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PostPosted: 01 Sep 2017, 07:47 
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Joined: 01 Apr 2017, 19:56
Posts: 49
Hello, thanks for the answers!
I have now finished to wire the groovewatt. It is working, but I have a problem on one of the channels that I could not solve. The problem is that there is a thump sound in regular intervals of arround 1 second. It is audible with the amp on max volume. I have tried swaping tubes and also swaping the power supply channels and the problem persists on this channel.
I also have some hum, but I guess I will get rid of it once I finish the enclosure, because I have followed Bruce tips on grouding. But, for now, the hum noise also oscillates on the same 1 second period. Any ideas? Thanks again.


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PostPosted: 01 Sep 2017, 10:05 
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Joined: 01 Apr 2017, 19:56
Posts: 49
A question about grounding: the tube shields should connect to the chassis ground or main star ground (after the X2 cap and 120 ohm resistor) together with the other ground from the circuit? For now I have them connected to the main star ground. What I have noticed is that the tubes are very microphonic. Tapping the shields or even tapping the chassis results in audible noise.


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PostPosted: 01 Sep 2017, 21:09 
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Joined: 04 Jun 2008, 20:59
Posts: 3853
Location: Arizona, USA
Hi, A really good question. I have not found the tubes I use to be all that microphonic. Then I have all mine inside the chassis in later builds. Only the first ones were exterior. Since they ought never need changing (mine are all the originals) and it is a more elegant looking unit. Easier to build IMO as well. All you have to insure is adequate ventilation and for that I use a perforated metal top.

Back to the shields.....I have tried the shields both ways. Unfortunately if they are on top of the chassis and it is metal then it is difficult to isolate them from the chassis. In my builds with the tubes inside I have found attaching them to the signal ground at a central point near the input signal ground works best. I measure just slightly over a db of improvement that way. Not much, but since I really hate hum and noise every little bit that can be eliminated (without bizarre methods) is worth it. IMO the attention to details is essential to having this or any number of other preamps perform at the optimum level. This design when well executed can have a S/N in the -90dbv range. Poorly built... IMO it will not be listenable. BTW in the photos I removed the odd shaped shield in the middle as it did not enhance the S/N. The power trannie is under the one cover and the other covers the input jacks and selector switch.

Good listening
Bruce
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PostPosted: 20 Oct 2017, 19:00 
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Joined: 01 Apr 2017, 19:56
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Got mine working good now. Eliminated all ground loops and now it is hum free!
Here are some pics!
Thanks for the project and the tips, Bruce!
Now I will focus on the Oddblocks!


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PostPosted: 21 Oct 2017, 15:02 
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Joined: 24 Oct 2010, 07:05
Posts: 282
Oh, very nice, neat and well thought. Is it point-to-point or PCB-based?


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PostPosted: 22 Oct 2017, 06:36 
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Joined: 01 Apr 2017, 19:56
Posts: 49
It's PCB based. It was fun to learn how to use kiCad.
On my version I have added a 30 second B+ turnon delay. Also, the regulated DC from a LM1085 has a 15 second slow rampup curve (using a RC network, a diode and a transistor on the programing resistors of the regulator). I wanted to treat the tubes as gently as possible.
I have omitted the 47uf Electrolytic from the elevated DC rails to groud, because it made no diference at all.
I have not used premium capacitors on the power supply, and on the Groovewatt itself I have only used the Audyn Q series. I have done this because it was my first tube build (although I have had past experience with electronics) and I was not sure I would make it, so I tried not to spend so much money. Also, the tubes are ECC803s and ECC81 from JJ (the normal version).
My Phono Cartridges are not that special either I guess. I have a Shure M97x and a Audio Technica M440mla.
It sounds great though! Much better than my receivers integrated Phono preamp (Onkyo TX NR-727).
Maybe it deserves some capacitor upgrades!


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PostPosted: 22 Oct 2017, 11:05 
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Joined: 04 Jun 2008, 20:59
Posts: 3853
Location: Arizona, USA
Hi, I'm glad it went together well and sounds good. I only use them in my system. Grounding is everything it getting a good build. When the basic circuit has a raw gain of about 60db any grounding issue becomes huge. Premium parts do enhance the sound, but it is a diminishing return on value. Standard Audyn Caps Plus work quite well in one of my units. Nearly as good as anything else I have tried. I just wish they were physically smaller.

Good listening
Bruce

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PostPosted: 14 Nov 2017, 23:02 
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Joined: 13 Nov 2017, 23:28
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Hi ,

Can someone please clear up some confusion I am having with the power supply in figure 4
now from the initial design data we are using a transformer with an output of 200volts yet after the bridge in figure 4 (red writing) the voltage has now managed to be at 270 volts ? Does the transformer in AC give out a much higher voltage than the nameplate says ( ie is the 200V nameplate supposed to be for use in DC volt applications) and is the peak voltage 200 x 1.414 ie 280 V are we drawing the 270 etc down from this with dividers and smoothing caps.

Please forgive me if this is a fundamental question and everyone is slapping their foreheads :eek: when reading this but I did electronics at school 30 years ago but have not applied it till now ( ought to be fun !!! )

regards
Clive


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PostPosted: 15 Nov 2017, 06:37 
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Joined: 24 Oct 2010, 07:05
Posts: 282
CliveStephenson wrote:
...power supply in figure 4 ... from the initial design data we are using a transformer with an output of 200volts yet after the bridge in figure 4 (red writing) the voltage has now managed to be at 270 volts? Does the transformer in AC give out a much higher voltage than the nameplate says ( ie is the 200V nameplate supposed to be for use in DC volt applications) and is the peak voltage 200 x 1.414 ie 280 V are we drawing the 270 etc down from this with dividers and smoothing caps.
The value 200V for the transformer secondary is RMS voltage (in short: RMS AC = DC voltage which makes the same power on a pure resistive load as the RMS AC on the same load) taken with full designed load. Its amplitude voltage is indeed 200 x 1.414 (in the same conditions). The 270V value is made, as you correctly stated, from the AC by smoothing the drops in the rectified sine voltage with help of capacitors; minus losses in the secondary, diodes, capacitors ESR + current to the load.


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PostPosted: 27 Nov 2017, 22:54 
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Joined: 13 Sep 2016, 21:22
Posts: 5
Location: Calgary - Canada
Hi everyone,
Thanks for all the support, answers and contribution! I wanted to share the pictures of the finished project!
It is a custom combo ForeWatt + GrooveWatt. Slightly different circuit to match my preferences but still deserved to be credited!
About a year from concept to finished product, 100% garage build, 90% from salvaged parts.
And I can confirm it sounds as amazing as it looks (to me at least!). I have an optional mesh shield but I didn't had it on for the picture. (And Yes, B/H are my initials)
Cheers!


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