Pre-In Input on Muzishare X7 Tube Amp

[Crazymerio]

Hello all.

I recently purchased a Muzishare X7 tube amp and have enjoyed it so far. I’m going to be upgrading my AV receiver soon as well to something that can do Atmos down the line but I’d rather use the tube amp in the system with some pre-outs from the new receiver.

What I’m not certain about is the usage of these “Pre-In” inputs on the back of the tube amp. What exactly are these used for? Would I run from the pre-outs to this input or just to another input (except for Phono of course).

Also, would there be any issues with that general setup of connecting the AV receiver Pre-Outs to a tube amp?

 

[gibbsy]

You would have to check the output voltage matches with the input voltage on the tube amp. The connection would be to pre-in. This would (without looking at the manual, so please don't take as gospel) allow the AVR to control the volume.

The problem is that tube amps don't tend to be that powerful and there may be a discrepancy in power and the tube amp may suffer as a result although it has 45 watts available.

What do you want to achieve by connecting to an AVR? It's connection will still be influenced by the pre-amp in the AV and also have that lovely warmth that tubes impart. That may lead to some timbre mismatch between the front left and right and a centre speaker.

I'd keep the tube amp for music and if you want to use the same front speakers then consider a speaker switcher.

 

[Crazymerio]

Thank you for the reply.

The goal is to use the same front L/R speakers for both the stereo system and AV system.

I haven’t used a speaker switcher before but looking into it they seem to suggest not using one with tube amps since you might not have the speakers connected back to your amp all the time or switching amps on the fly could be an issue.

How dangerous is that for the equipment? I was curious about how much of an issue power and timbre matching might be so it’s good to hear some feedback on that.

In your experience, would a speaker switcher still be a better solution?

 

[Bachemar]

I suspect the timbre mismatch would be subtle at best, and you might not notice it in real world usage. If the tube amp is loud enough for your music listening (depends on your speaker efficiency) then power should also be fine for HT usage - assuming you don’t watch movies at significantly louder levels than your music. Tubes distort gracefully and don’t “clip” beyond the rated power, so those 45 watts can easily stretch to match the AVR for short bursts. Assuming the amp is well made.

The main concern I would have with using a tube amp for HT, would be the annoyance of having to wait for the tubes to warm up every time I want to watch some TV, and the cost of tubes - using up your tube life just to have the TV running in the background.

 

[Bachemar]

If you want to go down the switch route, you would need to look for “amplifier selector” switch, and ensure that special care has been taken to make at least one of the amp inputs to be tube friendly (a resistor across the input to create a minimum load when not active) There are a few of these out there but they tend to be expensive - unlikely to find something less than $100.

Niles audio had a switch on Amazon that some people on forums had recommended. I don’t know if it was tube friendly though.

 

[Crazymerio]

If you want to go down the switch route, you would need to look for “amplifier selector” switch, and ensure that special care has been taken to make at least one of the amp inputs to be tube friendly (a resistor across the input to create a minimum load when not active) There are a few of these out there but they tend to be expensive - unlikely to find something less than $100.

Niles audio had a switch on Amazon that some people on forums had recommended. I don’t know if it was tube friendly though.

I’ve been looking into this and it seems I’ve opened up a pretty big can of worms for my level of knowledge.

On the AVS forums I saw a discussion on using an Amplifier Switcher with a solid state AV receiver and a stereo tube amp and I’m not sure if I understand some of the conclusions made. I get that I need a load on the Tube Amp in order to avoid damaging the unit but does this necessitate adding a resistor to the output channel or do some amplifier selectors account for this?

I’m looking into the Beresford TC-7220 which seems like it might work for my purposes but I’m not sure if I also need to add a resistor to the Tube Amp alongside it and if so whether it just needs to be a 150ohm resistor or a 32 ohm resistor as others have mentioned.


Additionally, I found this passage:

“If the tube amplifier is on while connected to the unpowered solid state amplifier, it could do some serious damage to the output stage of the solid state amplifier. With the solid state amplifier off, there is nothing to prevent the output transistors from being 'back biased' from emitter to base. If this is over 5 volts or so, the output transistors may be destroyed.”
Does this mean that it’s impossible to have a tube amplifier and a solid state receiver connected to an amplifier switcher or is there some caveat to this? Does the receiver always need to be on in order to run the Tube Amplifier?
Apologies for all the questions. If there’s a resource I should look into instead please feel free to redirect me.