DCAudioDIY.com

DC Area Audio DIYer's Community
It is currently March 28th, 2024, 5:18 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 45 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next
Author Message
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 7:42 am 
Offline

Joined: March 12th, 2013, 11:12 am
Posts: 738
I'll second Roscoe's idea, experiment with layout. My 1626 preamp with a LCLC (also DC on filaments) is very quiet with my horns, it would be dead quiet on your Proacs.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 8:16 am 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1780
Nothing works better to deal with radiated magnetic fields than distance. With sensitive circuits I often put the transformer in a separate enclosure.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 12:48 pm 
Offline
User avatar

Joined: January 15th, 2015, 7:19 am
Posts: 1697
Location: Baltimore MD
I only see two chokes in the power supply. Maybe just an early in the build picture
The second cap in the pi can be larger, maybe 100uf.
Choke input filter would require a higher voltage B+


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 2:13 pm 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1682
FerdinandII wrote:

FWIW, I vaguely remember Roscoe fighting to get the ripple eliminated on one of his preamps, with 5-6 sections of C-L-C filtering....it never got to inaudible IIRC.


That was a filament supply for 26s….

That said, I’ve built several tube line stages with just a CLC supply that were more than quiet enough, so I’m not convinced it’s a power supply problem…. Grover, can you put a ‘scope on the power supply and see what you actually have as far as ripple?

Roscoe

_________________
I can explain it to you, but I can’t understand it for you.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 2:19 pm 
Offline

Joined: June 4th, 2013, 2:39 pm
Posts: 487
Pelliott321 wrote:
I only see two chokes in the power supply. Maybe just an early in the build picture
The second cap in the pi can be larger, maybe 100uf.
Choke input filter would require a higher voltage B+


Yes, I added the 15H choke later.

Thanks for the suggestions, everyone. No change in the layout offers relief. And the more filtering I add the worse it sounds. :-( Choke input would require a different power tranny, I might try that. OTOH I feel like a light-weight reg'd supply might be a better answer. I might have something here I could try.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 2:20 pm 
Offline

Joined: June 4th, 2013, 2:39 pm
Posts: 487
Roscoe Primrose wrote:
FerdinandII wrote:

FWIW, I vaguely remember Roscoe fighting to get the ripple eliminated on one of his preamps, with 5-6 sections of C-L-C filtering....it never got to inaudible IIRC.


That was a filament supply for 26s….

That said, I’ve built several tube line stages with just a CLC supply that were more than quiet enough, so I’m not convinced it’s a power supply problem…. Grover, can you put a ‘scope on the power supply and see what you actually have as far as ripple?

Roscoe


I could, if I knew how. ;-) I'd need a cap to the probe, right? Some on Audiokarma modelled the original CLCLC in PSUD and got 3mV ripple.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 2:58 pm 
Offline
User avatar

Joined: February 28th, 2013, 3:31 pm
Posts: 1780
Most scopes have the ability internally to select a DC , AC, or ground mode.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 2:59 pm 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 1682
Grover Gardner wrote:
OTOH I feel like a light-weight reg'd supply might be a better answer. I might have something here I could try.


Gas tubes are easy ;)

Roscoe

_________________
I can explain it to you, but I can’t understand it for you.


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 3:40 pm 
Offline

Joined: June 4th, 2013, 2:39 pm
Posts: 487
tomp wrote:
Most scopes have the ability internally to select a DC , AC, or ground mode.


This is a USB scope. I can look it up. ;-)


Top
 Profile  
 
 Post subject: Re: 6AH4 preamp
PostPosted: February 27th, 2023, 4:05 pm 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 1701
Location: Parkville, Maryland
I hate to bring up the obvious -- but it is an open bread-board without shielding.

Contained within a steel or aluminum enclosure (aka. Faraday Shield) the circuit is protected from airborne issues like hum and RFI/EMI.

_________________
Walt


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 45 posts ]  Go to page Previous  1, 2, 3, 4, 5  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 40 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

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group