Gain on Mingda MC7R...

[John (big)]

Having bought my Mingda MC7R from atomheartmother from the classifieds of the wam, I realised that the gain was a little more than I had originally thought OK with phono not so much with some CD's or Tuner.

The result of a post from Mark the Ming was that I traveled to the palatial home/office of Mark Manwaring-White, one half of Mingda UK. The house is overlooked by the Malvern Hills with breathtaking views (if only). I was made very welcome with tea on tap. I had no idea until Mark proceeded to probe the MC7R's interior how well made it was, also apparently all of the transformers are hand wound in house & seemingly bullet proof. He also gave a genuine dire warning about buying from anyone in China other than Mingda as a lot are not the genuine article ie. just like fake Apple shops etc.

Once ensconced on a chair I watched Mark do a mod to increase the longevity of the rectifier valve, move & replace capacitors de-solder & re-solder resistors with the aplomb & skill of an expert Mark has literally been playing with valves since he was a boy in short trousers though not my age he is no longer a boy.

The MC7R was then tried/tested on MC 805 mono blocks, nice, then the enormous MD 90 monoblocks 150w push pull ball busters or 90w in velvety triode mode connected to various TDL speakers all seemed well. Mark was also kind enough to check the values in my phono stage, all OK.

Today I put the MC7R back into circuit no valve rush, quiet background on phono also no over load of power amp that until it was gone I was not aware of sounded beautiful worth the journey and the few £'s charged. However on CD still a little cramped on the volume control but usable, I have tried some JAN 1976 GE CV4017/5751's not much difference in volume however on extended listening though they opened out the soundstage the bass disappeared. Contacted Mark he has come up with a plan to make the MC7R variable gain.

Despite not quite arriving at the perfect solution yet, I am using some 10db attenuators I had made 20 or more years ago (advent of CD) I feel can recommend Mingda UK & this preamp was not even bought from them in the first place it was an import, I call that back up.

 

[old_school]

I was looking closely at the Mingda preamps a while ago. If there was a version with variable gain (preferably three positions) and a tape loop, I'd be looking at it with some desire.

 

[John (big)]

Whilst I wait to get back to "Mark the Ming" for the variable gain mod. Mark suggested I tried a pair of ECC82/12AX7 in the ECC83/12AX7 holes.

ECC82/12AU7's (17) have lower gain than CV4017/5751's (70) which are lower gain than ECC83/12AX7's (100)

I made a phone call to "Daren" the supplier of some superb NOS Chinese CV4004's (H/Q ECC83) that I put 3 of in my Croft phono stage, he did me a deal on a pair of CV4003/M8136 very high quality ECC82/12AU7 substitute; yet again he has come up trumps, whilst only a slight drop in volume/gain the space around instruments is improved, the sound stage is more forward of the speakers & deeper behind, voices both male & female are to die for both treble cleaner,clearer bass even deeper, I already thought my One Thing Quad57's went deep, I'm running out of adjectives.

I believe the valve was made by RFT Funkwerk.

 

[hullevad]

RTF is from the old east German factory. They are quite good! Almost as good as the expensive west German Siemens valves (RTF´s are not lasting as long as the original Siemens). At the money a no brainer!

 

[Philv]

Why not just use attenuators? Or is there a reason not to?

 

[old_school]

Why not just use attenuators? Or is there a reason not to?

I tried attenuators, but they seemed to suck some of the dynamics out. I had better results with an old Rothwell passive than I did with the attenuators (also Rothwell). Can't explain that one.

 

[John (big)]

I tried attenuators, but they seemed to suck some of the dynamics out. I had better results with an old Rothwell passive than I did with the attenuators (also Rothwell). Can't explain that one.

I understand Goldenjacks create less of a veil indeed some say none at all, despite this I feel lowering gain in the pre-amplifier has to be a more elegant solution & variable gain the icing on the cake...

John

 

[John (big)]

Yesterday I braved the rain and the ultra cautious & would be F1 Mercedes drivers on the 140 mile route to Mark the Ming in Malvern as ever I was made very welcome, I must have drunk him out of his stash of rare Chinese Red tea.

Not content with giving me 2 levels of gain on The MC7R with 2 neatly fitted toggle switches on the side, drilling the stainless steel with cobalt drills was an exercise in it's self, add some very neat wiring inside the chassis & I now have 3 levels of gain for a reasonable fee.

Today I have listened to the system any of the levels works with my Croft 3 valve phono stage indeed the sound is even more open, no attenuators ? bass in abundance where present on the record however there is a more liquid treble with more definition I played Parsley sage Rosemary and Thyme by Simon & Garfunkel which I have had since it's release I heard inflections I had not noticed before.

There is still a smidgen more gain than perfection for me, I texted Mark he is fault finding my old behemoth solid state amplifier, Mark said he would change the value of a couple of resistors next time I'm there no charge.

I hesitate to add the usual rider since Mark is so personable and we get on well so I can't say I am entirely unbiased.

 

[dudywoxer]

The Ming was mine for a short while, and although I could not live with its gain level, it did give a very enjoyable sound, when you could use it. I hope that having it ''sorted'' you are left with a pre that fulfils its promise.

 

[John (big)]

dudywoxer this is a keeper.

John

 

[John (big)]

On Tuesday I drove to Malvern to "Mark the Ming" with my son who is at college studying electrical engineering. I took the MC7R & my Leak Troughline Stereo with Tim de Paravicini stereo decoder, the leak had a couple of duff caps replaced and needed realigning.

