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Groovewatt - tube RIAA phono preamp
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Author:  metaldog99 [ 06 Jun 2018, 10:55 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

I appreciate all of the guidance and information regarding this.

I finally found my Groovewatt wiring error late last night, so I hope to be able see some results soon.

Bruce - regarding "the core and its case" of the PLT, I assume you access the core by opening up the case of PLT? And by case, you refer to the black housing of the PLT?

Thanks,

Phil

Author:  gofar99 [ 06 Jun 2018, 14:12 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Too many parts....4 different SUTs. I was looking at the separate wires in the Silk Audio SUT. It has separate connections for the core and housing. For the PLT just be sure the case of the SUT via its mounting screws is connected to the shields not the enclosures. Keep left and right channels separate though.

Good listening
Bruce

Author:  metaldog99 [ 06 Jun 2018, 17:07 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

So....

1. SUT - Left channel input shield tie to Left channel output shield tie to Left channel PLT housing. Repeat for right channel. Shields isolated from enclosure.
2. SUT - Enclosure floating or tied to chassis ground (with switch)?
3. Tonearm ground - tie to GrooveWatt chassis ground?
4. Groovewatt - tie chassis ground to Forewatt chassis ground if necessary?

Updated diagram:
Attachment:
Cable grounding-5.png

Thanks again,

Phil

Author:  poty [ 07 Jun 2018, 05:09 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

metaldog99 wrote:
1. SUT - Left channel input shield tie to Left channel output shield tie to Left channel PLT housing. Repeat for right channel. Shields isolated from enclosure.
2. SUT - Enclosure floating or tied to chassis ground (with switch)?
1. Yes.
2. I'd not add any switch.
metaldog99 wrote:
3. Tonearm ground - tie to GrooveWatt chassis ground?
Yes, but you drew this connection incorrectly in your drawings. You connected it to the signal ground.
metaldog99 wrote:
4. Groovewatt - tie chassis ground to Forewatt chassis ground if necessary?
I would not connect this, but you wrote "if necessary," so I think that practice will judge. Again: in your drawings you connected the wire to the signal ground.

Author:  metaldog99 [ 07 Jun 2018, 10:57 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Updated - does this look correct?
Attachment:
Cable grounding-6.png


Phil

Author:  poty [ 07 Jun 2018, 11:11 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

From me - yes.
As you can see the Groovewatt and Forewatt chassis are connected through the mains safety ground and do not need any additional connections.

Author:  gofar99 [ 07 Jun 2018, 21:21 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Yes they are attached that way and it usually works fine, but If the units are far apart or on different mains circuits I find the extra wire to be useful. I may be an extremist in some ways, particularly about hum and noise and at least in my system this seems to make thing just a tad quieter. It may be related to the complexity of my system, three turntables (2 with SUTs) , a reel to reel, a DVD, a cassette recorder, a satellite receiver, line stage preamp, active electronic crossover and 4 power amps. And oh by the way, I want a S/N of -90. Simpler systems may not need extensive grounding. Try it both ways with a simple jumper wire and see which way works best for you.

Good listening
Bruce

Author:  metaldog99 [ 08 Jun 2018, 10:57 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Thank you again for all of the help and guidance. I appreciate you taking the time to provide all of this useful information.

My chassis finally arrived yesterday, so I hope to have everything in place and working within the next few days.

Phil

Author:  metaldog99 [ 12 Jun 2018, 11:38 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Bruce,

I have some questions after spending time working on fitting the boards and components within the chassis.

1. Any recommendations on how to fit the shielding around the PS transformer and IEC? I have several sheets of mu metal that I can fashion a box out of, I was wondering
  1. Should it be a closed box or if just a cover is sufficient?
  2. Should the 2.2K on the output be close to the 1.0uF capacitor or the connector?
  3. Can a dual conductor shielded cable be used as input and output connection from the board to the RCA connectors? (one wire for each channel with a common shield)

I've reread the article from AudioXpress, and another question
  • In the Pre-Operation Verification section, you recommend "check the voltages at the midpoint of the first two stages". Which points in the circuit are the midpoint(s)?

Thanks again for the help,

Phil

Author:  gofar99 [ 12 Jun 2018, 13:59 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, The better you can enclose the transformer the better it will be. The quietest preamp I have has both a mu metal cover and a steel enclosure over the entire power supply. They are quiet with either, but this one is about 3 db quieter. I usually put the 2.2 K resistors at the jacks. You can use two conductor shielded cable. There is some possibility of very low level cross talk between the channels, but considering the low impedance of the circuit and the low level of the signals it is unlikely to be audible. I personally use single conductor shielded cables. The voltage indicated is the one that is on the hot side of the output coupling capacitor when measured to a signal ground. It is on the cathode of the upper triode and anode of the lower one. It should be about 1/2 the B+ applied to the anode of the upper one. A wide tolerance is fine and most likely you will deviate by as much as 10-20%. This is because the two sections of the tube are generally not matched. I suppose if you got ones with matched sections it should be really close, but they cost more and don't offer any real advantage. If you find that the deviation is over about 25% then something might not be wired correctly. I would swap another tube into that position to check first though.

Good listening
Bruce

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