• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Douk Pre-amp Tube Rolling (Russian 6N3P-E)

H-713

Senior Member
Joined
Jan 24, 2021
Messages
364
Likes
607
I have done a number of those as well with no difference seen. I did it for Topping DAC and at least once for Hypex based power amp builds.
I had in mind putting together a relatively simple amplifier circuit and comparing a few different op-amps with the APx555. That way you don't have a DAC or a power amplifier to mask the distortion and noise of the op-amp.

More useful for those of us who like to design our own equipment, so I understand if it's too niche for ASR to bother with.
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
37,893
Likes
161,490
Location
Seattle Area
I had in mind putting together a relatively simple amplifier circuit and comparing a few different op-amps with the APx555. That way you don't have a DAC or a power amplifier to mask the distortion and noise of the op-amp.

More useful for those of us who like to design our own equipment, so I understand if it's too niche for ASR to bother with.
I can do that if you can get agreement from others that it is useful thing to test. Hate to do it and have people say, "well, you should have tested this circuit instead of that."
 

KSTR

Major Contributor
Joined
Sep 6, 2018
Messages
2,075
Likes
4,589
Location
Berlin, Germany
I had in mind putting together a relatively simple amplifier circuit and comparing a few different op-amps with the APx555. That way you don't have a DAC or a power amplifier to mask the distortion and noise of the op-amp.

More useful for those of us who like to design our own equipment, so I understand if it's too niche for ASR to bother with.
With any of today's audio OpAmps used in a typical low-gain line-level circuit, you won't see much of anything unless the circuit design is bad/unsuited to begin with. Even with the AP you need to apply a trick to reasonably to see any distortion above the noise floor to artificially increase the gain the OpAmp itself sees without changing the total circuit gain.

For measurements see Samuel Groner's legendary report: http://www.nanovolt.ch/resources/ic_opamps/pdf/opamp_distortion.pdf. He also used the noise gain trick because, quoting Groner "One of the main problems when measuring opamp distortion is the fact that for essentially all devices the distortion of a typical amplifier configuration with low noise gain is well below the measurement limit of even the best currently available equipment for distortion measurement. This is especially true at low and medium frequencies (say below 5 kHz) and for THD+N measurements, where noise of the oscillator source and the analyser often make up a significant contribution of the reading"

At high gains (Phono, MicInput, etc) you'll start to see something, though.
 

xarkkon

Active Member
Joined
May 26, 2019
Messages
227
Likes
329
Cool analysis, especially on the humming. That has been my experience with the Bottlehead Crack as well. Thought I just had defective tubes the first time around. Looks like its just ****** tubes working as intended. Heh.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
11,660
Likes
25,959
Location
The Neitherlands
The amount of hum depends largely on the anode current and anode size.
The higher the current (lower resistance basically) and the smaller the anode the less it can pick up hum.
When the tubes are shielded (also from mains transformer hum eminating from in the amp as well) there is no need to pick up hum.
Feeding the heaters with DC (as is done in this amp) also helps.
 

Mojo Warrior

Member
Joined
Mar 28, 2019
Messages
90
Likes
108
I never drank the grape koolaid for tubes but I do wonder how some of the better manufactures stuff measures. Anyone have a newish Luxman or McIntosh that can be tested?

There's no reason to believe that a brand name will alter the pathetic performance of vacuum tubes. They are the limiting factor. If the SINAD is 50 dB that is all it is capable of doing. Testing reveals that everything about the myth of sonic superiority comes down to the "magic tubes" hypothesis hence the pursuit of the holy grail.

We are still waiting for someone to submit "magic tubes" to Amir for testing. I suspect we will be waiting for eternity.
 

NiagaraPete

Major Contributor
Forum Donor
Joined
Jun 23, 2021
Messages
1,055
Likes
799
Location
Canada
Well the posted specs for a bottom model Lux is pretty good. Certainly not like solid state though.
Screen Shot 2021-12-07 at 10.47.08 AM.png
 

DualTriode

Addicted to Fun and Learning
Forum Donor
Joined
Oct 24, 2019
Messages
639
Likes
398
Hello All,

Looking for the sweet spot.

I borrowed this process from Nelson Pass.

Somewhere I have a plywood breadboard with a 9-pin tube socket and a couple of rows of euro type screw mount connectors.

Also I have a Keysight N5772A 600VDC variable power supply.

After more than a few late nights I found that you can dial in the supply voltage and swap in and out cathode resistors to adjust the bias current and grid voltage.

Tubes most definitely do have a sweet spot (or grid voltage, plate current range) where the noise and distortion is minimized.

I found that the JAN GE 5760’s were fairly consistent. The 6NP3 is the Russian version or nearly equivalent to the 5670.

