I've got a problem. In the system, the power amp is placed in the speakers. So, there is a long preamp cable from the master control to each power amp. Many distortions. Hums, strange guitar sound, etc.
At first I tried to solve it by putting balanced xlr instead of unbalanced RCA between every gear. It helps, but not all.
Apparently there is ground loop. This cannot be broken by balanced driver.
I wanted to use signal transformer, to break ground loop. Looking in the net, Jensens are expensive, because will use quite some of them. Tried the cheap Asian made, the result are not good. The highs are missing.
So wanted to DIY this like transformer. Anyone can help how to built the good one? What will be the core size, winding numbers, wire sizes etc?
Please dont direct me "just buy Jensen !"
At first I tried to solve it by putting balanced xlr instead of unbalanced RCA between every gear. It helps, but not all.
Apparently there is ground loop. This cannot be broken by balanced driver.
I wanted to use signal transformer, to break ground loop. Looking in the net, Jensens are expensive, because will use quite some of them. Tried the cheap Asian made, the result are not good. The highs are missing.
So wanted to DIY this like transformer. Anyone can help how to built the good one? What will be the core size, winding numbers, wire sizes etc?
Please dont direct me "just buy Jensen !"
You are wasting your time.
You only need a transformer at the receiving end.
Buy EDCOR.
http://www.edcorusa.com/sound/matchers/s2s10k_10k.htm
You only need a transformer at the receiving end.
Buy EDCOR.
http://www.edcorusa.com/sound/matchers/s2s10k_10k.htm
I used to design and build moving coil step up transformers in the 70's.
A good transformer is a carefully crafted series of tradeoffs. The reason that Jensen's are so widely known and respected is that they are very well designed and manufactured using very good materials, and overall the pricing is reasonable considering what you get.
As DJK so diplomatically pointed out, you don't need transformers at both ends. You can use just a line bridging/receiving transformer at the input side of your equipment, and drive it from either an active balanced or single ended source. With good transformer design, you can expect to get over 60-80 dB of common mode rejection at line frequencies.
The primary design goal for any transformer is to have as high an effective magnetizing inductance on the primary as possible (this minimizes the source impedance reuqired to drive it and sets the LF extension corner frequency and low frequency distortion), while at the same time minimizing the uncoupled leakage inductance between windings and lamination hysterisis effects, as the latter are the main mechanisms for HF roll off in the transformer. Typical lamination materials for high performance audio transformers are made of a moly permalloy alloy with very thin lamination thickness. I don't have the source catalogs any more that I used in the 70's; these are specialized items.
This is a juggling act; if you want really "good" group delay numbers in the low frequencies, you need to extend the LF response to below 2 Hz, but this makes getting good HF response more difficult. A reasonable minimum target for a good sounding transformer is at least 3-4 Hz -3 dB point on the bottom end, and 80-100 kHz on the top end.
My favorite line bridging/input transformer is the Jensen JT-6110K-B. This part has good bandwith driven from a 600 ohm source (-3 dB at 0.15 Hz and 120 kHz), and 130 dB of CMRR at 60 Hz.
Now, if you have very low impedance line driver circuits, you can "cut corners" a bit and use/design a line transformer for a low impedance drives; this makes things easier, as long as you have the necessary driver. I did this in one electronics crossover for which I desired balanced outputs with true isolation (non active balanced), and used the JT11SS. This part has much lower primary magnetizing inductance, and is really happiest being driven from a 75 ohm or lower impedance source (TRUE 75 ohm power bandwidth capability, not just LF impedance from feedback loop!). In this case, AD715 video buffers, which are in a high power SIP package (kind of like the gainclone chips) were used.
Distortion and bandwidth are dependent on source impedance- below 50 ohms is desirable. For this kind of transformer, the tradeoff is that lower primary inductance lowers the net leakage inductance, which improves the bandwidth in the top end substantially (to beyond 450 kHz). The tradeoff is needing a brute of a line driver. Can't really drive units like this well with DIP8 opamps. But for DIY, that shouldn't be a big deal...
