Originally Posted by purrin
The 2A3mk4 and 4-45 will sound quite different (but still have the EC house sound) from the ZDT:
- Different output transformers. In particular, the 4-45 OPT is quite different from the rest because it has trick tertiary winding which is used for a small amount of feedback.
- Interstage transformers instead of a cap. A faster less constipated sound. More resolving.
- Different tubes. 45, 2A3, 6c33c all sound quite different. The 45 and 6c33c tubes have a consistent sound. But within the 2A3 family, there is a huge variety of sounds depending upon manufacturer and model.
- HF filament heater on 4-45 and 2A3mk4. More openness, deeper stage. DHT (45 and 2A3) will by itself provide a more impressive stage, but the HF heater takes it to another level.
- Parallelled output tubes. Better center stage, stable imaging, image precison, layering, separation. More current / power at low Z loads. Drives orthos much better than BA, older EC models.
- Stiffer power supply. There's been a lot of recent PS work which has now been integrated with the latest amps. Better quality tighter bass.
I’m biased to the EC house sound, very nice to have new phone/speaker amps to consider. The Jeff Korneff 45’s are highly acclaimed, but can't bet against EC. Also can’t pigeon hole Craig into stereotypical tube sound using the 2A3 or 45 or 6c33c, so still really have to listen to them to hear what he's done. Just replaced the 6c33c's, the idea of consistency in driver tubes is a valid benefit.
What I still like about the ZDT is the nuanced, complex sound Craig gets with a simple SET circuit. No negative feedback, and at 6 watts the 6c33c tubes are run very conservatively limiting distortion. He got an unbelievable frequency range with the custom PSS trannies. I guess Jack is now only doing transformers for his own amps, so onward and upward.
I actually thought the ZDT would use interstage coupling, but it seems some tubes like them and some don’t. Also, many hold that capacitors actually have the less congested sound and adhere to the simpler is better school of thought. They can be rolled like tubes, those new Jupiter copper caps might be good candidates. Sure much less expensive than good interstage transformers which helps explain the $4,500.
Paralleled output tubes as well as interstage transformers both have potential for quality bass. When paralleling output tubes the power supply has to double output. As you say, that stiffer supply should also contribute to better bass. That would be a big plus with low Z speakers, the ZDT already does a great job with orthos and no doubt both the paralleled amps do as well.
Wonder why the 45’s are putting out 2 watts instead of 3? That 33% difference might help with speaker selection. I finally found a wide range speaker with really great detail and without a bright rising response in the Alpair 12P. Though at 92db sensitivity 6 watts is barely enough so even at 3 watts would have to go another way.
Informative post, thanks.
Edited by northshore - 5/17/14 at 11:16am