2. amps-preamps
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Passive Pre-Amp into Integrated Amp to Prevent Clipping?

On my previous system (DAC -> active speakers), I had some serious issue with clipping, even at low volume (volume was controlled by the active speakers). So I solved that by sticking a passive pre-amp (Schiit Sys which is a pot-based passive attenuator) in between the DAC and the active speakers. I used a 0 dbFS 60 Hz sine wave test tone (60 Hz because I would be sure my Fluke TrueRMS multimeter would measure it accurately since the Fluke is mainly used for home AC power applications) from my PC into the DAC-Preamp chain and measured the RCA output level with the multimeter at the SYS outputs. Then I turned the SYS volume down from 100% (measured 2 Vrms) until the multimeter measurement matched the active speakers’ input sensitivity (750 mVrms). Never touched the SYS volume knob again (I used the active speakers’ volume knob for adjusting listening level) and never had any clipping issues afterwards. And as they say, the rest is history. (Actually, if anybody has any feedback on my methodology, that’d be great).

Not quite. I finally decided to upgrade my system to one with passive speakers. The system I decided to go with is a Yamaha R-S202 stereo receiver with ELAC Debut 2.0 B6.2 speakers. The DAC hasn’t changed. (It’s an old DIY Ross Martin 24-bit DAC I was gifted from a friend. I don’t think Ross Martin is in business anymore because his website is down.)

The Yamaha receiver, being an integrated amp, already has a built-in pre-amp (I do not know if it has an active pre-amp stage or simply a passive volume control upstream of the power-amp section - does anybody know?). The spec’ed input sensitivity is 500 mVrms. Given that I had clipping issues with the old active speakers, which had a sensitivity of 750 mVrms, I assume that my clipping issues would get worse if I go DAC -> Yamaha?

Do I need to stick the SYS in between DAC and Yamaha (calibrate SYS volume to 500 mVrms output and do not change so I can use the full range of the Yamaha’s volume knob for adjusting listening level without ever clipping)? Would there be any disadvantages with respect to sound quality?

I did check the chain for proper impedance bridging. The minimum damping factors I calculated would be SYS/DAC = 13.74 and Yamaha/SYS = 17.74 so I wouldn’t be running into many issues with frequency roll-of. I’ve frequently come across the statement that damping factors > 10 is a minimum and >20 is best. Would there be any issues with respect to sound quality using damping factors between 10 and 20?

Thanks.
carlosaudio51
11 responses Add your response
atmasphere's avatar
atmasphere
11,793 posts
 
The spec’ed input sensitivity is 500 mVrms. Given that I had clipping issues with the old active speakers, which had a sensitivity of 750 mVrms, I assume that my clipping issues would get worse if I go DAC -> Yamaha?
I doubt it.
Apparently the volume control of the active speakers was downstream from the input (IMO a poor design choice), which meant the input could be overloaded.


If you are running into the line level input of your amp, the first thing the signal is likely to see is the volume control, so overloading the input will be impossible.
carlosaudio51 OP
9 posts
 
Thanks for the feedback. I'm not familiar with the design details of active speakers but I'm always looking to learn more. The speakers were Edifier R1280T.

And yes, I'm using the line level inputs on the Yamaha.

I tried the system without the SYS in the chain and unfortunately the Yamaha started clipping even at low volumes (20/100). Not sure why but a couple of theories:

1) DAC is old. I've had it for 3.5 years and my friend had himself bought it used from somebody else. So maybe it's showing it's age. Unfortunately I do not have another DAC with a comparable 2Vrms output. Would a DAC/headphone amp with pre-outs work for this test? I assume no, since I would be introducing an active pre-amp before the Yamaha.

2) Maybe I am misidentifying what I'm hearing as amp clipping? What I hear is a very sharp but short lived annoying crackling distortion on bass-y notes. Not necessarily very deep bass. The noise is heard at basically all audible volumes of my Yamaha. This was the exact same situation with my old DAC -> active speakers setup.