~Jon
A good transformer is a carefully crafted series of tradeoffs. The reason that Jensen's are so widely known and respected is that they are very well designed and manufactured using very good materials, and overall the pricing is reasonable considering what you get.
As DJK so diplomatically pointed out, you don't need transformers at both ends. You can use just a line bridging/receiving transformer at the input side of your equipment, and drive it from either an active balanced or single ended source. With good transformer design, you can expect to get over 60-80 dB of common mode rejection at line frequencies.
The primary design goal for any transformer is to have as high an effective magnetizing inductance on the primary as possible (this minimizes the source impedance reuqired to drive it and sets the LF extension corner frequency and low frequency distortion), while at the same time minimizing the uncoupled leakage inductance between windings and lamination hysterisis effects, as the latter are the main mechanisms for HF roll off in the transformer. Typical lamination materials for high performance audio transformers are made of a moly permalloy alloy with very thin lamination thickness. I don't have the source catalogs any more that I used in the 70's; these are specialized items.
This is a juggling act; if you want really "good" group delay numbers in the low frequencies, you need to extend the LF response to below 2 Hz, but this makes getting good HF response more difficult. A reasonable minimum target for a good sounding transformer is at least 3-4 Hz -3 dB point on the bottom end, and 80-100 kHz on the top end.
My favorite line bridging/input transformer is the Jensen JT-6110K-B. This part has good bandwith driven from a 600 ohm source (-3 dB at 0.15 Hz and 120 kHz), and 130 dB of CMRR at 60 Hz.
Now, if you have very low impedance line driver circuits, you can "cut corners" a bit and use/design a line transformer for a low impedance drives; this makes things easier, as long as you have the necessary driver. I did this in one electronics crossover for which I desired balanced outputs with true isolation (non active balanced), and used the JT11SS. This part has much lower primary magnetizing inductance, and is really happiest being driven from a 75 ohm or lower impedance source (TRUE 75 ohm power bandwidth capability, not just LF impedance from feedback loop!). In this case, AD715 video buffers, which are in a high power SIP package (kind of like the gainclone chips) were used.
Distortion and bandwidth are dependent on source impedance- below 50 ohms is desirable. For this kind of transformer, the tradeoff is that lower primary inductance lowers the net leakage inductance, which improves the bandwidth in the top end substantially (to beyond 450 kHz). The tradeoff is needing a brute of a line driver. Can't really drive units like this well with DIP8 opamps. But for DIY, that shouldn't be a big deal...
~Jon
I think that having electronically balanced inputs or floating electronically balanced outputs and using shielded twisted pair wire is enough to solve the hum problem. If one side is unbalanced, impedance balancing resistors would be required. See Douglas Self site [search in google] to understand' impedance balancing' concept
" I think that having electronically balanced inputs or floating electronically balanced outputs and using shielded twisted pair wire is enough to solve the hum problem. If one side is unbalanced, impedance balancing resistors would be required. See Douglas Self site [search in google] to understand' impedance balancing' concept"
Well neither of you understand where the hum is coming from.
To eliminate the hum requires galvanic isolation, ie: a transformer.
Very good transformer tutorial at Jensen and Rowland sites.
Well neither of you understand where the hum is coming from.
To eliminate the hum requires galvanic isolation, ie: a transformer.
Very good transformer tutorial at Jensen and Rowland sites.
I think Eva's proposal would also be fine.
The hum due to ground loops is caused because normally we use
ground as the signal reference. Then we connect our system grounds
at different points to earth. As a result the ground at one end is different from the ground from the other end (typical some millivolts at 50Hz/60Hz), which means our signal references are different... !
If you would use a signal that is not related to ground/earth, but only the difference between two non grounded wires is carrying the information, and use symmetrical/differential input, then the 50Hz/60Hz currents in the ground loops will not directly add hum to signal.
But it only works if you do not mess up the signals with wrong ground connections again... So a twisted pair would not be bad, if you want to screen such twisted pair then you should connect the screen only at one end to ground other wise the different ground levels may cause a current in the screen, which might couple into the signal by induction...
