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Groovewatt - tube RIAA phono preamp
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=3545
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Author:  metaldog99 [ 28 May 2018, 22:16 ]
Post subject:  Voltage measurements

I finally finished the boards for the GrooveWatt, and my voltages are as follows:

Ch 1
206.1V
192.9V
186.9V

Ch 2
206.1V
192.1V
185.2V

Heater
"E" - 69.6V
"F" - 63.5V
E-F = 6.13V

Is the slight variation in B+ something I need to tweak or adjust somewhere?

All measurements were made after about an hour of power ON. Using JJ ECC803S and ECC81S Gold pins.

Thanks.

Attachment:
IMG_5623 (1).jpg

Author:  gofar99 [ 29 May 2018, 10:21 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, looks like a good build. The voltages are fine.

Good listening
Bruce

Edit: I may have asked before...where in AZ are you?

Author:  metaldog99 [ 29 May 2018, 11:07 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Thanks, Bruce. I am waiting on a chassis to be delivered before I wire up the signal connectors, so hopefully within a week or so I should have sound running through it.

I live in East Mesa, out by the Phoenix arrow on the mountain if you are familiar with the area (near the gun range).

I've worked for a defense contractor for the last 15 years, and spent much of that time in your area, working at Fort Huachuca on many TDY assignments with the Army Electronic Proving Ground.

Phil

gofar99 wrote:
Hi, looks like a good build. The voltages are fine.

Good listening
Bruce

Edit: I may have asked before...where in AZ are you?

Author:  metaldog99 [ 29 May 2018, 11:45 ]
Post subject:  Grounding

Bruce,

I have questions regarding the use of mu metal for shielding.

I am encasing the transformer in a steel box within the chassis. I am not sure yet if I will need additional shielding - but I have enough mu metal sheets available if necessary.

Are the mu metal shields to be grounded? What I've viewed and read online is mixed depending on the application.

Thanks,

Phil

Author:  gofar99 [ 29 May 2018, 12:53 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi Phil. Try the steel first. You can always add more shielding later. In my latest build I used some Mu metal between the power supply section and the active circuitry.

I will send you a PM in a while.

Good listening
Bruce

Author:  metaldog99 [ 02 Jun 2018, 18:17 ]
Post subject:  PLT-1 + Dynavector 23RS

Bruce,

Final prototype assembly is nearly complete. I am using a Dynavector 23RS with PLT-1 SUT, and I am uncertain as to the PLT-1 wiring. For this cartridge, is this wired in parallel (10 ohms) or serial (40 ohms)? I was going to craft a switchable configuration for hi/low settings, but that will have to wait until I get some better housings.

I was assuming that with the Dynavector outputting 0.2mV, that I would use the LO (parallel) configuration of the PLT-1.

Since you use a similar setup, can you advise?

Thanks,

Phil

Author:  metaldog99 [ 05 Jun 2018, 15:41 ]
Post subject:  Grounding - Tonearm + SUT + GrooveWatt + ForeWatt

I have tried to implement grounding as Bruce discusses in this link.

The diagram below depicts how I currently have all the components wired (single channel only).
Attachment:
Cable grounding-3.png

Also included is the schematic which indicates how I implemented the SUT - a pair of Softone PLT-1's in a small, steel Hammond box. (schematic is from Softone website).

    1. The three units which have enclosures (SUT, GrooveWatt, ForeWatt) all have external ground lugs, isolated from the enclosure (labeled "A", "B" and "C"). Should these be explicitly connected? I am not certain on how to treat the ground for the SUT.
    2. Does the wiring make sense and is it correct? All of the shields of the internal coax are connected together at the input and output connectors for both the Groovewatt and Forewatt (labeled "2" and "4"). The coax shield at the board end is unconnected. Each board ground (the PS and gain boards for both preamps) is tied directly to the ground bus at the input/output connectors ("2", "3", "4", and "5")

Thanks for any and all comments and suggestions.

Phil

Author:  gofar99 [ 05 Jun 2018, 21:57 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Humm..(bad pun) You are apparently using the chassis ground symbol as the signal one and vice versa. Regardless, I place a ground wire from the turntable chassis to the SUT enclosure then to the phono preamp chassis ground and finally to the line stage preamp chassis ground. I don't find any is needed to the power amps. The signal shields do not connect to the chassis at any point. Ever.

For the PLTs I have the core and its case (not the enclosure) attached to the signal grounds. Each channel has a separate ground via its own shield wires. If you tie them together at the SUT and there is more than a few inches of wires to either the turntable or the preamp then you will probably get hum. I keep the left and right channel shields separate from each other until they get to the phono preamp input. As noted above the various chassis all all interconnected with a single ground wire. The only connection between the chassis and shields occurs inside the line stage preamp. That is through the X2/Resistor link. No other connection between them should be made as you will almost certainly have a serious ground loop. I have a hum free system. At my usual listening level the gain is set for around -40db (yes there is a digital control) There is no hum at all until at full gain and then only audible with your ear on the speaker. 40 db of headroom is huge. If you could actually achieve it the level would be similar to a jet aircraft nearby.

A hint with any SUTs.....regardless of how well shielded they can pick up hum. I try to keep mine at least 1 meter away from anything with a transformer or motor. Power wires and wiring inside a wall can also be a source of hum. I also find it handy to be able to tilt and twist the enclosure as it will change the orientation of the cores and often have a major influence on hum pick up. I really like SUTs, but while the "gain" is essentially free, it is not entirely a free lunch.

If all this seems to come off as high handed....I am fanatical regarding hum and noise. If there is any at all I do everything to eliminate it so the info above is what I do to achieve it. There are other ways to do all this but I have never found any that work as well.

On the positive side (I always like to end with that) your choices of componets are ones that will give a superior sound. I ought to know as they are ones I use myself. For fans of high output cartridges I use the second generation Grado Sonata. Another superior sounding device when feeding a Groove phono preamp.

Good listening
Bruce

Author:  poty [ 06 Jun 2018, 02:58 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Just to clarify several things. You wrote:
gofar99 wrote:
The signal shields do not connect to the chassis at any point. Ever.

gofar99 wrote:
The only connection between the chassis and shields occurs inside the line stage preamp. That is through the X2/Resistor link

The 2 phrases contradicts each other first thing, but they are not completely true either. The "X2/Resistor link" exist in the Groovewatt too and (not pictured) in Oddwatt.
In my opinion the "external" ground wire should be ended at the first device which case has the connection to the mains safety ground.

Author:  gofar99 [ 06 Jun 2018, 10:10 ]
Post subject:  Re: Groovewatt - tube RIAA phono preamp

Hi, Actually when you think about it they are correct. The shields never connect directly to the chassis, they connect to the signal ground which connects to the chassis via the X2 and resistor. No direct connection would probably have been a better choice of wording. :)

Good listening
Bruce

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