Preamp issue

[2tuby]

I am having a problem with my preamp would like some feedback/guidance from the members of this forum.
For the past two years my system has been a WIIM Pro to PSAudio Stellar Gain DAC to Backert Labs Rhumba 1.0. preamp to Classe CT2300 amp to Harbeth SHL5 speakers,
System worked fine and I liked the sound. But, then you get the itch. . .
I read a thread on this website about the poor bench measurements of the PSAudio DAC and was interested in trying to an r2r DAC so I purchased a used (one year old) Denafrips Pontius II 12th DAC. Today I swapped out the PSAudio DAC, fired up the system and listened for about 5-10 minutes, then there was a POP in the speakers and the Rhumba preamp went into its mute mode. I shut everything off and restarted the components now have low frequency(100Hz?), low volume, vibrating sound coming out of both speakers. I have swapped out pieces from a second system an definitely isolated the problem to the Rhumba preamp.
I am going to have the pream repaired. But since the Rhumba preamp failed shortly after swapping in the Denafrips DAC-
Could the Denafrips DAC have caused the preamp to fail? How? Was it just coincidence? Should I have the Denafrips tested as well or just return it and find a different r2r unit? Your input will be appreciated. Thank you in advance.
Happy Holidays

 

[Blumlein 88]

Welcome to ASR.

Sort of impossible to say at a distance. Were you using NOS and switched to OS or something like that?

According to this review here, if the Pontius encounters intersample overs while in OS (Oversampling mode) it creates an audible high level pop. Creates a votlage spike which could be responsible for your issues.

Denafrips Pontus 2 (12th Anniversary Edition) Measurements - GoldenSound

Measurements of the Denafrips Pontus 2 12th Anniversary R2R DAC, and testing to see whether claims of NOS capability are true.

goldensound.audio

The suggestion is to attenuate any signals by 3 or 4 db in your playback software. I would ask for a refund if the DAC doesn't function as it should myself. Even then they are unlikely to cover the repair needed on your preamp possibly caused by the DAC's poor design.

 

[somebodyelse]

That intersample overs issue still doesn't result in a signal outside the normal output voltage range. It shouldn't cause a preamp failure unless the preamp is also poorly designed.

 

[SIY]

It shouldn't cause a preamp failure unless the preamp is also poorly designed.

Take a look at the website for the makers of this preamp. Not very confidence-inspiring.

 

[2tuby]

Welcome to ASR.

Sort of impossible to say at a distance. Were you using NOS and switched to OS or something like that?

According to this review here, if the Pontius encounters intersample overs while in OS (Oversampling mode) it creates an audible high level pop. Creates a votlage spike which could be responsible for your issues.

Denafrips Pontus 2 (12th Anniversary Edition) Measurements - GoldenSound

Measurements of the Denafrips Pontus 2 12th Anniversary R2R DAC, and testing to see whether claims of NOS capability are true.

goldensound.audio

The suggestion is to attenuate any signals by 3 or 4 db in your playback software. I would ask for a refund if the DAC doesn't function as it should myself. Even then they are unlikely to cover the repair needed on your preamp possibly caused by the DAC's poor design.

Blumlein 88
I have read that article about the signal “folding over on itself” at high volume. When my preamp popped volume control was at 1/4 or about 60db. I like the look, feel, and sound of the Denafrips but if the synergy between the DAC and the preamp is poor I will return it.

 

[2tuby]

Take a look at the website for the makers of this preamp. Not very confidence-inspiring.

Somebodyelse said,
I have been at the Backert Labs website already. Not much info on the website, especially for one of their older units.
I have called and spoken to the Backert people previously when I was purchasing the used unit. Good guys. I would have called yesterday when it happened but too close to the holiday. I will call tomorrow.

Take a look at the website for the makers of this preamp. Not very confidence-inspiring.

 

[Chazz6]

Have you compared the maximum output voltage of the two DACs?

 

[2tuby]

Have you compared the maximum output voltage of the two DACs?

Chazz6-
How would I use a voltmeter to measure the maximum output voltage?

 

[Chazz6]

How would I use a voltmeter to measure the maximum output voltage?

I would set the voltmeter carefully on the shelf and look on the Web for specs of the two devices.

 

[Blumlein 88]

The Stellar Gain Cell dac can output 20 v RMS according to spec.

