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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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What differentiates good audio xmfrs from bad ones?
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones because they are better than the new crop. So what is the difference? It must be some sort of physical attribute. The way they are wound, insulation, etc. Is there a way to tell using just an oscilloscope? I'm just curious. I am very happy with the way my tube amp sounds. Thanks, Eric |
#2
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What differentiates good audio xmfrs from bad ones?
wrote:
I see really expensive audio output and power transformers for sale as well as cheap ones. And lots of folks really want older ones because they are better than the new crop. So what is the difference? It must be some sort of physical attribute. The way they are wound, insulation, etc. Is there a way to tell using just an oscilloscope? I'm just curious. I am very happy with the way my tube amp sounds. Thanks, Eric Frequency response delivering full power is what I think. Some trick winding process is likely to cost more. Greg |
#3
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What differentiates good audio xmfrs from bad ones?
Some things:
Quality of the core material. Care and bulk of wiring. Frequency range to be covered. Power requirements. After which, like anything else, all about materials wound on the thighs of virgins on Walpurgis Night. Peter Wieck Melrose Park, PA |
#4
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What differentiates good audio xmfrs from bad ones?
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#5
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What differentiates good audio xmfrs from bad ones?
On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, wrote:
I see really expensive audio output and power transformers for sale as well as cheap ones. And lots of folks really want older ones because they are better than the new crop. So what is the difference? The core of a transformer has laminations, because a solid metal lump would have electrical conduction losses (eddy currents) to cause large heat losses (and reduce output efficiency). A power transformer has thick laminations (60 Hz losses are small anyhow, but at 60 kHz, that would be inefficient), and a switchmode transformer is made of high-electrical-resistivity ferrite (at 60 kHz, the size can be small, though such a low-magnetization material wouldn't be great for lower frequency power). Audio transformers are most efficient when made from very thin laminations of soft iron, which is a more expensive construction than is used for either 60 Hz or 60 kHz power transformers. It just has more small parts. |
#6
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What differentiates good audio xmfrs from bad ones?
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#7
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What differentiates good audio xmfrs from bad ones?
On Thu, 10 Jan 2019 14:19:27 -0800 (PST), whit3rd
wrote: On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, wrote: I see really expensive audio output and power transformers for sale as well as cheap ones. And lots of folks really want older ones because they are better than the new crop. So what is the difference? The core of a transformer has laminations, because a solid metal lump would have electrical conduction losses (eddy currents) to cause large heat losses (and reduce output efficiency). A power transformer has thick laminations (60 Hz losses are small anyhow, but at 60 kHz, that would be inefficient), and a switchmode transformer is made of high-electrical-resistivity ferrite (at 60 kHz, the size can be small, though such a low-magnetization material wouldn't be great for lower frequency power). Audio transformers are most efficient when made from very thin laminations of soft iron, which is a more expensive construction than is used for either 60 Hz or 60 kHz power transformers. It just has more small parts. Thanks for the edifying reply. Some time back I wanted to use the mains power as a frequency standard when adjusting a generator. I was worried about connecting my 'scope directly to 125 volts so I used a 12 volt out step down xmfr. The wave form was really distorted. So I guess this was a perfect example of the xmfr being made in a way that was unsuitable for audio. Thanks Again, Eric |
#8
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What differentiates good audio xmfrs from bad ones?
On Friday, January 11, 2019 at 9:07:33 AM UTC-8, wrote:
Some time back I wanted to use the mains power as a frequency standard when adjusting a generator. I was worried about connecting my 'scope directly to 125 volts so I used a 12 volt out step down xmfr. The wave form was really distorted. That can happen because of saturation and remanence: the addition of a load on the low voltage side (like, a light bulb) will help greatly. The best small-signal audio transformers are potted in protective shells, in order to prevent strain on the magnetic laminations (which makes the magnetic core do those nonlinear things). |
#9
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What differentiates good audio xmfrs from bad ones?
wrote:
Audio transformers are most efficient when made from very thin laminations of soft iron, ** Soft iron has not been used since the days of Michael Faraday. Thin laminations of silicon steel is the norm. Some time back I wanted to use the mains power as a frequency standard when adjusting a generator. I was worried about connecting my 'scope directly to 125 volts so I used a 12 volt out step down xmfr. The wave form was really distorted. ** You exaggerate. ..... Phil |
#10
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What differentiates good audio xmfrs from bad ones?
whit3rd wrote:
The best small-signal audio transformers are potted in protective shells, in order to prevent strain on the magnetic laminations (which makes the magnetic core do those nonlinear things). ** Where does this utter drivel come from ??? ..... Phil |
#11
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What differentiates good audio xmfrs from bad ones?
