| lumanauw |
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 !" |
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| joan2 |
hi,
tell me what materials (core size/types) magnet wires are available at your end...
likewise, you desired input/output impedance, or the signal levels that your diy traffo will see, then we can try....
tony |
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| lumanauw |
Hi, DJK,
DIY line transformer will not give satisfactory result? Is it have to use certain core material? |
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| JonMarsh |
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 |
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| Eva |
| 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 |
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| djk |
" 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. |
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| ChocoHolic |
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.
:D
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/mant...a57ce63977f7adb
They work, but are not really high end...
:rolleyes:
Cheers
Markus |
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| Eva |
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' |
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| Nelson Pass |
| quote: | Originally posted by Eva
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 |
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. |
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| ChocoHolic |
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. |
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| lumanauw |
Mantelstormfilter is quite different than isolation transformer. It does not break ground loops, but seems can handle ground voltage difference, due to inductance.
Where can I see sites with calculation for DIY line transformer? |
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| djk |
"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. |
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| ChocoHolic |
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" :att'n:
@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 |
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| carlosfm |
My recommendation went to Texas and I'm still laughing.:D
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. :idea:
BTW if the earth is not good (as in too many cases), it creates more problems than it solves.
IMHO and whatever. |
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| Eva |
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!!! |
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| ChocoHolic |
...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 |
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| ChocoHolic |
...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.. :mad: :mad: |
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| djk |
"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. |
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| fdegrove |
Hi,
| quote: | | On a diy site where people make their amps, a recommendation to open the amp and disconnect the earth wire goes to Texas!!! |
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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| Magura |
| quote: | Originally posted by fdegrove
Hi,
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,;) |
If you hold an issue of elektor you can find such a list of directions.
Magura:) |
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| fdegrove |
Hi,
| quote: | | If you hold an issue of elektor you can find such a list of directions. |
True....
I stopped buying that decades ago already...their tube stuff made my toes curl too much, you see.:D
Thanks M.,;) |
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| Magura |
| quote: | Originally posted by fdegrove
Hi,
True....
I stopped buying that decades ago already...their tube stuff made my toes curl too much, you see.:D
Thanks M.,;) |
Pretty much anything you find in elektor makes my toes curl....a LED torch anyone?? ;)
Magura:) |
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| imix500 |
| Having a good central ac power source is always a good place to start. I can't tell you guys how many people plug in interconnected equipment into whatever outlets they can find having God knows what ground potentials and wonder why they have problems? Not implying anything lumanauw, but it happens. For instance- at a very well known theatrical sound shop I work for here in NY, much of the gear is self-powered and with a central distro, there are rarely any ground loop problems with the rigs. Every peice of equipment with a ground lug is appropriately plugged in, and all signal interconnects are grounded all the way through. Of course ground loops do happen for often just plain wierd reasons and we always carry iso transformers just in case. But in theory if everything is at the same ground potential and the equipment is behaving, there shouldn't (operative word here) be problems. |
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| Eva |
In Spain in modern buildings you usually find earthed outlets only in kitchens and bathrooms. In living rooms and nearly all other rooms outlets usually have no earth connection
Most consumer electronics come without earth connection, examples : TV sets, CD/DVD/VCR players, compact stereos, audio amplifiers and most hi-fi equipment
Nearly all small home appliances come without earth connection [only big ones like washing machines, fridges, dishwashers or microwave ovens provide it]
Some PA equipment comes without earth connection, examples : Mixing consoles, equalizers, reverb modules, compressors/expanders, small amplifiers, etc...
In power amplifiers, big toroidal transformers are the part to blame since they are the main cause for ground loops and 'humm' due to their excessive capacitance from primaries to secondaries. They usually show too high capacitive leakage even if they pass the 3750V isolation test. [This is the reason why I hate toroidal mains transformers, SMPS tend to have much lower leakages and capacitances] |
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| lumanauw |
| If the whole system is in the living room, it would not be a big problem to have central AC power line for all gears. But I'm dealing here is in big church hall. I cannot put central AC line, too many cables. So just plug every equipment to the nearest AC plug. |
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| imix500 |
| Yeah, chances are that's what's causing at least some of the problem. Not enough current on one circuit to power the whole rig? It really would be worth your while to run power fom a central source via extention cords if possible. If you must draw from several different outlets, some good quality iso transformers should do the trick. And if your runs are over 10 feet or so from the board to the speakers, you really should be sending a balanced signal if the speakers have a balanced input. Unbalaced signals can become unreliable and noisy after a short distance. |
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| joan2 |
| i thought the thread starter wanted to diy his own input transformer!!! |
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| carlosfm |
| quote: | Originally posted by joan2
i thought the thread starter wanted to diy his own input transformer!!! |
:D
Well... he may not need to do that.
