New preamps?
- Thread starter Mistertaz
- Start date
The 300B plates are dissipating only about 6 or 7 watts. They ought to last a long time.
We have noticed a bit of microphony, but it seems like it will be controllable as we only hear it when we thump the chassis. Doesn't seem to be picking up enough vibration from the speakers to be a problem. Shawn had the second channel about 30% built by last night, so I hope to report about the stereo pair this afternoon.
We have noticed a bit of microphony, but it seems like it will be controllable as we only hear it when we thump the chassis. Doesn't seem to be picking up enough vibration from the speakers to be a problem. Shawn had the second channel about 30% built by last night, so I hope to report about the stereo pair this afternoon.
Second channel had this mysterious hum, that sounded to me like a ground loop. Shawn and I spent two hours trading out nearly every part of the bad channel with the good channel in frustration and then, finally, I realized that one of the three traces I was supposed to cut on the power supply PC board in order to mod it for this application was not cut and hence causing - you guessed it - a ground loop. Palm print on forehead. Before we left tonight we got it fixed and fired up both channels, playing some our favorite vinyl demo tracks with the Tube Phono and active step up prototype.
Holy s**t! It's not just a bigger badder lower midrange as one would expect. The bass is big and bad too, the midrange resolution is crazy good and it's like the power output of the system has gone up maybe a factor of 10. This is a keeper, and a very satisfying result of my spending the last year or so trying to come up with the ultimate version of my "low output impedance/no transformers/no cathode followers" line stage. Thanks to PJ for putting up with my theories over the past year and cooking up circuits based upon them, including this one.
You guys who have Paramounts, start saving your pennies. This circuit is a match made in heaven.
Holy s**t! It's not just a bigger badder lower midrange as one would expect. The bass is big and bad too, the midrange resolution is crazy good and it's like the power output of the system has gone up maybe a factor of 10. This is a keeper, and a very satisfying result of my spending the last year or so trying to come up with the ultimate version of my "low output impedance/no transformers/no cathode followers" line stage. Thanks to PJ for putting up with my theories over the past year and cooking up circuits based upon them, including this one.
You guys who have Paramounts, start saving your pennies. This circuit is a match made in heaven.
jlschweiger
New member
I just unwrapped a new piggy bank... 
InfernoSTi
New member
OK, so now you are telling me I need to save for the DAC, the Paramounts, AND the 300B pre amp? Done...I'm officially saving for all three....I don't need to shop around anymore for anything! Congratulations, Doc!!!
John
John
Yeah the output impedance is a bit high relative to most headphones. And adding an output transformer to lower the output impedance is going to reduce the gain, so you might find you need a second stage to get enough gain from your source. Next thing you know, you have designed Paramount instead of this preamp.
Chris
New member
Sounds like the "ULTIMATE Foreplay" to me...... I know we are only talking about matching it up with BH gear, and I know amp matching with a DHT OTL pre can be difficult, what amps (impedences etc.) would be a bad match do you think, in other words, could this amp be used as a "generic" reference pre with SS amps, OTL tube amps, I even have a 1000 watt OTL hybrid amp... I know the best combo is to match it to YOUR amps, I guess i just want to know how flexible it would be as a generic reference pre also? thank you very much.....
Paul Joppa
Moderator
Output impedance is quite low, about 600 ohms. It should be able to drive pretty much anything.
Paul Joppa
Moderator
Long time yet. This was just the proof of concept - testing whether a directly heated triode actually sounds better than indirectly heated, given similar operating conditions. It's cobbled together from a pair of Crack chassis plates, Eros power supply parts, and some duct tape (just kidding!) Would a 2A3 sound as good? Don't know yet. Still undecided on the best filament power arrangement and bias method - right now it's just a chip regulator for the filaments. Also, we have two other quite different designs that also sound really good. But we already have two preamps, can't see adding three more!milosz said:
