I have used the extension rods on one of my BA3 builds. The other one is laid out just like this, and is just as quiet. I actually used the rods in the one I built that had the 10 mm face plate. the controls wouldnt go all the way though the thick panel without cut outs in the back of the panel. So, I used the extension rods, and located the pots all in back. Same way with my DCG3 build.
The BA3 FE units I built were modeled after 6l6's build guide to the letter, including layout and most parts, switches etc. He used that project to put his version of this line stage in, our layouts are virtually identical, including the power supply upgrade. I am at a loss on this one, any ideas appreciated.
Next thing is to carefully inspect the boards, but if mistake there, I did it on both boards, and the darn thing works and sounds great otherwise. Very confusing.
Russellc
As it turns out, the 2U would have been fine. I didnt need all that sink, but 2U is what I used before. The sink would have cleared just fine. Probably a little less expensive as well.
Russellc
Not sure what you mean by ground the inputs....do you mean run a wire from the ground side of input to my main ground? As far as galvanic contact between all panels, no. If I put one lead (meter set for continuity buzz) on the main ground bolt, I get a buzz where I should, but continuity only to floor pan. I find this changes after screws are put in and out a few times.
Mine buzzed with no chassis, 6l6's did not. His, and most people's are silent, I think I botched something....on other hand it does work and actually sound good.
Of all the projects I have built, this is the simplest one except B1 and it is giving me most trouble! Time to give 3 legged devices once over and check teenie device work.
Russellc
For grounding inputs I use a RCA male with just at short inside. It is just to try to isolate the problem. If this removes the hum we know a little more.
In theory if your side panels is not connected to ground the side panel could pickup hum/noise that could couple capacitive to the input wires. Very little noise is required at the preamp stage to be audible (eg. 0.1 mV at input could be 1 mV at output which could be 10 mV after power amp).
In theory if your side panels is not connected to ground the side panel could pickup hum/noise that could couple capacitive to the input wires. Very little noise is required at the preamp stage to be audible (eg. 0.1 mV at input could be 1 mV at output which could be 10 mV after power amp).
Todays fire up worse than ever. One channel set to 1.3 mV, low as I could manage, suddenly went to 300+ mV, back down to 14 mV, then settled at 1.6 VOLTS! not even hooking this up to my JBL mule work amp.
Looking at boards carefully, then if nothing found, scrapping this one and re purpose case or wait until hits store and try again. Something WAY wrong here.
Thanks for the tips, I think I just major flawed this one. Forensics time!
Russellc
Looking at boards carefully, then if nothing found, scrapping this one and re purpose case or wait until hits store and try again. Something WAY wrong here.
Thanks for the tips, I think I just major flawed this one. Forensics time!
Russellc
Probably of no use, but here is a few closer up pics, all the three legged devices are in the right place and oriented correctly. re flowed one of the pots three legs, seemed offset would jump around when I put the screw driver to it, or took it away.
Russellc
Russellc
Attachments
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Most amps are difficult to get much below 50 mV DC offset. To get stable below 10 mV you need a very stable PSU (it seems you have that) and you need to be able to control the temperature of the line stage so it's temp is stable within….maybe 1 degree. That is difficult. When you measure offset with top off the temp goes down and when you put top on temp goes up and offset will drift. Be happy with let us say 20 mV if your power amp is not DC coupled and will amplify DC.
Regarding hum is it important to know if hum is coupled magnetic/electrical to signal wires or from PSU or caused by ground loop. Is it 60 or 120 Hz hum? ....you can measure using Arta software and Focusrite (same method when building BA3-pre).
Seems like 60 hz hum...typical hum like I would chase down in tubes.