Here's the schematic for the Glassware stereo - mono switch. It came with 3 sets of resistors for R1 - 10K, 15K, and 30K. These seem high since the summing circuits I always see use 470R.
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Really ?
Nobody built this BA3 no feedback front end to drive a Single ended Output stage?
Seems to be specified in configuration guide but no takers, why is that ?
I finished building my F5, hooked up the BA-3, and what do you know -- a ground loop (as well as a good bit of gain "whoosh"). F5 is dead silent without a pre connected. Tried another pre on the F5 -- bit of hum with that one too, but less. Tried two sets of shielded interconnects -- no difference. Tested BA-3 with a cheater plug -- ground loop quieter, but still evident.
Here's another picture of my finished BA-3. Even though the F5 seems quiet, should I be inspecting there too? Both amplifiers have safety and signal grounds bolted directly to the chassis at different points. No NTCs or other components in the ground plain, in the event that's helpful.
Everything sounds good otherwise -- I just hate hum!
Here's another picture of my finished BA-3. Even though the F5 seems quiet, should I be inspecting there too? Both amplifiers have safety and signal grounds bolted directly to the chassis at different points. No NTCs or other components in the ground plain, in the event that's helpful.
Everything sounds good otherwise -- I just hate hum!
Try lifting 0V from the chassis of the F5 first then the BA3, if the hum stops, install ground loop breakers.
Never disconnect the mains safety earth.
Thanks — tried different combinations of removing 0 v from chassis. With 0v removed just in the F5, the hum is gone in one channel and significantly lower in the other. Don’t want to pollute this thread since it’s clearly not strictly a BA-3 issue! I’ll double check the signal chain in the channel that’s still humming. Still dead silent with no inputs on the F5.
Appreciate the tips as always!
Appreciate the tips as always!
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A few thoughts:
Connecting ground in different places can potentially cause problems. Try connecting them at the very same place. Alternatively, try inserting a CL-60 between PSU/Signal ground and AC Mains Earth point. Sometimes, a little resistance removes a problem. Another thought is to use one of the diodes from a bridge rectifier between PSU ground and Mains Earth. I've had some amps that needed a direct connection in order to prevent hum. Some needed a diode, others needed a CL-60 to remove hum. Experiment with different configurations.
Connecting ground in different places can potentially cause problems. Try connecting them at the very same place. Alternatively, try inserting a CL-60 between PSU/Signal ground and AC Mains Earth point. Sometimes, a little resistance removes a problem. Another thought is to use one of the diodes from a bridge rectifier between PSU ground and Mains Earth. I've had some amps that needed a direct connection in order to prevent hum. Some needed a diode, others needed a CL-60 to remove hum. Experiment with different configurations.
Thanks -- in preparing both my BA-3 and F5 builds, I had overlooked the role of the CL-60 in the grounding scheme. I had mostly focused on the role of the CL-60 as an inrush current limiter in these designs, which I didn't feel I needed for the BA-3 and am using the DIY Audio Store Soft Start Board for in the F5. I hadn't thought through the fact that the design I was implementing would introduce a massive ground loop, mainly because I've never built a pre/power amp combo (the F5 is my first power amp after a half dozen or so preamp/headphone/phono stage builds).
I ordered a bunch of CL-60s today so I will start there -- lifting the BA-3 and/or F-5 grounds. Really appreciate you sharing that it can be a trial and error situation. I'm most concerned that the hum is so much more prevalent in one channel, but we'll see what happens. I'll report back once I'm able to try some options.
I ordered a bunch of CL-60s today so I will start there -- lifting the BA-3 and/or F-5 grounds. Really appreciate you sharing that it can be a trial and error situation. I'm most concerned that the hum is so much more prevalent in one channel, but we'll see what happens. I'll report back once I'm able to try some options.
Is there a schematic somewhere which includes an e.g. 50k pot/attenuator for vol. control? …...I want to see how it interacts with R1 and R2.....just to be sure. I can probably see it from the way 6L6 wire it in the start of the thread but just to be 100% sure I do it right when time comes…….
MEPER, all good, go for it.
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