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September 15, 2019, 10:21:57 PM

Author Topic: Adjusting 300B filament voltage  (Read 661 times)

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Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #30 on: August 21, 2019, 03:48:55 AM »
You could also get a 115:120 autoformer or power transformer to sit ahead of your BeePre.


Excellent idea! Thanks PB. And I can install a cheap analog panel mount voltmeter to monitor voltage.

Quote
Dropout occurs when input voltage and output voltage get too close together.  That's why low line voltage is an issue.  The regulator will not overheat with some other major problems going on.


OK, so I think I understand this part, b/c you've explained it to me before and I've read up a bit about regulators.  But then why/how does a draw of 1.3A cause dropout?  And why couldn't the heater circuit handle the 1.4A draw of an EML 300B Mesh? The LM1085 is good for at least 3A output - so I don't think the 1085 is the limiting factor. Just throwing out guesses here: Are the transistors current limited? Or does voltage output of the secondaries sag as the Volt-Amps demand approaches the VA rating of the secondaries? Is the power demand of 13.5V (after rectification) @1.3A just too much for the PT to handle? Or does something else explain this?


If the issue is limited VA output of the secondaries, then a relatively simple solution would be to get a separate heater transformer with higher VA rating. Does that make sense?


cheers and many thanks, Derek
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #31 on: August 21, 2019, 04:52:37 AM »
But then why/how does a draw of 1.3A cause dropout?
The voltage available from the raw DC supply drops, not necessarily only because of the 1.3A, but also because of low line voltage. 

  And why couldn't the heater circuit handle the 1.4A draw of an EML 300B Mesh?
The noise elimination circuit also has some series resistance, and drawing extra current through this will reduce regulated voltage.

If the issue is limited VA output of the secondaries, then a relatively simple solution would be to get a separate heater transformer with higher VA rating. Does that make sense?
The 6.3V secondaries have some extra current to give.  If you bought a power transformer that had two 7V/4A windings, that would bring up the raw voltage a bit as well.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #32 on: August 21, 2019, 04:56:33 AM »
Awesome. Thanks PB. 7V/4A windings maybe hard to find. But I figure I can go with 10V/4A and use dropping resistors to dial in the voltage.


cheers and thanks, Derek
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #33 on: August 21, 2019, 05:09:53 AM »
10V/4A with a bridge instead of a doubler might also work.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #34 on: August 21, 2019, 05:31:00 AM »
Cool. Thanks PB.

Along these lines, I might also be able to go with 12.6V/3A with full wave and skip the doubler. I can play around with PSUD to see what works.

Is there a rectification advantage to using a 4-diode bridge instead of two-diode full wave other than not needing a center tapped secondary? I.e., does a bridge produce less ripple?

For modelling the heater circuit in PSUD, do you have a recommended load resistor value? Or can I just use PSUD's default value (I forget what it is)? Guessing that the answer is: add up all the resistance in the heater circuit and plug that in - but just want to be sure.

Edit: one more question - I plan to install switches on the transformer to allow for nominal +5V, 0V, -5V changes to the mains voltage. Shorting or non-shorting? I have no idea which is best for changing between windings.

Apologies for all the questions - I'll try to stay quiet for a while after this ;D

cheers and thanks, Derek
« Last Edit: August 21, 2019, 08:21:29 AM by Deke609 »
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #35 on: August 21, 2019, 09:34:18 AM »
In PSUD, you can change the resistive load to constant current. Most of the questions you're asking can actually be pretty well answered by doing some modeling in PSUD and looking at the power transformer current, ripple, output voltage, etc. 

If you're asking about +5, 0, and -5V switches for a step-up before the BeePre, I would just leave it at +5, there isn't much penalty for having a little extra AC voltage.  Otherwise I would recommend non-shorting switches.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #36 on: August 21, 2019, 09:41:51 AM »
Cool. Many thanks PB.  that constant current feature will sure make things easier.


cheers, Derek
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #37 on: September 04, 2019, 09:49:42 AM »
I'm going to try using an autotransformer to adjust mains volatge going to my BH amps. Since it's an autotransformer, it offers no isioation from mains power - but I figure this is ok since all BH amps have their own isolating transformers.


