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Old 6th December 2005, 11:13 PM   #1
gelder is offline gelder  United States
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Default Grounded Grid Help

I have decided to build a Grounded Grid Preamp as my first diy Tube project and I have a few questions. It is the Grounded Grid design from " Audio Reality " by Bruce Rozenblit.

My first question is: Can this preamp be built in the style of the Bottlehead foreplay? In other words; can the components be top mounted on a plate and then put in a wood frame? I ask because the few examples I have come across are all in an enclosure.

Secondly, I am using the schematic from page 87 of the above mentioned book, and was wondering if anyone who has built this preamp from this schematic is aware of any mistakes in the schematic, or has any suggestions for minor improvements?

I plan on getting all of the components in the next few weeks and hopefully will start the build soon after the holidays.

Thanks
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Old 7th December 2005, 12:22 AM   #2
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no reason why you couldn't mount everything on a top-plate. the only issue with the schematic i'm aware of is the 7812 regulator pin-out. ground is the center pin, i believe the schematic is a bit misleading in this respect.
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Old 7th December 2005, 02:22 PM   #3
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Yes, Thats exactly how I've built a number of them. I used an alumnium top plate on a nice oak base, mine were built for under 100.00 including NOS Tung-Sol toobes. The grounded Grid however is just an OK line stage..... HOWEVER you might want to read these two threads before you buy all the parts..... Then you won't waste time and go through what I did to get where I now am.

Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid.....


Plus this one........12B4A Linestage
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Old 7th December 2005, 03:06 PM   #4
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Gelder

I have build one as you planning for.
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File Type: jpg img_1293b.jpg (24.2 KB, 359 views)
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Old 7th December 2005, 03:13 PM   #5
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Mark

I have built both line stage for 5687 and GG. I find the GG is more storng in its dynamic and 5687 is strong in vocal image.
Have you built 5687 line stage and compare it with 12B4 before?
What circuit do you recomment for 12B4 (include PSU).

Thanks
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Old 8th December 2005, 12:04 AM   #6
gelder is offline gelder  United States
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I just wanted to say thanks to everyone for the replies and the real nice pic. I didn't think it would make a difference which way it was built but I do feel better now that it has been verified.

Thanks again.
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Old 8th December 2005, 03:31 AM   #7
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Hi Vangogh,

My 12B4 circuit is based on .Brian Beck's circuit that uses an LM317 as a CSS. This runs the current at 30ma which does indeed place this tube just about in its optimum curve. I am just powering it from a variable H-V bench supply at the moment. I plan on building and testing this circuit later this week. It has very low impedance over a very wide range so it should work very good with the 12B4. Quite number of others have heard this line stage now and most agree its about as good as it gets...

I have not worked with the 5687, however the plate resistance is about twice what the 12B4 is so it might be more confined to use at higher input impedances than my 2's. My GG now resides on the shelf along with all my other DIY line stages.....

Mark
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Old 8th December 2005, 02:44 PM   #8
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Thanks very much Mark

Looking forward to see your result.
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Old 11th December 2005, 03:00 AM   #9
gelder is offline gelder  United States
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Default Another question

I am putting together my order for the Grounded Grid components. In doing so I have another question.

The original schematic shows two 120 volt transformers in a voltage doubler arrangement, and a separate 12 volt transformer.

I am wondering if I could just get one 200v-0-200v + 12v transformer?
It seems like that would be a lot easier.

If so, how different would the circuit then become?

Thanks
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