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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 Nov 2018, 21:09 
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Joined: 06 Jun 2008, 18:23
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The new premium stepper
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PostPosted: 30 Nov 2018, 01:49 
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wow nice


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PostPosted: 26 Dec 2018, 19:08 
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Elite twins, one for me and a commission job.
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PostPosted: 04 Jul 2019, 19:19 
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After building a hybrid headphone amp with a 4SU front end and a PT2308 chip HP amp back end I added a HP chip amp section to Elite. The two Grant Fidelity Psvane globes look the part and are divine sounding as a preamp but make an excellent HP amp. When the headphones are plugged in they disconnect the output RCAs on the rear. When no headphones are plugged in the HP section of the preamp is disconnected so it doesn’t interfere with the excellent sound of the preamp.
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PostPosted: 13 Aug 2019, 00:40 
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Ever tried to fix something which is not broken because you think it shouldn’t work that way it does. I have made four of these active load preamps. In the second last one I added a headphone driver. When head phones are plugged in the jack it cuts out the RCAs out which are used when Elite is just a preamp.

To get better performance from the preamp/HP amp I moved the pot from the backend (where it is on the other three builds) to the front end. That meant the expensive Jansen CuPIO output caps could feed directly into the HP chip amp with no other input cap needed.

The reason why this cct. is described with attenuator on the rear is because active load is very microphonic. With the attenuator on the output you hold the noise down and the music level very quickly swamps any noise from the tubes. BUT put the pot on the front you get the full microphonic noise unattenuated and the music level lower. Fortunately some old RCA 6SN7s aren’t naturally noisy and with these in the system the preamp/HP amp is very good. But put some better Psvane or Chuguang tubes in the noise swamps the music.

I’ve spent two weeks trying to get the microphonics out. It’s a part of the build. Best I can do is move the pot to the backend and add some interstage caps into the HP chip amp section. Best way to go.

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PostPosted: 13 Aug 2019, 10:39 
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Hi, I suspect the tube types are the main source of the micro phonics. However I use the SRPP (aka active loaded triode) configuration with 12AU7 types all the time and it is the basis for the kit Forewatts. The volume control is in the input side. They don't have the problems Mark is running into. The volume control in the front insures that the circuit cannot be over driven, the penalty is that the residual circuit noise is always present at the output. With the Forewatts this is quite low and typically in the -85 dbv or better range. Mine typically show about -92 dbv.

Good listening
Bruce

EDIT: is it possible to put a rubber or silicone damper around the tubes like "EAR" often does? It won't be as pretty , but then it might solve the problem.

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