DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 05 Apr 2020, 19:18

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 415 posts ]  Go to page Previous  1 ... 3, 4, 5, 6, 7, 8, 9 ... 42  Next
Author Message
PostPosted: 20 Jun 2011, 12:25 
Offline
Banned

Joined: 15 Mar 2010, 08:32
Posts: 487
Location: Canada
Hi.
mwhouston wrote:
AVC ??.

AVC=Autotranformer Volume Control. Or it is also called magnetic volume control. It is a single-wound tranformer with tappings to select volume levels using a selector. Price depends mainly of how fine is the volume steps. One with 3dB asks for USD200, & one with finer 2dB steps asks for USD400!!:bawling:

Yes, an AVC is an 'elegant' volume control with non-linear frequency & phase response despite its lofty price that intimidates many many DIYers, including your truly.

Like any pot, an AVC can be used to build a passive linestage which does not generate high orders of harmonic distortions & noises like an active linestage always does.

Passive linestage is always my very way to go as it complies my audio philosophy of simpler-the-better-musically. I am yet to be impressed by an active linestage or premap, brandnames or DIYs vs a well-built passive linestage in term of music neutrality, airlness & transparency.

That said, many DIYers do not want any irons in the signal path despite output transformer, a huge signal path bottleneck, is always used as there is no other choice in tube/loudspeaker hi-low impedance matching. Cost is alway the first consideration as a DIYer. Besides, I don't think I want to insert another frequency & phase non-linear bottle-neck in the signal path. Another can of worms to tackle?

Let's take a look at some sicentific facts of an AVC which is basicaly an inductor. Its limited inductance (being built small) will comprise the LF & its capacitance will attenuate HF.

Take an example of an AVC of 10H inductance. At a minumum volume setting of -43dB, LF
response is flat at 10Hz & phase shift is 1 degree.
At -20dB volume setting, it was -0.3dB at 10Hz & 9.6 degrees phase shift.
At 0dB full volume, -0.5dB at 10Hz & 12 degrees phase shift !! :worried:

There are more limition in choosing the upstream O/P load capacitance & impedance. in order an AVC can work properly.

I think we have gone too O.T. Maybe we should start a new thread for AVC.

c-J

_________________
"If the facts don't fit the theory, change the facts" quoted Albert Einstein.


Top
 Profile  
 
PostPosted: 20 Jun 2011, 16:54 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5191
Location: Australia
cheap-jack: I am aware of the transformer type attenuators. My seapkers are 91db effecient and the SET can play loud but only with some (and not much needed) preamping. If I use my Pass B1 preamp (source follower) I can't get full volume but my BoZSE works perfectly as does this single stage valve pre.

The only time I would use an AVC is as an attenutor after of before a preamp gain stage.

_________________
Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


Top
 Profile  
 
PostPosted: 20 Jun 2011, 19:52 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1627
Location: US Pacific Northwest
mwhouston wrote:
Rp=28K up from 20K and Rc=800ohms down from 1.1K. What do you think Matt?
In a single word... WOW! :shock:

Take a look at the new analysis. Especially at the distortion numbers. You really hit the sweet spot!
Attachment:
Screen shot 2011-06-20 at 5.43.28 PM.jpg

The only hitch in this circuit is that the input potentiometer setting affects the feedback loop. This is why I left it out of the analysis. But even without the negative feedback, the distortion numbers are impressive.


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
PostPosted: 21 Jun 2011, 08:08 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5191
Location: Australia
Matt: You mean I did something right? I was following Les' suggestion drop one raise the other. Glad to know I have a Signature version of the original unit. I'm planning a Special Edition version. I'll use the same values but beef-up the PS.

I'm not putting the pot on the front. I'm puting on the output. This way I retain the high impedance input with a 100K output Z (Alps blue velvet pot). This also means the preamp has to handle the full V swing of the CD player. The preamp should be able to handle 5Vpp swings without any problems. It's taking everthing my Oppo BDP-83SE is throughing at it now without so much as a strain.

Tonight I sprayed the enclosure beaten copper in a Epoxy Enamel paint. I have used this colour twice before and the finished is "different". I finished an Oatley phono preamp with the paint and the 6SN7 driver stage with it. I'm away for most of the weekend but hopefully I will have the preamp assembled before then.

http://retro-thermionic.blogspot.com/2010/07/6sn7-remote-driver-stage-for-be-bamp.html
http://mongreldogaudio.blogspot.com/2010/03/mongrel-dog-audio-jan6418-valve-phono.html

_________________
Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


Top
 Profile  
 
PostPosted: 21 Jun 2011, 14:27 
Offline
Banned

Joined: 15 Mar 2010, 08:32
Posts: 487
Location: Canada
Hi.
mwhouston wrote:
The preamp should be able to handle 5Vpp swings without any problems.

