Does anyone care to ask an amplifier designer a technical question? My door is open.

@krelldreams My verdict, with this passive unit, in my system is as follows: The system with the passive has clear high and mid frequencies, good space, and sounds spacious... but it is a bit brighter, a bit leaner, and is less pleasant to listen to than with the preamp. I’d call the sound with the preamp “smoother” and “warmer”. The vocals through the preamp were slightly veiled compared to the passive though, which annoyed me. So.. after this exercise, I believe that either a better quality passive, or a more transparent preamp, is what I’d want. What design elements could improve the sound of a passive device? Clio wrote about a phono preamp with passive level control and aux inputs. What a great idea!

We make those phono preamps with a aux for people who appreciate that kind of thing. One other advantage is that you only power the phono section when you need it. Otherwise it is completely off, thus saving the tube life.

From a pure business sense I should talk preamp up and passives down, however that is not my truth. Passives are a great solution when used properly which is: dont load them with a lot of cable and dont load the source. This is easy today with low impedance sources.

Of course an active preamp is going to add a little distortion. Typically you can count on about 0.1 % per volt of output if there is no feedback. We dont know how every preamp colors the sound because we dont know what the designer is doing inside, perhaps intentionally. Some designers cheat the game by intentionally making something colored. They know someone will love it. Dont go assuming all preamps are designed on a level playing field, especially these days.

As someone said here he likes the microphonics of his 6SN7 preamp and calls it euphonic. Microphonics can pay a large role in preamp sound. Go tap on some tube preamps and see what comes out.

The thing that intersts me is that most complain that the bass of passives is usually lacking. However the bass of passives goes to DC with no phase shift. Tube preamps do not go to DC and at 40 Hz will start to have some phase shift. Is the phase shift what they like?

Is the phase shift what they like?

Could very well be Roger, that’s why I posted this as the possible explanation.

Especially in this case with a 0.47uf Wima coupling cap on the output of the Mani phono which is then loaded with his 5kohm pot to ground, it’s a high pass that’s -3dB @ 67hz, and if it’s 1uf still -3db @ 32hz.
The fix: Pot should be 10kohm or even 20kohm and the cap 1uF or more.

Mani top https://ibb.co/WsFNvhk

Mani bottom https://ibb.co/RyV6Gmt

Cheers George

I have a technical question regarding a PP EL86 tube amp I am modifying. I would like to upgrade the power supply. The current power supply is very, very simple and while simplicity is good I think a more robust supply could help sound quality.

A couple of questions and these should also have application for many others here.

1) All filaments are AC heated! Not DC. No filtering, no rectifier....Love you hear your comments on this. Would converting to a CLC filter with possible voltage regulation be worth doing?

2) 5U4 rectifier Tube receives 350 VAC and post tube VDC of 476 with no load. The plate supply is a simple RC only. 100 ohm resistor followed by two 680uf electrolytic caps in series. This feeds the vintage Scott output trannys. If I wanted to add a choke where should it be placed and how do I determine the value correctly. Like to know how you would design the plate supply for this simple PP el84 amp.

I ask your opinion of SS voltage regulation on both filament and plate supplies. Is it something you regard as very important? 

Thanks in advance.

@ramtubes

For those who will likely disagree: If burn in exists in these devices why did we not know about it until recently. I find no references to burn in in the 50s 60s 70s.. when did it start?

And if burn in occurs in cabling, why don’t we see people producing these measurable results between a new and burned in cable? The suspicious thing is that when most cable manufacturers are hyping either the technical reasons why their cables produce better sound, or telling you the cables need burn in, they are always appealing to some objective, technical phenomena whose existence is known because it was measurable. "Here’s a technical problem with cables you need to know about, that we have solved via our manufacturing process!"

But when they tout that they have "solved" one or more objective technical problems in cable design, they typically don’t demonstrate they’ve solved the problem in any measurable way. Instead, the results go straight to hype, marketing and the subjective impressions of audiophiles and reviewers. Same with burn in. Funny that.

As I’ve mentioned before in such discussions, audiophiles think everything changes substantially with "burn in," fuses, resistors, cables. And yet companies like Vishay and others - responsible for selling cabling, resistors etc to professional industries - industrial, computer, and incredibly spec-sensitive applications in avionics, military and aerospace design - don’t go on about "burn in." If the specs actually changed that much over time of a cable or resistor or fuse from when it was delivered new to in-use, this is something customers employing them in sensitive applications would need to know (and it would obviously be very problematic if those industries could not rely on a product actually meeting the stated specs, out of the gate).

And, again, you see (as far as I know) none of this "please burn our product in for 100 hours before application, as the specs will change" when the rubber hits the road, when you sell these things to engineers who can identify B.S. from marketing.

So my question is, why is it tubes are able to do that? Is it a matter of tubes being lowest in distortion at lower-signal levels (where imaging resides?), and transistors in their curves highest?

Back in the 90's when emulating gear in digital, we found that adding even order harmonic distortion brought the image forward and wider, i.e. more tube like. Odd order made the image deeper and more triangular, i.e. more SS like. By careful adjustment of O/E ratios, we could alter the sound stage. We were using 24bit digital and adding distortion at the 16th bit or 0.0015%.

Mani phono pre [only for example, not a slur against Schiit]

In the upper left corner is a 3 terminal voltage regulator. These devices are notorious for varying between manufacturers and within manufacturers as die changes are implemented or offshored. Additionally, these are active devices with feedback and as such can have horrific impedance and phase characteristics which affect the sound of the circuit powered therefrom. On the same DUT, the regulator can make it sound boxy, shrill, dull, warm, etc. With the same regulator, circuit changes which alter the current draw can cause the same sonic changes.