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Old 30th August 2012, 04:33 PM   #1281
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The Pass Pub: The High-End Off Topic Thread
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Old 30th August 2012, 04:37 PM   #1282
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.... just as example

boyz , stay on topic , please
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Old 30th August 2012, 04:39 PM   #1283
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Quote:
Originally Posted by lhquam View Post
Sure, the input stage could be something other than a complementary follower, but I think there are good reasons for that choice. The input stage needs to have a fairly low output impedance, because of the load imposed by the transformer, which is about 100R at 20Hz and 200R at 40Hz. This suggests a complementary follower stage rather than common drain. Sure, an opamp could be used and would provide the benefit of more voltage gain. But that would lead us off of the Pass Path.
in my opinion gain is not needed and the jfet follower the F6 has just passes the signal on in two directions, enough (like 0 dB - 700 mV RMS while the transformer and the input buffer can go up to +20 dB) to saturate the output stages far above the 2,4V max and deliver linear behavior.
So this is the Pure Pass Policy: keep it simple.
The input config (jfet follower or like Jensen shows in its appl notes with an opamp) is trivial.
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Old 30th August 2012, 05:28 PM   #1284
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Quote:
Originally Posted by Zen Mod View Post
OPA1632 is SUSY chip - diff in , diff out

it demands pretty lowish impedance feedback net, and it's having low output impedance

I was using it connected to sec of Beyerdynamic 1:10 mic xformer ; xformer ditto on outputs of two (diff connected ) PCM1704 , then feedback net defining reflected impedance back to chips , to have linear freq through audio band

driving xformer with small bridge power amp , to drive output of small power amp ........

........ may I laugh ..... just a little ?

Absolutely ZM; please do; it'll lower your blood pressure. Did you slip above and call Conceptual F6 a small power amp [bolded]; how big?. That's the trick. Make ZM laugh and hell reward you with free info.

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Old 30th August 2012, 05:32 PM   #1285
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naah .....

what's one small,redundant,power amp ....... between friends ........

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Old 30th August 2012, 05:47 PM   #1286
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Not meant to be OT, but I was thinking that beautiful SUSy chip with really nice distrtion numbers and low output Z would be kinda cool driving x-former symmetrical output stage. Somewhat redundant, but not altogether ridiculous. This is DIY.
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Old 30th August 2012, 05:52 PM   #1287
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well - if you need some gain , you can really put it instead of buffer and make nice integrated , with ball input
you can then connect two primaries in symmetrical manner , with overall FB connected from their CT to gnd (need to check that on paper , but seems logical in this moment )

but - do not forget that 1632 (and TSHA cousins ) like lowish impedance NFB net , resulting in lowish input impedance ; you need ball$ to drive it , too
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Old 30th August 2012, 05:56 PM   #1288
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Yup. got lots of bal...I mean preamps capable of that.
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Old 30th August 2012, 06:01 PM   #1289
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Originally Posted by Antoinel View Post
A....... Did you slip above and call Conceptual F6 a small power amp [bolded]; how big?.......
certainly

with usual FW PSU it can't be big - 25W/8 and 50W/4

Pa mentioned scaling ....... I think at least up to 3 pairs can be driven easily , with good results ; PSU voltage of OS can be at least double

so - 100W/8 is easily obtainable
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Old 30th August 2012, 06:03 PM   #1290
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Originally Posted by buzzforb View Post
Yup. got lots of bal...I mean preamps capable of that.
then you have double naked situation - you don't need OPA for gain ...... and using it instead of simple and effective buffer is .......... just imagine number of small critters packed in chain , due to necessary compromises in construction of every chip
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