Many thanks Peter! After I reworked the wiring per your suggestion, the hum is completed gone and I am happily enjoying music from this wonderful machine now.
Hi guys I'm back from post 2095 where I mentioned having issues with attenuation thinking it might be the 10k valab stepped attenuator. I replaced the 10k valab with a 50k valab but the same thing happens which results in a barely audible signal throughout until reaching max where it's loud and proud and sounds very good.
I built it as a stereo configuration following Peter's instructions closely yet I've still somehow got it wrong.
Any ideas would be greatly appreciated.
I built it as a stereo configuration following Peter's instructions closely yet I've still somehow got it wrong.
Any ideas would be greatly appreciated.
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I see few twisted pairs. Just the mains cable to the left of the transformer. The mains pair next to the left channel amp has big LOOP AREA.
Every circuit has two wires. The Signal Current Flows from the Source to the Receiver and Returns to the Source.
If you break one of these wires the signal current cannot flow.
If you put a big loop area into these two signal wires you create an aerial that picks and emits interference.
Single wires MUST incorprate a LOOP area that is bigger than a twisted pair, or coaxial cable. Single wires will not perform as well as twisted pair/coaxial.
Sort ALL your signal connections into pairs and run them as PAIRS, either close coupled, or twisted.
Every circuit has two wires. The Signal Current Flows from the Source to the Receiver and Returns to the Source.
If you break one of these wires the signal current cannot flow.
If you put a big loop area into these two signal wires you create an aerial that picks and emits interference.
Single wires MUST incorprate a LOOP area that is bigger than a twisted pair, or coaxial cable. Single wires will not perform as well as twisted pair/coaxial.
Sort ALL your signal connections into pairs and run them as PAIRS, either close coupled, or twisted.
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solidcore copper wire in thick hardish insulation is easily twisted.
Just allow the individual wires to contra rotate as you wind them together.
Don't try to grip one end of the pair in a vice and the other end in a drill chuck and hope you will get a neat tight twist.
Longer lengths exceeding 1m are more difficult. I regularly twist interconnects in pairs, or star quads, that are ~ 3m long. Just takes time.
Just allow the individual wires to contra rotate as you wind them together.
Don't try to grip one end of the pair in a vice and the other end in a drill chuck and hope you will get a neat tight twist.
Longer lengths exceeding 1m are more difficult. I regularly twist interconnects in pairs, or star quads, that are ~ 3m long. Just takes time.
If this is happening, then you are not doing the same thing.
Do not try to twist each wire.
Better now
I thought I'd share my finished dual mono lm3875 premium kit.
I started by gutting out an old CD carousel chassis, reinforced it with aluminum to support heavy 300va traffos and built a stereo version with a 10k valab stepped attenuator.
Sounded real nice after installing rf (which I neglected at first and fixed thanks to Mark Whitney) as long as volume was on max since every step below that was barely audible. I tried a 50k which gave the same results.
I researched and then asked for help here which led me to rewire the mess I had. Well since I was going to rewire I might as well just start over and maybe find out what was causing the issues with attenuation. I discovered that I had installed the 220ohm in r2 where 22k should be so thinking that's where the major issue was with attenuation, I was content to believe that without experimenting further.
At this point I was set on a complete revamp to go dual mono without a pot (for now?)
I cut up that aluminum to suit the new layout, twisted all wires (thanks AndrewT) and started testing. I have to say listening to amp now this makes it worth the effort and seems a small price to pay IMO. Sorry for lack of pictures but I keep getting errors trying to upload them.
I thought I'd share my finished dual mono lm3875 premium kit.
I started by gutting out an old CD carousel chassis, reinforced it with aluminum to support heavy 300va traffos and built a stereo version with a 10k valab stepped attenuator.
Sounded real nice after installing rf (which I neglected at first and fixed thanks to Mark Whitney) as long as volume was on max since every step below that was barely audible. I tried a 50k which gave the same results.
I researched and then asked for help here which led me to rewire the mess I had. Well since I was going to rewire I might as well just start over and maybe find out what was causing the issues with attenuation. I discovered that I had installed the 220ohm in r2 where 22k should be so thinking that's where the major issue was with attenuation, I was content to believe that without experimenting further.
At this point I was set on a complete revamp to go dual mono without a pot (for now?)
I cut up that aluminum to suit the new layout, twisted all wires (thanks AndrewT) and started testing. I have to say listening to amp now this makes it worth the effort and seems a small price to pay IMO. Sorry for lack of pictures but I keep getting errors trying to upload them.
Ive seen this when i have left a tab open for a while and I try and search the forum on it, seems to go away when i click on the DiyAudio logo for home screen then start again.
When the amp is wired correctly, there's no pop at any time.
Are you switching source aquipment at the same time? If it's just the amp, check the grounding.
Hi Peter!
Glad to hear fro you. I am switching off backwards, from Gain clone when shut down. It is a power amp for me with a diy 6922 pre. I am not sure because of installing 2 tranny (local made) which cause the pop. Switching on is fine but sometimes receive mmmm for seconds as I know it is from the pre. I did simply connect the inlet earth to the chassis weeks ago but still the same. Is there any better grounding to recommend? Fyi, it is original premium kit with all parts given and no mode. I did install the little caps provided after rectifying. Now all in an aluminum, 1 chassis. Appreciate your advice.
Best regards,
Alfred.
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I just bought the kit from Peter and built it for my son. I also built a pair of Fostex small bass reflex speakers to go with it.
Al works great and sounds excellent, but everytime I turn on and off my desk lamp it makes a significant pop in the speakers. Is there any way to deal with it?
Thanks,
Radu
Al works great and sounds excellent, but everytime I turn on and off my desk lamp it makes a significant pop in the speakers. Is there any way to deal with it?
Thanks,
Radu