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omg.... [message #32185]

Sat, 27 October 2007 18:00

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

are y'all just not building anything these days? Lots of fun over here, tearin' into a few nice output transformers, building some more amps...:)
cheers,
Douglas

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What'cha have in mind? [message #32186 is a reply to message #32185]

Sun, 28 October 2007 09:19

Wayne Parham
Messages: 18792
Registered: January 2001

Illuminati (33rd Degree)

I'd like to do a nice phonp stage build. Seems like it would be a fun group build. Some of the guys were talking about a switcher. Easy to do, but still worthwhile. Could do them together too.

I always stay pretty busy, and I have a list of things in front of me. I used to be able to get through new projects much faster, but these days, I have a lot of priorities. I just finished with the Prosound Shootout, which is a pretty good amount of work to do, actually. Before long, it will be time to get ready for the Lone Star Audiofest. In between times, I have two basshorn projects I'm working on, one new and the other an improved version of an existing model.

What have you been up to these days?

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Phono pre [message #32187 is a reply to message #32186]

Sun, 28 October 2007 10:17

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

hey-Hey!!!,
I have been working out one for a while now. To do it with a single PS, I'd have to work out some details with Heyboer for winding one with a few electrostatic shields( to isolate the heater winding and primary from the HV). It would be easier with multiple dual-bay transformers( two chassis, yes? )

It is fairly simple, gain stage, pasive RIAA gain. First stage will use a pair of 6BK7's in parallel( -3dB in noise from a single ), and terminate with a single 6BK7 stage with a DN3545/2540 mu-follower CCS. Schematics soon I'd say...:)
cheers,
Douglas

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Re: Phono pre [message #32188 is a reply to message #32187]

Sun, 28 October 2007 14:37

Wayne Parham
Messages: 18792
Registered: January 2001

Illuminati (33rd Degree)

I'm definitely interested. I'd like to build a top-notch phono stage.

On a related note, I wonder how much variance there is in adherence to the RIAA curve in the equalization circuits of popular phono stages. There has to be some, because I've heard systems that were bass heavy and others that were bass shy. Some could be attributed to cartridge loading, I suppose, but I think a lot of it was from deviation from the RIAA curve.

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Re: Phono pre [message #32189 is a reply to message #32188]

Sun, 28 October 2007 15:37

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

hey-Hey!!!,
It would be neat to measure a few that's for sure. The overall accuracy depends on how the basic R-C filter is executed. What makes up the R for one. Is it mostly plate resistance, or is it done some other way...:)
cheers,
Douglas

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Re: Phono pre [message #32190 is a reply to message #32187]

Tue, 30 October 2007 14:56

SteveBrown
Messages: 330
Registered: May 2009

Grand Master

Here's one I've been interested in building for some time. Had the pleasure of hearing it at Gary's - really outstanding phono stage. Sounds at least a bit similar to your thoughts, Douglas. I really like the passive equilization - always a better way to go in my opinion.

Phono Stage

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Re: Phono pre [message #32191 is a reply to message #32190]

Tue, 30 October 2007 15:32

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

hey-Hey!!!,
There is a single addition, a MC stage. I am not sure I like the idea of step-up transformers. Probably do a nice FET-input OP amp configured for ~20:1 gain. Easy access to C and R loading. Those little pF polystyrene caps are pretty sweet. The two chassis design will let me build a low voltage supply and run it through the same umbilical. Black AMP connectors will do...:)
cheers,
Douglas

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Re: Phono pre [message #32192 is a reply to message #32191]

Wed, 31 October 2007 07:05

SteveBrown
Messages: 330
Registered: May 2009

Grand Master

Douglas, a MC stage sounds good, nice to make it variable gain to accomodate the low and mid MC outputs. I like the idea of making the loading variable too. The thought of a two chassis implementation is nice, but I always worry about more complex grounding issues. Still, plenty of folks doing it and having good results. Are you thinking dual mono PS or no? Regulated?

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Re: Phono pre [message #32195 is a reply to message #32192]

Thu, 01 November 2007 13:53

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

hey-Hey!!!,
I think I won't regulate. Choke input above critical current will be fine I think. I'll also need a smaller bi-polar supply for the MC-stage's OP amp. Two chassis with power on one and signal on the other. DC heaters amounting to about an amp and a half of 6.3 will be needed. Again, LC filter with good diodes. For B+, a pair of damper diodes should make a dent in the overkill quota...:)

I will start with something quite like the Bottlehead seduction, but with a relaxed PS instead of run to 99% of redline, and tubes chosen for something other than minimum filament draw.
cheers,
Douglas

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