Field Coils for Audio Systems

[Zeotrope]

The problem is if you choose a very high current, distortions increase rapidly. the field coil heats up the voice coil, the achievable volume with low distortion decreases. can sound very good at low levels but horrible at high levels.

Would a high voltage field coil be beneficial in this case, since current is lower? Eg, RCA made a 115V and 13V field coil driver, the voice coil was identical. The high voltage draws 170mA, whereas the low voltage draws 1.7A.

 

[DasguteOhr]

Would a high voltage field coil be beneficial in this case, since current is lower? Eg, RCA made a 115V and 13V field coil driver, the voice coil was identical. The high voltage draws 170mA, whereas the low voltage draws 1.7A.

Not easy to tell
Power=voltage × current
But that's only half the truth, you would have to know the wire thickness with which the field coil is wound. whether it is running at the limit of its capacity or not. It is best to measure with an infrared thermometer how much the voice coil heats up over hours without signal

 

[Atmasphere]

I suspect, once again, that if the power supply behaves as a constant current source that would do the best job, since the current is what seems to be important for the field coil. I suspect the Tungars, as they heat up, slowly increase their output voltage, which helps keep the current at the right spot as the FC heats up.

If you think about it, it can only be something like this that might account for the preference since any power supply that does not hum has to have a fair amount of capacitance if not regulated. If that is the case the rectifiers won't affect the sound at all.

 

[Zeotrope]

I went from a lab PSU (Lambda) to a solid state PSU from WVL. The difference was not even close. Adding vibration isolation and AC and ground filtering made another huge difference.
Everything you can do to rectify and filter the DC will be noticeable.
I’m not even referring to current stability, which does seem to be the preferred choice for the best sound.

 

[Atmasphere]

I went from a lab PSU (Lambda) to a solid state PSU from WVL. The difference was not even close. Adding vibration isolation and AC and ground filtering made another huge difference.
Everything you can do to rectify and filter the DC will be noticeable.
I’m not even referring to current stability, which does seem to be the preferred choice for the best sound.

Was the Lambda able to do constant current? That's very different from regulated voltage!

 

[Zeotrope]

Was the Lambda able to do constant current? That's very different from regulated voltage!

No, it's very rare for a lab supply to offer true constant current. Most lab supplies will not automatically adjust voltage to maintain current as resistance varies, even though they have a "constant current" function!
My WVL PSU is constant current for the 12V supply but constant voltage for the 115V supply. The latter drivers the midrange, and that's where I noticed the biggest improvement -- so it's not even due to the constant current source!

 

[Atmasphere]

No, it's very rare for a lab supply to offer true constant current. Most lab supplies will not automatically adjust voltage to maintain current as resistance varies, even though they have a "constant current" function!
My WVL PSU is constant current for the 12V supply but constant voltage for the 115V supply. The latter drivers the midrange, and that's where I noticed the biggest improvement -- so it's not even due to the constant current source!

OK- it sounds like you've not tried constant current then.

I really think its worth a shot! I'll be setting that up on my own field coils but it will have to wait until I'm back in town.

 

[Zeotrope]

OK- it sounds like you've not tried constant current then.

I really think its worth a shot! I'll be setting that up on my own field coils but it will have to wait until I'm back in town.

I am using CC on the low voltage coils.
I haven't tried it on the high voltage - it's difficult to find a PSU that does CC at ~100-115V. Wolf also felt that the benefit would be greater for low voltage.

 

[DasguteOhr]

I am using CC on the low voltage coils.
I haven't tried it on the high voltage - it's difficult to find a PSU that does CC at ~100-115V. Wolf also felt that the benefit would be greater for low voltage.

For test maybe good enough

https://www.amazon.de/Labornetzteil-4-stelliger-LED-Anzeige-Gebereinstellknopf-Ausgangsschalter/dp/B0B11H2LJQ/ref=asc_df_B0B11H2LJQ/?tag=googshopde-21&linkCode=df0&hvadid=604401811108&hvpos=&hvnetw=g&hvrand=2896408204627070735&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9068137&hvtargid=pla-1730837103551&th=1

 

[Zeotrope]

For test maybe good enough

https://www.amazon.de/Labornetzteil-4-stelliger-LED-Anzeige-Gebereinstellknopf-Ausgangsschalter/dp/B0B11H2LJQ/ref=asc_df_B0B11H2LJQ/?tag=googshopde-21&linkCode=df0&hvadid=604401811108&hvpos=&hvnetw=g&hvrand=2896408204627070735&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9068137&hvtargid=pla-1730837103551&th=1

Thanks. This is not true constant current however. It will just switch between CC and CV at a preset threshold. It’s not what we need for true constant current.