Then I added the SYS back into the chain and found out that for knob positions 3-5 o'clock (max is 5 o'clock), the distortion was present. Below that, it wasn't. For reference, the "calibrated" 500 mVrms position I had it at before was around 1 o'clock.

Not sure if this helps but any ideas are welcome.
atmasphere's avatar
atmasphere
11,793 posts
 
That suggests that the Yamaha also has active circuitry prior to the signal reaching the volume control. IMO as a designer this is a bad move as this means the input circuitry can be overloaded as you've experienced. If the volume control was properly placed as the first thing the signal encounters overload would be impossible. Soit sounds like the SYS is still important to be that first volume control.


This has nothing to do with the age of your DAC.
carlosaudio51 OP
9 posts
 
I guess that’s what I get for being a cheap audiophile. I'll keep the SYS in the chain.

I’m already saving for a future system (<$2,000) with separates (DAC -> pre-amp -> power amp -> speakers). Hopefully the future system will be made of quality-designed components so I won’t have this issue.

Anyway, thanks for the responses.


mesch
3,479 posts
 
A very nice system can be had for under $2000. If you enjoy the Elacs I would keep them and purchase an quality integrated amplifier and a more modern DAC. Both could be purchased as recent production models, however used.   

I also own a SYS and use it as a passive preamp with a NuForce STA 200 amplifier (currently selling for $400).  
carlosaudio51 OP
9 posts
 
Yeah, I'll definitively be looking at other forum posts for suggestions on the components for a $2000 system in the future.
erik_squires
16,049 posts
 
2V is exactly the standard for DAC's into RCA's.

No modern receiver will have a problem with that.
carlosaudio51 OP
9 posts
 
OK. What do you think is happening on my system? If I go DAC -> receiver I have clipping even at low volumes (20/100). If I add the SYS before the receiver and reduce the volume to about 3 o'clock, the clipping is gone.
atmasphere's avatar
atmasphere
11,793 posts
 
OK. What do you think is happening on my system? If I go DAC -> receiver I have clipping even at low volumes (20/100). If I add the SYS before the receiver and reduce the volume to about 3 o'clock, the clipping is gone.
Its pretty obvious that the receiver has active circuitry which can be overloaded before the volume control. The only good reason I can think of for a design character like this is that the receiver also has a DAC built-in, to which you are supposed to connect your digital source using a TOSLINK or HDMI connection.
carlosaudio51 OP
9 posts
 
Yes, it does have one. Granted, the Yamaha R-S202 does NOT have physical digital inputs (TOSLINK, coax, USB, etc.) but it DOES have Bluetooth, which means there's a DAC somewhere in there to convert the output of the Bluetooth receiver into analog. Even so, I have had the Bluetooth turned off on the receiver all this time. Interesting...

I don't have another receiver or DAC to do some testing to erik_squires' reply.

I know at this point on the post we're getting far into the weeds, considering that the solution is to have the SYS in the chain BUT I'm interested in the theory behind this so let me ask this:
-Erik_Squires said that most DACs output 2V thru RCA.
-Atmasphere said that the receiver likely has active circuitry (such as a DAC) built-on which can be overloaded.
-Most receivers I looked at have DACs built-in (either in the form of physical digital inputs or Bluetooth connectivity like mine).
-So is it best to use the receiver's built-in DAC to avoid overloading its analog inputs (when using external 2 Vrms DAC)? Or is this a situation of poor design choices (like Atmasphere suggested) probably because I have a cheap receiver ($129)? Are there better designed receivers that have built-in DACs but do NOT suffer from overloading the input, if an external DAC is the source?

Regardless, I've gotten what I needed out of this post. I understand start drying out since I'm asking stuff way beyond the scope of the original post.
atmasphere's avatar
atmasphere
11,793 posts
 
-Atmasphere said that the receiver likely has active circuitry (such as a DAC) built-on which can be overloaded.
I was not talking about a DAC- just that there is active circuitry prior to the volume control. If you were using the built-in DAC this wouldn't be happening.


Are there better designed receivers that have built-in DACs but do NOT suffer from overloading the input, if an external DAC is the source?
Of course! Price plays a role of course.
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