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Old 2nd October 2007, 06:03 PM   #1
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Default Simple Hi-end 845 amplifier

Follows this link and send here your comment

http://www.audiodesignguide.com/New845/New845v2.html
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Old 2nd October 2007, 06:07 PM   #2
Glowbug is offline Glowbug  United States
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I'm impressed

If I ever replaced the SV811's I'd want to go to something like that...
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Old 2nd October 2007, 06:12 PM   #3
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Why SV811 ? Which model of SV811 ?

I have some SV572-3 in my house, it could be a good choice to replace the 845
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Old 3rd October 2007, 10:18 PM   #4
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That soft turn on is a must with ss diodes. That will save a lot of space of course.

Hmmm, Does it really need dc filaments all through?

Also, How much does it weigh?

I bet it really sounds terrific. Congratulations!
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Old 3rd October 2007, 11:40 PM   #5
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Yuck.
Severely compromising a really nice tube (845) by poorly implemented gain and driver stages.

Why even bother?
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Old 4th October 2007, 02:41 AM   #6
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Brett,
We'd like a more positive contribution!!
What in particular do you see as the compromises in the gain and driver stages?
Are they simple to fix?
Do you have any suggestions for superior alternatives?

Cheers,
Ian
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Old 4th October 2007, 03:09 AM   #7
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Read Lynn Olson's Amity and Karna pages for details. I almost entirely agree with it, especially for PP design. In SE, which is not my preference, I'd do things a bit differently.

Put simply; the 845 is a wonderfully linear tube. The 12AX7 is most definitely not, neither is a trioded EL34. So the excellent sonic and distortion properties of the power tube are going to be masked (very) greatly by the lesser performing driver and initial gain stages. As a SE845 is a project requiring quite a bit of resource, why not start with a better design?
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Old 4th October 2007, 03:15 AM   #8
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Brett
Yuck.
Severely compromising a really nice tube (845) by poorly implemented gain and driver stages.

Why even bother?
Hi Brett,
I'd be curious as to what your specific objections are and what you would do differently..

If you are objecting to transformer drive have you ever heard an amplifier based on this topology?

(I suspect the 20mA EL34 plate current used was to allow the use of reasonably priced interstage transformers. Notice that all of the tubes used are readily available and inexpensive including the 845.)

My design choices would be different, but these are mostly minor quibbles and I bet it sounds good (based on local copies of some of his other designs) - Andrea's designs are quite popular and I imagine the design choices were dictated by his desire to design and build something that others could copy with a minimum amount of difficulty.

Edit:
Cross post I guess.. Your post answers some of my questions..
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Old 4th October 2007, 03:44 AM   #9
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Quote:
Originally posted by kevinkr


Hi Brett,
I'd be curious as to what your specific objections are and what you would do differently..

If you are objecting to transformer drive have you ever heard an amplifier based on this topology?

My design choices would be different, but these are mostly minor quibbles and I bet it sounds good (based on local copies of some of his other designs) - Andrea's designs are quite popular and I imagine the design choices were dictated by his desire to design and build something that others could copy with a minimum amount of difficulty.
I really like IT's and have used them before in at least a half dozen designs. My forthcoming electrostatic headphone amp will also use them.

I'm not really interested in doing a complete redisgn of another persons amp, and I don't have a need or desire for an SE845 so I don't intend doing one today. But for a couple of off the cuff suggestions;

Driver: 2A3, or a 6W6 or EL38 trioded, and use some cathode feedback via one of the Lundahl's windings. All these will need a different IT, say 1677

Gainstage: How much gain do you need? There are lots of options here from 6SN7 to ECC99 to 6C45 to mu stages to pentode C3m. All these flavours will be preferable to a 12AX7 in any way IME
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Old 4th October 2007, 04:02 AM   #10
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by Brett
I really like IT's and have used them before in at least a half dozen designs. My forthcoming electrostatic headphone amp will also use them.

I'm not really interested in doing a complete redisgn of another persons amp, and I don't have a need or desire for an SE845 so I don't intend doing one today. But for a couple of off the cuff suggestions;

Driver: 2A3, or a 6W6 or EL38 trioded, and use some cathode feedback via one of the Lundahl's windings. All these will need a different IT, say 1677

Gainstage: How much gain do you need? There are lots of options here from 6SN7 to ECC99 to 6C45 to mu stages to pentode C3m. All these flavours will be preferable to a 12AX7 in any way IME
I think Andrea's stated design goals are just a bit different from yours or mine, based on comments from his site. FWIW I think you and I are basically on about the same wavelength when it comes to design choices based on your tube and transformer recommendations. One difference is I am now firmly in the SE camp having started in the PP camp countless aeons ago.
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