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 26 Jan 2021, 17:48

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 532 posts ]  Go to page Previous  1 ... 26, 27, 28, 29, 30, 31, 32 ... 54  Next
Author Message
PostPosted: 23 May 2011, 01:53 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5318
Location: Australia
Matt: I have a confession to make. This is a technician to engineer type confession. I didn't raise the filament potential on the 6SN7. I just simply run out of room and time. Not impossible to retro-fit just difficult. Do you think it is essential or just a nice to have?

_________________
Projects: "Sortilege" - 180W Tripath Class D Mundorf upgrade amp | “Mantra” - tube MM phono preamp | "Carbon” - MM phono preamp | 180W RAW Class D amp |


Top
 Profile  
 
PostPosted: 23 May 2011, 07:06 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5318
Location: Australia
Matt: I decided to have another go at the hum. I think the best improvement so far is the placing of a 1uf 50V cap across the filament of the 300Bs at the socket. Is there anything wrong with placing something larger across the filament like a 10uf or 100uf.

_________________
Projects: "Sortilege" - 180W Tripath Class D Mundorf upgrade amp | “Mantra” - tube MM phono preamp | "Carbon” - MM phono preamp | 180W RAW Class D amp |


Top
 Profile  
 
PostPosted: 23 May 2011, 09:11 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1727
Location: US Pacific Northwest
mwhouston wrote:
I didn't raise the filament potential on the 6SN7. I just simply run out of room and time. Not impossible to retro-fit just difficult. Do you think it is essential or just a nice to have?
Don't worry about this. To be honest, I've never experienced any filament to cathode leakage with a 6SN7. Every one I've ever used has been dead quiet with AC on the heaters.

mwhouston wrote:
Is there anything wrong with placing something larger across the filament like a 10uf or 100uf.
My only concern is the start up of the LT1085 into a large capacitive load. There is already a 200uf cap at the regulator output. What I would suggest (more work I know) would be to swap out the 200uf caps at the regulators in the PS with 1uf tantalum caps and put the 200uf aluminum electrolytic caps directly across the heaters at the 300B sockets.

And I do still strongly recommend two 6800uf electrolytic caps paralleled across the 6SN7 filament supply lines at the connector in the PS chassis. I really think this will help.

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


Top
 Profile  
 
PostPosted: 23 May 2011, 15:50 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5318
Location: Australia
I placed an additonal 4700uf cap on the 6SN7 heater filtering right where it leaves the PS. It made no difference. So adding extra filtering to the 300B HT did nothing, extra filtering on the 6SN7 heaters did nothing. I'm sure the only improvement has been the small cap I placed across the 300B heaters at thier socket.

Puzzeling isn't it?

_________________
Projects: "Sortilege" - 180W Tripath Class D Mundorf upgrade amp | “Mantra” - tube MM phono preamp | "Carbon” - MM phono preamp | 180W RAW Class D amp |


Top
 Profile  
 
PostPosted: 23 May 2011, 16:18 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1727
Location: US Pacific Northwest
Well, I not surprised 4700urf on the 6SN7 heater had no effect. That's less a 2.4dBv (1.2dBW) difference under the assumptions I made earlier. This change would be imperceptable at the speakers.

And we already determined that the 300B HT was not to blame.

Only thing left is the 300B heater getting polluted. Have you tried moving the 200uf cap on the heater regulator output to the 300B socket? I would do this on one channel and then see if you can tell the difference between the two.

Do you have an oscilloscope to directly check the ripple levels?

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


Top
 Profile  
 
PostPosted: 23 May 2011, 16:48 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5318
Location: Australia
Yes I have a scope. I was just trying the shot gun technique. I'll take another look tonight.

_________________
Projects: "Sortilege" - 180W Tripath Class D Mundorf upgrade amp | “Mantra” - tube MM phono preamp | "Carbon” - MM phono preamp | 180W RAW Class D amp |


Top
 Profile  
 
PostPosted: 24 May 2011, 07:50 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5318
Location: Australia
More confessions from down under: The 200uf caps after the regulators were not installed. Oops! So I put them in. You would think that would fix the slight hum problem. NO. It didn't. I added 100uf to the heater posts at the 300B sockets. NO effect. I removed the additional 47uf at the 300B sockets (HT+) and replaced it with my fav. a 0.1uf poly. Just to control any high frequency sh+i*t that may have found its way there.

