Question 1

I have a full range 103db speaker and my hearing is sensitive to speaker hiss at idle.  Does this amp generate speaker hiss at idle?

Accepted Answer

My speakers are 89 dB sensitivity and I can hear tube hiss at 12 o'clock on the volume control if I put my ear on the drivers without music playing.
Not a problem at listening position and at 12 o'clock the music is plenty loud in my biggish room (40x18x9).  At 105 dB it may be a problem but I guess you won't need to crank it to 12 o'clock either.
Hope that helps.
Overall I am very happy with the purchase.  Great value, great sound, well built amp.  The support service has been quite responsive too.
Good luck

Question 2

What's the difference in sound characteristics between this 300b amplifier vs an el-34 amplifier such as the boyuurange mt-34?   thank you...

Accepted Answer

The 300B sound is magical in the midrange, with less definition than EL34 in the bass and treble regions.
If you're into vocals,300B is the way to go, not so much rock or electronica.

Question 3

How is it that you isolate the rectifier board from the chassis?

Accepted Answer

Vinh, I took an audio recording of the hum just to try and find out exactly what kind of hum it is. I inspected the recording through a spectrogram. It turns out the hum is actually a chord of hums. There are hum notes at 95hz, 120hz*, 240hz* 360hz*, 600hz, and 720hz (*these were the loudest notes).

I used a multimeter and checked for continuity between the IEC and RCA grounds. There was continuity. I opened up the unit and removed the exact rectifier board screw you described, as per your instructions. The hum was still present. There was still continuity between the IEC and RCA.

I then tried removing all but one of the screws (I did not remove the screw that transformed the hum into a buzz when removed). The hum was still present. I checked the IEC and RCA for continuity with these three screws removed; there was continuity. Since removing those three screws did nothing, I put them back.

Out of curiosity, I removed the one screw with the metal ring that was a part of the board underneath it. After I removed this screw I checked for continuity between the IEC and the RCA; There was NO continuity when this particular screw was removed (again, this is the screw that when removed, added unbearable buzzing to the amplifier output). I put that screw back since I already documented what this unit sounded like with this particular screw removed.

Nothing I did to the rectifier board solved my hum issue. This is a low-level hum coming from 96dB sensitivity speakers that sit about one meter away from my listening position.

Other bits of diagnosis information: If I listen to loudly mastered music playing at a low to moderate volume, I don’t hear the hum. If I listen to quietly mastered recordings at low to moderate volume, the hum is noticeable. The hum does not change whether the volume knob is at minimum or turned to maximum. The hum does not change when the input is changed between Aux, CD, and Tape. The hum did not change when there were absolutely no inputs plugged into the amplifier. Swapping the positions of all the tubes did not change the hum.

I am completely baffled.

Question 4

Can this amp drive a pair of  def. tech.bp7002:
frequency response 15-30,000 hz
sensitivity 92 db
8-ohm imped
up to 400 watts?
thx!

Accepted Answer

Definitely, unless you are playing hard metal rock to ear splitting level.
It drives my 8 ohm, 87 dB sensitivity speakers to satisfying level.
Go for it.

BOYUURANGE A50 MKIII 300B HiFi Single-end Class A Valve AMP Integrated Tube Amplifier with Tube Cage

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