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It came just before 6, and by 6:13 was installed and playing in place of the Rotel RCD-940AX.
The two tuner-preamps have very similar specifications. Well, so much for specifications. The sound is quite different. The Adcom has a more robust feel with much more solid bass - even tighter and more solid than the Rotel with the bass control at 2 o'clock.
Soundstage of the Rotel is very wide, much less so with the Adcom, which has a stage similar to my NAD C350. Both have good localization of voices and instruments, and a good sense of depth. On the other hand, the speakers do seem to be a source of some of the sound with the Rotel, while with the Adcom and the NAD, the speakers do not seem to be the source. Given the big difference in the imaging and the weaker bass, I'm wondering if there are some phase funnies in the Rotel. A couple of weeks ago I did measure the frequency response of the Rotel and it's virtually flat from below 20 Hz, to over 20 kHz with the right channel 0.5 dB stronger at the 9 o'clock volume control position. That's about my normal listening level, so I moved the balance to 11 o'clock to compensate. That did center the image.
The GTP-400 arrived very well packed in a large box full of foam peanuts, and it was wrapped in at least three layers of bubble wrap. It took longer to unpack than to hook it up!
At this point, I prefer the more robust sound of the Adcom as the overall balance is better, and detail seems better defined. It also makes the Rotel RB1050 sound better than it has with anything else I've tried.
Jerry
Follow Ups:
Given the big difference in the imaging and the weaker bass, I'm wondering if there are some phase funnies in the Rotel.
Interesting observation. While I trusted your judgement, I found it curious that the difference in stage width between two amps would be that significant. As you say, some of that may not be "real".
I have, however, experienced that with preamps including my previous Audio Research SP9 MKIII which had measurably narrower separation than my current unit. Which is why I implemented passive attenuators in a previous CD player arrangement.
The difference in stage width by itself isn't unusual; but coupled with the rather weak bass, it set off alarms. I was blaming the amp; but the Adcom GPA-400 makes it clear, the amp is fine.
The Rotel RB1050 is dual mono; but the input impedance is 18k ohms. Not super low. Both preamps are spec'd at a 100 ohm output impedance, so they should handle 18k easily. But if the amp's impedance changes a lot in the low bass, from maybe a too small coupling cap it would act like a high pass filter. I've got the schematic, so I have to check that.
Jerry
The Rotel RB1050 is dual mono
Are the transformers stacked or do both channels share one as with the Adcom - which otherwise appears dual mono.
RB-1050 pic
Both use a single toroidal transformer with separate windings for each channel, and, of course, separate rectifiers and filter caps.
That's not the case with the NAD C350 which uses separate windings for low and high current power supplies, and then switches between them depending on the load and drive level. The C350 has even a narrower soundstage; my guess would be because of the shared PS; but my big old Onkyo receiver has a wider stage and a massive single supply.
I've read arguments for both dual and single supplies. In the end, it's probably the execution.
Jerry
I've read arguments for both dual and single supplies. In the end, it's probably the execution.
Agreed. And joules!
The power supply for my new microRendu streamer weighs 13 lbs. :)
Get in a good days listening and rotate some pieces and let us know how the Adcom sounds in different situations
Looking forward to reading about your findings.
charles
Jerry,
Borrow a tube preamp with a FET buffered O/P and the "sand" preamps will be (IMO/IME) "left for dead".
If you feel like DIYing, the 6SN7 design I've uploaded is linear as the day is long on the Summer Solstice.
Eli D.
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