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Old 11th June 2003, 01:32 PM   #11
protos is offline protos  Greece
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If you look inside Naim amps the earth only connects from the Ac input socket to the chassis. Nothing else is connected there so the circuits are floating with respect to AC ground. Perhaps that's why they are so quiet.
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Old 11th June 2003, 01:38 PM   #12
Nuuk is offline Nuuk  United Kingdom
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Quote:
The real question is do you connect the 'center tap' of your PSU to earch as well ?
Out of interest, the two transformers that I used for my first GC PSU came from some 'old' Arcam A60 amps and they have an earth wire coming from the transformer together with the two primary connections!
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Old 11th June 2003, 02:11 PM   #13
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Originally posted by DRC

My most recent experience of 'ground loops' occured after my cable TV intallation was upgraded with a cable modem. This resulted in severe interferance breaking through the shields from a DVD and PC (no problems prior to modem). Nothing I tried could eliminate this totally (ferrites/earthing/un-earthing/messin' with the cable TV shield/hasselling the cable co/etc/etc) and I eventually had to resort to optical links . Sometimes no amount of fiddling with earthing will fix a problem ....
Dave
You gan stop that ground loop with a 1:1 isolation transformer.
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Old 11th June 2003, 02:20 PM   #14
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Originally posted by Nuuk

Out of interest, the two transformers that I used for my first GC PSU came from some 'old' Arcam A60 amps and they have an earth wire coming from the transformer together with the two primary connections!

On my basement I discovered a nice little 2x20v toroid from an old Nokia modem I sent to the dust bin some years ago.
I always keep the nice things...
That little toroid has an earth connection too.
I'm using it on my new preamp (it's playing, but it doesn't have a box yet, it's laying on the floor).
Hey Nuuk, fantastic sound I'm getting with my new preamp + Gainclone!
OPA627 + BUF634 = Ultra-high-end.
Deam, now I have to listen to all those CDs again.
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Old 11th June 2003, 05:38 PM   #15
Nuuk is offline Nuuk  United Kingdom
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OPA627 + BUF634 = Ultra-high-end.
Carlos, whats a BUF 634? I've got some OPA627's that I am planning as using as a buffer for the GC's.

Are you using the OPA627 as a buffer or amp?
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Old 11th June 2003, 05:56 PM   #16
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Originally posted by Nuuk


Carlos, whats a BUF 634? I've got some OPA627's that I am planning as using as a buffer for the GC's.

Are you using the OPA627 as a buffer or amp?

Nuuk, the BUF634 is a buffer (unity gain) capable of 250 ma current output.
You use that in the feedback loop of an op-amp and you can have the power amp on the other end of your house!
Use the op-amp to get the gain you whant, and the BUF634 to get more current.
Go to www.ti.com, search for BUF634, and dowload the datasheet.
I made a preamp "based" on the schematic on the datasheet for an headphone amp.
Man, this is high-end, I can tell you.
Impressive.
I haven't made a box for it yet, as soon as I have it done I'll post some photos.
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Old 11th June 2003, 06:01 PM   #17
Nuuk is offline Nuuk  United Kingdom
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Use the op-amp to get the gain you whant, and the BUF634 to get more current.
So you are using the OPA627 for gain! Did you think of making it an inverting amp to go with the IGC?
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Old 12th June 2003, 09:28 AM   #18
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Talking High-end preamp

Quote:
Originally posted by Nuuk

So you are using the OPA627 for gain! Did you think of making it an inverting amp to go with the IGC?

Nuuk, in fact I'm making a standalone preamp.
With a gain of 2.4.
It will wave 6 line-ins, 3 buffered tape loops (again, with OPA627) and 2 pre outs.
It's much more useful to me to have a standalone preamp.
I wont put anything inside my Gainclone, I don't see any advantage.
With my standalone preamp I can even think of (later) biamplification of my Epos speakers.
I tell you, the preamp is laying on the floor, on my room, connected to my main system and it just sounds glorious.
The boards are all done.
What is missing is to complete it with a nice box.
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Old 12th June 2003, 01:50 PM   #19
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It will wave 6 line-ins, 3 buffered tape loops (again, with OPA627) and 2 pre outs.
Oh, just a budget model then Carlos I hope you get the OPA627's cheaper than we do in the UK!

My current preamp has two tape buffers but I only ever use one, and then only once a week to record a late night/early morning radio programme while I get my beauty sleep and dream about Gainclones

I'm thinking of taking the 'bare minimum' approach with just a pot between source and (buffered?) GC's. I'm not even sure if I will use a selector switch and mayjust rely on plugging and unplugging to select the source.

Even if your preamp is separate from the GC's, you could still invert the signal so compensate for the inverting mode of the GC's!
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Old 12th June 2003, 03:05 PM   #20
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Originally posted by Nuuk

I'm thinking of taking the 'bare minimum' approach with just a pot between source and (buffered?) GC's. I'm not even sure if I will use a selector switch and mayjust rely on plugging and unplugging to select the source.

Even if your preamp is separate from the GC's, you could still invert the signal so compensate for the inverting mode of the GC's!

You can at least use one of those little double up-down metallic switches.
I have found they are very good for signal.
Some time ago I made a little amp for my son, for it's bedroom, with only two line-ins, with one of these switches.
With one device playing, I switch to the other line-in, take the volume to the maximum and I can't hear anything!
Absolutely no crosstalk.

Well, I prefer the non-inverting topology for preamps.
Gainclones are different animals.
Anyway, as I have the positive speaker terminal connected to the star ground, it's not inverted again!
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