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11 hours ago, Laowei said:

No, was traveling to our contract manufacturing sites in Shenzhen and Zhuhai frequently for work. Laowei (or laowai) is Pinyin Mandarin for foreigner/stranger/any non-Chinese. I'm a blue eyed, blonde haired, fat old American guy. 

 

 

I'm fatter than you!!!

 

 

 

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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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10 hours ago, fat joey said:

 

 

I'm fatter than you!!!

 

 

 

Lol! Today this may be true.

Been eating more healthy for the last 7 months, and have lost 60 pounds. Half way to my goal with another 60 pounds to lose. One day at a time. 

 

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Thanks!!

Yes, big knob is volumen control and small is a input selector.

All my Stax outlet are made with acrylic transparent material so I can use a led inside.

 

9Ii7pyU.jpg 

 

With my universal PSU.

 

Sn7Ixuw.jpg

 

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15 minutes ago, spritzer said:

One note, it's a bad idea to twist the output wires on any electrostatic amp.  This adds to the over all system capacitance which is bad. 

Thanks Birgir. I did not know it. I'm going to find a way to get them as straight as possible. :unsure:

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Thank you pose, pixels appreciated. Give me the opportunity to steal good ideas.

I like the led stax connector. Can that be bought somewhere? At the PSU, there seems to be something Arduino on the back panel - what's that?

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You are wellcome

Yes, I use an Arduino. A friend had an idea and he designed the software and all adaptation work. Arduino is controlling soft-start, times, temperatures ... on my Carbon, Arduino controls the input selector too. If I have a problem with temps for example, Arduino cuts HV trafo current.

 

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To date I have been using my Grounded Grid without either of the servo enabled. Similar to my Blue Hawaii, it takes the GG about 80 minutes to reach stable state offset without the servo even though it runs much cooler compare to the Blue Hawaii.

Last night I engaged the opto servo and made some observations this morning. I am using OP27 and 4N25. I have TL081 on hand but cannot use them in place of the OP27 because I run 18VDC rails on my front end.   

I first adjusted the cold-start offset to +12VDC (reference to ground) in order for the servo to work. I measured the offset between the left channel + output to ground, the right channel exhibits very similar operation. The balance has been previously adjusted to as close to 0 VDC as I could after the amp is fully warmed up.

With the opto servo engaged and from a stone cold start (time pint T, room temp regulated to 24 C), the offset is about - 3.3VDC, it steadily went down to - 0.3VDC at T + 3 min.. At T + 5 min. point the offset is about + 0.3VDC. It went down to + 0.005 VDC at T + 29 min.. At the T + 60 min. point the offset is about - 0.16VDC and the heatsink temp is at a steady 36 C. At this point I lost patience and decided I prefer to listen to some music instead of staring at the voltage meter.

I've read in the thread somewhere that the TL081 is faster acting than the OP27. At a fraction of the cost of OP27, I think the TL081 is worth a try if your front end supply rail is less than 18VDC (TL081's max. voltage supply rating). Hope someone can chime in and share their experience.  

Edited by mwl168
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Thanks all, but I only learn from you. :unsure::unsure:

I like to use OPA27 OP27, I think that's more fast as 4N25. 

My experience with OP27. Cold-start offset after a "standby" of 2 min, I start with -10 Vdc (ref to G) and only need 3 min. to measure  arround ~0,3Vdc. 5min I can measure 0,008Vdc

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6 hours ago, mwl168 said:

Hope someone can chime in and share their experience.

I saw an OP07 in one of Kevin's pictures and have been using them

Mouser lists it for +-18v rails, data sheet says max is +-22v

they are under a dollar

OP07CP

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Turn trimmer up to max resistance. Measure voltage at pin2 op27 to ground with one decimal resolution and I bet you'll read 000.0 within a few seconds after applying the high voltages. That servo works.

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After a second thought. Probably a bad idea put a test pin at pin2 OP27, might affect the servo. But the small variation at one output could very well be variation in the balance. +0.160V then you have -0.160V at the other output.

I have four amplifiers with similar servos and they all have perfect offset behavior and the servos kick in instantly.

Edited by JoaMat
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I've read in the thread somewhere that the TL081 is faster acting than the OP27. At a fraction of the cost of OP27, I think the TL081 is worth a try if your front end supply rail is less than 18VDC (TL081's max. voltage supply rating). Hope someone can chime in and share their experience.  

My experiences involved D.C. Servos on I/V stages (0 feedback, D.C. coupled). Opamps I tried included the OP27, TL071 and TL081 (or dual equivalent). The TL081 was the best of the bunch in terms of lowest offset. Stages were either rbroer's (diyaudio) or Colin's (cetoole).



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8 hours ago, JoaMat said:

I have four amplifiers with similar servos and they all have perfect offset behavior and the servos kick in instantly.

Yes, my Carbon works with OP27 and the off set is 0Vdc instantly.

Now I don´t know. Do you think that I have a problem with servo on the GG?

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I use a similar opto servo as on Kevin's boards. Differences are KSC2690A for PZTA06, VOL618A for 4N25 and no resistor/trimmer cross KSC2690A. This servo works instantly on my DIY T2, Carbon, Grounded Grid and Grounded Grid with tube input. The amplifiers also have balance servos. With multimeter one decimal resolution I read 000.0 at the outputs. My impression is that the opto servo works well.

I've no idea what the problem with your Grounded Grid is. The servo works on your Carbon then it should work on the Grounded Grid as well. I'm sure you will solve this, might take some time though but it will be worth it.:)

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6 hours ago, JoaMat said:

I use a similar opto servo as on Kevin's boards. Differences are KSC2690A for PZTA06, VOL618A for 4N25 and no resistor/trimmer cross KSC2690A. This servo works instantly on my DIY T2, Carbon, Grounded Grid and Grounded Grid with tube input. The amplifiers also have balance servos. With multimeter one decimal resolution I read 000.0 at the outputs. My impression is that the opto servo works well.

I've no idea what the problem with your Grounded Grid is. The servo works on your Carbon then it should work on the Grounded Grid as well. I'm sure you will solve this, might take some time though but it will be worth it.:)

 

8 hours ago, jose said:

 

Yes, my Carbon works with OP27 and the off set is 0Vdc instantly.

Now I don´t know. Do you think that I have a problem with servo on the GG?

 

Don't think you are using the opto servo - you only have the one jumper engaged next to the op27 socket. So this would explain your higher starting voltage I think.

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2 hours ago, GeorgeP said:

 

 

Don't think you are using the opto servo - you only have the one jumper engaged next to the op27 socket. So this would explain your higher starting voltage I think.

I think having only one jumper shorted is the correct way. 

IIRC, to engage the opto servo, you need to have both the OP27 and 4N25 installed and short the jumper next to 4N25.

To engage the OP27 servo, you short the other jumper and don't need to install  the 4N25 and leave the jumper next to 4N25 open.

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