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I just switched out my Rogue Metis Magnum preamp for a Mapletree Ultra 4a SE preamp. Mostly every pair of 6sn7s I used in the Rogue were noisy, scratchy and microphonic. It was so bad a pair of short bottle, side getter, GE 6sn7 GTBs became my go to pair only for acceptable noise levels.
Switching the same pairs into the new Mapletree mostly everyone is quiet as church mice. Any thoughts? Different design or design flaw in the Rogue.
Follow Ups:
I retube a ton of gear and certain Rogue products have a tendency towards this problem. It may be that this circuit is designed around a lower gain or quieter new production 6SN7. So it is a different design but I think a case could be made for the Rogue being a bit of a problematic design. To be fair I have seen this in a few other models from different manufacturers.
Thanks for the response. In reading various posts in does seem certain Rogue models have this problem with the 6sn7s. I'm very happy with the Mapletree and will be keeping it over the Rogue. It doesn't have remote control volume but the adjustment via remote on the Rogue is so imprecise it won't be missed.
Design Compromise, not just your unit:
Soundstage Review: "The noise level could be lower, but if you select an amplifier with a moderate input sensitivity, like Rogue Audio's Atlas (1V sensitivity) and avoid super-high-sensitivity speakers, noise should not be a problem."
The go-to sources are:
heater voltage too high,
too much (too little) plate current or voltage,
noisy/cheap plate load resistor,
noisy/cheap resistors,
noisy power supply,
poor mechanical layout,
poor circuit board layout,
cracks in the circuit board traces,
lead free solder problems
Cheap electrolytic capacitors
If the noisy preamp has more gain than the other, then the tube microphonics will be exacerbated. Ceramic tube sockets may also contribute to this but I think you should try some 5692 tubes which have low microphonics anyway.
At least, that's where I'd start. If all of your 6SN7's except the GE's are "scratchy/ noisy" (not sure about the microphonic part) in the Rogue, but not in the Mapletree, then I'd suspect bad contact of their pins in the Metis. The sockets may also need to be re-tensioned.
Other culprits could be bad solder joints, faulty capacitors, incorrect operating points due to other bad components etc. Cleaning and tensioning the sockets is a good, cheap place to start. I just use some DeOxIt on a Q-Tip with some of the cotton torn off, but there are other (possibly better) ways to get it done also.
If you choose to re-tension the sockets also, please remember to discharge the power supply caps through a resistor.
Cory
Different circuit design
Alan
Thanks Alan, good to know.
Frank
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