Re: Building a DIY amp with NVA amplifier boards
Posted: Fri Sep 07, 2018 5:13 pm
Some progress here after work.
Started by changing the earthing arrangement in the nva based amps.
Went back to star earthing the 0V connection to the amp board and 0V connection psu on front end at the clean end of the output stage 0V . Speaker return to dirty end of 0V at rectifier end. Also put wires along side each other that were in the same current loops. Effect was bugger all. Still a moderately loud hum, no reduction at all.
Started messing about with the transformers whilst amp was switched on . I noticed the hum changing volume as I moved the little toroid around . Disconnected the psu's for the other adjacent mono bloc and tightly twisted the lead in and out wires on both the transformers still connected. This helped a lot and the hum reduced in volume considerably. Played around with position of both transformers and got them in a position where the hum is only just audible with my ear touching the mid driver.
Feel like I have got somewhere with this. I can still hear a noise through the speaker when I move a screwdriver along the faraday cage of the TIS cable. I am listening to one channel with all 3 drivers and the other with just the big 12" on the end of the Avondale amps. Sounds promising even though listening to the whole of the left channel and a third of the right.
Gonna play around and tidy up the arrangement in the pre amp next which looks like your usual diy work in progress (think spaghetti junction).
So does it still sound like I have an earthing problem or not ?
Started by changing the earthing arrangement in the nva based amps.
Went back to star earthing the 0V connection to the amp board and 0V connection psu on front end at the clean end of the output stage 0V . Speaker return to dirty end of 0V at rectifier end. Also put wires along side each other that were in the same current loops. Effect was bugger all. Still a moderately loud hum, no reduction at all.
Started messing about with the transformers whilst amp was switched on . I noticed the hum changing volume as I moved the little toroid around . Disconnected the psu's for the other adjacent mono bloc and tightly twisted the lead in and out wires on both the transformers still connected. This helped a lot and the hum reduced in volume considerably. Played around with position of both transformers and got them in a position where the hum is only just audible with my ear touching the mid driver.
Feel like I have got somewhere with this. I can still hear a noise through the speaker when I move a screwdriver along the faraday cage of the TIS cable. I am listening to one channel with all 3 drivers and the other with just the big 12" on the end of the Avondale amps. Sounds promising even though listening to the whole of the left channel and a third of the right.
Gonna play around and tidy up the arrangement in the pre amp next which looks like your usual diy work in progress (think spaghetti junction).
So does it still sound like I have an earthing problem or not ?