You will only get lucky if you are exactly knowing what you are doing.
I think, a galvanic isolating transformer at the input is much easier to handle. It typically also works if nobody knows what he is doing.
This is not meant in a negative way.
In fact I love transformers, because I love rugged and forgiving systems.
There are also special cables available, which include a transformer
that does not isolate but simply adds exactly the difference of the ground signal also to the signal itself ... We call them "Mantelstromfilter" in Germany...
But they should be popular in various regions, not only Germay.
http://www.hifi-regler.de/hifi/mantelstromfilter.php?SID=aec44f172ecb9eef1a57ce63977f7adb
They work, but are not really high end...
Cheers
Markus
The hum due to ground loops is caused because normally we use
ground as the signal reference. Then we connect our system grounds
at different points to earth. As a result the ground at one end is different from the ground from the other end (typical some millivolts at 50Hz/60Hz), which means our signal references are different... !
If you would use a signal that is not related to ground/earth, but only the difference between two non grounded wires is carrying the information, and use symmetrical/differential input, then the 50Hz/60Hz currents in the ground loops will not directly add hum to signal.
But it only works if you do not mess up the signals with wrong ground connections again... So a twisted pair would not be bad, if you want to screen such twisted pair then you should connect the screen only at one end to ground other wise the different ground levels may cause a current in the screen, which might couple into the signal by induction...
You will only get lucky if you are exactly knowing what you are doing.
I think, a galvanic isolating transformer at the input is much easier to handle. It typically also works if nobody knows what he is doing.
This is not meant in a negative way.
In fact I love transformers, because I love rugged and forgiving systems.
There are also special cables available, which include a transformer
that does not isolate but simply adds exactly the difference of the ground signal also to the signal itself ... We call them "Mantelstromfilter" in Germany...
But they should be popular in various regions, not only Germay.
http://www.hifi-regler.de/hifi/mantelstromfilter.php?SID=aec44f172ecb9eef1a57ce63977f7adb
They work, but are not really high end...
Cheers
Markus
Balanced signal transmission is inmune to ground loops. With properly designed equipment the ground loop currents may even be left flowing freely through the screen of the twisted pair [connected at both ends] and nothing will happen. For better CMRR, impedance balancing is also required
Note: A 'Mantelstromfilter' appears to be nothing but a 'common mode filter'
Note: A 'Mantelstromfilter' appears to be nothing but a 'common mode filter'
Eva said:
You can also find a discussion in the A75 article(s) on
www.passdiy.com. This works quite well, but there's nothing
like a Jensen or comparable transformer for the finest in
noise rejection and avoiding ground loops.
Indeed there are similarities between the current compensated chokes of common mode filters and the transformer of a "Mantelstromfilter".
In both cases the voltage drop across both windings is the same.
In a common mode filter this simply gives a high impedance against HF
and helps to suppress line EMI.
In the "Mantelstromfilter" one can describe the behaviour as follows:
The winding which is inserted in the shield has a high impedance and by this i avoids high currents in the shielding.
It does not avoid that the voltage at the left ground point is different from the right ground point. But this difference which is across the first winding is beeing transformer into the signal wire. So it simply adds the error of the ground references to the signal, resulting in good error compensation.
In both cases the voltage drop across both windings is the same.
In a common mode filter this simply gives a high impedance against HF
and helps to suppress line EMI.
In the "Mantelstromfilter" one can describe the behaviour as follows:
The winding which is inserted in the shield has a high impedance and by this i avoids high currents in the shielding.
It does not avoid that the voltage at the left ground point is different from the right ground point. But this difference which is across the first winding is beeing transformer into the signal wire. So it simply adds the error of the ground references to the signal, resulting in good error compensation.
"For better CMRR, impedance balancing is also required"
OK, lets examine this.
I do an opamp receiver with a trim pot and null it to a CMRR of 100dB.
Now I hook it up to a real cable with real connectors and a real source.
A 1 ohm imbalance in the source impedance (can you say 'connectors', coupling caps?) will degrade the performance by about 60dB to only 40dB CMRR (assume typical 5K receiver impedance).
