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Separate power supplies for power and pre/driver tubes
Separate power supplies for power and pre/driver tubes
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Old 8th March 2017, 09:36 PM   #1
tizman is offline tizman  Canada
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Default Separate power supplies for power and pre/driver tubes

Hi All.

The purpose of this thread is to explore the different ways that tube amp power supplies can be built in order to avoid cross talk between channels and, more importantly, to minimize any electrical coupling between the input stage and the output stage. What really got me thinking about this is an old article written by Harvey Gizmo Rosenberg regarding the building of the ultimate DIY amplifier. Among other things, he extolled the virtue of having entirely separate supplies for pre and power tubes in addition to the separation of channels.

The article is located here,
PLITRON’S DREAM AMPLIFIER
His argument, if I understand it correctly, is that the sharing of supplies between the power and pre tubes causes the stages to modulate each other in an undesirable and audible way, and that building to avoid this produces an audibly superior amp.

To do what he recommends would require mono blocks with two separate power supplies in each one for a total of four power supplies in each stereo pair. If you followed the recommendation of the article, you would also build the power supplies using CLC or LCLC filters. In fact, he recommends using as many chokes as possible, including in the filament supplies. The end result would be a very large and very heavy pair of mono amps, that would be very expensive to build.

I am hoping to hear from you all with regard to other less expensive (and heavy and complicated) methods of decoupling and electrically isolating pre and power sections, as well as filament from B+ and, in one power supply stereo amps, the channels from each other.

Thanks to you all in advance for any and all suggestions, and for all your past help. It is much appreciated.
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Old 8th March 2017, 10:05 PM   #2
JMFahey is offline JMFahey  Argentina
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It definitely wonīt hurt.

Itīs your time and money, if you feel itīs justified, go ahead
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Old 8th March 2017, 10:09 PM   #3
tizman is offline tizman  Canada
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I picked up a pair of 40 watt Plitron push pull output transformers recently, and I may go the whole hog on an amp using them as per Dr. Gizmo's recommendations. Right now I have three amps on the table, and I was hoping for suggestions to get a similar result without building four CLCLC or LCLC supplies per stereo amp. Two of the amps I'm building, a 5998A SET amp and KT120 SET amp have one power supply, and the other one, a 45 amp, is comprised of a pair of mono blocks.

Last edited by tizman; 8th March 2017 at 10:14 PM.
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Old 8th March 2017, 10:28 PM   #4
Eli Duttman is offline Eli Duttman  United States
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FWIW, I'm slowly gaining momentum on a #46 (DHT "El Cheapo") project that's been simmering for years. I will be exploiting a concept publicized by Pete Millett, which obtains 2 rails (1 "tall" and 1 "short") from a CT winding. The rectifying diodes do a superb job of blocking cross modulation. I've uploaded a "hen scratch" schematic that illustrates the concept, but the DHT "El Cheapo" will use Schottky diodes everywhere.

Look closely and you'll see that the "short" rail is FWCT and the "tall" rail is bridge.

You could exploit the idea in your monoblocks. A single power trafo per amp is all you need.
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File Type: jpg 2 Rails - 1 Winding.jpg (277.4 KB, 382 views)
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Old 8th March 2017, 10:43 PM   #5
toriversen is offline toriversen  Norway
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Hi,
I just have to give a comment to this, in the last five power amps I have built ( I usually build 5 - 8 amps a year) I have used a well regulated powersupply for pre/driver circuits, this has in my opinion, given a real improvement when it comes to the sound quality of the amplifier. This is just to give an input.....for further thoughts.
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Last edited by toriversen; 8th March 2017 at 10:57 PM.
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Old 8th March 2017, 10:53 PM   #6
tizman is offline tizman  Canada
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Thanks for the schematic Eli. Another method to add to the list. With respect to using diodes, do you think that it is possible to block all cross modulation through the use of diodes alone?
toriverson: Is the well regulated power supply for pre/driver stage a separate one from the power stage's supply?

Last edited by tizman; 8th March 2017 at 10:57 PM.
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Old 8th March 2017, 11:01 PM   #7
toriversen is offline toriversen  Norway
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I have used a separate rectifier and filter from the same transformer used for the HV, I will post some schematics later.
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Old 8th March 2017, 11:28 PM   #8
smbrown is offline smbrown  United States
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I did this once using a power transformer with multiple windings. There were three supplies: output, driver and C- for bias (300B). All choke loaded and all tube rectified. Since I didn't try a more conventional supply I can't say which was better but I can say it made it super easy to make changes to the driver without disturbing the output stage. It also ended up weighing a ton!
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Old 8th March 2017, 11:52 PM   #9
TonyTecson is offline TonyTecson  Philippines
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Separate power supplies for power and pre/driver tubes
i have been doing this....since i make my own traffos, it is easy for me to make
several secondaries on a single core...

my upcoming 1624 pp amp build will have this, separate traffos for filaments,
B+.....
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Old 9th March 2017, 12:33 AM   #10
leadbelly is offline leadbelly  Canada
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It seems that everyone is replying to the title of the thread and not the content. The paper cited in the OP is near nonsense. How about some proof of audibility? Keep adding "C"'s, never worrying about resonance?
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