+4dBv or -10dBu?

[hugoo]

作者: silent_fish

You could be right.

DAC2 has four different output level, adjusted by a rotary switch on back panel.
DC coupled, short circuit proofed output ci...

check out this:
Special +4/-10 Edition: More than you want to know about how dB's work
http://www.sweetwater.com/expert-cen.../d--04/14/2000

[silent_fish]

They are just voltage in different scale(log), but how does it explain the max input level of 21.3 dBu.

[hugoo]

作者: silent_fish

They are just voltage in different scale(log), but how does it explain the max input level of 21.3 dBu.

maybe it means you should not use a device with output level > 21.3dBu? as it will cause overload on SPL?

just guessing here..

[silent_fish]

My understanding is:

I think 21.3dBu is max non-distortion voltage (9v) for the input of SPL

Under 9v, if input level and output level doesn't match, it simply means volume pot doesn't work in a optimized way(either too loud or too soft).

Many hi-fi review said the higher the voltage, the better the sound.

Even if I use max DAC2 output(5.48v), it's still in the working zone of SPL preamp, it's just the volume control won't work well with my amp, input sensitivity for the kwa-150 is less than 1V, the SPL will have to do a lot of attenuation.

[hugoo]

Then if set both DAC2/SPL to +4dBu, are you getting optimal performance from ModWright amp, comparing to other settings?

[silent_fish]

Since the source is still +4dBu, SPL is simply expecting +4dBu as max input level, I don't think there is an improvement. Unless there is difference in audio quality while SPL is doing attenuation.

I think tt's better for source have higher voltage output.

[hugoo]

作者: silent_fish

Since the source is still +4dBu, SPL is simply expecting +4dBu as max input level, I don't think there is an improvement. Unless there is difference i...

Yeah, as they say it's better to keep the line as hot as you can (without causing distortions) and only do attenuation at the last stage... in this case, at the SPL pre-amp.

[nattawa]

作者: silent_fish

You could be right.

DAC2 has four different output level, adjusted by a rotary switch on back panel.

DC coupled, short circuit proofed output ci...

Have no access to this web site from work and no way of dumping water during the day.....sux

The spec of max. input of 21.3dBu could mean two things: 1) it happens to be the same level as that of the max. output, therefore, the maxim input level at unity gain without introducing distortion from system overloading (the max. output level, by the way, is almost always determined by the voltage of the power supplies of the amplifier.), or 2) the maximum allowed input level without burning something up in the input stage circuit.

By putting the level switch on the preamp to -10dBV you give it 3.9 times as much amplification (or 11.8db) as you would to a +4dbu input, therefore, the maximum allowed input level is reduced accordingly by 3.9 times, or 11.8db.

There is nothing wrong by feeding a +4dBu signal into a -10dBV preamp in your case, as this is equivalent to feeding a +15.8dbu signal into a +4dbu input setting, still well under the maximum allowed input level. There will be no distortion from overloading, nothing is going to be burning up, either. The only problem is that you wont be able to use much of the range of the volume pot -- volume control can be coarse and erratic, tracking between channels can be poorer than it otherwise can be, and that you might not be getting as good a performance as would with a level matched system in terms of signal-noise ratio.

[hugoo]

嗯，好像看懂了。
那用个-10dBV的pre-amp去feed一个+4dBu的amp,会是什么结果？

[nattawa]

作者: hugoo

嗯，好像看懂了。
那用个-10dBV的pre-amp去feed一个+4dBu的amp,会是什么结果？

这要看pre-amp的电压增益是多少和具体输入电平是多少。以SPL 2control为例，选用-10dBV灵敏度时，音量旋钮扭到最大，总增益是6.6+11.8=18.4dB （其中6.6是前级内部固定增益） 因为后级功放灵敏度是+4dBu, pre-amp输入端只要信号电平达到 4-18.4 = -14.4dBu，就可以让后级达到最大输出。或者说，当给前级注入+4dBu的信号，比如用DAC2设置于+4dBu@0dBFS，为了避免后级过载，音量旋钮要关小、让信号先衰减-18.4dB，也就是衰减掉88%.

这样的器材搭配比较恰当的用法是，DAC2设置在+4dBu @ 0dBFS，用2control的+4dBu输入，这样后级满输出时前级工作在0db增益附近。更好的用法是把DAC2设置在+7.2dBu @ 0dBFS，把SPL换成无源前级（或带buffer的无源前级），就完全避免了不必要的信号衰减和再放大。

[silent_fish]

谢谢,回答得很专业,很详尽

[hugoo]

作者: nattawa

无源前级（或带buffer的无源前级）

Thanks Nattawa, very professional!

I am using w4s stp-se which is a passive pre-amp with buffer, feed by an Apogee pro DAC with high output (over +4 for sure), drive a active pro monitor with +4db input sensitivity, sounds pretty good to me. If I use SPL, it sounds "aggressive" sometimes, and volume had to be kept down to very low settings, which can be a bad thing as you said..

[silent_fish]

I don't know your stp -se is passive, what kind of passive technology (transformer, resistors, others) it uses?

[hugoo]

作者: silent_fish

I don't know your stp -se is passive, what kind of passive technology (transformer, resistors, others) it uses?

Not sure what technology it is using..
From its description, it's kind of passive-active design, when volume is <63, it's passive (no gain), when >63, gain stage kicks in. Its volume control uses only resistors and relays, I was told that it's better than a chip or volume pot, that's all I know about it technically