To illustrate how silly it is not to use a transformer I will use a 10K log volume control set to half volume as an unbalanced source (900 ohm source impedance).
With a transformer on the receiving end there will be about 90dB hum rejection, about 50dB better than active balanced.
The EDCOR stereo transformers cost $22.
That's in a nice metal box with jacks and everything.
What's it going to cost you to build your active circuit that isn't going to work as well?
Studio gear uses octal plug-in transformers. The ones I have list for $130 each. I was able to buy five used ones on eBay for $80 delivered. The $11 per channel ($22 stereo) EDCOR sound at least 95% as good, I really can't tell the difference (while I can measure the difference, I generally listen to my stereo rather than measure it).
A good set of transformers is a one time purchase, you buy/sell/trade the electronics, but you keep your transformers.
OK, lets examine this.
I do an opamp receiver with a trim pot and null it to a CMRR of 100dB.
Now I hook it up to a real cable with real connectors and a real source.
A 1 ohm imbalance in the source impedance (can you say 'connectors', coupling caps?) will degrade the performance by about 60dB to only 40dB CMRR (assume typical 5K receiver impedance).
To illustrate how silly it is not to use a transformer I will use a 10K log volume control set to half volume as an unbalanced source (900 ohm source impedance).
With a transformer on the receiving end there will be about 90dB hum rejection, about 50dB better than active balanced.
The EDCOR stereo transformers cost $22.
That's in a nice metal box with jacks and everything.
What's it going to cost you to build your active circuit that isn't going to work as well?
Studio gear uses octal plug-in transformers. The ones I have list for $130 each. I was able to buy five used ones on eBay for $80 delivered. The $11 per channel ($22 stereo) EDCOR sound at least 95% as good, I really can't tell the difference (while I can measure the difference, I generally listen to my stereo rather than measure it).
A good set of transformers is a one time purchase, you buy/sell/trade the electronics, but you keep your transformers.
Hi DJK!
...how does this happen...?
1 Ohms unbalance in driver+cable versus 5K receiver impedance would surely drop the CMRR, yes.
But due to my understanding I would have expected about 74 dB remaining, not only 40db...
40db is the CMRR which I would expect at 50 Ohms imbalance and
5k receiver impedance...
Additional question: Is there a certain reason for a low input impedance path against ground (5k) ?
I would tend to design a high input impedance against ground.
And if a certain input impedance is required to run the signal source in a optimized point, then I would put the required impedance between the differential inputs, but not against ground.
Where do I mess up the things?
I agree to your good results with a transformer.
And I would also prefer a good signal transformer more than
a "Mantelstromfilter", but I do not understand the poor experiences which seem to have happened to you with electronical balanced signals. .... might be better for me to learn this here, than experiencing the same under "unfortunate circumstances"
@Lumanauw
Back to the original question:
A self made signal transformer is difficult, if you want good quality.
Especially if you want to go to low frequencies (say 15Hz) and allow
high signal levels (say about 5Vrms) and at the same time want good high frequency behaviour up to 25kHz. Some years ago I was thinking about such a transformer and found that I did not easily gain satisfiying results as the designs which offer good low frequency behaviour are typically showing low resonance frequencies due the high number of turns and the related high winding capacitance.... Didn't look very promising to me and I had only standard ferrites on hand .... Since that I am just wondering how professional signal transformers are handling this, but I never investigated their details.
Just from theory I would prefer a core material with a high permeability and high saturation fluy density.... may be some of the amorphous metals of the VAC transformers which are used for ADSL applications in telecommunications... just an idea, not investigated..
Bye
Markus
...how does this happen...?
1 Ohms unbalance in driver+cable versus 5K receiver impedance would surely drop the CMRR, yes.
But due to my understanding I would have expected about 74 dB remaining, not only 40db...
40db is the CMRR which I would expect at 50 Ohms imbalance and
5k receiver impedance...
Additional question: Is there a certain reason for a low input impedance path against ground (5k) ?
I would tend to design a high input impedance against ground.
