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Old 30th September 2007, 06:37 PM   #11
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Hi

You could look at this extensive blog of John Broskie. Lots of interesting circuits, but I believe that the second and third circuit presented under "back to bipolar power supplies" are extremely simple and will work pretty fine (but so will many others)!

http://www.tubecad.com/2007/04/blog0104.htm

Good luck, Erik
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Old 30th September 2007, 09:04 PM   #12
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The advantage of using cascoded SS device CCSes as loads is a HIGH AC impedance, without I2R heating losses. That, in turn, promotes maximum linearity from the CF.

A look at the ECC99 data sheet suggests to me that the 150-0-150 winding of Hammond a 369BX power trafo bridge rectified (end to end) by 4X Schottky diodes and choke I/P filtered would make a satisfactory bipolar PSU. Put a 30 H. Hammond 157G choke between the CT of the rectifier winding and ground. That way, a single "beefy" inductor serves to filter both rails. A pair of 15 KOhm bleeder resistors connect ground to the O/Ps of the bridge. A HIGH WVDC 10 nF. ceramic cap. goes in parallel with the 30 H. choke to protect the SS diodes from inductive kick back spikes. Stacked 15 muF. 'lytics followed by paired lighter duty chokes (say Hammond 156Ms) and a 2nd cap. stack complete the PSU. RC sections following the initial LC setup might be feasible at the lowish draw in this preamp.
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Old 30th September 2007, 10:12 PM   #13
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Hi Eli

I agree with you, so my earlier post was not ment to state that the idea you described was not good... it is just that the AIKIDO output stage is maybe easier to build, and with the high PSRR an appropriate power supply would not be hard to make.

Anyway your last post has taught me a new thing: filtering of a dual supply rail using a single choke. I didn't know it could be done this way! Thanks!

Erik
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Old 1st October 2007, 12:17 AM   #14
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Erik,

I'm the last person to criticize Broskie. However, I believe the Aikido has gain and this thread's originator needs a "unity" gain design.

The trick of the choke in the ground leg is also useful in a unipolar supply, to avoid exceeding insulation limits. People tend to forget that PSUs are inherently differential. We make them single ended or bipolar by grounding a point.

I have a marked tendency towards "overkill" in PSU design. I take the admonition to build on granite, not sand, very seriously. The PSRR of a CCS loaded cathode follower is excellent. Still, a low noise and well regulated PSU can't hurt.

FWIW, Santiago is in the same time zone as Plainsboro. While you head towards Summer, we head towards Winter.
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Old 1st October 2007, 12:17 PM   #15
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Eli,

I apologize up-front if I am not understanding you. I believe at a high-level you are saying that the PSU has a tremendous influence on the output of a line stage/preamp and that if I intend to build the Aikido, I should use this type of PSU to supply power? Clearly, you are leaps and bounds ahead of me with experience and knowledge. I have a basic background from my Amateur Radio days about 30 years ago and have a knack for not forgetting anything I have learned.

So is it fair to say I use the Aikido in conjunction with this type of PSU?
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Old 2nd October 2007, 12:43 AM   #16
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Quote:
So is it fair to say I use the Aikido in conjunction with this type of PSU?

Negative! The Bipolar PSU I outlined is intended for use with CCS loaded CFs. Remember, while it's a FINE design, the Aikido has gain and that's the last thing you need. AAMOF, you may have to add a padding resistor to the CDP I/P to make it behave like the tuner I/P does.

The sonic quality of the "unity" gain circuity I have in mind is (IMO) superior to that of your simple SE. That is not a problem, as you are likely to use the line stage with other amps you build in the future.

BTW, do you want a ganged stereo level control or individual controls for each channel? I highly recommend PEC hot molded Carbon controls. They sound good, without bankrupting you.
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Old 2nd October 2007, 01:01 AM   #17
jayme is offline jayme  United States
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I built a 6SN7 Aikido. It does have too much gain, and I did pad it down with some resistance to reduce the input voltage. When I compared it to a simple passive 50K pot, the pot wins out, of course.

My amp has an input sensitivity of .7V to play at full volume, with a 100k input impedance. (Much like the original poster).

With an amp that does have a high input impedance, is there any advantage to using a CF as an output buffer?



P.S. I did learn quite a bit building my Aikido. It is a fine design if you need gain. I think I'll rip out the parts and use them to build a a single-ended EL-34 amp now. I just need to buy some output transformers.

P.S.S. I might just try a TVC now for a preamp...
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Old 2nd October 2007, 01:01 AM   #18
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Thank you Eli. I do expect that this will not be the last amplifier I build. I now understand what you have recommended. I agree with having the highest quality preamp since any imperfections it introduces are amplified it would seem to me this is where you need to lay down a solid foundation to build upon.
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Old 2nd October 2007, 02:32 AM   #19
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Quote:
Originally posted by jayme
I built a 6SN7 Aikido. It does have too much gain, and I did pad it down with some resistance to reduce the input voltage. When I compared it to a simple passive 50K pot, the pot wins out, of course.

My amp has an input sensitivity of .7V to play at full volume, with a 100k input impedance. (Much like the original poster).

With an amp that does have a high input impedance, is there any advantage to using a CF as an output buffer?



P.S. I did learn quite a bit building my Aikido. It is a fine design if you need gain. I think I'll rip out the parts and use them to build a a single-ended EL-34 amp now. I just need to buy some output transformers.

P.S.S. I might just try a TVC now for a preamp...

Similar experience here - my active pre has way too much gain with the Simple SE. I bypassed the line stage, and swapped in a 25k PEC pot and all is well.

I'd like to try a TVC some time, too.

Bill
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Old 2nd October 2007, 03:39 PM   #20
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Quote:
Originally posted by Eli Duttman
Erik,

I'm the last person to criticize Broskie. However, I believe the Aikido has gain and this thread's originator needs a "unity" gain design.

The trick of the choke in the ground leg is also useful in a unipolar supply, to avoid exceeding insulation limits. People tend to forget that PSUs are inherently differential. We make them single ended or bipolar by grounding a point.

I have a marked tendency towards "overkill" in PSU design. I take the admonition to build on granite, not sand, very seriously. The PSRR of a CCS loaded cathode follower is excellent. Still, a low noise and well regulated PSU can't hurt.

FWIW, Santiago is in the same time zone as Plainsboro. While you head towards Summer, we head towards Winter.
Hi Eli

In my previous post I was referring to a schematic by Broskie with only the second stage of the Aikido, fed by a bipolar power supply. This stage has no voltage gain, it is only a buffer with high PSRR (I tried to attach the schematic, but it did not work). I imagine that your idea could perform even better, but it could also be more complex to build, don't know.

Since saturday I am at my parent's place, a small town in Brazil. I already visited some people, working on something for the university...but actually getting claustrofobic from this small town. In three weeks I am going back to hothot Santiago, backpacking for three weeks through Argentina, work somewhat more at ECLAC, and afterwards finally back to the Netherlands.
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