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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 29 Jul 2013, 09:42 
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Joined: 05 Jun 2012, 13:10
Posts: 196
Location: Darboy, WI, USA
Thanks Matt. I find Edcors website to be a little bit hard to sort through all the power transformers.

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PostPosted: 14 Sep 2013, 23:28 
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Joined: 06 Apr 2009, 10:08
Posts: 1394
Location: US Pacific Northwest
Well, I have no idea why this happens, but the 4S preamp that I had half wired one year ago is now complete. I finished it today after having to order a couple of 0.47µf coupling caps. This is the one I showed earlier in the Blue Pomona chassis. Here is what it looks like.
Attachment:
Assembled.jpg
And just to show you that I'm not just fooling you, here is the flip side completed.
Attachment:
4S Completly Wired.jpg
The performance of the little unit proved very good. Here is the measured gain/phase data using a generic 12AU7.
Attachment:
Gain-Phase Plot.png
The preamp is dead quiet; power supply ripple is better than -100dBv and there is no perceptible output noise with it connected to my 6V6 Lacewood amp (with both turned all the way up). Here it is in use with my Lacewood amp.
Attachment:
4S In Use.jpg
And it looks even better in the dark.
Attachment:
4S Preamp Tube Glow.jpg
I was really surprised at how well this opened up my Lacewood amp. It provided much more power and drive than using my iPod alone. And the combo sounds great together.

Now that I've got this one done, I need to attack my next preamp project. It's a 4S universal followed by James-Baxandall tone stacks and a low noise cathode follower. This will really allow me to tailor the response of my setups on the fly. I can hardly wait.


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PostPosted: 15 Sep 2013, 07:31 
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Joined: 06 Jun 2008, 18:23
Posts: 4834
Location: Australia
Blue? You have been looking at too many of my crazy colours. Love the tube rec. this has to be the next step in taking these great little preamps to the next level. I would love to build another tube phono stage with tube rec.

I always found the 12AU7 to sound the best of those small triodes. In Stereophile one senior reviewer said a system always sounded better with a preamp than without wether it needed it or not.

Looks great and very neat and compact. 10 out of 10 Matt.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 16 Sep 2013, 13:10 
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Location: Darboy, WI, USA
I've noticed people saying that minimizing the stages of an amplifier tends to give a 'cleaner' sound; ie. the amp affects the music moving through it less, but then people also note that pre-amps give a better sound even when there is no need for additional amplification.

What gives? When do stages end and pre-amps begin? Beauty is in the ear of the listener?

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PostPosted: 16 Sep 2013, 14:20 
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Joined: 02 Mar 2009, 12:41
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Location: Vänersborg, Sweden
Remember that amplifiaction is not about voltage amplification but also current gain. If the power amp has low Zin a preamp/line amp with current gain but no voltage gain (gain = 1) have to be used.

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PostPosted: 16 Sep 2013, 18:28 
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RossD wrote:
I've noticed people saying that minimizing the stages of an amplifier tends to give a 'cleaner' sound; ie. the amp affects the music moving through it less, but then people also note that pre-amps give a better sound even when there is no need for additional amplification.

What gives? When do stages end and pre-amps begin? Beauty is in the ear of the listener?

Just talking about simple preamps, SS or tube, from what I understand most sources CD players etc. don't have good drive capability. Power amps can some times put demands on the source which the source is not able to cope with with. The preamp acts as a buffer and voltage gain section or as a go between. I maybe right off kilter here but that's how I understand it.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 16 Sep 2013, 20:42 
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Joined: 05 Jun 2012, 13:10
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Location: Darboy, WI, USA
Ok, so can we define "drive" in terms of units? Or equation? I am still digesting the first chapter of Morgan Jones Valve Amps

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PostPosted: 22 Jun 2014, 08:40 
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Joined: 22 Jun 2014, 08:31
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Location: Trinidad & Tobago
Hi Folks
I'm new to the group and from Trinidad in the Caribbean. Love the simplicity and effectiveness of this design. Will post a few pics of my unique implementation as the build progresses.

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PostPosted: 22 Jun 2014, 10:33 
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Joined: 22 Jun 2014, 08:31
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Location: Trinidad & Tobago
In my home studio, I have an Alesis RA500 Reference Power-Amp driving our homebrew Voice of the Theater type speaker cabinets (father-daughter project when she was just 10-years old).
I require a new preamp unit, what I would really like is both a Solid-State Preamp and a Tube Preamp. I would also like Tone and Balance controls, VU Output Meters and Peak indicating LEDs.
So my project here is to build a preamp encompassing all the above ideals in one classy enclosure with switchable Solid-State / Thermonic pre-amplification. The tube should also be highly featured on top of the enclosure, housed in a nicely CNC machined, aluminum cage.
I Like the simplicity and versatility of this 12A*7 design so incorporating this is a no-brainer, since I happen to have a couple such bottles saved-up for a “nice project” since electronics school in the 70’s.
The Philips TDA1524A promises to be a nice solid-state preamp IC with simple voltage referenced volume, tone and balance controls, so this will be the platform for the s/s bit …..hell, there’s even a kit available http://www.electronickits.com/kit/compl ... l/k100.htm
I do have a CNC Vertical Machining Center in my workshop so the tube-cage was easy enough.
Got a couple round, retro style VU meters around here somewhere so those will be pressed into service.
Front and rear panels will be engraved on my CNC Router/Laser Engraver. Chassis will be 1/16” aluminum sheet and the side-panels would be some oiled mahogany courtesy my woodworking friend.
This promises to be a fun build and a nice cool project and I will post pics as I progress .....so we start with machining the platform for the bottle:

Image

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PostPosted: 22 Jun 2014, 10:44 
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Joined: 22 Jun 2014, 08:31
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Location: Trinidad & Tobago
Preliminary panel layout:

Image

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