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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: 10 May 2017, 12:01 
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Joined: 29 Dec 2016, 03:06
Posts: 18
While studying different RIAA deemphasis sistems (because learning is fun) I've found this phono stage that uses a different aproach:

6moons audio reviews: Trafomatic Audio Reference Phono One

The RIAA network is neither in the feedback path nor in the classic passive filter between stages. It's in the plate load. Maybe some of you were aware of it, but for me it's the first time I see something like this. Well, it makes sense, and it seems to work allright.

I've made a very quick simulation on LTSpice, using jfets instead of tubes, and with some tweaking of resistors and capacitors values I've obtained a decent result (not accurated, just promising). What it can be appealing is that you lose a lot less signal than with a passive filter.

Can it be a good alternative system, or has it been tried before and has it been rejected for not being good enough?


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PostPosted: 10 May 2017, 20:46 
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Joined: 04 Jun 2008, 20:59
Posts: 3845
Location: Arizona, USA
Hi, There were answers to this on another web forum. They seemed fine. Putting the network in the anode of a tube is effectively pretty much the same as being in the cathode. That is because the B+ is a low impedance path for the signal. It is just a bit awkward as there is significant voltage on the components and more opportunities for shorts that might cause damage or be harmful if contacted. I personally prefer passive RIAA equalization between stages. I'm not convinced you lose more signal in passive over that method. To get the 40 db slope necessary you need to boost 20 and cut 20. No free lunches.

Good listening
Bruce

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PostPosted: 11 May 2017, 04:37 
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Joined: 29 Dec 2016, 03:06
Posts: 18
I was thinking about making a first simpler version, using jfets, just to see how it works. Of course then voltages across the filter network will be significantly lower, less prone to the damages you point out.


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