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, 21:46

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 218 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7 ... 22  Next
Author Message
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 23 Mar 2009, 12:26 
Offline
User avatar

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

When I bought the Adcom, one channel was extremely warm to the touch, the other was warm after listening sessions. I took it back to the shop and I was good buddies with the salesman, so he cracked it open on the spot and commented that the bias was way off on one channel. He commented that he could tweak the bias to run warm but then he backed off and set the one channel to spec. It must have gotten out of the factory with a final bias adjustment.

As I've been working on this project, I've noticed that the Adcom would never get warm as it did before during long listening sessions. The bias has to be off from factory spec, so it will be fun to check my results after some tweaking and getting the bias set the way that I want it.

_________________
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: 23 Mar 2009, 17:01 
Offline
Project Author
User avatar

Joined: 14 Oct 2008, 17:35
Posts: 906
Location: Dartmouth, Nova Scotia
You are doing a really good job. :up: I'm glad that article was useful, it really made me realize just how bad these pots are, because I had an amp with the same problem, one channel sounded completly different from the other. I readjusted the bias of the cheap open pots, and about a month later it sounded off again! As soon as I replaced them, it sounded twice as good as it did!!

About a week ago I replaced the 300 ohm pots with some 10K pots. :shock: It too made a big difference! And they were a piece of cake to adjust.

I took a before and after picture to show just how crappy they really were, one was black oxidised and the other some what clean, WD40 did nothing for them!!!!! :o

Keep up your hard work, hope you get your boards soon too, with mine I hard wired the PS with solid copper wire as NVA does... http://nva.sclnz.com/

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


Top
 Profile  
 
PostPosted: 23 Mar 2009, 22:07 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Attached are two images of the right channel pcb. One was taken before changing components and the second is after I've changed components and reflowed the solder joints on the power transistors. I've already indicated more than once that the condition of the solder joints is poor, so a good inspection of your board is in order and remove old solder and reflow with your favorite solder.
Attachment:
adcompads.jpg
Attachment:
right_new1.jpg


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: 24 Mar 2009, 12:24 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
I've got the trim pots on order from Digikey and they should be here before the end of the week.

Unfortunately, the guy in Croatia who does pcb's on the cheap told me I should have my board by now, which I don't after checking my mailbox last night. I put it in plain words that if I don't receive a board by end of week, I want a refund. Fortunately, he has responded within hours of each of my emails. I hope to report a good ending to all of this and that the board arrives safely.

If not, I mentioned Futurlec as a good option which would run about $35 for the board. They can take the ExpressPCB file and generate the board. I would prefer to learn how to lay out a board with pro software, but some of the free apps I found for Linux will take some time to learn and the libraries for parts are skimpy.

_________________
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: 24 Mar 2009, 17:34 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
If it is KK-PCB, I would not worry too much. Mark has purchased from them before with no problems.
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 24 Mar 2009, 19:58 
Offline
User avatar

Joined: 11 Dec 2008, 10:23
Posts: 217
Location: Austin, TX
Gio,
I bought this from ebay from procad69. Ever heard of him?

_________________
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: 24 Mar 2009, 21:53 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
No, but let us know how it turns out.
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 28 Mar 2009, 22:24 
Offline
User avatar

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

Good news, Bad news...well, not so bad. I finally got the PSU pcb today. Funny, I had a premonition Thursday night that it had been eaten by the USPS machinery. And that's kind of what happened. Friday night, I received the board inside an official USPS envelope with an official apology for the delay. From the looks of the envelope, the sorting machine did not much like the inflexible board within. It definitely looks like it got stuck in the rollers as part of the envelope was shredded. Fortunately, the board seemed to survive the ordeal.

The good news is that I got the electrolytics, the film caps, the resistors, and the 2 rectifiers soldered on the board and the board is setting mounted inside the chassis.

The bad news - the board is basically done homebrew style. Don't get me wrong, they did a pretty good job for a board that would cost me at least $45 elsewhere. But it's obvious that the etching ate through to the board itself in spots as there were a few pinholes in the board. My advice on an upgrade is that you have the board done at a pro shop. These guys did it using the photoetching technique and it shows.

I've decided that I'll have to tweak the board a bit. Unfortunately, I left my tolerances too tight and I had to pull out the dremel tool to shave enough off the board that mounts closest to the chassis wall. Because of this, I couldn't line up the board to mount it correctly on the 3 standoffs. Also, this left a 1/4" clearance from the big caps to the chassis back side. This gives me just enough room to have the output wiring in place, but way too close to mount the binding posts. Since I have so much wood on hand, I'll probably cut a piece to size and drill the necessary holes with a twist bit and a Forstner bit and mount it on the outside of the chassis. It will be ugly but it will work.

The good thing is that I have room to spare between the psu board and the transformer. I can extend the psu dimensions closer to the transformer and give the big caps some breathing room. I'll post a new drawing as soon as I get time.

Photos to come. What I can see now with the boards in place that I've dramatically cut down on all the wiring throughout the chassis. Now it will be AC/DC power lines and signal lines - and that's it. I spent all afternoon cleaning up the solder joints on the left channel - which made the right channel look like a pretty decent job compared to the awful job I saw today. I ate up 10 ft of solder braid. But it is worth it to see the clean boards without tons of flux and bad solder joints on the power transistors.

You'll also see on the psu that the layout looks more tidy. In my next version of the board, I want to see if I can get the snubbers in there. It will be a tight fit but I think I can make it work.

_________________
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: 29 Mar 2009, 12:14 
Offline
Editor
User avatar

Joined: 28 May 2008, 21:53
Posts: 4591
Location: Winnipeg, CANADA
That is too bad about the PCB quality. I was going to give them a try as their prices are great, but perhaps I should pass.
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  
 
 Post subject: Re: Adcom GFA-535 rework
PostPosted: 29 Mar 2009, 12:39 
Offline
User avatar

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

I decided to tin the traces with copper, so I got some steel wool and cleaned the board. I noticed as that I continued to progress in tinning the board with solder, it flexed more and more. It is bowing downward a good bit. I'm definitely going to have to get a board redesigned when I have the time. For now, this should work. :xfingers:

_________________
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  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 218 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6, 7 ... 22  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 9 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