According to Amir's review it has 4 volts at unity gain. It is said to be capable of 12 db gain which would be 16 volts. Needless to say it can output more than the Denafrips. I think it is safe to say @2tuby wasn't using it at max gain, but I don't know. Maybe it was and the preamp was turned way down. A preamp wasn't needed for the Stellar gain cell DAC. The preamp probably has 10 db gain or at least the 1.4 version does. The Classe amp in use clips with an input of 1.88 volts by spec above 300 wpc into 8 ohms. Way, way too much gain in the system as connected. Would the transient of the Denafrips from oversampling overs cause damage? Maybe, hard to say, it apparently can cause very loud popping. The max peak voltage of it would only be something like 6 volts or a touch over 4 volts RMS. If replacing or bypassing the Backert preamp makes eveyrthing work the only thing known is the preamp has a problem.
I don't know the poster's needs for inputs and such. Seems his system does not need a preamp at all unless some analog inputs are in use.

 

[Willem]

You really do not need either a DAC or a preamp.

 

[OldManMatt]

My guess is that the issue lies within the preamp. I did not look up your preamp model but I'm pretty sure it's tube based. As an owner of probably 5 or 6 tube preamps they always have some type of issue from time to time. Either something in the power supply or power to the tube filaments,heaters. For starters you could examine your tubes.

I had an issue not to long ago where everything shut down. When I started everything back up I heard some noise coming out of the speakers. Took the preamp out, flipped it over to take some readings with all the tubes loaded. As it was running I noticed that one of the filaments was not lighting up on the cathode follower tube. Switched it out & everything was good again with the preamp.

I'm no tech & obviously a bad tube might not be your issue. When you were doing your Turn On sequence with your system was the Denafrips the last thing you turned on? If so then maybe there is some correlation to the dac being the issue..maybe unloading a big dc spike into the preamp & causing an issue. I'm sure you remembered to always turn the preamp on first & last in your On & Off sequence.

 

[Mart68]

I think that if the problem was with the Denafrips DAC there would be a lot of people reporting the same issue.

Looking at how the pre-amp is sold inspires no confidence in it.

The power supply: - Backert Labs tube preamps

The U.S. Patent on our power supply, which we call GreenForce, is Patent No. US 8,411,475 B1, date of patent April 2, 2013. Introduction The power supply that runs most audio equipment today is called a “linear” supply. It was designed in the 1920s and hasn’t changed much. In more...

backertlabs.com

Their 'technical' section on how their - patented - power supply works:

''GreenForce provides better current linearity, feeding the regulator with current more nimbly than other power supplies, thereby improving the accuracy of dynamics and other audio cues in your music.''

Fix it, sell it. If you do still want a pre amp get an old Sony or Yamaha.

 

[OldManMatt]

"Feeding the regulator with current more NIMBLY than other power supplies"...that definitely had me raising one eyebrow higher than the other.

I am probably one of very few people in this forum that can appreciate a good tube preamp. But they can be a real pain in the butt at some point.. especially when you pair them with all solid state gear.

The designer has to really truly know what they are doing as far as incorporating some one of a kind power supply & biasing the tubes to where you are getting the sound you desire while having very low internal & power supply noise..& still being very stable long term.

Maybe the preamp is due for a checkup from the manufacturer. If this is an older unit maybe they have made advancements in their patented power supply. I'm sure they will be able to help you figure out your issue when they get a chance to talk with you.

 

[antcollinet]

If this was a result of one or more denafrips inter-sample event of the kind described, then the transient produced (transient from full positive to full negative - or vice versa - from one sample to the next) is basically a full power impulse. As such it is infinite bandwidth - or at least as infinite as the output stage will allow. Who knows what that might do to a poorly designed tube pre.

 

[2tuby]

Reporting back-
Why the system popped and the Backert Preamp went to mute is still a question but, I found the source of the low frequency hum. To find it I swapped components in and out. I have 2 amps, 2 DACs, 2 sets of speakers and 2 preamps besides the Backert so I did some A-B testing. Lots of combinations. When using my PSAudio DAC/preamp I did not have the hum but when I used the Pontius DAC with either the AI Modulus 3 or the Backert preamp I had the hum. The culprit was my WiFi extender. When I disconnected it, the hum went away. I am assuming that the extender was noisy enough, the preamps had enough gain and Pontius and cables had little shielding resulting in the problem. Live and learn.
Thanks for your replies. Have a Happy New Year. I will, my music is back.