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Dynaco QSA-300

107.217.100.105
Posted on July 6, 2016 at 13:06:54
dpsutphin
Audiophile

Posts: 5
Location: Texas
Joined: October 26, 2015
 I am working on a Dynaco Quad amp. Channels B & D work fine. Channels A & C are distorted with low output. There are no signs of bad capacitors on either board. All fuses check good. Should I look into replacing or rebuilding the two boards? Is there some internal adjustment I need to make? I know this is essentially two identical 150s wired together on one chassis. What doesn't make sense is that one channel on each side works fine, and the other is distorted. I have switched speakers on each channel to rule out a bad speaker. Any ideas about what to look at next? Thanks for your help.

 

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Are you sure that, posted on July 6, 2016 at 15:06:23
E-Stat
Audiophile

Posts: 37666
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 Channels A and B share the same board?

To minimize crosstalk and optimize power supply effectiveness (since rear channel power requirement is typically lower), I think it would be a good idea to run channels A and C off the same board and power supply.

 

RE: Dynaco QSA-300, posted on July 6, 2016 at 15:21:56
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 I built one in the 70's. I seem to remember there was a build option to permanently bridge it making it 150 X 2 instead of 75 X 4. I'm sure the schematics and probably the kit instructions are online somewhere. Does it look factory wired? I would also check the finals right away. Good luck.

ET

HiFi engine has the kit instruction manual/schematic and it talks of the ways it can be internally wired in the kit instructions. Its a 28 page thing. I would read it and check how yours is wired. I seem to remember someone wiring one side together for running a sub and the other in stereo for standmounts therefore making a three channel amp. Read the we tion toward the end called combining channels. This explains how to make it a two or four channel amp and how to optimize it for 2-4 ohm loads or 8-16 ohm loads. It involves jumpers on board pc-43.

ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: Are you sure that, posted on July 6, 2016 at 18:16:06
dpsutphin
Audiophile

Posts: 5
Location: Texas
Joined: October 26, 2015
 I will check the wiring and see which board they are wired to. I just assumed that since A and B are on one side and C and D on the other that they would share the board on that side. But I guess since these were kits that people put together, it could be wired differently. Thanks for your help.

 

RE: Dynaco QSA-300, posted on July 6, 2016 at 18:18:45
dpsutphin
Audiophile

Posts: 5
Location: Texas
Joined: October 26, 2015
 I will check that out. Maybe I only have one bad board. Just depends on how it was wired when it was put together. Thanks.

 

RE: Dynaco QSA-300, posted on July 7, 2016 at 04:33:44
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 The amp has two boards. You'll see when you read through. There are pictures too. What is unknown is how it is wired since that is up to the builder or could have been modified by any owner.

ET
ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: Dynaco QSA-300, posted on July 7, 2016 at 10:17:27
dpsutphin
Audiophile

Posts: 5
Location: Texas
Joined: October 26, 2015
 Just wanted you to know that clicking on the link in the post to the schematic / manual takes you to one of those fake virus alerts. Looks like someone hijacked your response.

I have examined the board, and it is wired as I thought. A & B are on one board and C & D on the other. I'll go to the manual and schematic from outside the link so I can figure out for sure how it is wired.

Thanks for your help.

 

RE: Dynaco QSA-300, posted on July 7, 2016 at 10:32:50
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 I didnt post a link. I just put the name of the website that had the pdf which I viewed without an issue.

ET
ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

If Mine... I'd move on., posted on July 8, 2016 at 19:17:14
bare
Audiophile

Posts: 1879
Joined: April 14, 2009
 Bin it ? Clearly you've gotten your 5$ worth by now.
Dyna was Cheap stuff, designed/built using a minimum of 'expensive' parts... 'nuff said.

 

RE: If Mine... I'd move on., posted on July 18, 2016 at 19:42:16
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi Dpsutphin, I had the Dyna QSA-300 in the late 70's. It was my first big stereo investment as I got a personal loan from a banker friend that hung out at the pub.
About 10 years ago I bought a Dynaco ST-150 that I was going to use mono as a sub amp. It was on a forum or ebay. I had a snag and was trying to make the fix on the amp.
Out of the blue came a soon to become friend that informed me that in the production run of the Dyna-ST-150 there were 2 different circuit boards used in that amp. The numbers, which I forgot were silk screened on each board.
The QSA-300 must have all the same intended boards which will have all the same markings for identification. Maybe one of those boards was not noticed as it was installed as I made that mistake with the 150. Remember the QSA-300 was 2 150's on 1 chassis.
I'm no expert but am trying to help you eliminate all possibilitys.
With my amp back then I used 1 channel out of the 4 to run a Dalquist sub woofer using a Ace crossover. my main speakers were Dalcos, a copy of the Dynaco A-30-XL as Dyna was making changes to produce the LMS series from Canada,......check the circuit board numbers and make sure their the same.......that amp is a monster...take care......Mark Korda

 

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