Dared MC-7P optimal tubes

I have the MC-7P with only the 5Z3P swapped with a NOS RCA 5U5G. Why did you use two different pairs for the four 12AX7's? Did it matter where you placed them? I want to try more myself, but not sure where to start. Tom in Tucson

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

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!

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

Nikos

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.

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?

BTW, the remote is acting up. The antenna is a wirewound bundle that is sensitive to orientation (left/right, up/down, front/back) and when I move it, results swing from unresposive to strange orienting remote positions. Any suggestions?

Phil, usually the feedback resistor is the one connected between preamp output and the first line stage tube cathode.
Do not go overboard with feedback, it will kill soundstaging and transient response.

A good tweak to reduce gain that also improves sound quality is to remove any cathode bypass caps in the line stage.

To get rid of ringing (actually RF oscillation), install 300 ohms to 1 K ohms (not critical value) carbon composition resistors in series with each tube grid. Allen Bradley brand is one of the best for this application, available from Parts Connexion for the whopping price of 0.30 each!
These are called grid stopper resistors and MUST be installed very close to the tube grid socket pin. Cut the resistor lead to be soldered to the tube socket no longer than 3/16 " (or 4.5 mm for the rest of the world).
This tweak will damp only HF oscillation and will NOT harm audio performance, unless you overdo the resistor value (1K is the safe upper limit, 300 or 470 ohms should do it).
Also, scope the power supply output to make sure it is not ringing and has no rectifier spikes.
Good luck

Can anyone tell me what the output impedence is of this Dared preamp?

I also looked all over the place for this info as I want to use both outputs to drive two amps for bi-amping. I sent an email and received this response:
"the output impedance is very low, I think at 100 Ohm range, so it works well with any type of amps.

thanks

Joe"

I just got a used MC-7P yesterday, it sounds very promising. Has anyone replaced those yellow 0.1 caps with something nice? If so how did it sound after?

I have started a thread at DIY Audio to see what others have done to upgrade this nice little preamp- if you have done anything with to mod yours please post it here:
http://www.diyaudio.com/forums/tubes-valves/205056-dared-mc-7p-upgrades.html#post2873405

Thanks Mark3d.

Based on the above commentary regarding gain, I'm assuming its not adjustable and that you have to mess around inside to reduce it, huh?