Another BPA 300 Build thread...newb perspective

[juluska]

With this connection there is little hiss proportional with the volume.

[juluska]

And if i connect the passive preamp before the drv134 the hiss turns huge and molest.

[CJ900RR]

Originally posted by juluska
And if i connect the passive preamp before the drv134 the hiss turns huge and molest.

Earth loop? Impedance mismatch? Have you read this?

Can you show a sketch of how everything is wired?

[juluska]

what about the resistor in drv134 board? I have ignore it.

[juluska]

Originally posted by CJ900RR



Earth loop? Impedance mismatch? Have you read this?

Can you show a sketch of how everything is wired?

wiring for drv134 test

[CJ900RR]

I am not familiar with the DRV134-board. Are the resistor supposed to be 300 Ohm? Output common-mode rejection?

Have you connected the DRV134 before the passive preamp? The DRV134 should be after the preamp. It's important to keep the wiring short, also to keep them the same length.

Also, the DRV134 should be driven by a low impedance source. What is the output impedance from your CD-player and what is the input impedance of your DRV134-board? The DRV134 works best when driven by a buffer or OP-amp with gain=1.

Have you read the datasheet for the DRV? Page 10 has some layout considerations.

And finally, check all your wiring so you don't have any groundloops in the overall set-up. Try one PA150-board stand-alone using only the preamp and see how it sound.

[pacificblue]

Originally posted by juluska
With this connection there is little hiss proportional with the volume.

There are a few hints at the bottom of http://www.epanorama.net/documents/g...tml]this page.

Did you check and re-touch all solder joints?

In your photos it appears that you don't use common shielding techniques. The pre-amplifier case does not seem to be grounded at all. The DRV134's power supply ground does not seem to be connected to PE.

Does any of your equipment have RF filters?

The biggest advantage of balanced wiring is that you run inverted signals through two closely spaced wires. So any disturbance will be canceled out, when unbalancing the signal. That means of course, you want both wires to see exactly the same disturbance. If you use separate cables for the inverted and non-inverted signal, that will not be the case. Imagine an electromagnetic disturbance source 1 cm from one of the wires and 2 cm from the other. The one further away will only pick up a quarter of the disturbance the one nearer to the source will pick up. Unbalancing will obviously not work to cancel the disturbance signal out. The two signal wires should be as near to each other as possible. You need twisted-pair shielded cable from the DRV134 to the amplifier.

The DRV134 PCBs are poorly designed, in that the output connections are not adjacent, but on opposite sides of the board. That forces at least part of the wiring not to be twisted pair, which is bad, given the vicinity to power supply wires due to the small form factor.

OT: green/yellow wires must never be used for anything but PE. Using them for Phase and Neutral is dangerous. They must not even be used for the PSU ground, only for the connection from the PSU ground to the PE star-point.

[HaLo6]

I just got my Primrose Audio custom toriods in the mail last week , they are really nice, potted and encapsualted! ... I just need to get resevoir caps and a case... but this project is taking a back seat until I finish my jukebox PC and Buff32....