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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: 17 Jun 2020, 11:20 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
I used in my pre-amp the initial drawing values and not the updated ones shown in previous threads. To me sound is fantastic but I am not of course a real audiophile man. The reason is that I had the initial components list where signal capacitor was expensive; the same the tantalum non magnetic resistors. Bruce, do you believe that this small changes introduced in previous threads will contribute significantly to better sound quality? It will be a considerable investment since this pre-amp has high end components and I want to keep standards


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PostPosted: 17 Jun 2020, 12:27 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, The original values are really quite excellent. I am really picky though. I'm told that happens as you age 8-) I find the new values better. Slightly better S/N as the impedance in the RIAA section is lower, but nearly as much loss as there is more gain in the second section. The flatness of the equalization is better. It was within 1 db from about 25HZ to 19K and down about 1.25 db at 20 and 20K. No rise so technically as many would list it +/- 0/1.25. The new components make it less that 0.25 db down at 20HZ and flat to past 30K. The bass response actually might cause some folks trouble as the -3db point is about 8HZ. This is in the area of rumble for some turntables and at the lower end of arm resonance values recommended. In that case I would decrease the size of the 0.33uf coupling capacitor to either 0.22 or even 0.15uf. None of my stuff has any problems with the high level of bass response, but some folks might.

As to whether of not I would change things in your build....if you are happy with the sound no. I used those values for several years in my main preamps and they were just fine.

Good listening
Bruce

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PostPosted: 18 Jun 2020, 12:21 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thanks Bruce. I really enjoy the sound and I will try different 12AT7 tubes to see the difference. I found two ECC801S original Telefunken and I am waiting to try them!!! Now I run the preamp with Sophia Electric 12AX7 and Genalex Gold Lion 12AT7.
Have a nice day
Dimitris


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PostPosted: 19 Jun 2020, 14:23 
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Location: Arizona, USA
Hi Everyone, This is a bit lengthy, You can’t get there from here. I have been doing some serious tinkering over the past two months. Sort of exploring what happens when you change things in phono preamps. Some has been quite rewarding. I found a new set of RIAA component values that result in a slightly flatter response curve. I can now get it to within a +/- 0.25 db level. Not too shabby for off the shelf components. Better still it sounds great. I like it better. With a quality turntable, arm and cartridge it is stunning. BTW I use several combinations of gear. With a Dynavector 23Karat RS-MR in an Origin Live arm on an Empire 598 turntable with Softone SUTs it makes me shiver. I discovered a few things about getting the noise levels even lower than before. Now at -80dbv. That is also where the “can’t get there from here” comes in. I have discovered that without going to what I would consider extremes it the end of the line. The only paths from there are: selected low noise tubes, negative feedback, active RIAA equalization, multiple parallel tube sections and solid state active devices. None of the choices appeal to me. The thing that I find limits the S/N is intrinsic tube noise. It does not seem that additional filtering nor can configuration changes make it significantly lower. I tried: DC to DC converters, AC to DC isolated supplies, linear regulators, various SMPS and huge capacitors. The only thing I didn’t use was battery power and I rejected that as too extreme for a user friendly preamp. Most things made the S/N worse, some greatly so. Now to be fair, the practical S/N limit for most vinyl record play back systems is about 55db. The theoretical limit is in the 70 db range but few devices can approach that. New records are seldom anywhere near that quiet and used ones depending on condition are usually a lot worse. So with at least 25 db of headroom above the typical level useable the residual noise is unlikely to be audible. In my system with a passive preamp and the electronic crossover (works at 45 HZ) set for zero db gain there is no noise or hum at all. Not even right at the speaker with the volume set for max. I have to add 12 db of gain to get anything at all. Then it is mostly low frequency stuff. It is virtually only tube noise. So for now unless I have some startling insights I am done with the preamp. After all it only took about 50 prototypes and 11 years. I hope it was worth the read.

Good listening
Bruce

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 Post subject: SUT wiring question
PostPosted: 13 Jul 2020, 21:21 
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Joined: 14 Jul 2014, 13:18
Posts: 43
Location: Arizona
I am wiring up a pair of Softone PLT-1's, and have a question on how they should be wired and connected.

Below is how I intend to connect and wire them for 1:12 turns ratio (cartridge is AT-0C8XSL):

Is this correct?


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PostPosted: 14 Jul 2020, 21:43 
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Hi, That seems to be correct. I like to keep them in a steel chassis with the chassis ground isolated from the signal ground. I run a separate ground wire from the turntable chassis to the SUT chassis and then another to the preamp chassis. It keeps hum lower. Also I have found with all SUTs that it seems better to keep the left and right grounds separate. Less interactions and less hum. I really hate hum. :down:

Good listening
Bruce

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