BTW, you can find those things for cheap (5~6 Euros) from car audio guys and give it a try. |
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| li_gangyi |
yeah...they're called engine noise removers or something like that...though I wouldn't really understand why a running rngine and alternator can cause such problems?? I'm not really sure if they are transformers though...an example here...
 |
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| carlosfm |
I have one from my PC in another room to my system.
It cost me 6 Euros.
Inside, it has two little trafos.:D |
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| lumanauw |
Hi, Joan,
| quote: | | i thought the thread starter wanted to diy his own input transformer!!! |
You are right. I WANTED to DIY line transformer. The cheap line transformer for car audio is exactly what I'm using right now, with bad sound. The highs are missing.
Looking at the net, Jensens are too expensive, so I wanted to DIY. Could you help me with the formulas? I can buy any size magnet wire and any size power transformer core here.
Someone said something about capacitance in line transformer. Is this the difficult thing to handle if we go DIY? Needs certain core material or wire material? |
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| carlosfm |
| quote: | Originally posted by lumanauw
Hi, Joan,
You are right. I WANTED to DIY line transformer. The cheap line transformer for car audio is exactly what I'm using right now, with bad sound. The highs are missing. |
You had bad luck, try another one, they are cheap.
My brother has one for car audio from the DVD player to the amp, because of problems (noise) with cable TV.
Believe me, no difference at all with or without it, and the noise is gone.
It may be pure luck, a cheap one that's good... |
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| lumanauw |
I wanted to "know-how" making audio transformer, especially with solid state output. After I am able to do line transformer, the next thing I wanted to DIY is the CT inductance for ZEN V-7T.
It's because here I cannot find anything Hifi, just that car audio isolator. |
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| ChocoHolic |
Hi lumanauw!
If you have access to ferrites, then you do not need to worry about the
resonance frequency of the ferrite material itself. Their resonance frequencies usually are high enough. Drawback is that their saturation flux density is typically somewhere between 300mT and 400mT...
The thing which may cause issues is the distributed winding capacitance withing each winding itself. This can be kept low if you
keep the number of turns as low as possible.
If we look at the formula for the required number of turns:
N = U / (4.44 x f x B x Ae)
Then we see that we should look for a core shape, which provides large cross section area. This pushes towards RM-shapes, EP-shapes, PM-shapes...., less fortunate are traditional E-shapes...
Furtheron I am afraid of the capacitance within one winding.
Less critical should be the coupling capacity between the two windings (I think.... please everybody correct if wrong).
Also isolation requirements are low.
So I would try to wind secondary and primary with paralleled wires in order to achieve a good coupling. Make sure that you connect primary and secondary in the same way to your connectors.
I.e. start of winding to signal and end of winding to ground.
Other wise you will invers the signal and (much worse) if not connected in same way then you should also be afraid of the coupling capacitance between primary and secondary...!
Which cores do you have on hand or can get?
Which driving impedance do you have? Which levels?
Probably normal line signal?
So the inductive impedance of the XFR should not drop below
10kOhms even at the lowest desired signal frequency.
Also we should be able to handle at least 1Vrms at 40Hz without saturation...., right?
Try to find out and tell wich cores you have....
May be I can go for a rough design proposal and explain my thoughts.
Starting with this, then some more trial and error + good luck
may bring success.
Good luck
Markus |
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| joan2 |
now there is two of us willing to help....just email me info as markus said and we'll continue from there...
we can continue this thru emails.... |
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| lumanauw |
Hi, all,
Thanks for the help. Tomorrow I will go to local electronic market here and find out what ferrites I can buy here. I have used EE19 (4.5x4.75mm), EE20(5.6x5.6mm), EE25(6.25x6.25mm). Also I can buy EE core without label but the core size is(4.95x9.95mm)
Those are small ferrites. Big Ae ferrite I can buy those used for flyback for TV. I also can buy toroidal ferrites in various range of sizes, but I cannot wind so much winding in toroids. Maybe we'll stick to EE or EI cores.
Any idea what Ae will be needed for line transformer? Will it about the size of EE20 or will size about TV flyback transformer?
