Crack too quiet?

[Kabnis715]

Friends, Roman, Bottleheads,

I just finished my build of the OG Crack - this is my first amp build, and the realization of nearly a decade of procrastination. It was such a pleasure to assemble.

Last night I voltage checked, then voltage double-checked, and everything looks to check out. My heart fluttered when I switched on the little beast and the tubes came to a slow glow. I popped in my HD600s, fired up foobar2000, and promptly logged an excellent two hour listening session.

The only thing that seems a bit strange to me is that I have to crank the Crack up to 8 or 9 o'clock on the volume pot to reach ideal listening levels. I typically listen at a moderate-loud level; by no means anything out of the ordinary or ear-threatening.

I'm running FLACs through optical SPIDF out from my PC @ 100% volume via foobar2000 => Leckerton Audio UHA-6S.MKii @ 100% volume (low gain setting) => Crack via phones output on UHA-6S.MKii => Senn HD600.

Channels are equal in volume and I'm not hearing any distortion, so I think everything's good to go. The highs are little harsh but I'm still very much breaking in my HD600s.

Is it normal for y'all to have to hit 9 o'clock on your Crack to feed HD600s? Anyone have any experience using the UHA-6S.MKii as a DAC for PC=> integration?

Thinking back to my voltage checks, the only (slight) uncertainty I have is that the final checks against the headphone input may have shot up to ~12V vs the expected ~9V ceiling, before leveling back down to 0. It only showed 12V for a split section before hitting 9V for a few before quickly leveling back down to 0. Would this indicate any issues with my headphone jack solder joints that may lead to subpar volume scaling?

Thanks so much!

[Paul Birkeland]

Leckerton Audio UHA-6S.MKii @ 100% volume (low gain setting)

What's the voltage output on the low gain setting?  Is the volume slider on your computer turned all the way up?

It is very uncommon for someone to find themselves with not enough gain out of the Crack, so I would imagine there is something going on ahead of the Crack that's diminishing your signal level.

As a reference, you can try listening straight out of your phone with a 1/8" TRS to RCA cable.  Most phones put out 0.2-0.5V of signal.

-PB

[Chris65]

The volume control at "8 or 9 o'clock" is a quarter turn or less from the fully counter-clockwise 'zero' position, which does not seem unusual.

[Kabnis715]

Sorry, still very much a noob in the electronics space but I checked the Leckerton sit and it lists the max output power using the standard op-amp at 40mW @ 300 Ohms. The power supply of the Leckerton is "±6 V, ground-centered, switching converter + low-pass filter." I can't post the the direct link to the product page here but a quick search for "uha-6s-mkii" will yield the Leckerton site and specs in case I'm reporting the wrong info!

I unplugged the TRS from from the UHA-6S and plugged directly into my phone; you're totally right, it's 30%-50% louder directly from my phone than when it's running through the dedicated DAC! It surprises me that my phone provides more juice than my PC + the UHA-6A with both maxed out. Every slider in the chain from my PC through the UHA-6A is 100%. I was hoping to use the higher quality DAC in my Leckerton but maybe it's underpowered? I can switch over to the high gain setting on the Leckerton but I thought it best to avoid adding gain above 0db that early in the chain.

I have a Schiit Modi 2 Uber arriving tomorrow so hopefully that'll clear up the DAC issues I'm having and supply a strong line-level source.

And my apologies for the confusion on my first message; I meant to say that I have to have the volume pot at 3 o'clock to get serviceable volume, or ~75% to max volume. In my mindbrain I associated 9 o'clock with 75% and made the erroneous report.

[Paul Joppa]

4-mW at 300 ohms is 3.5 volts, so it should be 20dB louder than a typical phone.

Incidentally, there is absolutely no problem with a volume setting of 75%, as long as you never need it to be greater than 100%.

[Kabnis715]

Thanks so much Paul! I received the Schiit Modi 2 Uber a few days back and it appears to be a much better dedicated DAC pairing than the Leckerton. Running via toslink to my PC outputting from foobar2000, the sound is crisp, clean, and I rarely move beyond 9-10 o'clock on the pento to reach peak volume levels. The Leckerton, when jacked up to 75% on high-gain, begins to sound a bit cloudy and strained. Perhaps it's because the Modi uses a dedicated power supply as opposed to the internal battery of the Leckerton?

Regardless, my wife is annoyed that I'm spending so much time with my Crack. A brilliant product, and SO much fun to build.