Burning Amplifier BA-2

Hi William, thank you for your input. RCA jacks are isolated, have checked for that. Changed grounding from CL60 to rectifier bridges, things improved, but are not solved yet. And I left the ground connections of the RCA unconnected, tried 220k but it effects offset. +D seems to be very sensitive and when stimulated the offset starts travelling up and down. This behavior gets worse with higher temp. Right Channel seems to be more effected then left. We are talking about 80 to 200 mV change, even more when I leave a cable or my Oscilloscope attached. Since I do not find another reason for this, I decided to exchange the voltage reference on both channels. Will update my findings.
 
This is perhaps ignorant, but why not build an F4 instead, since you drive the BA-2 without a front end? They are the same amps, but the F4 has the buffer you need in front of the OS. A BA-2 without an FE just makes for more hassle. But hope you solve it man!
 
The idea behind it was to have a chassis for the OS which could be used for an BA2 and a F5T V3 and to be able use the FE also for both OS. That’s why I built the FE BA3 as a preamp. Since the power supply and the chassis is were the money goes. I know BA3 has also too much gain for the F5T, but that could be adressed easy, there are a lot of posts in regard to this. I should get the voltage references by end of the week, I`ll see then. If I don`t move foreward this weekend I may end up by stripping out the BA2 and implementing the F5T into the chassis. Gives me the opportunity to build a BA2 without making tradeoff for multiple use purpose later on. So nothing will be lost in the end. 😉
 
The idea behind it was to have a chassis for the OS which could be used for an BA2 and a F5T V3 and to be able use the FE also for both OS. That’s why I built the FE BA3 as a preamp. Since the power supply and the chassis is were the money goes. I know BA3 has also too much gain for the F5T, but that could be adressed easy, there are a lot of posts in regard to this. I should get the voltage references by end of the week, I`ll see then. If I don`t move foreward this weekend I may end up by stripping out the BA2 and implementing the F5T into the chassis. Gives me the opportunity to build a BA2 without making tradeoff for multiple use purpose later on. So nothing will be lost in the end. 😉
your argument makes the case for an F4, not the BA-2.
 
Andy, according to Pa`s article about BA2 it should also be possible to use it as I intend to:

The BA Variations​


Before publication, I have received several requests for clarification and expansion:

It's obvious that for the follower designs we can create a front end independent of the main amplifier. As the quarters are tight in the BA chassis, this is a good idea, as it will allow placement away from the noisy power supply and give us considerable flexibility in switching out different circuits without having to take the amp apart. As I said, most of the BA designs will be followers without feedback, so you should feel free to go this route. Variac refers to these as BAGS. I forget why.
 
William, yes, even if nothing is connected to the amp and I simple look at +D = RCA input with my scope I get this floating offset.
Multimeter on Speaker Terminals, touch +D and offset is not stable anymore. Better when OS is cold, worser when warm.
Since I`m on a business trip, I can`t perform measurements right now.
 
As I understand, when FE and OS are in the same chassis only +D will be connected between the two PCB`s. But then they would share the same PSU and FE would be connected to star ground. In case of a BA3 FE.
I`ve set up BA3 as a preamp, if I connect the pre with the amp by the use of an RCA cable and gnd of the RCA jack is connected to star ground of the OS I should have the same condition. At least that’s what I assumed. That`s what I was starting of with. Am I wrong?
 
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If you combine the BA-3 FE with the BA-2 OS, you have a BA-3 amplifier.

The BA-3 amplifier build guide is here: https://www.diyaudio.com/community/threads/ba-3-amplifier-illustrated-build-guide.258301/

The build guide shows the BA-3 FE board signal out is from D (signal +) and G. (ground). At the BA-2 output stage the D (signal +) from the FE connects to D(GS) on the bias board and G (ground) from the FE connects to Ground on the power supply board. RCA connectors and interconnect cable in between the FE and bias board and OS should not affect the circuit.

Speaker out from the output stage is at OUT (GS) on the bias board to the speaker out+ connector, and power supply ground is to the speaker out- connector.

Power supply ground is connected through a ground lift to chassis.
 
Thanks Ben. I‘m reading the guides and documents since September, but obiously haven‘t notized the sentence exactly describing my Problem in 6L6 build guide for BA3:
DC offset is adjusted by pot P2 on the bias board. Place a DMM set to DC volts on the speaker outputs and adjust for zero. If you have DC offset that drifts rapidly, it’s likely the TL431 is faulty. Replace.
That’s what I concluded, will get the voltage references this weekend. Then I‘ll see. Thanks everybody for guiding me!!