On Friday, January 11, 2019 at 3:36:18 PM UTC-8, Phil Allison wrote:
whit3rd wrote: The best small-signal audio transformers are potted in protective shells, in order to prevent strain on the magnetic laminations (which makes the magnetic core do those nonlinear things). ** Where does this utter drivel come from ??? From a guy with a Ph.D who did a bunch of magnetism studies. When unloaded, power transformers have lots of undesirable signal-handling features. |
#12
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What differentiates good audio xmfrs from bad ones?
On Saturday, January 12, 2019 at 10:41:18 AM UTC+11, whit3rd wrote:
On Friday, January 11, 2019 at 3:36:18 PM UTC-8, Phil Allison wrote: whit3rd wrote: The best small-signal audio transformers are potted in protective shells, in order to prevent strain on the magnetic laminations (which makes the magnetic core do those nonlinear things). ** Where does this utter drivel come from ??? From a guy with a Ph.D who did a bunch of magnetism studies. ** Really ?? Has he got a web site - I could do with a good laugh. When unloaded, power transformers have lots of undesirable signal-handling features. ** More and worse drivel than the last lot. Give up - you have NO clue about audio or mains transformers. .... Phil |
#13
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What differentiates good audio xmfrs from bad ones?
On Fri, 11 Jan 2019 15:07:21 -0800 (PST), whit3rd
wrote: On Friday, January 11, 2019 at 9:07:33 AM UTC-8, wrote: Some time back I wanted to use the mains power as a frequency standard when adjusting a generator. I was worried about connecting my 'scope directly to 125 volts so I used a 12 volt out step down xmfr. The wave form was really distorted. That can happen because of saturation and remanence: the addition of a load on the low voltage side (like, a light bulb) will help greatly. The best small-signal audio transformers are potted in protective shells, in order to prevent strain on the magnetic laminations (which makes the magnetic core do those nonlinear things). I had no idea! But I should have. So if I had loaded the xmfr down some the wave form would have more closely resembled a pure sine wave. Because of the tube amp I bought I have got the bug a little to learn about audio stuff in general and tube stuff in particular. I ordered a B&K Precision 4100 function generator last night and when it gets here in a week or so I'll be hooking up the TEK 465B to an audio xmfr, and some others, to see how the waveform gets distorted with frequency, voltage, and waveform. Thanks, Eric |
#14
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What differentiates good audio xmfrs from bad ones?
On Friday, January 11, 2019 at 7:31:12 PM UTC-5, wrote:
On Fri, 11 Jan 2019 15:07:21 -0800 (PST), whit3rd wrote: On Friday, January 11, 2019 at 9:07:33 AM UTC-8, wrote: Some time back I wanted to use the mains power as a frequency standard when adjusting a generator. I was worried about connecting my 'scope directly to 125 volts so I used a 12 volt out step down xmfr. The wave form was really distorted. That can happen because of saturation and remanence: the addition of a load on the low voltage side (like, a light bulb) will help greatly. The best small-signal audio transformers are potted in protective shells, in order to prevent strain on the magnetic laminations (which makes the magnetic core do those nonlinear things). I had no idea! But I should have. So if I had loaded the xmfr down some the wave form would have more closely resembled a pure sine wave. Because of the tube amp I bought I have got the bug a little to learn about audio stuff in general and tube stuff in particular. I ordered a B&K Precision 4100 function generator last night and when it gets here in a week or so I'll be hooking up the TEK 465B to an audio xmfr, and some others, to see how the waveform gets distorted with frequency, voltage, and waveform. Thanks, Eric Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION". Only the primary voltage matters. But to a second order, if the transformer core is near saturation unloaded, when you load the secondary, the primary current and the primary resistance will in effect LOWER the primary voltage and reduce the core saturation. So considering the second order effect of primary winding resistance, yeah, loading a transformer _may_ reduce the distortion a little. mark |
#15
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What differentiates good audio xmfrs from bad ones?
wrote:
Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION". Only the primary voltage matters. ** And of course the input frequency - the two operate in reverse proportion. But to a second order, if the transformer core is near saturation unloaded, when you load the secondary, the primary current and the primary resistance will in effect LOWER the primary voltage and reduce the core saturation. ** True even when the applied primary voltage has no changed one tiny bit cos it is coming form the mains supply. So considering the second order effect of primary winding resistance, yeah, loading a transformer _may_ reduce the distortion a little. ** With a tube amplifier, the effect can be very marked - since the voltage applied to the primary drops when a load is applied to the secondary. The source impedance of a pentode or beam tube output stage is pretty high, triodes are somewhat better. Only those amplifiers with large NFB ratios avoid the issue. ...... Phil |
#16
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What differentiates good audio xmfrs from bad ones?
"
Has he got a web site - I could do with a good laugh. When unloaded, power transformers have lots of undesirable signal-handling features. ** More and worse drivel than the last lot. Maybe he has a minor in AP. AudioPhoolery. |
#17
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What differentiates good audio xmfrs from bad ones?