I spent more time with the 12AU7 and found that even if the 2nd and 3rd H’s were fairly consistent the 5th, 6th H’s and on up could be all over the place.

The harmonics beginning with the 2nd have the typical stair steps of decreasing HD’s.

Yes most often the 2nd H is the highest step, however the 3rd, 4th, and on up are stair stepping down not far behind.

Tube distortion is rarely if ever just 2nd Harmonics.

Also keep in mind that with the APx555 or any other Analyzer large sample size and averaging only filters out the appearance of noise on the FFT plots. In real time the noise swamps or masks most of the lower magnitude Harmonic Distortions that we see on the FFT plots.

Thanks DT

https://www.keysight.com/us/en/assets/7018-01235/data-sheets/5989-1330.pdf
 
Last edited:

dfuller

Major Contributor
Joined
Apr 26, 2020
Messages
1,996
Likes
2,750
There's no reason to believe that a brand name will alter the pathetic performance of vacuum tubes. They are the limiting factor. If the SINAD is 50 dB that is all it is capable of doing. Testing reveals that everything about the myth of sonic superiority comes down to the "magic tubes" hypothesis hence the pursuit of the holy grail.

We are still waiting for someone to submit "magic tubes" to Amir for testing. I suspect we will be waiting for eternity.
Brand no, but circuit design very yes.

Tubes most definitely do have a sweet spot (or grid voltage, plate current range) where the noise and distortion is minimized.
Yep, and within reason this can be predicted by looking at the transfer functions of the plate curves.
 

DualTriode

Addicted to Fun and Learning
Forum Donor
Joined
Oct 24, 2019
Messages
639
Likes
398
Brand no, but circuit design very yes.


Yep, and within reason this can be predicted by looking at the transfer functions of the plate curves.

Hello,

Okay you are on.

Show us the 5670 plate curves and show us how to plot rp, mu and transconductance at the operating point of your choosing.

Describe to us what the FFT plot will look like at the operating point that you have selected.

Looking at the curves what will the 20 to 20k noise will be for your selected tube.

Within reason that is.

Otherwise I will believe that you are blowing smoke.

Thanks DT
 

pseudoid

Major Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
1,671
Likes
965
Location
SoCal
Thanx for the link @SIY, but please remember that most ASR readers are not AES members; hence, don't have access to view such links. [sorry!]
Note that there's enormous variations from tube to tube (or section to section in multisection tubes) even from the same brand or manufacturer, it's the nature of the beast.
In the olden days, when it came time to replace tubes; we believed that purchasing "Matched, Quad" sets of tubes was the only way.
It used to add about $50 to the price of the purchase but they actually came with comparative test-results graphs.
I have nooooooooooooo idea if such 'matched-quad sets' sounded any better or had less hum, but that was the only way to "roll", back then.:cool:
 
Last edited:

SIY

Master Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
8,390
Likes
18,855
Location
Alfred, NY
Thanx for the link @SIY, but please remember that most ASR readers are not AES members; hence, don't have access to view such links. [sorry!]
It's worth buying. Or contacting Merlin for a reprint.

I of course would NEVER suggest using Sci-Hub.:rolleyes:
 

pseudoid

Major Contributor
Forum Donor
Joined
Mar 23, 2021
Messages
1,671
Likes
965
Location
SoCal
Direct quote of Thomas Jefferson pertaining to Intellectual Property:
“That ideas should freely spread from one to another over the globe, for the moral and mutual instruction of man, and improvement of his condition, seems to have been peculiarly and benevolently designed by nature, when she made them, like fire, expansible over all space, without lessening their density at any point, and like the air … incapable of confinement or exclusive appropriation. Inventions then cannot, in nature, be a subject of property.”
I used to love this quote, but me thinx Jefferson was myopic (and had nice pipe-dreams) about the world in the 21st Century.
He would have never imagined where even the "news" media has put-up self-defeating pay-walls for information.
I am confoozled as to how "yesterday's old news" could possibly make it into the future history [errrrr....] books.
This is the real info-wars and AES is head deep into it. Sadly, there is no going back.:(
Apologies for the OT rant.
 

captainbeefheart

Active Member
Joined
Apr 18, 2022
Messages
276
Likes
355
Confirms my experience that all tube devices are distortion generators.

Not all, depends on the design.

That Luxman is most likely a distortion generator on purpose, they want their amp to stand out in a crowd and once you have an amp with 1% THD at 10 watts it's certainly going to be colored. Take a look at the sensitivity, 180mV for full power!! Given the same tube selection one could easily add feedback and get the distortion down to .1% THD at full output, increase bandwidth and lower noise floor. Feedback is an amazing thing yet many tube amp manufacturers don't use it as they should. It's not the devices that make the difference between SS and tubes, it's the amount of feedback used.
 
Top Bottom