A couple more things I can think of with relation to the slight hum. The chassis and negative of the HT is connected to mains earth?? I could take it off at the socket and have a listen. Also I connected the electro-static shield of the tranni to the mains earth. Any comment on this one??

One last thing. Mechanically the amp and the PS are extremely close. The 300Bs about 6" from the mains tranni and 4" from the choke. On Friday night I take the amp to a member of the Melbourne Audio clubs home. He (Ron) listened to the amp for about 4 or 5 hours on the Opera afternoon at my place. Loved it. It may be quieter at his place. I will try seperating the PS and amps more. He also has low efficiency small diameter drivers so the hum will be down in value. MY 6AS7 amp, which has an extremely small amount of hum on my 91db efficient Osborns, Ron said was dead quiet on his speakers with his ear pressed against the grill. I just smiled when he made the "quiet" observation.

Just found a pair of tubes cheaper than I paid before. Mable, anyone delt with them?

On Saturday I deliver the amp to the client. He also has low effeciency speakers. I'm happy to keep the amp by paying out Qian. If I do just don't tell the wife. I would love to keep the best amp I have ever, ever made.

Can anyone find the TJ Full Music 300BSEs (matched pair) for around the $600 to $700 mark?? I'd love a pair.

Since I started this post the amp has been on for about 1 hour. This entry is an edit to the original post. The amp is decidedly quieter. All the mods, fixes and additions have defintely made an improvement. The left speakers is dead quiet the right, at 1 meter the hum cannot be heard. We have definitly made good improvement. Let's hope Qian hates it (haha).

_________________
Projects: "Sortilege" - 180W Tripath Class D Mundorf upgrade amp | “Mantra” - tube MM phono preamp | "Carbon” - MM phono preamp | 180W RAW Class D amp |


Top
 Profile  
 
PostPosted: 24 May 2011, 09:00 
Offline
Project Author
User avatar

Joined: 06 Apr 2009, 10:08
Posts: 1727
Location: US Pacific Northwest
Those 300B plates do make big field probes. Do you have a cage you could put around the amp to see if it makes a difference. I just use some metal window screen and some 1"x2" pine to build a little Faraday enclosure to drop over the amp.

What did the o-scope show about the various power supplies?

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


Top
 Profile  
 
PostPosted: 24 May 2011, 14:05 
Offline
Project Author
User avatar

Joined: 06 Jun 2008, 18:23
Posts: 5318
Location: Australia
Matt: I haven't scoped the PSs. And I may not get the chance. I'm having someone over to audition the amp on Thursday and taking it to Ron's place Friday and have to have it Qian's place Saturday morn. But at this point I'm very happy with how it is performing. The omission of the 200uf cap after the regs. played a big part in the hum. After I made this correction I felt there was little improvement. I have since discovered our central heating has developed a hum when it cuts in. This was masking the quiet hum of the amp. After an hour of listen, when the heating had stopped I realised the amp was much improved. The left channel perfect with the right channel slightly hummier and the one nearest the PS.

The amp is so big and heavy I have limited table top to place it on therefore it is a little cramped where it is. There is a chance I will be building my own if I purchase the 300BSEs I have just located. I'll let you know. Thanks for your patience, support and guidance.

_________________
Projects: "Sortilege" - 180W Tripath Class D Mundorf upgrade amp | “Mantra” - tube MM phono preamp | "Carbon” - MM phono preamp | 180W RAW Class D amp |


Top
 Profile  
 
PostPosted: 24 May 2011, 15:53 
Offline
User avatar

Joined: 14 Feb 2010, 13:13
Posts: 715
Location: Lisbon, Portugal
mwhouston wrote:
I placed an additonal 4700uf cap on the 6SN7 heater filtering right where it leaves the PS. It made no difference. So adding extra filtering to the 300B HT did nothing, extra filtering on the 6SN7 heaters did nothing. I'm sure the only improvement has been the small cap I placed across the 300B heaters at thier socket.

That´s the way I remove Hum from my AC heaters ( I always use AC heaters on my projects ). Puzzeling just like you, usually with a 47nF ceramic capacitor. There is always one tube socket that the capacitor has a greater effect. When I find that tube, I start playing with the capacitor´s value.

Later, if i´m still chasing Hum, I get my headphones, and start playing the game again.

It can take some time, but it really worth! I got superb results on my latest project, the Hi-Fi FM Tube Tuner.

Cheers,
Miguel


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 532 posts ]  Go to page Previous  1 ... 26, 27, 28, 29, 30, 31, 32 ... 54  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 15 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