L0rdGwyn's DIY Audio
Feb 5, 2021 at 2:30 PM Post #2,101 of 2,524

L0rdGwyn

Headphoneus Supremus
Joined
Nov 22, 2016
Posts
3,255
Likes
4,989
Location
Cleveland
No, I thought that was low sensitivity. I mean if the 2Vrms input signal is somehow *over-driving* the first tube stage. Or is this super unlikely?

Gotcha, just wanted to clarify. So a 1Vrms input (high sensitivity) vs. a 2Vrms input (lower sensitivity). What that would represent is too much gain in the amplifier for the source. Assuming it is in an integrated amplifier with a variable gain stage and an power stage, the issues I see are 1) the amplifier is going to get loud very early in on the volume pot 2) the power stage can be driven to clipping / unsafe volumes more easily by accident 3) the S/N ratio of the amplifier will lower, i.e. higher noise floor for a given output voltage relative to a lower, more appropriate input sensitivity. Maybe others can think of additional issues but that's what comes to mind for me.

As far as the over-driving concern, the 2Vrms input will be attenuated by the volume pot. The goal of the gain stage is to swing enough voltage with some headroom at low distortion to drive the power stage to full output. The power stage should clip well before the gain stage, if that makes sense. If the gain stage is clipping before the power stage or the power tube is not being driven to full power output at maximum input signal, you should probably be using a higher gain input tube. This is all assuming getting max power output out of the amplifier is the priority. Does that answer your question? Sorry if it doesn't, I'm a little delirious on 2 hours of sleep.
 
Feb 5, 2021 at 2:33 PM Post #2,102 of 2,524

L0rdGwyn

Headphoneus Supremus
Joined
Nov 22, 2016
Posts
3,255
Likes
4,989
Location
Cleveland
Going to keep rambling about my 801A amp since I am super hyped for it at the moment. Like I mentioned, made some changes that are going to get the performance right where I want it to be (in theory, will need to confirm).

Here is a photo of the seven tubes going in this amplifier as it is currently designed. This is sort of how I envision them being arranged on the top plate.

DSCF6390.jpg
 
Last edited:
Feb 5, 2021 at 2:51 PM Post #2,103 of 2,524

Xcalibur255

Headphoneus Supremus
Joined
Feb 4, 2008
Posts
3,607
Likes
1,773
Gotcha, just wanted to clarify. So a 1Vrms input (high sensitivity) vs. a 2Vrms input (lower sensitivity). What that would represent is too much gain in the amplifier for the source. Assuming it is in an integrated amplifier with a variable gain stage and an power stage, the issues I see are 1) the amplifier is going to get loud very early in on the volume pot 2) the power stage can be driven to clipping / unsafe volumes more easily by accident 3) the S/N ratio of the amplifier will lower, i.e. higher noise floor for a given output voltage relative to a lower, more appropriate input sensitivity. Maybe others can think of additional issues but that's what comes to mind for me.

As far as the over-driving concern, the 2Vrms input will be attenuated by the volume pot. The goal of the gain stage is to swing enough voltage with some headroom at low distortion to drive the power stage to full output. The power stage should clip well before the gain stage, if that makes sense. If the gain stage is clipping before the power stage or the power tube is not being driven to full power output at maximum input signal, you should probably be using a higher gain input tube. This is all assuming getting max power output out of the amplifier is the priority. Does that answer your question? Sorry if it doesn't, I'm a little delirious on 2 hours of sleep.
No, it does. I'm just theory crafting as to why my amp sounds like a replay gain experiment gone wrong half the time. I don't think I'm on the right track with this one though. Thanks for the help.

I do think the 50K pot in the amp should absolutely be a 100K pot instead but I doubt this alone can take credit for the trouble I have. It does indeed get too loud too quickly.
 
Feb 5, 2021 at 3:30 PM Post #2,104 of 2,524

L0rdGwyn

Headphoneus Supremus
Joined
Nov 22, 2016
Posts
3,255
Likes
4,989
Location
Cleveland
No, it does. I'm just theory crafting as to why my amp sounds like a replay gain experiment gone wrong half the time. I don't think I'm on the right track with this one though. Thanks for the help.

I do think the 50K pot in the amp should absolutely be a 100K pot instead but I doubt this alone can take credit for the trouble I have. It does indeed get too loud too quickly.

So the pot impedance won't affect the signal attenuation, what the pot impedance represents is the input impedance of the amplifier, what the source sees looking into the input. Assuming a source with a low output impedance, like most DACs these days, the value of the pot isn't super critical assuming it isn't extremely low, 50K should be just fine. What you would need to decrease the volume is a resistor voltage divider in front of the pot so it does not get the full output of the DAC. Another option is to decrease the output voltage from the DAC if that is a feature. I think we talked about it before, but if you haven't already, I think it is worth trying a parallel resistor on the output transformer secondary.
 
Feb 5, 2021 at 5:40 PM Post #2,106 of 2,524

whirlwind

Headphoneus Supremus
Joined
Mar 21, 2007
Posts
9,614
Likes
10,718
Location
At The Crossroads
Going to keep rambling about my 801A amp since I am super hyped for it at the moment. Like I mentioned, made some changes that are going to get the performance right where I want it to be (in theory, will need to confirm).

Here is a photo of the seven tubes going in this amplifier as it is currently designed. This is sort of how I envision them being arranged on the top plate.

DSCF6390.jpg

That is a nice layout!
 
Feb 7, 2021 at 7:56 PM Post #2,108 of 2,524

bcowen

Headphoneus Supremus
Joined
Jan 3, 2018
Posts
8,343
Likes
18,265
Location
North Carolina
Just got home, was out of town for the weekend. Finished up the filtration system for the ultrasonic record cleaner. Look familiar @bcowen ? :)

IMAG3007.jpg

Tomorrow I will start the DarkVoice modifications.

