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In Reply to: Re: Unreg or reg PSUs ? any improvment ?! posted by Legendre on February 25, 2005 at 08:24:59:
Interesting to learn that Atma-sphere now uses a CRC filter for output supply. Per Speltz's Tweak, I use CRCRC, where the first R = 0.21 ohms and the second R = 0.1 ohm. But there is value as you suggest in partially reducing the tremendous load on the rectifiers that occurs when one uses only a huge capacitance after the rectifiers. I use 2000uF - 0.21ohms - 2000uF - 0.1 ohms - 10,000uF in my CRCRC filter. There is no doubt in my mind that this Tweak improved bass response AND S/N ratio. I think Ralph's argument with Harvey did center on his belief that one needs to keep the impedance of the supply as low as possible and that this would become a problem with any feasible inductor in the filter. Of course, Harvey was free to use huge free-standing monster inductors in his homebrew modified M60s. Moreover, I think Ralph and others had tested the CLC option and found that the sonics were not satisfying, i.e., not as good as with no inductor at all. I agree with you, HR seldom had any concrete advice to give; his writings were more for entertainment value.
Follow Ups:
Hi Lew and Bill,Dangit, now I've got to get the soldering iron out AGAIN! I like the idea of the CRC filter in the output sections of my M60's. I have the 1 ohm 5W resistors "in stock" for plate resistors already.
Question: When installing the resistors, do I need two resistors per side (+ to +, and - to -)? I haven't been in there since I upgraded the caps to 2 X 5600 uF per side.
Thanks,
Not sure I understand your question. If you are going to create a CRC network, you will need ONE resistor per phase, not two, but a total of two resistors per monoblock amplifier. If the factory is using a 1.0 ohm value, as per someone else's post, then I suppose that's OK. Speltz's earlier proposal was to use no more than an 0.5 ohm resistor. I finally used 0.2 ohms and 0.1 ohms, respectively in a CRCRC network. I would not recommend going any higher than 1.0 ohm. Use a "smaller" cap in the first position, e.g., 1000 or 2000uF, then R, then C = 5600uF. Part of the improvement you will hear is due to simply increasing the total capacitance.
Hi Lew,Thanks for your reply, Lew. Since the output supplies float, I was assuming that I would need a resistor for both the negative and positive sides of the caps in each phase. For the two capacitors in each phase, a one-ohm resistor would "bridge" the negative terminals together, and another resistor would bridge the positive terminals together in each phase. I am referring to Paul's power supply tweak schematic (URL attached), where he does this with four caps and six resistors per phase of the amp, three resistors on the + side and 3 resistors on the - side for each phase.
Hope I haven't confused you (and me)more!
Thanks,
William
If you follow Paul's advice, you will be doing the right thing. You (and Paul) are correct, one needs separate resistors for the plus and minus sides, which does add up to 4 resistors per monoblock for a CRC network.
Hi Lew,I contacted Bill Layer, and you are correct. He said that the factory M-60's use a 1 ohm 5W resistor only on the positive side. He said I could experiment with 0.5 ohm resistors on each polarity, but that it probably wouldn't help. Bill reminded me that the negative supply doesn't completely float, that it is coupled to ground through 600 ohms.
Thanks, Lew!
I think I am in at least up to my eyeballs if not over my head, but I don't see how it matters that the negative supply is grounded while the positive supply is floating, with respect to the CRC filter network. I yield to Bills' superior knowledge, but if it can't hurt, why not use CRC networks on both the positive and negative supplies? Were you able to check Speltz's Tweak? I haven't tried to access the old ASOG Tweaks pages, but I think they still exist. I believe that Paul did use CRC or CRCRC networks on both sides.
Hi Lew,Yes, Paul definitely uses CRC's on both polarities. I have the link to his tweak site on my post of 2/28 if you want to revisit it.
Thanks, Lew.
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