First question. Will ferrites better than metal core? What is the one in Jensen core, and also what is the one inside the cheap car audio isolator? Tube amps usually use special metal instead of ferrites?
| quote: | | Furtheron I am afraid of the capacitance within one winding |
Is this about special winding techniques?| quote: | | So I would try to wind secondary and primary with paralleled wires in order to achieve a good coupling. |
OK, understand that.| quote: | | Probably normal line signal? |
Yes, normal signal. Like the one comes out from CD player, or DVD player. But I wanted it universal, also for the ones that comes out from preamps, voltage maybe higher than CD player.| quote: | | So the inductive impedance of the XFR should not drop below |
OK, understand that.| quote: | | Also we should be able to handle at least 1Vrms at 40Hz without saturation...., right? |
Is this standard requirement? I will follow standard.
Another question. What will the magnetwire size? 0.1mm is enough? Can use ordinary magnetwire or needs special properties? |
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| lumanauw |
Just calculating a little.
The Faraday law for determining N for certain core size.
N=Vx1x10(exp8)/(4.44xAexBxf).
Chocoholic, there is 1x10exp(8) in the equation, right? Ae in cm2, B in Gauss, f in Hz.
If the ferrite size is 8x8mm, with B=3000gauss, f=20hz, V=1V, then the winding number N=587turns.
But I dont see any Kohm here. Usually line transformer spec like Jensen's is 10k:10k.
The equation for knowing impedance from L is R=wL=2xpixfxL
To get 10K in 20hz the L must be 79Henry?
To get 1H it is very big windings. We must get 79H?
Or the specs in the Jensens are 10k:10k in what Hz? Is it in 20hz? |
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| lumanauw |
Curious, I went to Jensen' website. From the JT11P1 pdf, and from the faq, I found these:
-The core material is "Custom Nickel/Molybdenum/Iron Alloy". If we use Ferrites (easier for me to get here) will it shows quite the same behavior?
- input impedance 13kohm at 1khz, DC resistance 1.45kohm
In the 11p1.pdf, I dont see any voltage figures. All in dB. How to translate this dB figure into how many voltage RMS the transformer can handle? |
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| joan2 |
hi,
material quoted by jensen is not available as a retail item anywhere...
your best bet is the silicon steel which is widely avialable....
you may not approach performance of jensens this way, but it can be worthwile to try... |
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| Steve Eddy |
| quote: | Originally posted by lumanauw
Curious, I went to Jensen' website. From the JT11P1 pdf, and from the faq, I found these:
-The core material is "Custom Nickel/Molybdenum/Iron Alloy". If we use Ferrites (easier for me to get here) will it shows quite the same behavior? |
I don't think ferrite will work well at all at audio frequencies.
| quote: | | In the 11p1.pdf, I dont see any voltage figures. All in dB. How to translate this dB figure into how many voltage RMS the transformer can handle? |
Most of the figures are in dBu, which is decibels referenced to 0.7746 volts.
To figure out RMS voltage, take the dBu figure and divide by 20. Then take 10 to the power of the result. Finally, multiply by 0.7746.
For example, the 11P-1 is rated for a maximum input of 20dBu at 20 Hz.
So, 20/20 = 1. 101 is 10. 10 x 0.7746 is 7.746 volts RMS.
By the way, CineMag makes transformers which as near as I can tell are every bit as good as Jensen but for significantly less.
Check 'em out.
se |
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| ChocoHolic |
Hi Lumanauw!
Yes, if caculate with cm^2 and Gauss..... , then you will need
the factor 10exp8....
I usually work with SI units m, m^2, Tesla instead of Gauss etc...,
so I do not need unit related multiplication factors.
(Please note 4.44 is derived not from units but from
pi x (square root of 2)....)
I can confirm your calculations and you can easily see, why I stopped my efforts when I wanted to go for larger signals below 20Hz.....
My proposal of 1V/40Hz were absolut minimum requirements, for a
suitable transformer.
If you wish some db headroom against standard 0db levels, as discussed above, and lower frequencies then you will need more turns.... or a bigger core....
I agree that ferrite is definitely not a fortunate choice for this.
Especially if you pick standard power materials as N27 or similar, then you get comparably low permeabilities and with this especially at low frequencies the XFR coupling is coming low and inductance also.... If you pick high perm ferrites then you must not press them
very much... If you press them, their permeability drops... Already normal mechanical work, metal clamps or glue can result in poor results... Also take care about the remaining gap, already a 50µm gap brings down the inductance if you use high perms...
