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In Reply to: RE: Can you elaborate further? posted by Lew on February 19, 2014 at 10:25:49
Hi Lew,
No, the power supply and circuit board are in the same full size chassis. The power supply has a pretty large power transformer, a big choke and it uses a 6C19PI power triode for the regulation. There are a couple of other tubes (rectifier and a voltage reference I think) in the circuit as well. I think a big part of the good sound is the power supply, which seems well done.
The circuit has a couple of JFETS for the MC input then there are three tubes in a circuit that I do not know how it works. Coupling caps are all Auricaps, which I find to be a very good cap.
I had assumed that the input was a cascode to lower noise and the output I was unsure of. The RIAA is passive.
Follow Ups:
Seems like the two power supplies are analogous but perhaps the 550 PS is more space-consuming, since the outboard chassis is needed. The RIAA circuits must be different, as you suggest, based on the difference in the number of tubes, if nothing else. What tube types are used in yours?
Mine uses a pair of 12AT7s at the input (one per channel), then 12AY7s for the second gain stage after the RIAA, then it had another single 12AY7, each half of which was used for the CF for one channel. I replaced that latter tube with an ECC99, blessed as a good idea by Mr Park.
If you can send to my private email or post some photos, that would be cool, and I can do the same.
All three are 12AY7s.
As I think I mentioned, my 550 is switchable for "MM" and "MC" levels of gain. There is a toggle on the front panel. In MC mode, the input signal goes to a JFET which just adds gain and then feeds the aforementioned RIAA circuit, which is all tubes. In MM mode, there is a relay that shunts the JFET to ground, thus bypassing it. Does the 650 also have provision for MC cartridges, using JFETs, or have we been over this ground, already?
Yes, but I will tell you again. THere are JFETs that switch in and out from a front panel switch...just like yours I think. I found that even with a high output MM that the MC input sounds better.
(1) I apologize. You did clearly tell about the JFETs before I asked my stupid question about whether it can handle MC cartridges.
(2) You don't mean to tell me that you use the MC inputs for MM and other high output cartridges, do you? Most likely that would result in dramatic overload of the RIAA circuit. I must be mistaking your intended meaning.
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