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4S Universal Tube Preamp Project (12A*7)
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Author:  Alex Q [ 26 Jun 2017, 19:33 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

mwhouston wrote:
Is the metal part of the alps at ground potential? These can buzz if not grounded.


YES,I scraped off the chassis paint where i install the switches and the pot except for the RCA jack they are isolated from the chassis.
Thanks!
Alex

Author:  mwhouston [ 26 Jun 2017, 21:01 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Once I relied on the Al top plate to carry the earthnegative of the PS from pint or point to point. I had a slight hum so I ran a direct earth wire to some of the points requiring earth. The hum stopped.

Did you use shielded wire to hookup from RCAs to the pot? If so try cutting away the shield wire leading to the driver tube. Earth that wire at the tube end of not earthed. Sometimes you can get an earth loop.

Author:  Alex Q [ 27 Jun 2017, 18:51 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Sorry for the late reply!No shielding for the wires,I used Solid 20AWG wire for the input and output RCA jacks to the switches and stranded 22AWG for the POT.I will double check all my ground connections just incase i missed something.

Thanks again!
Alex

Author:  john55 [ 09 Aug 2017, 09:53 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I finished building the 4S about two weeks ago, and I have it hooked up to the Lacewood V.2. that I built earlier this year. I've only tried it with a 12AU7 and a 12AY7. Both sound really nice, but I lean toward the 12AU7. These two amps together are a really nice combination driving Fostex bass reflex/backloaded horn hybrids.
Last year I built a 6EM7 Vertical Amp which I reluctantly sold to a friend to finance the Lacewood. I like the idea of building another one to try with the 4S. Has anyone tried a 6EM7 with a 4S?

Author:  mwhouston [ 09 Aug 2017, 17:15 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I would definitely use 4S with any other amp, tube or SS. You can swap out the tube and this will allow you to fine tune the sound. Lately I have been suing a 4S driver stage to drive power tubes namely the 6L6. I'm using top of the range Psvane "T" series MKII 12AT7. I like the sound. If you can try a 12AT7 but my all time fall back is a 12AU7.

Author:  john55 [ 13 Aug 2017, 09:36 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Thanks for the advice. I'll definitely build another 6EM7 but perhaps not vertical. Back to the 4S. My next valve order was going to have 12AT7 included in it to try in the 4S, but since your reply I've been reading up on the Psvane "T" series MKII 12AT7 and I've bitten the bullet and ordered one as the write ups sound really good. Hoping it sound as good as everyone says does.

Author:  mwhouston [ 13 Aug 2017, 17:09 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

john55 wrote:
Thanks for the advice. I'll definitely build another 6EM7 but perhaps not vertical. Back to the 4S. My next valve order was going to have 12AT7 included in it to try in the 4S, but since your reply I've been reading up on the Psvane "T" series MKII 12AT7 and I've bitten the bullet and ordered one as the write ups sound really good. Hoping it sound as good as everyone says does.


Do you have a link to the write up?

Author:  john55 [ 14 Aug 2017, 01:55 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

I read this article in a magazine...........

You asked me a couple of months ago to compare the stock Raytheon 12AT7 with the Psvane. Because I also had a Mullard, I included it as well.
My system consists of Stereomour upgraded with Triad chokes and all AuriCaps + JJ 2A3s and Psvane 12AT7.
Speakers are Lowther PM5As in plexiglass open baffles and Great Plains 416s in the enclosure below the window tuned to 25Hz. Electronics: First Watt B1 preamp, First Watt B5 xover at 120Hz, rebuilt Adcom 5500 for woofers.

Observations:
1. All three tubes are very musical. If you did not do A/B/C comparisons you would be happy with any of them
2. The Raytheon and Psvane were most alike and more dynamic
3. Mullard was more veiled and less dynamic but very musical
4. This is when it got complicated comparing the Raytheon and Psvane
5. Raytheon had more clarity in the upper registers. I noticed it on one track of Foreverly in the percussive section. 2 sticks were hit together, smaller than drumsticks and more like big hardwood chopsticks. This is minor but easy to hear.
6. The Psvane had a larger soundstage and more articulation. Articulation is the only word I could think of. It sounded louder and had the greatest dynamics therefore giving more emotional impact. Plucked strings or drum strikes were very defined.
Remember my Stereomour is only used from 120Hz up.
Conclusions: the Psvane grabbed me the most. I found myself listening to one track after another even though I wanted to go to bed. This took me 3 weeks with some listening most every night and taking notes.

I also read this post.... http://www.audiocircle.com/index.php?topic=88490.0

I also read quite a few write ups on Psvane 12AU7's and 12AX7's. The general opinion seems to be very positive.

Author:  john55 [ 26 Aug 2017, 11:53 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

Just received and fitted the Psvane "T" series MKII 12AT7 ( I found a supplier who would sell them individually as opposed to matched pairs ).
This valve must have been made for the 4S. Mellow doesn't describe it.

Author:  mwhouston [ 26 Aug 2017, 18:03 ]
Post subject:  Re: 4S Universal Tube Preamp Project (12A*7)

john55 wrote:
Just received and fitted the Psvane "T" series MKII 12AT7 ( I found a supplier who would sell them individually as opposed to matched pairs ).
This valve must have been made for the 4S. Mellow doesn't describe it.


As I have probably said, I'm using them as a driver tube in a 6L6 power amp and I think it is the best sound I have ever had. Fortunately the Psvane aren't overly expespnsive.

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