Moving Ahead
Well-Known Member
DOH!!!! I feel your pain. So close yet so far.
Re Cap on my Hitachi HA-1100 today
- Thread starter RuffzGuts
- Start date
RuffzGuts
Super Member
Ahhh what do you do, what made it worse was the first thing i done was pull outputs to test and thought they were all good, then checked drivers good also...thought id got away with murder...
spent the rest of the day chasing a short on the amp board..near drove me nuts...eventually traced it straight back to one of the outputs that i obviously didn't test properly!..I was very happy about it at that stage as you can imagine.
Bink, my understanding is that its not a good idea to operate a DC coupled amp with outputs removed...though it would not of helped here anyway as this was final assemble and outputs need to be on before heat sinks are refitted....also the outputs are a little fiddly to get back in....everything lined up etc.
It was a stupid mistake.
Anyway, i have borrowed a 2SB655A from another amp i have here to keep me moving for now...from what i can see this is almost a suitable replacement, Though i do hope i can find another 2SB612...its bad enough chasing parts for an amp that comes to you broken...when you bust good parts it hurts...
As you can imagine I have had to pull the thing right down again and recheck everything..several fried resistors were replaced...An earth trace was blown off the board..
I have now replaced trimmers, and managed to get her out of protection.....
Now i have no gain on the channel that blew the output....getting a signal..just very low volume...
still playing, although a little wrung out with it at the moment...I wish I had just put the cover back on!!! sounded beautiful as it was.
spent the rest of the day chasing a short on the amp board..near drove me nuts...eventually traced it straight back to one of the outputs that i obviously didn't test properly!..I was very happy about it at that stage as you can imagine.
Bink, my understanding is that its not a good idea to operate a DC coupled amp with outputs removed...though it would not of helped here anyway as this was final assemble and outputs need to be on before heat sinks are refitted....also the outputs are a little fiddly to get back in....everything lined up etc.
It was a stupid mistake.
Anyway, i have borrowed a 2SB655A from another amp i have here to keep me moving for now...from what i can see this is almost a suitable replacement, Though i do hope i can find another 2SB612...its bad enough chasing parts for an amp that comes to you broken...when you bust good parts it hurts...
As you can imagine I have had to pull the thing right down again and recheck everything..several fried resistors were replaced...An earth trace was blown off the board..
I have now replaced trimmers, and managed to get her out of protection.....
Now i have no gain on the channel that blew the output....getting a signal..just very low volume...
still playing, although a little wrung out with it at the moment...I wish I had just put the cover back on!!! sounded beautiful as it was.
Moving Ahead
Well-Known Member
Thats karma......
Now that you got something going, get another amp and use pre in /out . See if the low gain is located in the early or later stage.
FYI
http://www.datasheetarchive.com/dlmain/Datasheets-16/DSA-317211.pdf
Now that you got something going, get another amp and use pre in /out . See if the low gain is located in the early or later stage.
FYI
http://www.datasheetarchive.com/dlmain/Datasheets-16/DSA-317211.pdf
RuffzGuts
Super Member
already done that...problems in the main amp....right now Im working on a six pack...tomorrows another day! although it has got me puzzled...disappointed as i would have liked to try and get that offset down for kicks if nothing else..didnt even get a chance to look at options due to stuff up
RuffzGuts
Super Member
Happy to report she's good on both channels now, I had missed a solder joint on that channel...
Bias with the the trimmer pots is now a treat to tune....from now on every amp i do gets new trimmers!
DC offset is around Left 68 & Right 72mV.
The amplifier sounds superb, I have the Yamaha NS-10M's hooked up in my workshop and it sounds almost tube like..
So, whats the Vote, put the Lid back on or keep tweaking?
Bias with the the trimmer pots is now a treat to tune....from now on every amp i do gets new trimmers!
DC offset is around Left 68 & Right 72mV.
The amplifier sounds superb, I have the Yamaha NS-10M's hooked up in my workshop and it sounds almost tube like..
So, whats the Vote, put the Lid back on or keep tweaking?
Moving Ahead
Well-Known Member
Well done. You must have learnt a lesson in all that.