May be the proposal of JOAN2 is good. Silicone Steel is easily available and offers high saturation. ...but losses at higher frequencies are poor... If you try this, I would propose to look for a core set which offers very thin blades.
Wire size of 0.1mm is easily sufficient, you could go even for thinner wires, but below 0.1mm it is difficult handle!!!
Also isolation properties are getting less at small diameters.
Bye
Markus |
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| tiroth |
| quote: | | By the way, CineMag makes transformers which as near as I can tell are every bit as good as Jensen but for significantly less. |
Does this mean you have gotten your samples Steve? Do tell! |
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| lumanauw |
Maybe we should use ordinary sheet metal core instead of ferrites, like SE wrote why. Here I can only buy the ordinary power transformer core. The ones for audio transformer (here called H14) is very rare.
Mr. Pass himself uses ordinary power transformer for load in his ZEN V7-T, not using special transformer with special material. And he reported good results.
First step. How can I know the number of windings or inductance needed? JT11P1 can handle 7.7Vrms at 20hz. Is this hard to achieve? From the photo the completed xformer is not so big.
If DIY resulting bigger than Jensen, its OK with me, the sound quality is first, size doesn't matter.
There is no connection between Faraday equation and final xformer impedance? Faraday is for knowing the number of turns for certain xformer working condition. No impedance figure here.
Impedance figure is the bridge for connecting this device to other device. Impedance is known by manual measurement? So what if the number of turns from Faraday equation differs with impedance measurement?
Here I have RLC meter. How to measure "impedance"? R+L? |
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| Steve Eddy |
| quote: | Originally posted by tiroth
Does this mean you have gotten your samples Steve? Do tell! |
Not yet. I said "near as I can tell" based on what I've seen of them and their legacy. Right now I'm up to my eyeballs working on some cables so won't be getting around to getting anything from CineMag for a while yet. Probably a few more weeks.
se |
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| Nelson Pass |
One advantage of ferrite cores is that they don't suffer
from Eddy currents. ;)
sorry, couldn't resist. |
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| Steve Eddy |
| quote: | Originally posted by Nelson Pass
One advantage of ferrite cores is that they don't suffer
from Eddy currents. ;)
sorry, couldn't resist. |
I gotcher ferrite cores right heah, pal! :grabcrotch:
Sorry, couldn't Pass that up. :)
se |
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| ChocoHolic |
The required numbers of turns are depending on the allowed flux density, the core cross section area and the time voltage product.
This is independed from the inductance.
The inductance depend from the permeability of the material.
The inductance then gives the inductive part of the transformers impedance. If you look at the transformer itself, then you can model the losses by two resistors. One in series with the inductance, this models the copper resistance of the wire. I would expect that we can neglect this compared to the required inductive portion.
The second resistor is in parallel with the inductance and models the losses in the core. Unfortunately these losses are depending very much on the frequency. Well in ferrites they would be quite low, as eddy currents in the ferrites are low in the audio frequency range... as Nelson Pass already stated.... also hysteresis losses are low in ferrites...
If we go for ordinary 50Hz power cores the frequency depending losses will be comparably high. I have no idea, if it would still work.
Please note that these loss models are very much simplified.
In fact the core losses do not exactly increase with the square of the applied voltage like the resistor would.
Measuring the inductance should work with a standard LCR meter.
The copper resistance can be measured with a standard Rdc measurement. The resistance which the RCL meter will display is giving a mixture of both resistors and will probably depend very much on the measuring frequency of the LCR meter.
Such line transformer is n interesting thing, but you may need several steps of trial and error.
Ans yes.... 7.7Vrms at 20hz as the JT11P1 can handle is difficult to meet.
@DJK:
Thanks for pointing out that you assumed much higher imbalance than 1 Ohm.
I agree, if we pick a simple topology with 1/2 NE 5532 then it will be hard to achieve higher common mode rejection than 40db.
But already 40 db is a step forward.
The best which I could achieve (ten years back ;) ) with a simple , but carefully balanced circuit was 56 db at 50Hz.
....do you have also experience with that instrumentation amplifiers which use 3 OP amps to set up one amplifier with high common mode rejection? I never tried them....
Bye
Markus |
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| lumanauw |
Problem no.1 is not solved yet. What core should we use? The choice is 2, one is ferrites, two is ordinary sheet metal power transformer core. | quote: | | One advantage of ferrite cores is that they don't suffer from Eddy currents. |
Is this about ferrites in general, or Mr.Pass is suggesting to use Ferrites for DIY line transformer?