LOL! There is a vague resemblance, to be sure. :smile:

US1.JPG
 
Feb 7, 2021 at 8:17 PM Post #2,109 of 2,524

L0rdGwyn

Headphoneus Supremus
Joined
Nov 22, 2016
Posts
3,255
Likes
4,989
Location
Cleveland
Cleaned one of my favorite albums to test out the new process.

At a 80dB volume level, the playback was so quiet when I dropped the stylus I thought I forgot to turn on the phono stage.

IMAG3014-2.jpg

Started stuffing the gyrator boards for DarkVoice stuff tomorrow. Will leave the leads long on the DN2540 in case there are issues, these are backordered for months, think I have about ten left.

IMAG3016-2.jpg
 
Feb 7, 2021 at 8:50 PM Post #2,110 of 2,524

bcowen

Headphoneus Supremus
Joined
Jan 3, 2018
Posts
8,343
Likes
18,265
Location
North Carolina
Cleaned one of my favorite albums to test out the new process.

At a 80dB volume level, the playback was so quiet when I dropped the stylus I thought I forgot to turn on the phono stage.

IMAG3014-2.jpg

Started stuffing the gyrator boards for DarkVoice stuff tomorrow. Will leave the leads long on the DN2540 in case there are issues, these are backordered for months, think I have about ten left.

IMAG3016-2.jpg

Excellent choice of tunes. :laughing:

If you have True Stories, listen to the first 30 seconds of Papa Legba. If you have your cartridge azimuth dialed in just perfectly, the sound effects at the very beginning start waaaaay right, go waaaay back behind the speakers, waaaay left, and then waaaay behind your listening seat before going back right and repeating. Huge, wide, 3D circle. Even though my couch (listening seat) is up against the wall, I've had people look behind them to see where the speaker is, the effect is so real. Way cool. I can tell more about cartridge alignment and setup with the beginning of that track than I can with the multitude of test LP's I have. This is only through the loudspeakers though....I cannot duplicate it with headphones. Yet. :laughing: Not that I listen to sound effects on a regular basis, just that this one is so telling of perfect cartridge alignment.


1612748479780.png
 
Feb 7, 2021 at 9:01 PM Post #2,111 of 2,524

JazzVinyl

Headphoneus Supremus
Joined
Jan 7, 2010
Posts
4,192
Likes
1,298
Excellent choice of tunes. :laughing:

If you have True Stories, listen to the first 30 seconds of Papa Legba. If you have your cartridge azimuth dialed in just perfectly, the sound effects at the very beginning start waaaaay right, go waaaay back behind the speakers, waaaay left, and then waaaay behind your listening seat before going back right and repeating. Huge, wide, 3D circle. Even though my couch (listening seat) is up against the wall, I've had people look behind them to see where the speaker is, the effect is so real. Way cool. I can tell more about cartridge alignment and setup with the beginning of that track than I can with the multitude of test LP's I have. This is only through the loudspeakers though....I cannot duplicate it with headphones. Yet. :laughing: Not that I listen to sound effects on a regular basis, just that this one is so telling of perfect cartridge alignment.


1612748479780.png

I love True Stories and the Papa Legba song! Going to see what happens here via my trusty LP. I also have a Weather Report LP that 'every single time'...I can make people look behind them to see a fellow who comes in with a triangle...!!!

We play the CD and the triangle guy is clearly heard, but the 'spacial cue' is not there!

Also....the "Naked" album by Talking Heads...I only have the CD version but OMG! Sound Quality on that one is vastly superior to my other Talking Heads CD's....Steve Lillywhite was in charge of the 'Naked' recording sessions, I believe, and on headphones...it is really immersive!

Cheers All...!!

:)
 
Feb 7, 2021 at 9:15 PM Post #2,112 of 2,524

L0rdGwyn

Headphoneus Supremus
Joined
Nov 22, 2016
Posts
3,255
Likes
4,989
Location
Cleveland
Excellent choice of tunes. :laughing:

If you have True Stories, listen to the first 30 seconds of Papa Legba. If you have your cartridge azimuth dialed in just perfectly, the sound effects at the very beginning start waaaaay right, go waaaay back behind the speakers, waaaay left, and then waaaay behind your listening seat before going back right and repeating. Huge, wide, 3D circle. Even though my couch (listening seat) is up against the wall, I've had people look behind them to see where the speaker is, the effect is so real. Way cool. I can tell more about cartridge alignment and setup with the beginning of that track than I can with the multitude of test LP's I have. This is only through the loudspeakers though....I cannot duplicate it with headphones. Yet. :laughing: Not that I listen to sound effects on a regular basis, just that this one is so telling of perfect cartridge alignment.


1612748479780.png

Unfortunately I don't have a copy of True Stories, just Remain in Light and Speaking in Tongues. I passed on a nice copy of True Stories about a month ago, I am now filled with regret :cry: maybe I'll go back and hunt it down!
 
Feb 7, 2021 at 9:25 PM Post #2,113 of 2,524

bcowen

Headphoneus Supremus
Joined
Jan 3, 2018
Posts
8,343
Likes
18,265
Location
North Carolina
Unfortunately I don't have a copy of True Stories, just Remain in Light and Speaking in Tongues. I passed on a nice copy of True Stories about a month ago, I am now filled with regret :cry: maybe I'll go back and hunt it down!

Oh, then you need Little Creatures too. I love David Byrne's voice, despite his weirdness. :smile::smile:
 

Users who are viewing this thread

Top