 

[DasguteOhr]

Thanks. This is not true constant current however. It will just switch between CC and CV at a preset threshold. It’s not what we need for true constant current.

do you know how to set a current limiter? I have to ask because such a power supply makes no sense otherwise.

 

[Zeotrope]

do you know how to set a current limiter? I have to ask because such a power supply makes no sense otherwise.

This is my point: these lab supplies are not truly constant current, so they don’t make much sense (other than as a basic way to power a field coil).
It needs to continuously the voltage (in small increments) to maintain the same current as the resistance changes. These lab supplies do not normally do that. I did find one model that did but it was expensive, bulky, and had a fan.

 

[DasguteOhr]

This is my point: these lab supplies are not truly constant current, so they don’t make much sense (other than as a basic way to power a field coil).
It needs to continuously the voltage (in small increments) to maintain the same current as the resistance changes. These lab supplies do not normally do that. I did find one model that did but it was expensive, bulky, and had a fan.

OK your decision. Any modern laboratory device can supply constant current. For example, your field coil has a current draw of 170 mA. You can set it to only have 170 milliamps no matter what voltage you set. is even short-circuit-proof if you are careless with the terminals plus or minus(dc). Tutorial how to do it.

P.S
oh i forgot constant current is like driving a car at full throttle and using only the brakes to regulate your speed. never more than 80% of the maximum power from the power supply, otherwise most will die from heat.

 

[Zeotrope]

OK your decision. Any modern laboratory device can supply constant current. For example, your field coil has a current draw of 170 mA. You can set it to only have 170 milliamps no matter what voltage you set. is even short-circuit-proof if you are careless with the terminals plus or minus(dc). Tutorial how to do it.

P.S
oh i forgot constant current is like driving a car at full throttle and using only the brakes to regulate your speed. never more than 80% of the maximum power from the power supply, otherwise most will die from heat.

Except that’s not true constant current. If you have watched the resistance in real time you will notice that it changes as the coil heats up. Most lab supplies will not vary the voltage to maintain constant current. The other aspect is that voltage needs to change depending on the voice coil’s signal. A lab supply will not do that.

 

[Atmasphere]

Except that’s not true constant current. If you have watched the resistance in real time you will notice that it changes as the coil heats up. Most lab supplies will not vary the voltage to maintain constant current. The other aspect is that voltage needs to change depending on the voice coil’s signal. A lab supply will not do that.

I suggest you try it before saying it. If its constant current as advertised then it will indeed vary the voltage in order to maintain current per the setting.

 

[Zeotrope]

I suggest you try it before saying it. If its constant current as advertised then it will indeed vary the voltage in order to maintain current per the setting.

I certainly have tried it, for years. It does not work as it needs to work for field coil drivers.
Anyone with a field coil speaker owes it to themselves to not use lab grade supplies - it will make a huge difference.

This is how these lab supplies all work (except for one outlier - I will try to find it) when it comes to constant current:
Constant current/constant voltage (CC/CV) automatic switching: Constant voltage and constant current values can be preset by the coding knob, and automatically switch between CC/CV according to the load state

This means that they will switch out of CC when the load changes. This is not what you want if you are trying to maintain a constant current for your field coil drivers.

The B&K Precision (BK9206-ND) will maintain a true constant current. However, it's expensive, in my case for 4 drivers the cost was $8,000. At this point, it's best to buy a true audiophile grade PSU.
From the data sheet: "Unlike conventional supplies with fixed output ratings, the 9200B Series automatically recalculates voltage and current limits for each setting, providing maximum output power in any Volt/Amp combination within the rated voltage and current limits"
This is precisely what you need and what 99% of lab PSUs do not do!

 

[Atmasphere]

I certainly have tried it, for years. It does not work as it needs to work for field coil drivers.
Anyone with a field coil speaker owes it to themselves to not use lab grade supplies - it will make a huge difference.

This is how these lab supplies all work (except for one outlier - I will try to find it) when it comes to constant current:
Constant current/constant voltage (CC/CV) automatic switching: Constant voltage and constant current values can be preset by the coding knob, and automatically switch between CC/CV according to the load state

This means that they will switch out of CC when the load changes. This is not what you want if you are trying to maintain a constant current for your field coil drivers.

Pardon me but something does not look right in this post.

Let's start with the load: the coil. Its a pretty constant load. Despite what volume or material is played, the current varies only very slightly over time with a regulated voltage supply, which has more to do with the coil heating than anything to do with program material. So we don't have to worry about the load changing.