SE and a peek at Jensen suggested that we do not use Ferrites. This is confusing. |
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| tiroth |
| It seems like "high quality" cores are all made from high permeability materials. I wonder if this is because with smaller tranformers, less turns, it is easier to control undesirables like leakage inductance, interwinding capacitance, etc. |
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| joan2 |
| for diy, use whatever is available to you.... |
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| ChocoHolic |
I think for a line signal XFR the high perm materials will be the better choice. But I would not say that high perm would generally be the right choice for high quality. ....especially not if you look to power applications....
@Lumanauw:
Eddy currents do also exist in ferrites, but at audio frequencies they are very low.
For your decision:
-Your stores do not offer high perm ferrites in the required size. The larger ferrites which you could get are for flybacks and will provide lower permeability. In fact you would face a hard battle to achieve the required inductance without real exzessive number of turns.
-You could try ordinary sheet metals.
-I had a look to my assortment and found two torroids of an amorphous metal manufactured by the VAC.
They provide high perm, high flux, low losses. But winding will be difficult as they are torroids. Please refer to the link.
I have two cores of the type W376 on hand.
In order to wind several hundred turns on this core you could
first wind the required wire length to a thin wooden stick.
I.e. 8mm diameter 30 cm length..... and then rewind from this primitive "magazine" to the torroid.
For the proposed torroids I would start first trials with about 500 turns. This will allow 2.5V signal at 20Hz and provide an inductance of about 5H (which is still very low). If you manage higher number of turns ..., fine....
I am also attaching an image of that cores.
You can send me your adress to methusalix.munich@gmx.de and I will send the two cores.
www.vacuumschmelze.de/dbw/public_va...ame=Pk003_d.PDF
Bye
Markus |
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| lumanauw |
Hi, ChocoHolic,
Thanks for the offering. I take "high permeability" material is a material with few windings already got high inductance?
Which have higher permeability, ferrites or sheet metal core?
In the local shop here I can find not-ordinary materials, like kool-U from mag-inc, various metal (dont know what inside, but metal), but they are all in toroidal shape. I've tried winding on small toroid, very-very difficult. So, in this project, E cores are my option. |
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| ChocoHolic |
Hi Lumanauw,
Ferrites for power applications typically show rel. permeability between 2000 and 3000 and max flux density between 0.3T...0.45T.
High perm ferrites show typically 10 000 ...20 000, but after real life handling (glueing, pressure etc, some remaining gap if a two core pieces have to be combined...) you can be lucky if you get effective values close to 10 000. Max flux density is typically lower than for power ferrites, about 0.25T...0.4T ...depending on material and temperature.
The material of my torroids is Vitroperm 500F (nano cristalline material from VAC) and offers a permeability around 20 000. Max flux densitity is around 1.1T.
Ordinary sheet metals show rel perms in the range of 3000 and 5000, I think.
Max flux density is around 1T.
I have heard of materials with rel permeabilities up to 100 000, but
I have no idea about the name or the manufacturer and also not if all the other material properties would work for a line XFR.
I am not aware of high perm materials, which could serve our purpose just with a few tunrs. You would need extremly high permeability combined with extremly high max flux density to achiev this.
.... you will probably have to wind a lot of turns.....
Often it is not showed, which rel. permeability the material has, but the AL value of the core.
L = AL x N^2
Good Luck and looking forward to your results
Markus |
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| lumanauw |
Hi, ChocoHolic,
Thanks for the info. So power ferrites and sheet metal cores doesnt differ so much in their permeability? Meaning using whichever will result in quite the same number of turns?
The first step I will take is hunt for available E cores. I will buy power ferrites and sheet metal cores in a couple of days. When I get the cores, I will report the size, to determine the winding number.
Problem no.2. The diameter of wires. What size will be in this project? It is only for line signal. I think about 0.1mm. Is it too big? |
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| ChocoHolic |
Hi!
....back again....
Sheet metals allow higher flux densities, so you will need less turns here.
0.1mm is probably thicker than what you require.
To thick? Well, not optimzed. Smaller would probably be better.
But thinner wires are difficult to handle (without good equipment).
You may face broken wires...
Bye
Markus |
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| ChocoHolic |
| ....but you may be right, if the required number of turns for the correct inductance is very high, then the saturation will not be the limiting factor..... |
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