the critter's been on for a couple of hours.

LeGrace: Posts : 388
Join date : 2016-08-07
Location : Ontario, Canada

Post n°18

Re: Transformer noise db level question

by LeGrace Wed Nov 16, 2016 7:27 pm

Before the transformers would get really hot, too hot to touch. Now they barely go beyond lukewarm, even after several hours. Remarkable change. Assume this is more due to retiring 2 power tubes versus changing taps.

Bob Latino: Admin; Posts : 3263
Join date : 2008-11-26
Location : Massachusetts

Post n°19

Re: Transformer noise db level question

by Bob Latino Wed Nov 16, 2016 9:49 pm

LeGrace wrote:Before the transformers would get really hot, too hot to touch. Now they barely go beyond lukewarm, even after several hours. Remarkable change. Assume this is more due to retiring 2 power tubes versus changing taps.

Yes - The power transformers on the M-125's are designed to support (supply current) for FOUR output tubes. When you use just TWO output tubes, the power transformer is loafing along and does not generate nearly as much heat ..

Bob

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°20

Re: Transformer noise db level question

by deepee99 Thu Nov 17, 2016 10:59 am

On the subject of xformer-bolt torque adjustments, IIRC there are at least one (and maybe two) grounding lugs secured by the underlying transformer-bolt nuts, so if you have a really loose or over-tightened one it's probably best to take the belly off the beast to make sure you're not comprising the lug's contact with the chassis or its attendant wiring. This shouldn't be a problem if you bought the amp assembled by Bob, Roy, or Audio Bill, but if it was a kit-build by yourself or some third party after-marketer, it's a consideration...
BobL, I guess for $10 and free shipping I'm going to have to buy one of those IR thermometer guns. Fluke has them, too, but they start at $250, which would put a crimp on the Christmas budget.

Kentley: Posts : 496
Join date : 2015-03-06
Age : 71
Location : Worcester, MA

Post n°21

Re: Transformer noise db level question

by Kentley Thu Nov 17, 2016 12:45 pm

"BobL, I guess for $10 and free shipping I'm going to have to buy one of those IR thermometer guns. Fluke has them, too, but they start at $250, which would put a crimp on the Christmas budget."

There are lots of things to use a temp gun on. Very nice in the kitchen (I like to ferment my own yogurt, where constant temp is a must). Also nice when weatherstripping around windows and doors.
Caveat: The gun is only accurate at short range. You won't be able to properly monitor your OPT burning from your listening chair. Best within 10 inches or so.

deepee99: Posts : 2244
Join date : 2012-05-23
Location : Wallace, Idaho

Post n°22

Re: Transformer noise db level question

by deepee99 Thu Nov 17, 2016 12:58 pm

Kentley wrote:"BobL, I guess for $10 and free shipping I'm going to have to buy one of those IR thermometer guns. Fluke has them, too, but they start at $250, which would put a crimp on the Christmas budget."

There are lots of things to use a temp gun on. Very nice in the kitchen (I like to ferment my own yogurt, where constant temp is a must). Also nice when weatherstripping around windows and doors.
Caveat: The gun is only accurate at short range. You won't be able to properly monitor your OPT burning from your listening chair. Best within 10 inches or so.

Well, hmm, should I start cooking yogurt I will have to consider a Fluke. (Got any decent recipes and procedures?) Current agenda is to not cook tubes and transformers.

Kentley: Posts : 496
Join date : 2015-03-06
Age : 71
Location : Worcester, MA

Post n°23

Re: Transformer noise db level question

by Kentley Thu Nov 17, 2016 1:01 pm

oh you silly silly man...
The $10 gun works perfectly well. I would consider the Fluke only if I were using it to monitor a uranium mine. Then again, Why Bother?

Peter W.: Posts : 1351
Join date : 2016-08-07
Location : Melrose Park, PA

Post n°24

Re: Transformer noise db level question

by Peter W. Fri Nov 18, 2016 8:59 am

Kentley wrote:oh you silly silly man...
The $10 gun works perfectly well. I would consider the Fluke only if I were using it to monitor a uranium mine. Then again, Why Bother?

Wouldn't you want a Geiger counter and scintillator for that - the counter for the mine, the scintillator for you?

Once upon a time my wife collected Fiesta Ware - briefly. So, I acquired a surplus Geiger counter, complete with scintillators, readers for same and so forth. Where this becomes peripherally relevant here is that there are a few radioactive tubes out there, including the 811A, technically a transmitter tube, but sometimes used as an alternate output tube for the 70 - with much adapting, of course.

Tube Nube: Posts : 707
Join date : 2008-12-06
Age : 60
Location : Calgary, AB

Post n°25

Re: Transformer noise db level question

by Tube Nube Fri Nov 18, 2016 2:36 pm

811 tubes are quite frequently "radio active" -- see here:

http://www.ameritron.com/Product.php?productid=al-811

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Re: Transformer noise db level question

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