Left channel was the one with physically blown transistors?
Any chance of getting photos of the boards?
Schematic for memory refresh:
Any chance of getting photos of the boards?
Schematic for memory refresh:
definately static in right channel especially when adjusting the volume and it just got a little louder all on its own. I know the preamp is good I just had it playing thru my main system and it has just been recapped.
Two posts above you write about static in left channel - so which channel is actually problematic?
Is static in one channel also there when feeding the amp with common signal (via Y splitter)?
330 am here. Going to bed if you have anything you need me to try just post it
Gnite, thanks for all the help
Gnite, thanks for all the help
It is the left channel, apologies it was late. Amp is connected to preamp with a regular rca jack patch cable woth the red and white ends. The left channel with static is also the one I had recapped earlier this year. Once i get back up there I will inspect solder pads and confirm correct caps were used and not a wrong size one inadvertently used.
It is a long thread - did you swap U701 module at some point earlier?
You could also post the list of new capacitors you used then - not possible to see on the photo.
You could also post the list of new capacitors you used then - not possible to see on the photo.
It is a long thread my apologies there was a lot going on with this thing. The channel in question the module was removed and transistors replaced in it. The transistors were HFE matched with a component tester I have. I will make a list of the caps I replaced, all of the electrolytics and some of the ceramics. I use Nicihcon caps either KW or FG series caps. I will post the exact values and locations as soon as I can.
I can say Molly and I had this amp playing fine at one point before all the pulsating light issues came about with no static in either channel. Makes me wonder if that frayed wire I found took out a tranny or resistor. I will be up in my work room later today , I have a honey do list that needs to be rectified first, lol
Phil
I can say Molly and I had this amp playing fine at one point before all the pulsating light issues came about with no static in either channel. Makes me wonder if that frayed wire I found took out a tranny or resistor. I will be up in my work room later today , I have a honey do list that needs to be rectified first, lol
Phil
Can be anything, you should start checking voltages again and comparing these to the values in schematic.
C705/708 can also be potential suspects if they are still 10V ones.
R704 and 702 are measuring -55vdc and 55 vdc on both sides of the resistor where the schematic shows it should be -.5vdc and .5vdc respectively, is this an issue?
So how much across/between the leads of C705 and C708 (each of them measured separately, not together)?
It will give indication of current through the resistor-diode chain that is in parallel with them.
Fixed. Loose solder joint again.. q701 emitter. Cleaned it up resoldered and now its playing just fine.
Playing it plugged directly into the surge protector and its working fantastic. Now ill put it all back together and hopefully its working still.
I appreciate the help and pointing me in the right directions.
Next up is the alpha II which I have been struggling with for 2 years, ever since I aquired it. Its never worked and I have the3 same issue. It wont adjust at all. The dc offset on one side is stuck at 16vdc instead of 20mv. Anyway thanks with this one. Ill put it together and hook it up in the main system downstairs and let you know the results
Playing it plugged directly into the surge protector and its working fantastic. Now ill put it all back together and hopefully its working still.
I appreciate the help and pointing me in the right directions.
Next up is the alpha II which I have been struggling with for 2 years, ever since I aquired it. Its never worked and I have the3 same issue. It wont adjust at all. The dc offset on one side is stuck at 16vdc instead of 20mv. Anyway thanks with this one. Ill put it together and hook it up in the main system downstairs and let you know the results
If you found the reason for the problem and fixed it then there is no need to dig further 🙂
I know Ill never buy another mosfet amp. Its hard to find good replacements if needed. Why was Mosfets even used?? Were they suppose to be superior to standard transistors?? As you can tell Im no electronics engineer but Im learning
They are a whole different ball game to the more common switching type of FET that most power amps these days use and far more linear.
There are no real downsides to designs using these, all your issues are nothing to do with the type of output devices fitted. Laterals are extremely rugged and almost self limiting in many overload conditions. They are easy to drive (voltage driven rather than current driven like normal transistors) and they are easy to bias with no complex thermal compensation needed. They are also capable of bandwidths light years ahead of ordinary transistors.
Best of all when used properly is that they sound wonderful.