[lousyreeds1]

All,

I'm hoping someone can help me resolve an issue I'm having with the handshake between my Anthem STR DAC/preamp and PrimaLuna EVO 100 integrated tube amp.  I'm trying to use the Anthem's fixed-level line out so the PrimaLuna can do volume control duties.  The sound is great overall in this configuration, but I hear distortion/popping at certain frequencies or on some material with fast transients.  This doesn't happen on every song - it's not a problem on some tracks with lots of dynamics and transients but is definitely a problem on some.

This issue goes away completely when I have the Anthem STR handle the volume control and just use the variable analog out into the Primaluna; but in that situation I have both volume controls active and the sound is significantly worse overall.

When I contacted Anthem tech support, they said there's likely an issue with the "gain-stage interaction" between the two units, and they thought the fixed-level output must just be "too hot" for the integrated amp.  They said there's nothing I can do other than just use the variable out and have both volume controls active. 

Could it really be that simple?  I'm hoping someone here might have additional insight that could lead me to a better solution.  The PrimaLuna's input sensitivity is 260mV, and the Anthem's output impedance (according to Stereophile) is 0.07 ohm at 20Hz and 1kHz, rising to 0.16 ohm at 20kHz.  I don't know if or how those numbers interact; perhaps this will make better sense to someone here.

Many thanks,
Oliver

[Doublej]

Can you replicate the problem you are having with the Anthem fixed output if you use the variable analog output on the Anthem and turn the volume up?

[lousyreeds1]

No, there’s no distortion or popping through the variable output, regardless of volume.  Thanks for your help!

[richidoo]

I have STR preamp. The main STR output sounds MUCH better than the line level. The line output still needs a current buffer, so there is probably a much "less good" opamp driving the line out than the circuit used in the main output stage. I never heard my line out distort, but I didn't use it any longer than took to hear how much better main output is.

If you set the STR volume control to 0.0 then the main outputs will make the same voltage as the line outputs, but with much better current sourcing and better sound quality, plus attenuation and even up to +6dB gain if needed. Main output is definitely the way to go.

The EVO input sensitivity just tells you how much voltage applied to the input will cause the amp to output its rated power at given load with the volume pot all the way up. So the input sensitivity is more about retaining full range of volume knob motion than it is about distortion or gain problems. Just adjust STR volume to make your EVO volume control have the right range of motion. Or technically even better is to turn up EVO to max and use the STR volume control. STR lets you program a maximum volume setting iirc.

[Rusty Jefferson]

....Or technically even better is to turn up EVO to max and use the STR volume control. STR lets you program a maximum volume setting iirc.

Agree with Richidoo the preferred way to run this should be with the amplifier volume all the way up (or with the amplifier section isolated if your integrated offers that) and use the dac/preamp to control volume. It looks like a nice preamp and I would assume it has a 32 bit volume control.

I didn't see a voltage spec for the dac/preamp fixed output but the SRT amplifier Anthem sells to use with it has an input sensitivity of 2.1 volts, so the dac/preamp could be over-driving your integrated if it had a 4 volt fixed output.

[rotarius]

Unfortunately, the STR line output is 3.3vrms.  It is overloading the primaluna input stage if the volume control is implemented between input and gain stages in the Primaluna.  This is not unusual, the STR output is the issue.

[lousyreeds1]

Thanks, everyone.  Richidoo, that's so interesting.  For me, the line out really does sound better.  Bigger, richer, fuller bass, less harsh, with no loss of detail.  But it's got that occasional distortion.  I guess I'm stuck choosing between that and what is - for me - an inferior sound coming off the variable out.  Am I hurting anything by using the line out if it's overloading the integrated's input stage, per rotarius's comment?

If I do stick with controlling volume from the DAC/pre with the integrated's volume at max, is there reason to think I'd get better performance by replacing the PrimaLuna integrated with the power amp version?  Seems like it can't be good to be using two volume controls at once.

Thanks again.

[rotarius]

Using 2 pots is fine.  You are going to have one at max anyway. Its not worth switching.  Now I will say, switching to another brand and type might yield great results.  Having owned Primalunas before, the output impedances are very high and result in a wide variation in frequency response, dependent on speaker impedance plot.  Works for some speakers, others not so much.