And if a certain input impedance is required to run the signal source in a optimized point, then I would put the required impedance between the differential inputs, but not against ground.
Where do I mess up the things?
I agree to your good results with a transformer.
And I would also prefer a good signal transformer more than
a "Mantelstromfilter", but I do not understand the poor experiences which seem to have happened to you with electronical balanced signals. .... might be better for me to learn this here, than experiencing the same under "unfortunate circumstances"
@Lumanauw
Back to the original question:
A self made signal transformer is difficult, if you want good quality.
Especially if you want to go to low frequencies (say 15Hz) and allow
high signal levels (say about 5Vrms) and at the same time want good high frequency behaviour up to 25kHz. Some years ago I was thinking about such a transformer and found that I did not easily gain satisfiying results as the designs which offer good low frequency behaviour are typically showing low resonance frequencies due the high number of turns and the related high winding capacitance.... Didn't look very promising to me and I had only standard ferrites on hand .... Since that I am just wondering how professional signal transformers are handling this, but I never investigated their details.
Just from theory I would prefer a core material with a high permeability and high saturation fluy density.... may be some of the amorphous metals of the VAC transformers which are used for ADSL applications in telecommunications... just an idea, not investigated..
Bye
Markus
Still laughing
My recommendation went to Texas and I'm still laughing.
On a diy site where people make their amps, a recommendation to open the amp and disconnect the earth wire goes to Texas!!!
Hahahahaha!!!
Connect two equipments to different mains plugs distant some meters from each other and both earthed and in many cases... ground loop.
BTW if the earth is not good (as in too many cases), it creates more problems than it solves.
IMHO and whatever.
My recommendation went to Texas and I'm still laughing.
On a diy site where people make their amps, a recommendation to open the amp and disconnect the earth wire goes to Texas!!!
Hahahahaha!!!
Connect two equipments to different mains plugs distant some meters from each other and both earthed and in many cases... ground loop.
BTW if the earth is not good (as in too many cases), it creates more problems than it solves.
IMHO and whatever.
Moving this to Texas is like hiding the cumbersome reality : 50% people disconnect their earth in all but one point of the signal chain to break ground loops
The other 50% of people actually does not even have any earth to connect their equipment to!!!. For example, in Spain it's very unlikely to find earth connections in buildings older than 15 years or in live audio performances and only a very small amount of sockets provide earth in most modern buildings
Also, in live audio most people intentionally disconnect earth from some equipment or remove earth-leakage circuit breakers because they don't like to see those earth-leakage circuit breakers tripping in the midle of a live performance
You have to feel the embarrasement when your lights or your sound suddenly disappear to understand this, but anyway I like the case of the mixing console earthed for obvious reasons... and most times you dont have any earth connection to begin with!!!
The other 50% of people actually does not even have any earth to connect their equipment to!!!. For example, in Spain it's very unlikely to find earth connections in buildings older than 15 years or in live audio performances and only a very small amount of sockets provide earth in most modern buildings
Also, in live audio most people intentionally disconnect earth from some equipment or remove earth-leakage circuit breakers because they don't like to see those earth-leakage circuit breakers tripping in the midle of a live performance
You have to feel the embarrasement when your lights or your sound suddenly disappear to understand this, but anyway I like the case of the mixing console earthed for obvious reasons... and most times you dont have any earth connection to begin with!!!
...yes, hiding reality is not good...
..would be better to promote how to make it safe and audiophile...
There is a big gap between reality and how it should be.
I would prefer to generally establish PSU which are providing
safe isolation even without earthing and give the choice
to earth or not!
Bye
Markus
..would be better to promote how to make it safe and audiophile...
There is a big gap between reality and how it should be.
I would prefer to generally establish PSU which are providing
safe isolation even without earthing and give the choice
to earth or not!
Bye
Markus
...even in Germany I recently found power plugs which did
not just have no earth connection....
You can find worse power plugs:
If no earth wires are not installed in the walls, then people tend to connect the neutral to the ground terminal of the plug.
Well, sometimes they mix up the wires and the power plug shows 230V at the node which should provide safe earth connection.... really no fun..
not just have no earth connection....