I'm going with the Hammond 168J - rated 2000VA and weighing 23lbs!  I plan to use a 10A fuse on the incoming mains power - so run it at a max of 1200-1250VA (depending on mains voltage variations).


And so here's my question: Am I correct that running the 168J well below its max VA rating gives me some latitude on how to wire it? Specifically, the Hammond schematic shows incoming hot wired to 115V with options to take 85, 95, 105, 110, 115, and 125V out. I want to take power from the 115 tap and use switches to connect mains incoming power to either 105, 110 or 115 for nominal +0V, +5V and +10V output options.  I figure I can  use  2 X SPDT switches (high voltage/current rated) - please see attached wiring scheme.


Does anyone see a problem with this?


many thanks, Derek
« Last Edit: September 04, 2019, 09:55:58 AM by Deke609 »
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #38 on: September 04, 2019, 10:14:43 AM »
I'm going with the Hammond 168J - rated 2000VA and weighing 23lbs!  I plan to use a 10A fuse on the incoming mains power - so run it at a max of 1200-1250VA (depending on mains voltage variations).
Is this just for the BeePre?


And so here's my question: Am I correct that running the 168J well below its max VA rating gives me some latitude on how to wire it?
You may find that the listed input/output voltages are not at all accurate with that transformer lightly loaded.
I figure I can  use  2 X SPDT switches (high voltage/current rated) - please see attached wiring scheme.
What you're doing would work, but something like this will be a lot simpler:
https://www.mouser.com/ProductDetail/CK/R10307RN02Q?qs=sGAEpiMZZMvNbjZ2WlReYgfl1vEqXQaLTI2c32B8PEc%3D


The Hammond 168B is a far better choice to use with the BeePre.  This is an instance where spending 5x the money will net you far worse performance.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #39 on: September 04, 2019, 10:17:22 AM »
It's for all BH amps - so, at minimum the Beepre and either Kaiju or an SII. And down the road, it might be running the Beepre, Kaiju and both SII's off of it at the same time.
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Paul Birkeland

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Re: Adjusting 300B filament voltage
« Reply #40 on: September 04, 2019, 10:24:51 AM »
So 168C, or maybe D.  The Kaiju and SII are quite a bit more tolerant to line voltage fluctuations and have the universal power transformers that allow you to wire for lower line voltage if that comes up, so you may want to consider making this a BeePre only effort, as you could really dial things in if you only used the BeePre on the autoformer.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #41 on: September 04, 2019, 11:44:28 AM »
Many thanks PB. Good to know that it should at least work in principle. I will weigh my options. I do like the idea of having everything plug into one unit. Maybe even my dac as well. The bigger plan is to incorporate 3-4 combo common/differential mode filters (already built), each rated 3A, and have 3-4 pairs of outlets - with switches for bypassing filtering and possibly even the autotransformer. I'm even contemplating using some high current/voltage schottky's with 1.5V forward voltage drop on switches to better calibrate the voltage. Plus an analog voltmeter dial to monitor what's going on.


cheers and thanks, Derek
Derek
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Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4

Offline Deke609

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Re: Adjusting 300B filament voltage
« Reply #42 on: September 04, 2019, 12:04:20 PM »
I'll add that much of fun for me is being able to think something up myself, build it, and have it work reasonably close to as planned. I 'm ok with the prospect that years from now (or perhaps much sooner) I'll look at the thing and realize that I could have achieved the same or better results for 1/5 the price and 1/4 the effort. And if I later choose to dismantle it, I'm pretty confident that the parts will get used in other projects. 


cheers, Derek
Derek
______

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Stereomour IIs (2A3 [EML 2A3 Mesh] and 45 Conversion [EML 45B] - both fully upgraded)  -> Audeze LCD4