On Thursday, January 17, 2019 at 4:19:56 PM UTC-5, Phil Allison wrote:
wrote: Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION". Only the primary voltage matters. ** And of course the input frequency - the two operate in reverse proportion. But to a second order, if the transformer core is near saturation unloaded, when you load the secondary, the primary current and the primary resistance will in effect LOWER the primary voltage and reduce the core saturation. ** True even when the applied primary voltage has no changed one tiny bit cos it is coming form the mains supply. So considering the second order effect of primary winding resistance, yeah, loading a transformer _may_ reduce the distortion a little. ** With a tube amplifier, the effect can be very marked - since the voltage applied to the primary drops when a load is applied to the secondary. The source impedance of a pentode or beam tube output stage is pretty high, triodes are somewhat better. Only those amplifiers with large NFB ratios avoid the issue. ..... Phil yep good point... so it is very possible for a tube amp to have a bit less transformer saturation distortion when loaded compared to unloaded. i.e. the distortion can go DOWN when loaded. m |
#19
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What differentiates good audio xmfrs from bad ones?
Look165 wrote:
NO ! Saturation is a value coming from the magnetic core, yes. But H (magnetic strength) is directly proportional to the current, not to the voltage, at constant frequency. ** WRONG !!! The applied AC voltage and frequency are what matter. The load is very important. This leeds the core to the satruration point if too high. ** TOTAL ******** !!! A free transformer (without load) rarely comes to saturation. ** Try using an unloaded 120V supply transformer on 240V and see what happens. Others here have it right cos they know that they are talking about - you don't. **** off you bloody idiot. ..... Phil |
#20
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What differentiates good audio xmfrs from bad ones?
Or, you know, you COULD just look this **** up and learn
how it works. https://www.ieee.li/pdf/introduction_to_power_electronics/chapter_12.pdf -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
#21
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What differentiates good audio xmfrs from bad ones?
it is about current,
the so called magnetizing current that flows even with no load. the additional current that flows in the primary when the secondary is loaded IS CANCELED by the current in the secondary. So it is all about the current that flows only due to the primary inductance and not due to the load current. Yours is a common mis-conception. I'm glad to help you learn. m On Tuesday, January 22, 2019 at 1:13:17 PM UTC-5, Look165 wrote: NO ! Saturation is a value coming from the magnetic core, yes. But H (magnetic strength) is directly proportional to the current, not to the voltage, at constant frequency. The load is very important. This leeds the core to the satruration point if too high. A free transformer (without load) rarely comes to saturation. Eddy's current (we call it Foucault's current in France) are proportional to I^^2, like copper losses. a écrit le 22/01/2019 Ã* 18:39Â*: On Thursday, January 17, 2019 at 4:19:56 PM UTC-5, Phil Allison wrote: wrote: Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION". Only the primary voltage matters. ** And of course the input frequency - the two operate in reverse proportion. But to a second order, if the transformer core is near saturation unloaded, when you load the secondary, the primary current and the primary resistance will in effect LOWER the primary voltage and reduce the core saturation. ** True even when the applied primary voltage has no changed one tiny bit cos it is coming form the mains supply. So considering the second order effect of primary winding resistance, yeah, loading a transformer _may_ reduce the distortion a little. ** With a tube amplifier, the effect can be very marked - since the voltage applied to the primary drops when a load is applied to the secondary. The source impedance of a pentode or beam tube output stage is pretty high, triodes are somewhat better. Only those amplifiers with large NFB ratios avoid the issue. ..... Phil yep good point... so it is very possible for a tube amp to have a bit less transformer saturation distortion when loaded compared to unloaded. i.e. the distortion can go DOWN when loaded. m |
#22
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What differentiates good audio xmfrs from bad ones?
On Tuesday, January 22, 2019 at 10:13:17 AM UTC-8, Look165 wrote:
Saturation is a value coming from the magnetic core, yes. But H (magnetic strength) is directly proportional to the current... A free transformer (without load) rarely comes to saturation. NO, that's exactly backwards: a 'free' transformer with negligible secondary current DOES near-saturate. The primary current and secondary current are in the opposite direction, so load (secondary) current CANCELS the magnetization caused by the drive (primary) current. A lot of secondary current (high load current) removes the risk of saturation. |
#23
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What differentiates good audio xmfrs from bad ones?
whit3rd wrote:
NO, that's exactly backwards: a 'free' transformer with negligible secondary current DOES near-saturate. The primary current and secondary current are in the opposite direction, so load (secondary) current CANCELS the magnetization caused by the drive (primary) current. A lot of secondary current (high load current) removes the risk of saturation. ** While adding load current does not directly alter the magnetising current in the primary, it does reduce the effective AC supply voltage seen by the primary. This is due simply to the resistance of the primary winding - current flow produces a voltage drop which must be subtracted from the external supply voltage to accurately model what is going on. Eg, say the primary current due to load is 1 amp and the winding has 5 ohms resistance - then the effective voltage is 5 volts LESS than the AC supply. ..... Phil ..... Phil |
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