Mark as usual made us welcome & for me liberal quantities of China tea. I explained to Mark that the volume control was noisey using my modded Muse DAC connected which puts out 4v of DC per channel, as part of the mods the output capacitors were removed on the Muse to improve SQ.

One of the input caps on the MC7R was found to be "leaky" so Mark replaced both caps with newer better quality ones. He then adjusted/lowered the minimum gain on the MC7R, this has taken a couple of extra visits as the output voltage of my various sources are different; short of carting my entire system to Malvern this was the only way, they are now individually catered for by the 3 levels of gain, I now have proper volume control on all sources; these are accessed by 2 extra toggle switches on the same side as the inputs.

The Leak Troughline was then subject to Marks attention, the day before I had opened the Leak & as they are known to seize & break I squirted GT85 into the pots where the graphite slugs are, GT85 unlike WD40 is plastic/nylon friendly & has PTFE in suspension.

Apparently all pots were free with minimal friction, using the obligatory oscilloscope Mark aligned the Troughline after a mod to stabilize the tuner. Whilst doing all this Mark had explained the various processes to my son, who subsequently told me he had picked up a few things

I live in RF central with 2 nearby airports and a plethora of mobile phone masts, I used copper foil wound around all phono leads earthed at one end to reject RF/Mains 50hz hum, with 3 clip on ferrites on speaker leads & mains leads plus star earthing, the MC7R is fitted with a pair of Mullard CV4004's I had & a pair of RFT CV4003/M8136's. With cartridge raised with my Croft phonostage switched on the MC7R on max gain full volume in to my Rogue Audio Atlas Magnum (100 ish watts) feeding the OTA Qad 57's there is very slight "pink" noise the system really is that quiet better than most solid state systems. I did not use ferrites on the phono leads as I think they sound sat on.

The Troughline has no discernable Hiss on station does not drift & sounds better than when I bought it.

Other than a pair of Mullard ECC83's or preferably CV4004's for the Croft I am unlikely to do anything for a long time.

 

[da22222]

[quote=John (big);

Other than a pair of Mullard ECC83's or preferably CV4004's for the Croft I am unlikely to do anything for a long time.

I had an MC7R for a while and eventually had it modded by Response Audio in the US...5751s help lower the gain AND work sublimely with this amp, in particular RCA or Sylvainia 3 mica 1950s

 

[John (big)]

I had an MC7R for a while and eventually had it modded by Response Audio in the US...5751s help lower the gain AND work sublimely with this amp, in particular RCA or Sylvainia 3 mica 1950s

When I bought the MC7R I tried a pair of NOS JAN GE 1976 5751 did not lower the gain by much, I found them to be "bright" with my set up some call it "accurate" ie fast with good bass , I have read the Philips JAN 5751 are not as bright; the Croft needs a pair of CV4004 because I nicked the pair as delivered out of the Croft & put them in the 12AX7 holes in the MC7R, the RFT CV4003 also help.

Had a sound off with the Ming da MC 2006 and another prototype valve phono stage without the CV 4004's in place the croft came a close 3rd whereas with CV4004's in place it has taken on and beaten all.

Whilst I am eminently happy/satisfied with the MC7R If I was not retired having had a taste of Ming da I would have upgraded to the MC300 as it is I (SHEMBO) am having to think about the price of the Mullards as I have a couple of other equally expensive hobbies...

 

[da22222]

When I bought the MC7R I tried a pair of NOS JAN GE 1976 5751 did not lower the gain by much, I found them to be "bright" with my set up some call it "accurate" ie fast with good bass , I have read the Philips JAN 5751 are not as bright; the Croft needs a pair of CV4004 because I nicked the pair as delivered out of the Croft & put them in the 12AX7 holes in the MC7R, the RFT CV4003 also help. Had a sound off with the Ming da MC 2006 and another prototype valve phono stage without the CV 4004's in place the croft came a close 3rd whereas with CV4004's in place it has taken on and beaten all.

Whilst I am eminently happy/satisfied with the MC7R If I was not retired having had a taste of Ming da I would have upgraded to the MC300 as it is I (SHEMBO) am having to think about the price of the Mullards as I have a couple of other equally expensive hobbies...

IMO avoid all Phillips JAN 5751s like the plague...They were produced mainly in 70's and '80s and are not a patch on 1950s black plates which are entirely different animals to later production brands. The best 12ax7 by far that I used with the MC7R (and other amps) was the 1950s foil getter Tungsram ECC83, nothing- including the CV4004-came close...

 

[smegger68]

Using all PSvanes in my MC-7r. 12AU7's in all 4 sockets. Sounds nicer than 12AX7's in the 2 front positions to my ears, more spacious and tonally accurate.

 

[da22222]

Using all PSvanes in my MC-7r. 12AU7's in all 4 sockets. Sounds nicer than 12AX7's in the 2 front positions to my ears, more spacious and tonally accurate.

Careful...Design points for 12au7s and 12ax7s are very different and could lead to greater distortion despite the lower gain...Most probably not dangerous however

 

[John (big)]

Careful...Design points for 12au7s and 12ax7s are very different and could lead to greater distortion despite the lower gain...Most probably not dangerous however

I should think it's ok Mark the Ming suggested that was a route I could try