Amplifier Connected Directly to Dac and Volume Levels

[Whoareyou]

So I have an Benchmark AHB2 with of course, only balanced XLR inputs.
I also have an Exasound E38 Dac, which is spec'd as outputting 2.1 Vrms on its line outputs.

So I thought I'd try connecting the Exasound directly to the AHB2 via RCA to XLR adapter cable, just because ... I can, and I wanted to see how it sounded. Also, I was hoping to eventually eliminate the preamp from my system in favor of a straight switch.

The sensitivity switch on the AHB2 configured to the highest setting for my Exasound's 2 volt line output.
My speakers are PSB Synchrony 1's, and with my preamp (Parasound P7) I can drive these to very high levels with the AHB2. All is very good.

This all changes with direct Exasound to AHB2 connection. With maximum Exasound volume, my levels are not anywhere loud as they should be.

The statement "This is the forum where we try to impress each other with how much we know ...", really does not apply to me .

Perhaps for someone who understands this stuff could provide additional information so that I can understand why my DAC does not drive the amp as I expected?

What are all of the relevant specs I should be looking at to get an idea of what is going on?

 

[McFly]

Whats the source into the DAC - and you've got the benchmark at 2V at the input switch ?

Reason I ask is theres a possibility the digital source is truncating to a half or 3/4ish scale digital signal , and your preamp was capable of pushing this up higher (than a DAC can, without full scale digital input) to satisfy the amps input sensitivity of 2V or even higher.

 

[Whoareyou]

Yes, it's definitely on the 2V setting. But you got me thinking about the source which is Jriver, and it's also using Dirac VST for DSP. As part of that, there is a DSD to PCM conversion (for the Dirac processing), and I think Jriver cuts 6db from signal as part of that processing. Then, there is also Dirac's headroom it bakes in for the processing.

But even with all of that, based on how everything works via the preamp, I never expected the decreased volume I am experiencing.

 

[Kal Rubinson]

The 2v sensitivity of the AHB2 is based on a balanced XLR input, not the unbalanced source of your e38. Dirac VST also saps the output. As for the "the AHB2 via RCA to XLR adapter cable," it doesn't convert unbalanced to balanced, it just accommodates unbalanced input.

Bridging the AHB2 raises the gain by 6dB but you then need more of them.

FWIW, the balanced output from the exa DACs is 4V.

 

[levimax]

EQ can use up a lot of headroom and often times you will need added gain from a pre-amp if you use it.

 

[Blumlein 88]

Also, your P7 has 14 db of gain. If your current direct connection is able to drive your amps to max output, then even though you have less gain that is fine just turn the volume up more. Of course it looks like maybe you are some 6 db or so short of being able to max out the amplifier output.

 

[Kal Rubinson]

So I thought I'd try connecting the Exasound directly to the AHB2 via RCA to XLR adapter cable, just because ... I can, and I wanted to see how it sounded. Also, I was hoping to eventually eliminate the preamp from my system in favor of a straight switch.

I am doing that but I use the s88 with balanced outputs and I bridge my AHB2s. Despite that, gain is marginal with Dirac VST via USB.

 

[restorer-john]

Plug the P7 back in and enjoy.

The highest gain settings on the benchmark compromises its performance somewhat, the maximum level of the D/A converter is only for full output 0dbFS signals and most of the time it's way below that.

What you think you are gaining in a simpler "straight line" set up, you are losing in usability, flexibility, maximum output levels, possibly S/N and the ability to plug in a whole bunch more sources. It's a backwards step.

 

[Daverz]

My Bryston 3B-SST can be switched between 23 dB and 29 dB gain. IME, the 23 dB setting is not enough for "realistic volume levels" on some recordings mastered at a low level. So either stick with a preamp or get a DAC with a higher voltage balanced output. Then you may find yourself on the mid gain setting most of the time and only needing to switch to high on some recordings.

 

[Whoareyou]

I am doing that but I use the s88 with balanced outputs and I bridge my AHB2s. Despite that, gain is marginal with Dirac VST via USB.

You actually got me thinking about using this type of configuration Unfortunately, I don't seem to have the proper equipment match to accomplish this. Now, if I can only find a good reason to replace my 38...... but at the moment I cannot.

 

[Whoareyou]

Plug the P7 back in and enjoy.

The highest gain settings on the benchmark compromise its performance somewhat, the maximum level of the D/A converter is only for full output 0dbFS signals and most of the time it's way below that.

What you think you are gaining in a simpler "straight line" set up, you are losing in usability, flexibility, maximum output levels, possibly S/N and the ability to plug in a whole bunch more sources. It's a backwards step.

For my current setup, I have to agree. It's just not worth it.

And thanks to everyone who replied. Every post was very helpful.

 

[Kal Rubinson]

Plug the P7 back in and enjoy.

I considered that for a while. Instead, I replaced it with a stack of Topping Pre90s which I leave at a fixed gain (depending on my current configuration) and control volume in the DAC.

 

[Fitzcaraldo215]

You actually got me thinking about using this type of configuration Unfortunately, I don't seem to have the proper equipment match to accomplish this. Now, if I can only find a good reason to replace my 38...... but at the moment I cannot.