Why you want to 'squeez' the operation point of the tube down into the less linear area of the transfer curves in order to get "5Vpp"? :confused:
Give me an example of CD/DVD player or phonostage that can deliver 5Vpp?

But it is all up to you as this is yr baby.

I agree you should move the volume control to the O/P circuit though. 8-)

c-J

_________________
"If the facts don't fit the theory, change the facts" quoted Albert Einstein.


Top
 Profile  
 
PostPosted: 21 Jun 2011, 14:40 
Offline
Banned

Joined: 15 Mar 2010, 08:32
Posts: 487
Location: Canada
Hi.
Suncalc wrote:
mwhouston wrote:
Rp=28K up from 20K and Rc=800ohms down from 1.1K. What do you think Matt?
In a single word... WOW! :shock:
Take a look at the new analysis

Why you set the load line at 250V instead of 280VHT?

c-J

_________________
"If the facts don't fit the theory, change the facts" quoted Albert Einstein.


Top
 Profile  
 
PostPosted: 21 Jun 2011, 16:41 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5191
Location: Australia
cheap-Jack wrote:
Why you want to 'squeez' the operation point of the tube down into the less linear area of the transfer curves in order to get "5Vpp"? :confused:
Give me an example of CD/DVD player or phonostage that can deliver 5Vpp?

Come up with a different operating point. I'm not saying I agree with the bias point etc. where it is just to handle 5Vpp I'm saying that should the preamp have to it could handle large voltage swing.

Give us your design specs.

_________________
Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


Top
 Profile  
 
PostPosted: 21 Jun 2011, 18:34 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1627
Location: US Pacific Northwest
Remember that this design implements a significant amount of feedback. This allows the input greater swing because the net grid voltage is offset by the feedback from the output. This also allows significantly more linear operation out of the stage.

c-J: Did you look at the distortion numbers from the load line analysis? (0.2% :thumbsup:)

The most extreme example of this principle is the cathode follower with 100% negative feedback. Simple 12AU7 CF stages routinely support 40v to 70v allowable input voltage swings with eye watering distortion numbers. This is the real reason they are so valuable as output stages on the back end of preamps. They support large voltage swings, have incredible distortion numbers, and support very low output impedance.

Let's face it, this is not your typical generalized gain stage. :sing:

_________________
Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


Top
 Profile  
 
PostPosted: 22 Jun 2011, 02:55 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5191
Location: Australia
Matt Does that mean you like it.

_________________
Projects:”Image” - Low Profile 100W Class D amp | ”fiih” - 150W Holton inpsired power amp | "Precision" - 300W Class AB Holton power amp | ”Gothic” - FET Push-Pull headphone amp


Top
 Profile  
 
PostPosted: 22 Jun 2011, 09:39 
Offline
Banned

Joined: 15 Mar 2010, 08:32
Posts: 487
Location: Canada
Hi.
mwhouston wrote:
Come up with a different operating point

I already suggested= -2.5V. You forget?
mwhouston wrote:
it is just to handle 5Vpp I'm saying that should the preamp have to it could handle large voltage swing.

If you want to build an active linestage to handle 5V signal swing.as you believe there are such signal sources readily exist, why don't you consider building a passive linestage?

A passive linestage can handle any lowest & highest signals imaginable as there is no active devices exist there to worry about overloading, harmonic distortions & noises etc etc etc. :smoking: Don't forget 5V signal can drive or even overload any power amps (typically sensitivity is 1-2Vrms for full O/P power). Technically, there is no need of any more intermediate gains !!!! :idea:

This is exactly what made me switching to building & using passive linestages many years ago when I found active linestages either slow down the music for the best design/built ones & distort the music for lousy ones.

Unfortunately one got to be well acquainted with music before one can hear the difference.
I do.

Whatever one design/build does not matter, what really matter is the music comes out of it is as intact as possible. This is the bottom line, correct?

c-J

_________________
"If the facts don't fit the theory, change the facts" quoted Albert Einstein.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 415 posts ]  Go to page Previous  1 ... 3, 4, 5, 6, 7, 8, 9 ... 42  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 7 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy