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 24 Aug 2019, 05:04

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 11 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: 25 Feb 2009, 09:38 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Folks,

My Adcom 535 was sounding on the tired side, so I opened it up and took a look. In a nutshell, the 4 6800uF caps look like they are on their last legs. Because they were not the usual caps (not the snap-in types) but consisting of 3 leads at the bottom (one a no connection), I've decided to take the plunge and design a psu pcb that will allow me to switch to snap-in caps, eliminate the funky speaker connectors, and remove the B set of speaker connections that I never really used.

The big caps are each paralleled with .22 uF mica cap and a 5.6k .5watt resistor. The resistor is white, small, and seems to be made of ceramic/cement material.

Here are my questions - would there be a possible improvement with the psu circuit if I upgrade the mica cap to a polypropylene type and the resistor to a .5 watt metal film type?

What cap would you recommend? The general consensus seems to be that you can use an MKP type, but I here there are some really good Panasonic film caps for cheap at Digikey.

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


Top
 Profile  
 
PostPosted: 25 Feb 2009, 11:53 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Here's one I found that is not too pricey, but it's over a buck:
http://search.digikey.com/scripts/DkSea ... =P12108-ND

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


Top
 Profile  
 
PostPosted: 25 Feb 2009, 18:39 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4578
Location: Winnipeg, CANADA
Those caps you posted look good for bypassing in a power supply circuit. They probably would provide some benefit over the mica caps, but I would suspect it would be small and perhaps not even noticeable. Cost is reasonable, so it may be worth trying.
Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


Top
 Profile  
 
PostPosted: 26 Feb 2009, 12:17 
Offline

Joined: 26 Aug 2008, 20:57
Posts: 415
Location: Atlanta
Check out the panasonic electrolytics while you are there.

I think (*think*) that extra lug is just an extra ground, I have seen them before. I think the dual caps always have 4 lugs...so it shouldn't really matter.


Top
 Profile  
 
PostPosted: 27 Feb 2009, 17:29 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Thanks for the input. I already had the big caps (united chemicon 10,000 uF) purchased when I tore everything apart, which pushed me into redesigning the pcb. Since there are so many of these amps out there, it would probably help out some folks if I create a thread on my upgrade of the psu.

The 535 is getting up there in age and as I noted in diyaudio, the big caps were bulging at the top and it was starting to sound lifeless.

I've got the board out for quote and probably arrive in a couple of weeks. Since it is a close match to the original, everything should bolt right in.

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


Top
 Profile  
 
PostPosted: 27 Feb 2009, 17:35 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Almost forgot to mention..I looked up the datasheets for the 2 bridge rectifiers. These are of the 4 A 200V variety. Looking at the specs, the graphs showed a drop in current capability with increasing temp. I found a similar rectifier from Fairchild Semi that runs at 6A and exhibits less sensitivity to temp change. I don't know if it will make a big difference, but maybe I'll hear some improvement with a part that can take more current.

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


Top
 Profile  
 
PostPosted: 01 Mar 2009, 15:35 
Offline

Joined: 26 Aug 2008, 20:57
Posts: 415
Location: Atlanta
Did ya bypass them with film caps? That might help too.


Top
 Profile  
 
PostPosted: 02 Mar 2009, 13:04 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
billnchristy -

I sent off to have the board built already and it hit me last night that I did not account for adding filter caps across the rectifier pins.. :bawling:

There is probably just enough space for me to squeeze them in there and solder them directly to the leads of each bridge. Closer is better anyway.

I was just noticing my chip amp 1875 kit and it uses the same Panasonic caps that I ordered. I suppose something like a .01 uF would be a good value to try. I've already got another order going from Digikey so I'll drop those into my order.

Thanks for the advice.

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


Top
 Profile  
 
PostPosted: 02 Mar 2009, 13:25 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Something a bit disappointing while working on this amp -

I pulled the stock caps, which have a rated value of 6800 uF. I tested the capacitance with my Fluke meter and they also registered about 7500 to 7800 uF. Not bad because they all came in above rating.

The United Chemicon caps I ordered are rated at 10,000 uF. When I measured them, they are measuring at about 8,300 uF. This is within +/- 20%, but I didn't think they would be that far off the mark. :confused:

_________________
Rega P25 and LFD Mistral phono (analog) or Oppo DVD Player (digital) > Aunt Corey's Buffered Pre > Adcom GFA 535 > Spica TC-50


Top
 Profile  
 
PostPosted: 02 Mar 2009, 19:37 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4578
Location: Winnipeg, CANADA
sonidos wrote:
There is probably just enough space for me to squeeze them in there and solder them directly to the leads of each bridge. Closer is better anyway.

I suppose something like a .01 uF would be a good value to try.

There should be room to squeeze them in or you may be able to solder them on the underside of the board. 0.01uF is good. Try use as low a voltage a possible to keep the physical size down.
Cheers

_________________
[ DIY Mains AC Power Cable Cord ] - [ Gobo LM1875 Amp Kit ] - [ Tang Band D4-1 Horn Speaker Kit ] - [ Monoblock Push-Pull KT88 Tube Amp Kit ]


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ]  Go to page 1, 2  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 3 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