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Old 16th November 2009, 12:45 AM   #181
kevinkr is offline kevinkr  United States
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Originally Posted by zigzagflux View Post
This is killing me. I have an AC heated 46-PP driving a 300B-PP with about 500uV of 120Hz hum, and I'm ready to rebuild the whole works with these current sources.

Enough already !
Do it man ! I mean rebuild it with the CCS

Edit: On second thought 500uV of 120Hz ripple on the output is actually a pretty good result. I have simple CCS's in my SE amplifier and I have just about that much 120Hz ripple on my outputs - even with 100dB efficient speaker system (-3dB @ 30Hz) it is not audible. So are you pulling our legs?
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Old 16th November 2009, 03:04 AM   #182
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No, those are true numbers, and yes, the hum is inaudible with 92 dB speakers until I'm about 3 inches away from the woofer. No complaints from that end.

This is more of an issue of having a setup that no longer requires nulling, and eliminates the major source of IM distortion in the amp. (how much IM do I have, no idea).

Rod's design is just so simple yet effective, it's hard to "just say no".
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Old 16th November 2009, 03:38 AM   #183
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by zigzagflux View Post
No, those are true numbers, and yes, the hum is inaudible with 92 dB speakers until I'm about 3 inches away from the woofer. No complaints from that end.

This is more of an issue of having a setup that no longer requires nulling, and eliminates the major source of IM distortion in the amp. (how much IM do I have, no idea).

Rod's design is just so simple yet effective, it's hard to "just say no".
I agree, particularly with the comments about nulling and IM, this is the problem I have with my PP 300B amplifiers - ccs based dc filament supplies would just kill those sorts of issues stone dead. I would say on that basis it would be very worthwhile if you have sufficient space.
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Old 16th November 2009, 07:02 AM   #184
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I do have a cathode bias cap though - this old schematic shows it on the +ve side, but I think I found the -ve side sounds better.
Rod,
Have you compared your "Y-solution" with using a single cathode resistor connected to the same ve-side as the cap?
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Old 16th November 2009, 07:55 AM   #185
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Rod,
Have you compared your "Y-solution" with using a single cathode resistor connected to the same ve-side as the cap?
Lars, not done that yet - on the 300B. I am overdue to replace that Cerafine cathode cap with an MKP, so when that happens, I could test it.

On the LP2, operated at 100V/8mA, two resistors to ground sounded best. The best sound had to be found by experiment.
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Old 20th November 2009, 11:00 AM   #186
martyh is offline martyh  United States
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Sorry to keep resurrecting this thread with basic questions but I am sooooo close to building my 26 pre and I really want to get it right the first time. The latest noob question is about grounding and parts location. The block diagram attached shows the grounding scheme and circuit block locations I am planning on using and hopefully it is understandable. Basically there are six wires running from the PS to signal chassis with the regulators on the signal chassis and the transformers and filters on the ps chassis. Iím particularly worried about the grounding scheme because I only have a 50% success rate getting remote supplies quiet. I gave up on it for years in fact until I built an idht transformer coupled pre last year. That one worked but I had no B+ regulators, otherwise the layout was similar. So, can anyone see obvious problems with this or offer any advice for improving the layout?

Thanks again,
Marty
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Old 20th November 2009, 04:58 PM   #187
kevinkr is offline kevinkr  United States
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Originally Posted by martyh View Post
Sorry to keep resurrecting this thread with basic questions but I am sooooo close to building my 26 pre and I really want to get it right the first time. The latest noob question is about grounding and parts location. The block diagram attached shows the grounding scheme and circuit block locations I am planning on using and hopefully it is understandable. Basically there are six wires running from the PS to signal chassis with the regulators on the signal chassis and the transformers and filters on the ps chassis. I’m particularly worried about the grounding scheme because I only have a 50% success rate getting remote supplies quiet. I gave up on it for years in fact until I built an idht transformer coupled pre last year. That one worked but I had no B+ regulators, otherwise the layout was similar. So, can anyone see obvious problems with this or offer any advice for improving the layout?

Thanks again,
Marty
It goes without saying that the signal and power ground meccas must be connected together via the umbilical, and there should only be one connection between the two.

One point in each chassis becomes the point where all grounds are connected together - those, and only those gnd points are connected together between the chassis.

Do not allow filament currents to flow through the ground path in the umbilical - they must return through their own return lead. No filament current should flow into any ground whether in the supply or audio chassis - so they should be grounded only in one place. (In my case usually the PSU except in the case of dhts where I ground in the audio chassis as there is audio current present in that case. )

In the case of full wave rectification the center tap should go to the negative terminal (or as appropriate for the supply polarity) of the first filter cap and from there to the common grounding point (star ground) or grounded end of ground bus if you are using a bus. Same basic rule applies for bridges as well, except obviously it is one of the outputs of the bridge rather than the CT. This serves to keep the high ripple currents out of the ground path, and generally results in somewhat less ripple on the output of that first cap as well.
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Old 22nd November 2009, 09:00 PM   #188
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Here's some numbers from my latest attempt to get all the voltages right.

PSU HT = 365vDC
Dropper resistor to glow tubes - 3.2K, 9W
Glow tubes - 150v and 105v total 255v
IXYS cascode active load - sense resistor 470R
Anode voltage 178v
Cathode voltage 11.2v
Current 6mA
Cathode resistor 1.85K (2.4K // with 8.2K) wirewound

Seems to sound pretty good - full and detailed.

andy
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Old 22nd November 2009, 09:41 PM   #189
mach1 is offline mach1  Australia
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Instead of a dropper resistor, why not use a ccs ? This will provide virtually infinite source resistance plus greatly enhanced psu rejection.
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Old 23rd November 2009, 09:13 AM   #190
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Originally Posted by mach1 View Post
Instead of a dropper resistor, why not use a ccs ? This will provide virtually infinite source resistance plus greatly enhanced psu rejection.
Would this be needed as well as the IXYS cascode? If so any designs you have in mind?

andy
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