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 27 Oct 2020, 22:37

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 218 posts ]  Go to page Previous  1, 2, 3, 4, 5 ... 22  Next
Author Message
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 17 Mar 2009, 18:20 
Offline
Project Author
User avatar

Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
Wouw, never heard that story before, lucky for you no damage was done, but in the case of of one of the stereos I had, it was not so lucky, it had a stinky old STK chip in it that made a snap, a crackle, and then a loud bang! to finnish things off, all because I had two pieces of speaker wire splaced together with wire caps and when I tripped over the cord one day the caps came off, so no more wire capping for me.

Now lucky for my Viking amp, it has a beefy output stage, and has both fuses on the +/- rails and at the output. But amazingly the ones on the output have high quality sockets for once, and there is no distortion produced by having them, although I bet I would notice an improvement by not having them, still rather be safe than sorry.

I would not worry too much about the PS voltages, but I would measure them just so you know what they are. It is easy to measure the tranny voltage, and by multiplying it by 1.4 you will get about the full rectified voltage going into your amp.

For a link to some info. on my reconstruction details for this amplifier this link might be useful for some upgrade ideas...
viewtopic.php?f=10&t=242&start=20

Good luck! :up:

_________________
My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700


Top
 Profile  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 18 Mar 2009, 22:18 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Ok, this is a photo of the right channel before any modifications. Note the key components I targeted for replacement. 2 electrolytic caps, a 1 k ohm resistor at the input, and a 22.1 k ohm feedback resistor.


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


_________________
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 18 Mar 2009, 22:27 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Here is same right channel board after replacement of the circled components.


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


_________________
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 18 Mar 2009, 23:52 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
One bit where I need some help - what is the right gauge wire to run to amp outputs? Reading the chart that Gio pointed out to me in another thread and what was used in the Adcom, 20 gauge seems to be what I need to use. Bummer - I found some cheap speaker wire but its 16 gauge.

_________________
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 19 Mar 2009, 07:51 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
16Ga would be just fine. BTW - what was originally used?

_________________
[ 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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 19 Mar 2009, 08:24 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Gio, oddly enough, it seems like they used 18 gauge for the signal wire and 20 gauge for the ground wire. I would have thought it would be reversed. :confused:

The original wire was tinned, braided wire. They sourced it out of Taiwan. On the insulation it was listed as Wonderful Wire, but I believe it was something sourced cheaply in bulk.

The 16 gauge speaker wire I bought for this project is from Tappan Wire. It's conventional pvc wire but it is finely braided copper and very shiny stuff, so it seems of good quality. I paid like $.34/ft. Inside the outer insulation is a pair, red and black. So for a single run of wire, I paid $.17/ft. Not bad. It's meant for in-the-wall installation for home theater systems.

_________________
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 20 Mar 2009, 11:32 
Offline
Project Author
User avatar

Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
Nice work on the upgrades :up: I have sometimes found improvement from upgrading the output capacitor, and for the low value ceramics on the driver transistors, silver micas work really well. another good upgrade is to replace the old carbon bias pot with a sealed multi turn type, much more precise. I just upgraded the bias pot in my Viking amp since they were quite dirty. All I did was measure what value the originals were set at and set the replacements to the same value, I will bias the amp properly later on, but it works like a charm right now.

Check this link out: http://www.tnt-audio.com/clinica/bias_e.html

hope this helps ;)

_________________
My Mini 12AU7 Tube Preamp, Pioneer SX-D7000, JVC XL-V221BK, JBL L80T, DCM TF700


Top
 Profile  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 20 Mar 2009, 12:25 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
Hi sonidos, do you have a schematic you can post?

_________________
[ 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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 20 Mar 2009, 12:50 
Offline
User avatar

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

Man, that is some good info. Much appreciated. I used the sealed multi-turn types in my diy projects and cringed when I saw the cheapies in the Adcom. As I've been following the F5 project, it started to dawn on me that I had never checked offset on the Adcom. The comments in that article seem to ring very true with what I'm hearing out of the Adcom.

Gio - I need your help. I was actually trying to post the ExpressPCB file on here this morning and I got an error that .pcb files can't be added. Since I've got the service manual in hand, I can scan it and place it on here. I can do it this weekend since I bartered with my wife for some time this weekend to work on this project. Will the site only accept an image file of my psu layout?

_________________
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 20 Mar 2009, 17:48 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
non image file will need to be zipped up before you upload them. Images should be fine/ Max file size is set at 250kB. If you have any problems, just email them to the address shown in the site banner and I'll see what I can do.

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  [ 218 posts ]  Go to page Previous  1, 2, 3, 4, 5 ... 22  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 6 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