Are you still concerned about dc? I wouldn't be.
You blew an output right? If it was mine I probably wouldn't be happy with mis-matched / non complimentary outputs.
Are you still concerned about dc? I wouldn't be.
You blew an output right? If it was mine I probably wouldn't be happy with mis-matched / non complimentary outputs.
Binkman
Lunatic Member
All right! 
:tresbon: Add the meter error and component %? damned good mate. run at low volume for awhile.. with all those nice components and amp design I bet she sounds sweet.
I would button it up. first recheck any internal chassis screws and make sure any pcb ground screws are good and snug. I say put the lid on because the whole chassis is in itself a large ground per theory. (i.e. I know sony's can be sensitive like that.)
:tresbon: Add the meter error and component %? damned good mate. run at low volume for awhile.. with all those nice components and amp design I bet she sounds sweet. I would button it up. first recheck any internal chassis screws and make sure any pcb ground screws are good and snug. I say put the lid on because the whole chassis is in itself a large ground per theory. (i.e. I know sony's can be sensitive like that.)
RuffzGuts
Super Member
Yes, learnt a few lesson's here..the main one being don't apply power before double checking things..It was a pretty easy mistake to make, the way that board goes on, you need to snap it to four different terminal blocks at once..
either way it shouldn't have happened, and yes I'm on the market for another output...the one i have borrowed needs to go back in a HK amp, I'm just not sure where im going to get it at this stage...little diode possibly
As far as the offset goes, well it does bother me a little. I would be happier if i knew it was normal for the amp..but hey, as i said the amp sounds wonderful, I'm looking forward to trying some different speakers with it..
It will remain open on my bench for a while...i was thinking about swapping a resistor in the comp pair circuit with a trim pot....maybe i will maybe not...really need to get onto other things..
Binkman
Lunatic Member
Don't worry about the offset.. you've had it on for x hours and the bias is stable? button it up. It hasn't gone wacky and gone into protection and that's good sign, too. (70 thousands of one volt is nothing well within spec.) I would take main power fuses at rated and put in some that are 1-2amps lower for added protection. I didn't look for speaker fuses in the rails.. if so not a bad idea of cutting those down or assure if something goes on one of the rails the fuses blow before the outputs get it. protection circuits as they are in vintage.. not so good. we see blown outputs all the time. if you're going to be running at higher output.
Also don't get wrapped up into watts per ch. at 4 ohms.. go for what sounds the best. You already know it sounds sweet. That puppy can produce some serious power so make sure you have coils rated in your speakers. hell you could blow out a pretty large night club easy. good investment in your time as you could get a very good price as serviced. I'd also bet another 10 could take it to a shop and put it on a scope find normal.
This is a perfect example of a good rebuild of a good design.
Also don't get wrapped up into watts per ch. at 4 ohms.. go for what sounds the best. You already know it sounds sweet. That puppy can produce some serious power so make sure you have coils rated in your speakers. hell you could blow out a pretty large night club easy. good investment in your time as you could get a very good price as serviced. I'd also bet another 10 could take it to a shop and put it on a scope find normal.
This is a perfect example of a good rebuild of a good design.
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RuffzGuts
Super Member
Its a great amp Bink, seems to be rare also....I know Samz sold one on the bay here a while back...wish id bought it now...there are no internal fuses, only the mains fuse..
I think i will button it up..spent today finishing my Marantz cd73..now playing the division bell Floyd through the amp, just in the workshop with the yammy 10's...its a little bit of heaven it is...
I think i will button it up..spent today finishing my Marantz cd73..now playing the division bell Floyd through the amp, just in the workshop with the yammy 10's...its a little bit of heaven it is...
SteveM
New Member
I been away for a while,and I know this is an old post, but I rebuilt one of these beasts a couple (or more) years back, and found a couple of 'gotcha' things in the design. Also, have original owner's manual with bias adjustment procedures. Absolutely LOVE the amp - loud, powerful and bulletproof output overload/thermal protection. Let me know if you still need help / are still interested.
70smidfiguy
Active Member
Hey Steve, just starting on one of these, would love to know what the gotcha's are (other than the weird TO3 sockets)
