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Old 12th October 2012, 03:21 PM   #581
Desmo is offline Desmo  Denmark
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Hi Disco,

No it's not novel. As you mention it has been done in many implementations during many, many years...

The thing is to find/use types that are suitable for the application. For instance in the Tram II preamp this will mean types that are at least rated at 2,5A continous current and has low rdc on around 0.1 - 0.2 ohm. Not many of those around, and the possible improvement over resistors is minimal because the induction will be relatively small.

I will try to wind some low rdc aircore coils to test with (similar to DHTrob that you are mentioning).
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Last edited by Desmo; 12th October 2012 at 03:23 PM.
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Old 19th March 2013, 12:11 AM   #582
4me2ctv is offline 4me2ctv  Canada
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Default Gyrator compatibility with other CCS?

Hi. I already have voltage controlled current sink (VCCS) installed and working in my amp. Is it possible to use the gyrator only in the positive leg to gain benefit? The VCCS I have uses a FET in the negative leg. I'm not sure what type of FET. The positive leg is direct to the filter caps then a diode bridge. So I believe there would be benefit in using the gyrator in the positive leg. That's why I'm asking. I believe the VCCS works quite well sonically so I'd rather keep them if possible.

Thanks,
Adrien.
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Old 23rd March 2013, 03:51 PM   #583
4me2ctv is offline 4me2ctv  Canada
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I should restate the question. Is the gyrator dependent on the CCS or can it be used separately? I have tried to find this information in this long thread. I believe it can but there may be something I missed.

Thanks,
Adrien.
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Old 24th March 2013, 04:52 PM   #584
FRUGIVO is offline FRUGIVO  Spain
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Quote:
Originally Posted by 4me2ctv View Post
I should restate the question. Is the gyrator dependent on the CCS or can it be used separately? I have tried to find this information in this long thread. I believe it can but there may be something I missed.

Thanks,
Adrien.
These are two completely independent circuits
operate separately
in this case are in series
separated by a filament that is the load resistance
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Old 29th April 2013, 08:12 PM   #585
4me2ctv is offline 4me2ctv  Canada
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I decided to try Rod's regulators to replace my voltage controlled current sink regulators. Last weekend I did a very quick test. My test filament power supply had very long wiring throughout, a cheap bridge diode, a cheap filter cap and a single bobbin EI transformer with a variac. My A+B test was to use Rod's regulator on one DHT 3C24 input tube only and listening to one of the stereo channels. I can report positive results. So much so that I will be redesigning my filament supply and using Rod's regulators for all 4 tubes. It's a major change so I wouldn't do it if the improvement was minor. If I was to try and describe the improvement, it is as though a veil was removed from the speaker. Micro details become clearer and more audible. There is more tone making the instruments more real like. I listened to orchestra violin concertos music on vinyl.

A BIG thank you to Rod for sharing his regulator with us.


Adrien.
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Old 29th April 2013, 08:34 PM   #586
работник
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Hi Adrien, Thanks for letting us know! I think you will have a nice surprise when you make the Stereo implementation - the improvement in the sense of "3D" with the Regulators is very pleasant!
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Old 20th May 2013, 11:34 PM   #587
4me2ctv is offline 4me2ctv  Canada
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I'm trying to figure out what the heatsink size is for running 2 regulators, each dissipating around 20W for a total of 40W. (5V*4A per regulator). I added a bit of V for headroom. If I use a heatsink that is about 1 deg C/W I calculate a junction temp of around 125 deg C. This is using 3 deg C for junction to mica to heatsink and 25 deg C ambient. Is this safe enough or do I need a bigger heatsink?

Thanks,
Adrien.
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Old 21st May 2013, 05:23 AM   #588
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A 1 K/W heatsink will give a 40 deg. C rise for 40W, giving a heatsink temperature of 65 deg C.

This heatsink temperature is safe for all versions of the regulator, so it is OK, provided the heatsink can reach its full performance, and that 25 deg C is the real maximum ambient temperature - which means the heatsink must be on an external surface of the chassis.

But keep in mind that the heatsink is designed to be able to circulate air to meet its 1K/W rating - so it should be mounted with fins vertically oriented, and without obstruction to air flow.

When the Regulator is running on the heatsink, the temperature can be checked, to ensure that it is below 70 deg. C.

If you have other metallic chassis parts near to the heatsink, making a good mechanical connexion between the heatsink and the chassis will improve the cooling. In practice, 2mm - 4mm thick Alu top plates are very efficient at cooling.


I hope they are sounding good!
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Old 23rd June 2013, 05:25 PM   #589
macm75 is offline macm75  United States
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As opposed to the traditional transformer/rectifiers/filters feeding the filament regulator, anyone using SMPS's instead?
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Old 28th June 2013, 08:52 AM   #590
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It's possible that a switching converter could be used as a pre-regulator for my Filament Regulators - but careful precautions are advisable.

I assume we are talking about the "off-line" (mains to dc low-voltage) converters.

The first caution is to measure the leakage current from the low-voltage output to safety earth (Ground). Some converters, including the expensive and well-certified FRIWO units I specified for my Handheld PC design work - have very high levels of leakage. It seems to be caused by high primary-to-secondary capacitance. Intentionally-placed capacitors, even.

With Cathode bias, or Filament-bias applications, leakage current is a disaster. The B+ return (System Ground) in our amps must be connected to safety earth (one way or another), and so any leakage current from the raw supply for the filaments will run through the cathode/filament-bias resistors. Leakage current of this kind is very noisy, and the outcome will be highly degraded sound.

Measure the leakage. Anything more than a few microamperes (ac) is probably too much. If you have a scope, connect the output of the converter to safety earth via a 100K resistor, and scope out the resistor, to assess the noise current.

With fixed bias amps, our cathode is at Ground potential. But the noise current will still run along the same conductors as our anode (music) signal current. check out the bandwidth of the noise. Is the impedance of the Ground circuit zero over this bandwidth? If not, noise injection is certain.

On the other hand, you may find a converter that does not leak. Maybe a salvaged Medical equipment converter?

For example, a medical PC 400W supply leaks 90uA:

ATX PC Power Supply Features 90 uA Low Leakage Current at 264 VAC

This is not good enough, in my view.

A Bear supply leaks 5uA:

Custom medical power supplies with ultra-low leakage current to be used in heart-connected instruments

This may just about be good enough. But it certainly illustrates the challenge.

Meanwhile, a good EI transformer has about 50pF interwinding capacitance, and about 100pF winding to Core. In this case, a 10V 50Hz common-mode pulse will give a peak current of 150nA, or 100uA if the frequency is 50kHz.

I have measured Toroidal transformers with 1000pF or higher of interwinding capacitance, and usually the core has no option but to float. The leakage current with these increases in proportion to the leakage capacitance - substantially worse than the EI.

Overall, I think the EI trafo, plus schottky rectifiers is the safest solution. But in this application measuring is quite sufficient to verify a converter.

In all cases, mount a converter at a distance from the signal wiring, to keep switching noise out of the amp.
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