Don Pearce wrote:
On Fri, 03 Dec 2004 12:09:01 +0000, Phil North
wrote:


Nick Gorham wrote:

Dave Plowman (News) wrote:


In article ,
Nick Gorham wrote:


Out of interest, what the input impediances of the amps in question ?
That could well be making a difference. And maybe input capacitance,
depending on the circuit of the phono stage.



I'd also be interested in the output impedance of the pre-amp. Does it
use
cathode followers?


That was my point...


From http://www.mei-xing.com/doce/pro20.htm

MM input level: 2.5mv
MC input level: 0.5mv
MM input impendence: 47k?
MC output impendence: 100?
MM signal to noise ratio: 91dB
MC signal to noise ratio: 86dB
Output impendence: 100K?

One day I will know what all this means!


One thing this means for certain is that you shouldn't buy this
amplifier. At 100k output impedance, if you connect it to a power
amplifier with a cable whose capacitance is as little as 100pF, the
response will be 3dB down at 15kHz. This is most definitely NOT a
competently designed amplifier.

d
Pearce Consulting
http://www.pearce.uk.com

I haven't followed the technical bits of this thread - so sorry if this
has been covered.

In HFW's Jan 2005 test of the Ming Da MC-7R preamp the output impedence
was found to be a problem and too high, causing buzzing. It was solved
by using resistors between the pre and power (a Quad 303), and the amp
was withdrawn from the market until the fault was fixed.

So there was an acknowledged design fault with this amp - it may have
been mirrored in the phono and you could have a pre-fix rogue. The
article does say that Ming Da were very good with email support - may be
worth contacting them.

For the technically minded I've scanned the 'measured performance' of
the amp.

-------
MEASURED PERFORMANCE

Preamplifiers commonly have a gain of x3, from CD input to line output.
The Ming Da offers more, x10, so to deliver 1V to a power amp it needs
100mV in -a relatively high sensitivity. There are no drawbacks to this,
since being a valve preamp it will swing 40V out, four times more than
most transistor jobbies. The volume control will need to be set quite
low, but as it is backed off input overload sets the signal handling
limit and this was greater than 6V, measurement revealed. It's more than
enough for all modern sources.
Bandwidth extended from 20Hz up to a very high 150kHz, within 1dB
limits. Below 20Hz there was a sudden and steep rise in gain to +10dB at
2Hz, possibly due to the way feedback has been applied. It wasn't a good
sign but the Ming Da seemed stable and able to cope. I strongly suspect
this will add a sense of depth or power to the sound, perhaps enhancing
'atmosphere', due to emphasis of subsonic aural cues. Distortion and
noise levels were satisfactorily low.
The Ming Da measures well, but its subsonic gain peak will influence the
sound. IMK

Frequency response 20Hz-150kHz
Separation 107dB
Noise -88dB
Distortion 0.14%
Sensitivity 100mV
gain x10
overload 6Vin/40Vout

(HFW Jan 2005, p.43)
--------

Rob