Constant current is a relatively new thing in lab supplies. When I was looking at them 10 years ago it was really rare. Now its commonplace. Based on the comments you've made I have several possible conclusions.
One is is you might not get the implication of what is meant by constant current.
Another is confirmation bias, brought on by the Veblen Effect.
Another is there may have been confusion about just exactly how the power supply you were using actually worked. What supply were you using 'for years'?

I'm not meaning to be confrontational here. A little background might help. The Chinese distributor that sells Classic Audio Loudspeakers in China approached me about 10 years ago to design a Tungar supply for the CAL speakers. John really didn't want to do it. I looked into it and bought Tungars to test them. I concluded in a report to the distributor that a constant current supply might be the thing rather than the Tungars. He did not want to pursue that since for him it was more about doing it with Tungars than anything to do with engineering; he acknowledged that my approach might be better. A year or two ago John contacted me about some design considerations in the Tungar supply with which I helped him and now there's a Tungar supply for his speakers. The supplier to CAL for the Tungar supplies is that Chinese distributor.

All this time I've been looking into the best means to set up the supplies using constant current. 10 years ago I was wanting a way to have the supply turn on when audio showed up at the speaker terminals, simply so the system would be easier to operate. Its one thing when you personally play the system; quite another when your wife or GF wants to do it and is confronted by all the devices that have to be turned on in the correct order! I still have plans of building a constant current source supply for the speakers; one that does not look like a lab supply; perhaps made as a base for the amps we make, something that has a bit more WAF.

 

[Zeotrope]

I've quoted what lab supplies do and do not do when it comes to CC. If you choose not to believe it, that's entirely up to you. I have nothing more to say on this topic. If you actually read the details of how almost all lab supplies define "constant current" you will see that it is not actually adjusting voltage to maintain a constant current. Why not attach a voltmeter to validate this for yourself?

Wolf von Langa makes constant current supplies and he may sell them without buying his speakers. Not advertising WVL - just saying that he understands what is required for a true CC source.

 

[DetroitVinylRob]

I wonder how much effect the Tungar power supply circuit actually effects the music vs perhaps simply separate SS PS (to also optimize voltage per driver) and a good mains conditioner (to limit AC and line noise)?

I’m currently utilizing a pair of BK Precision 1621A.

I don’t even begin to understand the science of much of this, but what I can attest to is a remarkably similar (from the above sonic descriptions) improvement after putting my lab power supplies and Atma-Sphere MA1 Mk3 amplifiers on a Shunyata Denali V2 feeding my Classic Audio T3 field coils.

 

[adrianywu]

Pardon me but something does not look right in this post.

Let's start with the load: the coil. Its a pretty constant load. Despite what volume or material is played, the current varies only very slightly over time with a regulated voltage supply, which has more to do with the coil heating than anything to do with program material. So we don't have to worry about the load changing.

Constant current is a relatively new thing in lab supplies. When I was looking at them 10 years ago it was really rare. Now its commonplace. Based on the comments you've made I have several possible conclusions.
One is is you might not get the implication of what is meant by constant current.
Another is confirmation bias, brought on by the Veblen Effect.
Another is there may have been confusion about just exactly how the power supply you were using actually worked. What supply were you using 'for years'?

I'm not meaning to be confrontational here. A little background might help. The Chinese distributor that sells Classic Audio Loudspeakers in China approached me about 10 years ago to design a Tungar supply for the CAL speakers. John really didn't want to do it. I looked into it and bought Tungars to test them. I concluded in a report to the distributor that a constant current supply might be the thing rather than the Tungars. He did not want to pursue that since for him it was more about doing it with Tungars than anything to do with engineering; he acknowledged that my approach might be better. A year or two ago John contacted me about some design considerations in the Tungar supply with which I helped him and now there's a Tungar supply for his speakers. The supplier to CAL for the Tungar supplies is that Chinese distributor.

All this time I've been looking into the best means to set up the supplies using constant current. 10 years ago I was wanting a way to have the supply turn on when audio showed up at the speaker terminals, simply so the system would be easier to operate. Its one thing when you personally play the system; quite another when your wife or GF wants to do it and is confronted by all the devices that have to be turned on in the correct order! I still have plans of building a constant current source supply for the speakers; one that does not look like a lab supply; perhaps made as a base for the amps we make, something that has a bit more WAF.

Surely, it is just a voltage regulator with a series sense resistor to keep the current constant. Should not be hard to implement. I used constant current to regulate the heaters of my preamp for a while, but changed them to voltage regulation. The reason was that the sensing resistors, after passing high current constantly for a period of time, started to drift and became too much of a bother to replace.
In any case, Ralph has a lot of experience with the Classic Audio speakers. What is your subjective impression with their new Tungar supply ? I found they made a real positive change, but then I would after spending $8K including shipping for them.