2. amps-preamps
  3. 1253132946

Dared MC-7P optimal tubes

Have one of these now and it is amazing. Stock 12ax7 tubes were way too soft so I popped a matched pair of Tung-Sol and a pair of Philips in place. Sound became WIDE and more accurate. Swapping the 5u4 with a NOS RCA improved inner detailing and removed muddiness in the bass and midbass. It's getting amazingly accurate for its modest price, esp. with cellos where it almost totally nails the timbre.

It sounds like it oscillates just a smidge (you really got to listen hard for this) and a tidge of sibilance remains.

So before I spring for a real set of good tubes, what combinations have found success in this low-cost wonder?

Matching it to a restored/upgraded McIntosh MC-2100 (toroid transformer, regulator in front end, caps, wiring, etc.). Input Z on the 2100 is now 100k fixed instead of 50k variable.
inline_phil
vetnik
23 posts
 
the first 2 (on the left) are the preamp tubes. the last two (on the right)are the phonostage tubes. If you don't use the mc7p phono stage you can use the preamp with only the first 2 tubes in place!

Nikos
casouza
239 posts
 
Nikos, I suggest that you call the distributor and make sure that the Dared preamp has a regulated heater supply for the 12ax7 tubes.
A plain, unregulated DC supply (as found in 95% of tube preamps) will shoot up 20% if you remove two tubes. The line stage tubes will not last long.
It is safer to plug two inexpensive tubes in the phono stage, if you have no use for it.

Phil, try Phillips Holland or Amperex 12ax7 / ecc83 to get rid of the sibilance.
Also, Herbie's labs dampers may help reduce microphonics, which subjectively increases treble distortion.
Have fun!
vetnik
23 posts
 

thank you very much Casouza, very useful info...

Nikos
inline_phil OP
11 posts
 
Sound is everything. Settled now on Mullard 12AT7's in place of the 12AX7's (left hand pair) because of the high gain in this preamp (too high).

I've documentd the tube swap and sonic differences (email me for a PDF at philip@okstatealumni.org for your copy).

After two weeks of break in, the sound is wonderful. More mods to come...in the spring when it warms up in my workshop.
inline_phil OP
11 posts
 
Finally put the preamp on the bench to see what the heck this sibilance is all about. A 1KHz square wave has a bit of ringing with current configuration. Ended up loading the interconnect cables at the amp end with a 1K ohm, 1/8 watt resistor to tame down the beast.

Wish I could figure out which resistor is the feedback. Gain sure needs to be reduced. Anyone know which resistor is the feedback on this unit?
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