My last Mch system, I used an ExaSound E38 balanced directly into a variety of amps: Spectron Musician III, Bryston PowerPac 120, Parasound A23. I used the predecessor ExaSound E28 balanced with the same amps, differing by Krell KAS-2 Monoblocs in place of the Spectron. I had absolutely no problems whatsoever, zero.

Of course, I sold that all. Now in a retirement home, I use my Smyth Realiser 16 with a set of Sennheiser 800s headphones. Yes, I use PC input via JRiver. But, no DAC, no amp, no speakers. I would take the Smyth over amp/speaker, because there is no room to contend with. I was extremely fond of Dirac, but there is no need.

 

[Kal Rubinson]

My last Mch system, I used an ExaSound E38 balanced directly into a variety of amps: Spectron Musician III, Bryston PowerPac 120, Parasound A23. I used the predecessor ExaSound E28 balanced with the same amps, differing by Krell KAS-2 Monoblocs in place of the Spectron. I had absolutely no problems whatsoever, zero.[/QUUOTE]
OK, Carl, but it will depend on the room and speakers as well as listening level preferences. That said, I have not yet run out of gas, even without the extra gain of the Pre90s. However, I inserted them because I felt uneasy running the system with less than 6dB of gain left in the tank. What if I wanted to gun it? Anyway, the Pre90s are transparent.

Of course, I sold that all. Now in a retirement home, I use my Smyth Realiser 16 with a set of Sennheiser 800s headphones. Yes, I use PC input via JRiver. But, no DAC, no amp, no speakers. I would take the Smyth over amp/speaker, because there is no room to contend with. I was extremely fond of Dirac, but there is no need.

I'm thinking about implants eventually.

 

[Whoareyou]

My last Mch system, I used an ExaSound E38 balanced directly into a variety of amps: Spectron Musician III, Bryston PowerPac 120, Parasound A23. I used the predecessor ExaSound E28 balanced with the same amps, differing by Krell KAS-2 Monoblocs in place of the Spectron. I had absolutely no problems whatsoever, zero...

My Exasound is unbalanced and that seems to make a big difference when mated with the low gain of the Benchmark. I have a feeling it would do much better with a higher gain amp (or if benchmark was bridged as suggested by Kal).

The 2v sensitivity of the AHB2 is based on a balanced XLR input, not the unbalanced source of your e38. Dirac VST also saps the output. As for the "the AHB2 via RCA to XLR adapter cable," it doesn't convert unbalanced to balanced, it just accommodates unbalanced input.
Bridging the AHB2 raises the gain by 6dB but you then need more of them.

That all makes sense. I did see the specs noting the higher gain for bridged mode, but for me, hard to justify in my current setup. In my room, the AHB2 has plenty of power for the Synchrony Ones. Even so, I think this amp is fantastic, and it is certainly tempting to buy another one.

I considered that for a while. Instead, I replaced it with a stack of Topping Pre90s which I leave at a fixed gain (depending on my current configuration) and control volume in the DAC.

So for multichannel, you are using the Pre90's in similar fashion to what I saw in your review for Benchmark LA4's, few years back?

BTW - Where the heck do you store all of this equipment? My wife is ready to kill me every time she looks at my closet of (what she considers) unused / unneeded "stuff"

 

[Kal Rubinson]

So for multichannel, you are using the Pre90's in similar fashion to what I saw in your review for Benchmark LA4's, few years back?

Yes but I do not really bother with using the IR splitter now. I set the Pre90s for 6dB of gain and leave them alone. Gain is controlled in the s88 or DAC8.

BTW - Where the heck do you store all of this equipment? My wife is ready to kill me every time she looks at my closet of (what she considers) unused / unneeded "stuff"

The Pre90s are tiny and, since I do not need to touch them, they are stacked on a low shelf in the rack.

 

[Whoareyou]

Yes but I do not really bother with using the IR splitter now. I set the Pre90s for 6dB of gain and leave them alone. Gain is controlled in the s88 or DAC8.

Interesting, and I am a bit surprised. I thought connected directly to amp, the S88 or Okto would be ok on their own.

 

[Kal Rubinson]

Interesting, and I am a bit surprised. I thought connected directly to amp, the S88 or Okto would be ok on their own.

As I said above, I have yet to top out the gain with the DACs direct to the amps but, because I am a bit compulsive about this, I am unhappy about getting so close. Adding a few dB of gain from the Pre90s gives me a little breathing room. I will continue to experiment with them.

 

[Whoareyou]

As I said above, ..... Adding a few dB of gain from the Pre90s gives me a little breathing room. I will continue to experiment with them.

Not sure how I missed that....

With this setup, what is approximate range of s88's gain control that works for you?
Thanks

 

[Kal Rubinson]

With this setup, what is approximate range of s88's gain control that works for you?
Thanks

Well, that depends on where you set the gain on the Pre90s. Up to +16dB is available but +6dB is what I use.
Remember, it is not absolutely necessary for me since I've never hit the limits on the s88. I did, often, need to run it as high as -6dB but now I never need more than -12dB.