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Just like Carbon we built. Same box, same PS. Relay=120s. Separated filament transformer.      

Another Grounded Grid lives.  Have been listening to it for about a week. Powered by the same GRHV/GRLV PSU I use to power my KGSSHV, Carbon and Blue Hawaii. 400VDC rails and 20mA plate current.

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Working with the 60mm counterbore in the back face of the front panel and the brackets for the top and bottom covers will be a challenge. I think a 50mm dia x 4mm thick spacer will do the trick, along with cutting those brackets for clearance and trimming the RK50 connector PCB by 1/4inch. At least it works on CAD, hopefully in real 3D too! 

Edited by Laowei
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Never mind the wiring rats' nest for now, it's making music! 

The problem I was having with one channel, worked out to be a cold solder joint on the global NFB resistor network on one tube. Was distorting the voltage (off by 10V) on its pzta56/lsk389 half and throwing the balance and offset WAY off. Once found and corrected, both channels are stable as a rock (while running 30 minutes) without the servo engaged. Under 1 volt balance and offset both channels.

First listened with my SR-207 then my SR-009 (with a lousy iPhone 6 Plus as source). Using 2000 vintage SED Winged C EL34s at 20mA. Damn, this amp kicks major ass! 

Now time to mount the transformers, clean up the wiring and build the umbilical, wire up the bi-color power switch, replace the 12V zeners with 18V ones, get the RK50 somehow mounted in to the case,  and button it all up. Will post glamour shots when done. 

Thank you Kevin for such an incredible 'stat amp. I'm really going to love this over my KGST. 

 

IMG_2092.JPG

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Looks excellent!

Trying to sort mine out as well, was suspecting the lsk389 are dead because while voltages are fine with inputs shorted they go crazy when fed a signal, but a cold solder joint on the nfb might explain that as well.

Where did you find the rings for the top lid? They look great! 

 

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Thanks! A work in progress. 

A few questions first to start the troubleshooting on your GG. I'm only an ape with a DVM so will outline a methodology.

  •  What are your basic power on measurements: HV+/HV-, LV+/LV-, heaters?
  • All LEDs on? 
  • Have you set your adjustments?  What do they measureme: CCS/balance/offset? 

Where in the circuit is your amp going crazy when signal is applied? Help us understand what is "crazy". 

  • On one amp board or both PCBs? If one channel is good, use that as a standard to look for differences in the other. 
  • On one half of one LSK389 or both transistors on package? 
  • Is the symptom only at the headphone output?
  • What are the LSK389 b,c,e voltages?

Your issue might not be with the NFB. My amp's balance was so skewed that I was burning the same 50k resistor as Whitigir. Needless to say the same symptom had a different cause in my amp. The above info will be a good start at opening communication for help with evaluating your GG problem. Should not be too hard to localize and correct. 

I bought all my case parts/metal work complete from Head-Case member joehpj. Really nice design and product, and a great guy to deal with. Here's a photo after first receiving and trial fitting the all case parts.  

IMG_1890.JPG

Listened to YouTube videos (MP3 audio with digital volume control) over iPhone on the GG with SR-207 last night. That combo was ridiculously great sounding. More headspace, bass slam and pitch, treble, detail, ambience, and just sounding quite a bit more natural than my Yggy>KGST> SR-009. Probably, the SR-009 on the GG really needs the refinement of the Yggy as source to really shine. 

Edited by Laowei
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Using 2000 year date code SED Winged C (with no wings on tube label). Bought them from Watford Valves about a month ago. Very impressed so far. Especially when listening to the lowly SR-207. 

Might try JJs later. Heard they had reliability issues in the past with their octal tubes. But so far no problem with the Svets and sparkle with my GG and 207s. Pretty spot on presentation for my tastes. Might be a little hot with my 009. Tubes need more time run in, though. 

Been awhile since I used and sampled EL34s. Never warmed to NOS Mullards. Preferred pre-JJ Tesla E34Ls back in the day. Or my absolute favorite beam power tube, NOS WE350Bs (which would self destruct in a GG). 

Edited by Laowei
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19 hours ago, Laowei said:

Your issue might not be with the NFB. My amp's balance was so skewed that I was burning the same 50k resistor as Whitigir. Needless to say the same symptom had a different cause in my amp. The above info will be a good start at opening communication for help with evaluating your GG problem. Should not be too hard to localize and correct. 

Very good guide. I'm away vacationing for a few days, so this will be next sunday's mental exercise. Whatever the error is it's symmetrical, cause both amp boards are acting up identically. I'll post back once I've investigated a bit more...

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Another Grounded Grid lives. 

Have been listening to it for about a week. Powered by the same GRHV/GRLV PSU I use to power my KGSSHV, Carbon and Blue Hawaii. 400VDC rails and 20mA plate current. Using EH 6CA7 - the true beam tetrode not pentode. Runs much cooler than the Blue Hawaii. 

A tough job remains to drill the holes on the top plate.

This is one fine sounding amp!

 

Grounded Grid - top.JPG

Grounded Grid - Bot.JPG

Grounded Grid - on.JPG

Grounded Grid - top 2.JPG

Edited by mwl168
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51 minutes ago, Whitigir said:

What chassis is this ?

 

very nice :) the chassis look to be fitting Megatron just fine ?

Thanks!

the chassis is BZ3608A I purchased from TaoBao. Also available on eBay. It should fit the Megatron fine except you don't need heatsinks for the Megatron. 

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25 minutes ago, bbest said:

It is very strange: topic was created at begin of 2016. And there is no serious impression about this amp yet or compare it with Carbon, Blue Hawaii for example.

Bench racing is for the fucktards on Head-Fi.

DIY build a GG and pitch in your own opinion here. 

Edited by Laowei
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5 hours ago, Laowei said:

Bench racing is for the fucktards on Head-Fi.

DIY build a GG and pitch in your own opinion here. 

I will tell you one secret - to leave someone's opinion is not prohibited here. I simply hesitate between the Carbon and GG.

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A few more pics of the Grounded Grid with the top cover on, including a side-by-side with the Blue Hawaii built using the same chassis.

Got a set of tube socket rings coming. Will decide if to use them when I have them in hand.

Drilled a few more holes on both the top and bottom plate of the Blue Hawaii to help ventilation inside the chassis and hope it'll run cooler. Will likely do the same for the GG.

Grounded Grid 1.JPG

Grounded Grid 2.JPG

GG and BH.JPG

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4 hours ago, Laowei said:

Really clean build. Great job! 

Any details on the PS? 

Thanks!

I posted about this "universal" PSU in the Carbon thread I think. It's a GRHV tuned for 400VDC rails and a GRLV tuned for 18VDC rails. It also has 2 sets of 6.3vac/4A secondaries from the Antek AS3T325 transformer (300VA, 325v/450mA x 2 and 6.3v/4A x 2). I put a switch and thermistors on the 325v secondaries to function as a manual B+ delay.

I originally had one resistor in series with each of the two 6.3vac secondaries to lower the filament supply to the EL34 but have removed them a few weeks ago when I realized I was already losing a few 10th of volts between the tranny and the amp board. 

I bought a 7-pin female chassis socket I intend to replace the male one I am using now but have not gotten around to do it. I don't have small children in the house to worry about but I have been known to do stupid things that only 5 years old would do (according to my wife).

 

Carbon - PSU.JPG

Carbon - PSU rear.JPG

Edited by mwl168
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