Xiangsheng 728A pre-amp into Yamaha A-S501 integrated amp - problem

[CharlieAudio]

I purchased a Xiangsheng 728A tube preamplifier. I ran its line output into the line input of my Yamaha A-S501 integrated amp. I fed two inputs to the Xiangsheng, a CD player and an Audioengine B-Fi, which receives wifi and outputs 2.2V on a line output. The B-Fi also has an optical output, which I left plugged into the Yamaha, and which continued to work fine.

The setup plays very low volume even when the volume is near max on both the Xiangsheng and the Yamaha. All six tubes in the Xiangsheng have an orange glow.

The same inputs fed directly into the Yamaha can be played at any desirable volume; I wouldn't go beyond 12 o'clock on the volume control.

The vendor states that the Xiangsheng is "Input Impedance：100K, Output Impedance：600 ohm." The Yamaha manual says its CD and other non-phono line inputs have sensitivity/impedance of 200 mV at 47K ohms.

Is there A) a specifications problem in the relation between these two components, or B) what would be the problem with the Xiangsheng? Thanks for any help deciding whether it is A) or B).

 

[BMC]

Try hooking up the preamp to a power amp and see what happens.

 

[CharlieAudio]

Try hooking up the preamp to a power amp and see what happens.

Ah, if only I had one available.

 

[BMC]

Did you try both outputs on the preamp to see if there is any difference?

 

[CharlieAudio]

Yes, I tried the outputs labeled High and Low. The vendor's website says both are actually high now, even though he uses chassis inventory that is still labeled both High and Low. (I understood that before making the purchase.)

I expected that I would need to manipulate the pair of volume controls to avoid over-amplification. Instead, the setup right now is useless.

 

[FlaCharlie]

I purchased a Xiangsheng 728A tube preamplifier. I ran its line output into the line input of my Yamaha A-S501 integrated amp. I fed two inputs to the Xiangsheng, a CD player and an Audioengine B-Fi, which receives wifi and outputs 2.2V on a line output. The B-Fi also has an optical output, which I left plugged into the Yamaha, and which continued to work fine.

The setup plays very low volume even when the volume is near max on both the Xiangsheng and the Yamaha. All six tubes in the Xiangsheng have an orange glow.

The same inputs fed directly into the Yamaha can be played at any desirable volume; I wouldn't go beyond 12 o'clock on the volume control.

The vendor states that the Xiangsheng is "Input Impedance：100K, Output Impedance：600 ohm." The Yamaha manual says its CD and other non-phono line inputs have sensitivity/impedance of 200 mV at 47K ohms.

Is there A) a specifications problem in the relation between these two components, or B) what would be the problem with the Xiangsheng? Thanks for any help deciding whether it is A) or B).

There is no issue with the specs. If the Yamaha only needs 200mV to be driven to full power then there's obviously a problem with the preamp.

Even if it had zero gain you'd get plenty of volume from your source and you've confirmed that the output of the source is fine. If it's new or still under warranty, send it back.

 

[CharlieAudio]

If the Yamaha only needs 200mV to be driven to full power then there's obviously a problem with the preamp. Even if it had zero gain you'd get plenty of volume from your source and you've confirmed that the output of the source is fine.

Thank you. That is the logical deduction, and I wondered whether anyone - perhaps the vendor - could argue otherwise.

 

[geespot]

Isn't the yamaha an integrated without pre/main connections, or am I missing something?

 

[CharlieAudio]

Yes, the Yamaha A-S501 is an integrated amp with several line inputs, a phono input, and an optical input. The advice I've read is that you can feed the output of a pre-amp into the line input of an integrated amp, being careful with the two volume controls.So I started with both controls at zero and gradually increased them. After both were well up, there was a whisper of the sound, and at full volume on both, there is still only a sound like someone talking semi-confidentially with you a couple of feet away. Isn't this the opposite of what should happen?

 

[CharlieAudio]

I must apologize. I discovered that I had the Yamaha input selector at the wrong position. Indeed, the curiosity is that anything was audible, but that does not change my stupid mistake.

Now that the setup puts out normal volume, I discover that this Xiangsheng 728A sends a strong hum to the Yamaha -- even when the Xiangsheng is powered off and unplugged. That compels me to keep the Yamaha volume control as low as acceptable and hence the Xiangsheng volume control at max. The more I raise the Yamaha volume, the more the hum intrudes. It sounds like 60 Hz to me. I moved the Xiangsheng about half a meter away from the Yamaha, but nothing changed.