Newbie question: A-B testing

[Mykall]

Hi all, long time lurker, first time poster.

Reading up on lots of posts from here, I recently invested in an A-B switcher, where I can perform sighted and blind (someone switches the order of the inputs and we cover the amps so I cannot see them) testing.

Spoiler alert: when properly level-matched between amps, I could barely tell the difference between amps sighted, and had essentially zero chance blind!

Couldn’t reliably tell the difference between a $200 FiiO K7, a Chord Hugo 2 or a Cayin HA 3A on my usual reference phones, Focal Utopia OG, ZMF Verite and Sennheiser HD600.

Even tube amps versus solid state is not easy to tell blind, even though I convinced myself a long time ago it was a night and day difference LOL!

On to my question:
I have read that it might not be so good to switch the load from one amp to another, especially for a tube amp. I have a Cayin HA 3A that I recently bought and I wanted to know if it might be bad for it? I read that it may be tough on the output transformers to keep switching the load.

Any guidance or links to best practices for doing this safely? So far the amp has been fine with no issues during A-B testing.

Thank you!

 

[Mykall]

I didn’t receive a response to my question, but I reached out to Cayin themselves, so I am posting their response below in case this is helpful to someone else looking to do the same thing some day (they did a great job with their response as it was very thorough).

Long and short of it, the Cayin amps have a built in dummy load on the headphone output section, so A-B switching the output section out or running the amp without headphones is a non-issue.

For anyone else looking to do this, if your tube amp either has resistors in the output section OR it was designed with a built in dummy load like the Cayin amps, it should be no issue and you can A-B test to your hearts content. Just don’t leave the tube amp running without headphones connected for 12+ hours a day, every day.

If anyone else is curious how I ran the A-B test, feel free to ask questions.

I expanded the set up to include cloning the optical outs from my source (Wiim Pro), and also another AB-switch for the composite cables, so now, I can also A-B switch not just amps, but DACs too via another A-B switch

Still can’t reliably tell the difference between the Amps, or DACs for that matter. I haven’t run a laptop into this set up yet, as I’m afraid to find out that I can’t tell the difference between a laptop headphone out and the $6,000+ I spent on amps and DACs when properly volume matched LOL!

—-

Dear XXX,
Thank you for reaching out to us.
You're right — in general, it’s not recommended to run tube amplifiers without a load, actually both transformer-coupled and otl, because it can potentially damage the output transformers and tubes.
I’m guessing you’re thinking that having to power off the amp each time is not only inconvenient, but also affects the sound, since the tubes cool down and you would need to wait for them to warm up again to get back to optimal performance, which wastes time during your A/B testing.
Well good news is, for the HA-3A, you can have some peace of mind for two reasons:

1. The output power of the HA-3A is relatively modest compared to tube amplifiers (those with tens or even hundreds of watts).
2. More importantly, we have included a dummy load inside the HA-3A design. If no headphone or load is detected, the system will automatically connect the internal dummy load to protect the output transformers. After all, it’s an amplifier built for headphones — plug in and unplug is just part of normal use, and thus practical reliability was an important part of the design, we certainly wouldn't want a headphone amplifier to behave like it has a self-destruct switch just because a user unplugged their headphones!

That said, even with these safety measures, we do not recommend leaving the HA-3A powered on without a headphone connected for very long periods of time.
If you are just switching back and forth within a few hours during A/B testing sessions, that's fine.
But if you plan to leave it powered on without a load for like 12 hours or daily, it could still gradually stress the output transformer and tubes over time.
I hope this explanation helps! Feel free to reach out if you have any more questions. If no, happy listening!

Best regards,
Cayin Support Team