Massdrop Cavalli Tube Hybrid Amp

Two wrongs don't make a right, but three lefts do...

 

I’m a total noob when it comes to tubes, so - are there alternatives to the stock EH6922 with less gain?
While I can comfortably listen to my LCD-2.2F without noticing the channel imbalance of the volume pot at low levels, the Elex’s slightly higher efficiency is causing problems when I’m using the internal SDAC.
At the moment I’m using the variable output of my EAD DSP-9000 Pro to counter the problem, but it’s up for sale as I want to declutter my work desk.
Or is it possible to change some resistor values inside the MCTH or get a different volume pot?
Because as it is now, not only does my speaker amp sound better with the Elex than the MCTH, but is easier to use at low volume as well - the pot of my speaker amp is at 11 o’clock for most listening sessions.

 

+1

 

https://www.amazon.com/Harrison-Labs-Line-Level-Attenuator/dp/B0006N41B0/

 

Great idea with an external DAC but with the internal SDAC? I don’t want to have masses of cables hanging from the back of the MCTH.

 

Yeah, you'd be a bit boned if you're using the internal DAC, sadly. I also totally didn't skim read your post and fail to register that bit. At all.

 

Not sure how she is wired, Captain but in the Crack, Doc says "You can solder a 33K resistor across each pair of outside lugs on each level of the volume pot, then solder a 75K resistor between the red wire coming from the RCA jacks and where it attaches to the volume pot, as well as another 75K resistor between the white wire coming from the RCA jacks and where it attaches on the volume pot.
This isn't all that different than an inline attenuator, but it will maintain high input impedance in the amplifier."

So resistors might be your answer, but you would have to add them from the dac output to the volume pot.The values for this unit I am not sure of. You will void your warranty.
Massdrop may replace the unit as the careful attention to volume pots may have been overlooked in your unit.

 

That kind of channel imbalance at 11 o'clock is not good. It could be happening at the pot, the tube, or the internal DAC. Scratching while turning the volume up and down is sometimes a symptom of DC on the output. Not sure why this would be as there are DC relay protections on the input side and output side. I would not try to fix it or mess with it if it is still under warranty.

 

If you don't mind a bit of soldering (see also the links on the page for purchasing it from Garage 1217 or the iFi equivalent):

https://diyaudioheaven.wordpress.com/headphones/headphone-attenuation-adapter/

These will raise the sub-1-Ohm output impedance of the amp a bit - the DIY/Garage version to 3 Ohms, the iFi version to c. 2.5 on one setting but purportedly under 1 on highest attenuation. Presuming the Elex has the same impedance response as the Elear/Clear (see measurements at Innerfidelity), raising the source impedance will boost the bass - but with the numbers of these adapters, the effect will be very small.

 

I realised my post was a bit unclear on some points, therefore I edited it.
The channel imbalance happens between 7 and 8 o’clock and is only a problem with the Elex when I go that low for background listening while reading something.
11 o’clock is the volume setting on my speaker amp for recreational listening - background listening happens there at 9 o’clock.
The scratching happens mostly when I haven’t used the MCTH for a few days and gets less if I turn the knob a few times before use - but it never goes away completely.

While that doesn’t change the gain of the MCTH, it should solve my problem equally well and might even lower the scratching noise. I even have most parts for the adapter in my drawer. Thank you!

 

Has anyone found a non-DYI LPS for the amp? Meaning that I can just order online. I assume the THX 789 would have the same power supply and just want to get ahead of the game since I'll be running both these amps at work.

 

THX spec sheet says 24V power supply, whereas the MCTH is 28. @dBel84 might be able to say if 28 would work for the THX. For an off the shelf 28, scan back in this thread or the MCTH power supply measurements one for the AliExpress unit @gixxerwimp is using.

 

Or maybe not - these things all look so similar my brain attributes Cavalli input to all of them. Sorry!

 

Sadly I don't know what the innards of yhe THX looks like

 

This is my post with the link to the LPS embedded: https://www.superbestaudiofriends.o...alli-tube-hybrid-amp.4866/page-32#post-202462

Here's the actual link: https://www.aliexpress.com/item/Fin...Supply-5V-9V-12V-15V-18V-etc/32832502096.html

 

Just a quick update from me regarding the CTH and running it on batteries.

I used two car batteries and got a constant 25.7 volts over the course of several hours. Admittedly these were two very large (100 amp/hour!) batteries, but as I had them around they were begging to be tried. There was very little voltage drop over this period.

Clearly the voltage regs in the CTH were doing a good job, as there was no difference in output between the power supplies. Something worth check when auditioning different supplies in case a slight difference in voltages and levels. I checked mine at the headphone output, and they were the same within 0.1dB so probably undetectable in listening.

The results using the batteries compared to the stock PS were the following:

Definite and obvious reduction in noise, it just sounded quieter, inky black background very apparent. At first it sounded like the volume had been turned down, but I rechecked the levels as above. Bass is certainly tighter, better control, more definition (bass drums, tympani, upright and electric bass) and seems to go deeper. The mids and the sound stage seems to be easier to hear into and instruments have bett separation. The highs seem as the mids, sweeter and contributing to the better sound stage.

All listening done with HD800's and with the CTH connected directly to my Yggdrasil.

So a good step forward then, and I think shows that either long term use on batteries would be worthwhile or obtaining a decent linear power supply. And probably one that has not only as well specced power transformer for the power demands but one probably with a "snubber" to kill the resonance of the TX and also a choke for better smoothing. I'm sure it would be dead easy to make a suitable one for the CTH.

 

Hey Bob,

Is the 2nd statement based on your personal experience? I think you said yours would be showing up in early June. Have you had a chance to try the AliExpress unit yet?

 

Have a look here.

 

Oops, senior moment. I read that and even liked it. Should have checked the measurements thread to refresh my memory.

Move along, folks. Nothing to see here ...

 

My favourite of the non-stock tubes I rolled has developed an intermittent buzzing / wheezing / whistling and become very microphonic, which I'm pretty sure it wasn't before (or at least didn't notice). Just rubbing my fingers across the top of the chassis can be heard through the headphones. Are these the signs of a dying tube?