Boyuu EL34 A9 Tube Amp

[LongRoad]

Originally Posted by gregas

So if the a9 has an put sensitivity of 750mv and my CD player outputs 2 volts, would this be the reason for Distortion at higher volumes?

that over 750mV will be fed to the amplifier causing signal distortion.
Be sure that the sensitivity of the input amplifier circuit must match the level of the output signal of the head unit. Input sensitivity is adjustable in the amplifier and sets the magnification factor, but high input sensitivity can lead to large signal distortions.

[VictoriaGuy]

Originally Posted by navydiver

I do also note that when the amp is powered off, music still plays through the speakers until the caps have significantly discharged.

If you take out the rectifier tube and power up the amp with speakers attached, do you still hear the hum?

Originally Posted by navydiver

I hear you 6A3sUMMER....snip.... Thing works very well for my needs.

I agree with 6A3sUmmer that a bleeder resistor should be added to the B+ supply, if one isn't already fitted. You should be able to find spots for connection of the bleeder resistor on the PCB.

[LongRoad]

Made an amplifier input divider, it works well, it is controlled by a regular source selection button.

[VictoriaGuy]

Originally Posted by LongRoad

Made an amplifier input divider, it works well, it is controlled by a regular source selection button.

Looks useful - it creates a 'Hi Level' (CD) input and a 'Lo Level' (Aux) input.

[6A3sUMMER]

A little excess gain in the amplifier is why we have volume controls.

Many CD players (with the DAC at full scale) have 2Vrms out.

Suppose you set the amplifier gain so that it is just below clipping (or just below high distortion) when the CD player puts out 2Vrms (DAC at full scale). But when you play a typical Chesky Records CD, the loudest section of the recording is -10dB below full scale. Now, your 10 Watt amplifier can only put out 1 Watt when listening to that CD (so you have to turn the gain up, but you can only do that if you have the excess gain available).

[navydiver]

All
Great success. Explained herein: YouTube

I am sure there is room for tweaking once I get to know this A9 a bit better. Got some listening to do to find any warts but for now am very happy with outcome!
Cheers and thanks all!
TMF

Another question I have:YouTube

Short and to the point, anyone know where I can get a cage for this amp (see linked video)?

[LongRoad]

Originally Posted by 6A3sUMMER

A little excess gain in the amplifier is why we have volume controls.

Many CD players (with the DAC at full scale) have 2Vrms out

I tried to explain clearly, but you persistently with one friend drank beer when I explained.
I do not urge everyone to make a divider, but in my case it is necessary.
Conclusion from my DAC 2.5V, send such a signal to your amplifier (750mv), then you will understand.


navydiver
BOYUU EL34 tube protection grill cover Reisong BOYUU A10 EL34 tube protection grill cover-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

[navydiver]

Originally Posted by LongRoad

navydiver
BOYUU EL34 tube protection grill cover Reisong BOYUU A10 EL34 tube protection grill cover-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

Thank you - I think that is for the A10 amp. Mine is the A9 which I believe is a different size? Will look at the site to see if they have an A9 version....

[VictoriaGuy]

Originally Posted by navydiver

Short and to the point, anyone know where I can get a cage for this amp (see linked video)?

If you're concerned about safety, and possibly fingers getting in the wrong places (kids, adults moving the amp or dusting), a (perforated?) bottom cover/panel could go on your list. Pretty easy DIY with a piece of Al from MetalSupermarket or something steel from old commercial gear. Al is easier to cut...

It's baffling to me how many DIY-type units come without bottom covers (Bottlehead Crack Headphone amp was the same @ $400+...)

Good work in finding the wiring error/errors and getting the amp running properly!

[navydiver]

Will look at the dimensions of the A10 when I get home and compare - thinking I might be able to DIY that one. Here is my A9 Sound Check video to give folks a feel as to how good one of these sound (of course the crappy phone mic doesn't really do it justice):

YouTube