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Is a preamplifier really necessary?


Flevoman

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A little education for some folks after reading some comments about digital volume controls throwing away information.

 

While some software based systems can degrade the sound this is by far not true for the vast majority of devices that use a "digital volume control".

 

I will attach a datasheet for a PGA2310 digital volume control IC.

 

"The heart of the PGA2310 is a resistor network, an analog switch array, and a high-performance bipolar op amp
stage. The switches select taps in the resistor network that determine the gain of the amplifier stage. Switch
selections are programmed using a serial control port. The serial port allows connection to a wide variety of host
controllers."

 

 

Many companies use this IC including McIntosh Labs for their digital volume control systems. It will not degrade your sound by throwing away information, that's just not how it works. Think of it as a digitally controlled precision analog volume control.

 

https://www.ti.com/lit/ds/symlink/pga2310.pdf

 

 

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Lumin streamers have a standard volume control and also an option to turn on the LEEDH processing in the software. There is a distinct difference between these two modes. I can’t say what method their standard volume control employs, but it is definitely not as good as LEEDH.

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49 minutes ago, Shakeydeal said:

Lumin streamers have a standard volume control and also an option to turn on the LEEDH processing in the software. There is a distinct difference between these two modes. I can’t say what method their standard volume control employs, but it is definitely not as good as LEEDH.

 

Different algorithms with different results. You can certainly have lossless digital volume control with little to no errors.

 

EDIT: Just looked and the LEEDH processing algorithm eliminates rounding errors. Uses more efficient whole number volume value to maintain audio information integrity. Modifies digital signal amplitude exactly, without any changes to it's shape and free from any kind of information loss.

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13 minutes ago, Crankysoldermeister said:

I thought we needed preamps for the buffering (impedance matching).

 

In today's world I don't see any sources that aren't already buffered and have a low output impedance.

 

I'd be so bold enough to say industry standards are 10k input and output of nothing more than 600 ohms, typically much lower, 100 ohms or less is easy and the norm.

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59 minutes ago, Crankysoldermeister said:

I thought we needed preamps for the buffering (impedance matching).

Buffering and impedance matching are two different things. But yes, buffering can be an important function of a preamp. If a device has a high output impedance, and it's trying to drive a low input impedance (especially one that is not purely resistive), then problems will occur. Those problems may range from low signal level to poor frequency response to increased noise. A high impedance buffer will solve all of them. The buffer may alter the sound somewhat, but in many cases the tradeoff will be worth it.

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1 hour ago, Westcoastdrums said:

As a DAC to amp user with nothing in between, I can confirm, sound is BETTER to my ears than with a Preamp in between.  Less gain staging, noise and coloration. Likely wont work for many that aren't all digital as I am however.  

I see you are using a RME.  Do you use RCA or XLR to your power amp?  I am interested in going DAC to poweramps in my digital listening and I am also looking for a quality DAC.  

 

Thanks

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Just now, Orbit said:

I see you are using a RME.  Do you use RCA or XLR to your power amp?  I am interested in going DAC to poweramps in my digital listening and I am also looking for a quality DAC.  

 

Thanks

I always use balanced cables when able. In my current setup, I am using balanced cables.  You should look hard at this RME ADI-2FS DAC IMO.  Punches far above its prices point and has tons of features including balance, parametric eqs and standard bass and treble with adjustable q and Fq.  

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3 hours ago, Edgar said:

Buffering and impedance matching are two different things. But yes, buffering can be an important function of a preamp. If a device has a high output impedance, and it's trying to drive a low input impedance (especially one that is not purely resistive), then problems will occur. Those problems may range from low signal level to poor frequency response to increased noise. A high impedance buffer will solve all of them. The buffer may alter the sound somewhat, but in many cases the tradeoff will be worth it.

 
I was thinking of passive preamps, and those tube integrateds that just have a volume control with no buffering. I thought it created an impedance mismatch that caused the frequency response to change as you rotated the VC. No? 

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6 minutes ago, Crankysoldermeister said:

 
I was thinking of passive preamps, and those tube integrateds that just have a volume control with no buffering. I thought it created an impedance mismatch that  caused the frequency response to change as you rotated the VC. No? 

 

What you describe is an impedance problem, but it's not because of a mismatch per se. In most line-level audio cases, it is desired to have as low an output impedance as possible driving as high an input impedance as possible. Ideally the output impedance is zero and the input impedance is infinite, so in that case a huge impedance mismatch is a good thing.

 

By comparison, in some telephone systems a 600Ω impedance match is maintained for maximum power transfer. In home audio we don't have to worry about that.

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2 hours ago, Crankysoldermeister said:

 
I was thinking of passive preamps, and those tube integrateds that just have a volume control with no buffering. I thought it created an impedance mismatch that caused the frequency response to change as you rotated the VC. No? 

 

As Edgar said we aren't always driving a resistive load.

 

I believe you are talking about as you turn traditional volume pot following R2/(R1+R2) which defines the voltage ratio output to input, as you further push the wiper down the resistance where R2 is much smaller than R1, you have now additionally increased the output impedance of the source before the volume pot. Say for a 10k pot, you could easily have 8,000 extra resistance added to your source no matter if it had a lower than 1 ohm output impedance it's now 8,000 ohms. When driving a reactive load like say the cable capacitance plus the input capacitance of the amplifier, you now can possibly shift the -3db corner frequency down lower into audible territory. For 8k ohms you would need 1nF of load capacitance to get below 20kH.

 

 

What this means is a passive preamp could create a situation where volume setting will effect frequency response. What you would do with a passive preamp is either keep the cabling short, or use an active buffer after it to create a low output impedance with enough current to not slew rate limit your largest peak amplitude and highest frequency of interest into worst case scenario load capacitance. It doesn't take much current for 2.8v peak, uA's even, but less than 100 ohms is ideal to easily drive 99% of the situations.

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A lot of information and also quite technical which I don't understand all that well,but thats fine.

If I may just bring this back to my current situation.  Is it correct if I say that I don't lose bits (audio signal) if I use the volume control on my Cambridge media streamer and remove my preamp?

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6 hours ago, Flevoman said:

Is it correct if I say that I don't lose bits (audio signal) if I use the volume control on my Cambridge media streamer and remove my preamp?

 Even if you were to lose some bits I highly doubt you'd ever be able to hear it, if the sound is different it would likely be due to other factors. Best way to find out is give it a try for a few days then switch back and see which you prefer. I've often times liked the sound of certain setups / equipment that I'm not supposed to according to the critics I guess I like certain distortion and coloring and not afraid to admit it bottom line I like what I like and trust my ears over what should or shouldn't be and why I almost always just recommend trying things out for yourself. 

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Several times I've tried to go direct without a preamp. It always sounds lame to me. I always seem to prefer a certain flavor that different preamps have.

Sent from my SM-G991U using Tapatalk

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I should also mention that my opinion/experience is only with Klipsch speakers. Other types of speakers (JBL) I have no problem running flat or with no preamp.

Sent from my SM-G991U using Tapatalk

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