BASH 500S schematic

Tube Radio

2012-02-24 6:29 pm
Does anyone know where I can find the schematic or a BASH 500S plate amplifier?

I want to look at the power supply section as I want to see what RFI filtering it has because when it is omn, I get a slight high pitched whine on an AM radio. I want to see how I can eliminate that.

Tube Radio

2012-02-24 6:29 pm

I can definitely do that for sure, but while that will work I'd prefer to also try and eliminate as much of it at the source as I can.

I may be looking to upgrade the amp with a four channel class D amp as I will eventually add two more subs to the existing two and want each to be able to have the level controlled individually to make the subs better integrate and if that happens, this amp mod here becomes somewhat moot, but would definitely help for if I use the amp elsewheres.
This amp complies with the radiation laws in your country. Maybe you expect to much from such shielding. EMF is radiated in form of a sphere around the emitter. It´s power get´s lower with the third pot to distance. So one meter is very close, but 3 meter very far away, speaking in power of the field.
If you run your radio with a shielded wire to the antenna, nothing will happen. If you just use some open wires to hear radio, you can sure dial in on the working frequency or some harmonic.

Think about using a DSP if you want to run 4 sub´s. This way you can adjust any parameter individually, so you get the best out of them.
The x-over and boost of your Bash is very limited and not good for such an installation.
Look at 3e-audio for example, you can run 4 amps with their DSP in balanced mode (no ground loops).
Except it does cause interference to radio communications.

Thing is there's regulations regarding RFI which sadly in more recent years have not exactly been enforced so there's a bunch of devices out there that can interfere with radio communications.

I may try to get a grounded IEC plug with a built in filter module and see if that works.
I would most likely ground it to the same ground the audio ground connects to.

I suppose the amp isn't grounded so as to avoid a potential ground loop which might happen if anything the plate amp input is connected to is grounded.

I looked and the amp does have decent RFI filtering.

I also decided to test the amp while I was looking at it and I noticed some phase shift which increased as I got closer to 20Hz.

It comes mostly from the input/crossover board with a slight bit coming from the amp board.

That has the effect of making the sub not integrate well.

Also the 350Hz 12 dB/octave LFE crossover on the amp board started exhibiting a phase shift as the frequency was increased.

I looked up an OP-AMP 12 dB/octave active crossover and saw the typical one uses two capacitors. I looked and there were three sets of two caps. Two sets looked similar far as the circuitry around them is concerned so I figured it had to be the third set so I desoldered one leg of both caps and that took care of the 350Hz filter so that there is now no phase shift.

Still need to increase the value of coupling caps to eliminate phase shift completely though.
I did a test where I fed a signal into the amp then measured the input voltage and the output to the amp board to see if it was possible to feed the signal straight to the amp board, but that requires a higher signal level so I have to use the original input section.

Now if I had the schematic I could see if it were possible to increase the gain of the amp board.

I could also see the input board and know for sure what needs to be done to eliminate the phase shift at 20Hz.

I increased the value of four coupling caps, but I was still getting phase shift at 20Hz but it wasn't as much as it was.
I eliminated pretty much all phase shift from the amp.

Three caps on the amp board I replaced with 160uF 50V caps as that's what I had on hand. Now Zero phase shift there.

I did the exact same with three caps on the input board. Zero phase shift there also.

Found the input board also had a low pass crossover on the LFE input so I removed two caps. That solved the phase shift that I had as I went higher in frequency.

I also removed the two caps used in the variable crossover as I thought those would do it, but I'll never use the variable crossover as I will always use the amp with an external active crossover.

I just have to test it when I get home from work.