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I believe it is oscillating, but I dont have a scope to test
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Nothing obviously wrong - it looks like you've put the input coupling cap off-board. Nothing wrong with this, but ensure that the leads are short, shielded and away from the high-current leads (trafo, speakers). Also recheck the polarities of all diodes, zeners and electrolytics. Check the voltages on the LM3886 and LM318 rails. Then check for shorts and opens, especially in the small-signal section with the lifted ground plane. Replace the LM318, and then the LM3886 as a last resort.
I have it connected to a heatsink when I apply power to it. 3 years ago I built the same exact amplifier but using boards supplied by Twisted Pear. Those worked on the first try, I have no idea what went wrong this time.
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That picture shows and insulated chip (TF package). Did you use an insulator for the new one?
I tried both, first I used the non-insulated (with the washer and heat pad) then after replacing several 318s, as a last resort, I swapped in an insulated 3886. Still the same hiss. I tripled checked all the resistors, caps, diodes, solder joints.... the only thing I havent done yet is de-soldering components to test if they are functional. Its strange that both boards produce the same symptoms.
Did you check each of the three little yellow ceramic capacitors for correct value? It is easy to misread those and put them in the wrong spot.
yes I did check the yellow tantalums, if I still remember correctly 2 are 22pf and one is 10pf.
Being consistant in symptom and on both channels means it is most likely a mistake duplicated.
Stats tend to releive parts as the culprit.
Tonight I will compare the twisted pear board to the ultimate bom board, component by component and see whats going on.
They are ceramic, not tantalum. The three values are 10pF, 22pF, and 220pF. If you mix the 22 and 220, instability could result.
You are a genius! Yes that was exactly what I did, I mixed up the 22pf and 220pf caps. The hiss is gone and the amp is dead silent.
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EXCELLENT!!!
Beautiful cases.
Care to do a GB on them? Or at least give me all the info to obtain 4 cases?
Beautiful cases.
Care to do a GB on them? Or at least give me all the info to obtain 4 cases?
I can tell you the materials I used to make the case. Its made from 1/4" aluminum plate for the front and rear panels, the Bottom and top are 1/8" aluminum (5.5" x 12"). The sides are made from this: (you will need them cut to 12" length"
8020 T Slot Aluminum Extrusion 15 S 3034 L x 48 N - eBay (item 370155124158 end time Jul-25-11 08:18:41 PDT)
I also have the templates for the machine shop to cut and engrave the front and rear panels.
It will cost around $150-$180 to complete a pair of cases depending how much the machine shop will charge you to cut and engrave all the material.
Hmmm, so they weren't pre-made? Then you did a very nice job!!
But if that's the case (punn intended) I will just order a pair of Par-metals Series 20's.
Hi Guys,
Just completed the first of 4 "linuxguru" Myref's and I have good and bad news.
Firstly, it makes music!!!!
Unfortunately, the only way to get it is to bypass the relay and connect speaker to power gnd.
I measured the voltage of my Nuvotem 25v transformer and I'm getting 29v!!!
Voltage after rectification is about 40v.
Part of the reason I expect is that the transformer is 230v, but I measured my mains to be about 245v......
Could this be the reason the relay isn't kicking in?
Just completed the first of 4 "linuxguru" Myref's and I have good and bad news.
Firstly, it makes music!!!!
Unfortunately, the only way to get it is to bypass the relay and connect speaker to power gnd.
I measured the voltage of my Nuvotem 25v transformer and I'm getting 29v!!!
Voltage after rectification is about 40v.
Part of the reason I expect is that the transformer is 230v, but I measured my mains to be about 245v......
Could this be the reason the relay isn't kicking in?
no.
Start checking pin voltages to determine what currents are flowing in the relay circuit.
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