You can find worse power plugs:
If no earth wires are not installed in the walls, then people tend to connect the neutral to the ground terminal of the plug.
Well, sometimes they mix up the wires and the power plug shows 230V at the node which should provide safe earth connection.... really no fun..
"Because of normal tolerances in the resistors and capacitors which usually determine a driver's output impedance, imbalances up to about 20 ohms should be routinely expected. This defines a 'real-world' source."
Bill Whitlock, Jensen-Transformers
(AES Preprint)
low priced pro gear use 5% parts in these type circuits:
http://sound.westhost.com/p51-f1.gif
I've seen this in a $20,000+ TAC Scorpion, and an expensive Allen&Heath:
http://sound.westhost.com/p87-f4.gif
A typical receiver might be a NE5532 with four 10K 1% resistors (I've seen 5% used). The minimum common mode input impedance is only 30K (granted, most are better. It just depends on the Beta of the input pair). 5K common mode input impedance looks very real here. The 1% resistors only give 40dB CMRR anyway.
With the first example as a driver and 5% parts, a 20 ohm mis-match would be in spec for the parts. That works out to no better than 48dB with a 5K receiver.
The chart I was using showed a 60dB degradation in CMRR from only 1 ohm mis-match but they were starting from an ideal 134dB CMRR where I was assuming a more realistic 100dB. I think I should have subtracted the 60dB from the 134dB number for my 1 ohm example though, not the 100dB.
In reality I have never found WIRE that was twisted better than 70dB, most is closer to 60dB.
Bill Whitlock, Jensen-Transformers
(AES Preprint)
low priced pro gear use 5% parts in these type circuits:
http://sound.westhost.com/p51-f1.gif
I've seen this in a $20,000+ TAC Scorpion, and an expensive Allen&Heath:
http://sound.westhost.com/p87-f4.gif
A typical receiver might be a NE5532 with four 10K 1% resistors (I've seen 5% used). The minimum common mode input impedance is only 30K (granted, most are better. It just depends on the Beta of the input pair). 5K common mode input impedance looks very real here. The 1% resistors only give 40dB CMRR anyway.
With the first example as a driver and 5% parts, a 20 ohm mis-match would be in spec for the parts. That works out to no better than 48dB with a 5K receiver.
The chart I was using showed a 60dB degradation in CMRR from only 1 ohm mis-match but they were starting from an ideal 134dB CMRR where I was assuming a more realistic 100dB. I think I should have subtracted the 60dB from the 134dB number for my 1 ohm example though, not the 100dB.
In reality I have never found WIRE that was twisted better than 70dB, most is closer to 60dB.
Hi,
Hmmm...I can understand why Al (Pinkmouse) decided to do that...
Yet the electrical wiring system as applied in houses in continental Europe is not the same in the U.K. nor is it in the U.S of A.
Anyway...
Quick question: how many of you living in continental Europe have outlets in your living rooms of which you're certain they're actually earthed?
How many of the audio apparatus you buy in the shops have a three pronged plug?
One thing I noticed, when it's imported from the U.K. or the U.S.A. it usually does have an earthed chassis but other than that?
Another quick question: how unsafe is it for audio gear not to have the chassis earthed?
Last question: does anyone have a clue where to find directions on the internet for safety regulations regarding domestic appliances for useage within the EU?
Cheers,
Hmmm...I can understand why Al (Pinkmouse) decided to do that...
Yet the electrical wiring system as applied in houses in continental Europe is not the same in the U.K. nor is it in the U.S of A.
Anyway...
Quick question: how many of you living in continental Europe have outlets in your living rooms of which you're certain they're actually earthed?
How many of the audio apparatus you buy in the shops have a three pronged plug?
One thing I noticed, when it's imported from the U.K. or the U.S.A. it usually does have an earthed chassis but other than that?
Another quick question: how unsafe is it for audio gear not to have the chassis earthed?
Last question: does anyone have a clue where to find directions on the internet for safety regulations regarding domestic appliances for useage within the EU?
Cheers,
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