Output volume of Auzentech X-Meridian -> Way to loud

[DanielPool]

Hey guys,

I'm not sure if this is totally the wrong place to ask this, so please be gentle if it isn't. I'm planning on cross posted between this forum and the class D amps to see if I can get an answer.

I'm using an HTPC (running Ubuntu Linux) as my source and have an Auzentech X-Meridian 7.1 sound card which I connect through to the inputs of 4x Sure 2x100W TK2050 Class D amps.

My issue is that the outputs of the Auzentech are known to be "hot" (5Vrms according to the spec sheet) and as a consequence the volume is extremely loud. Right now in order to get the volume to a "normal" listening level I have the volume control in Linux set to 1% (according to the alsamixer approximately -48dB of attenuation, though I'm not sure of the accuracy of that figure), any lower mutes the output.

If I drive the amps from the motherboard sound card, the volume level is perfectly acceptable but as I'm using analog out the sound quality is quite poor. The whole reason for using the X-Meridian is that it's analog quality is supposed to be really good.

I've set the gain switches on the Sure amps to the lowest settings, but it is still incredibly loud. I've searched high and low on the internet for means to lower the output voltage of this card and therefore the volume, and though others have complained about it, I've not yet found any viable solutions.

So I was wondering if anyone had any suggestions for how to lower the volume with minimum loss of quality to the sound. I've been considering resistors in the interconnects or stepped attenuators as solutions. I suppose that a passive pre-amp could also perform this task. I am though an audio newbie, so would appreciate any advice people can give.

Thanks in advance,
~Dan

 

[phofman]

5V is way too much. How about a simple voltage divider Voltage divider - Wikipedia, the free encyclopedia , total resistance 5k, output voltage 2V, i.e. 3kohm at the top, 2kohm at the bottom? For each line. Or perhaps lower resistances, experienced DIYers here would certainly help.

Or replacing the SMD resistors around the output buffer operation amplifiers to lower their gain. That would be a nicer but more tedious solution.

 

[DanielPool]

I agree that replacing the SMD resistors would be a nicer solution, I've been hunting everywhere to try and find someone who has tried this ... come close a lot of times, but mostly it's just guys who've spent $300 on a card known for it's analog performance asking questions about out puting sound via the SPDIF

The voltage divider sounds interesting, don't I need an earth though (looking at the wikipedia diagrams)? I've also had someone suggest an L-pad attenuator which would also work. I *could* save myself soldering near my interconnects again (which seem to melt at the slightest suggestion of heat) but that is quite pricey, or I could DIY it

My problem is now that I can't find any documentation on the X-Meridian's output impedance, so I'll have to measure it with a potentiometer and a multi-meter.

Thanks for your help though,
~Dan

 

[phofman]

I agree that replacing the SMD resistors would be a nicer solution

Well, it would not be that complicated. All you need is to sketch schematics of the output buffer, measure values of the two SMD resistors setting gain of the operational amplifier and bridge the feedback one with a regular resistor to get a newly calculated value (approx 2 x lower). If you are OK with the new output value, you can solder e.g. an SMD resistor on top of the original one.

It does take a bit of experience though, but certainly no rocket science.

but mostly it's just guys who've spent $300 on a card known for it's analog performance asking questions about out puting sound via the SPDIF

That cannot surprise you, can it?

The voltage divider sounds interesting, don't I need an earth though (looking at the wikipedia diagrams)? I've also had someone suggest an L-pad attenuator which would also work.

L-pad is the voltage divider described on wikipedia.

I *could* save myself soldering near my interconnects again (which seem to melt at the slightest suggestion of heat) but that is quite pricey, or I could DIY it

Of course DIY, I doubt you will find anything ready-made for reasonable price. I would try to build the voltage divider directly into jack connectors. It would require some tiny SMDs though, but doable. Or just make short attenuator extensions with male and female jacks. You have many options.

 

[DanielPool]

Well, it would not be that complicated. All you need is to sketch schematics of the output buffer, measure values of the two SMD resistors setting gain of the operational amplifier and bridge the feedback one with a regular resistor to get a newly calculated value (approx 2 x lower). If you are OK with the new output value, you can solder e.g. an SMD resistor on top of the original one.

It does take a bit of experience though, but certainly no rocket science.

I may spend some time doing just that. I have a 2nd X-Meridian arriving in a few days from e-Bay. I've been looking at some of the mods for the card anyway and wanted to have some contingency should my soldering skills (or lack thereof) rob me of a soundcard. I'd been compiling a list of the modifications that some people have tried which I might try out. Unfortunately it's not a simple board and not labelled at all, the oamps are fairly obvious though as are the resistors around them so as you suggest it might not be that difficult. I've attached a picture below which should give some idea of what is going on.

That cannot surprise you, can it?

No, it doesn't surprise me. More frustrate me ... that and wading through 100+ pages of people asking the same question again and again rather than read around 6 posts up . The internet is awesome in the information it makes available, but terrible at the same time in the amount of rubbish there is (and at this point I'm quite aware of just how much rubbish I likely put on it ... see below)

L-pad is the voltage divider described on wikipedia.

Yup, I feel suitably embarrassed So that's my internet junk for the day. Looking at the schematic now it makes total sense that they are one and the same. What was scaring me with the L-Pad wikipedia page (and some other sources I've found) is that they talk about using measurements from the output and input impedance of the sources to calculate the resistor values for a given attenuation. I was directed to the figures for my amp from the Tripath datasheet, but I think that I might have to measure the impedance of the card. Or does it matter that much, you threw out a few resistor values ... can it be that generic (after all you can buy pricey in-line attenuation components).

Of course DIY, I doubt you will find anything ready-made for reasonable price. I would try to build the voltage divider directly into jack connectors. It would require some tiny SMDs though, but doable. Or just make short attenuator extensions with male and female jacks. You have many options.

Not sure I'm up to soldering SMD's into the jack connectors yet ... especially as the jack connectors I bought from Maplin (yep, they were cheap ones) seem to melt before the solder does. Thankfully I have a variable temperature soldering iron, otherwise I think that I would have to resort to trying to use a hair dryer to make my interconnects

Thanks for the help though, I'll post more about my success / failure as things happen.

~Dan

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