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Designing a universal diff-in/diff-out Head Amp
Designing a universal diff-in/diff-out Head Amp
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Old 14th January 2019, 08:29 PM   #111
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
I used two JFET followers on a floating 9V battery (split by two big R's to make a false ground) drove the 2K mic inputs fine, there is DC at the source but they are always AC coupled. You can then use any cart termination you want.
Scott,

With the in between buffer your solution can use the full set of Riaa time constants in the digital filter and it is still possible to experiment with a lower Cart termination giving a pole at 75usec and leaving this time contant in the digital filter.
It would be nice to know if this results a an improvement in sound reproduction.
I suppose you used something like this for the buffer: Designing a universal diff-in/diff-out Head Amp

But why then are you using a battery instead of the phantom power ?

Hans
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Old 14th January 2019, 09:12 PM   #112
scott wurcer is offline scott wurcer  United States
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Originally Posted by Hans Polak View Post

But why then are you using a battery instead of the phantom power ?

Hans
For 1 meter connections the pseudo-balanced/single ended connection worked fine. Of course this is also the simplest way one FET and three resistors per channel and some bypass caps.
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Old 15th January 2019, 01:07 AM   #113
billshurv is offline billshurv  United Kingdom
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Designing a universal diff-in/diff-out Head Amp
Had to go off and bang my head on a wall for a bit as was being stupid as usual. I think that both a buffer and straight in should be tried. I might even for a giggle try my microtrackII if I can get it working mainly as this has no published specs* for the mic input and also has the least compliant phantom power known (about 30v apparently).



Based on what we have found from test records +/-1dB is as good as it gets and so worrying about the exact input impedance is a waste. OTOH phantom powered buffers will offend so many delicate souls it's worth doing just for the fun value



*The user manual has no figure, but on the web have found a couple of references to the mic input being '>5.3k'. That's sooo helpful.
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Old 15th January 2019, 04:39 AM   #114
nezbleu is offline nezbleu  Canada
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Designing a universal diff-in/diff-out Head Amp
Quote:
Originally Posted by billshurv View Post
OK, Thanks. Just to recap, the average bit of gear we are looking at has 3 types of input
1. Mic, balanced usually with Phantom power

2. Instrument (unbal)
3. line in (balanced)
I am watching this thread with much interest as I just took delivery of a Behringer UMC202HD. Promptly realized I have no 1/4" adapters and the local pro shop wants $15 per. I can wait a few more days to hook it to while some online-bought adapters make their way to me. I would rather buy local but not when they are ripping me off for cables and adapters.
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Old 15th January 2019, 10:31 AM   #115
billshurv is offline billshurv  United Kingdom
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Designing a universal diff-in/diff-out Head Amp
And today discover that the unit my guinea-pig friend has (Zedi-10FX) has no spec for input impedance on mic inputs as well. Does look like Scott's little buffer is the right way forwards.
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Old 15th January 2019, 01:39 PM   #116
scott wurcer is offline scott wurcer  United States
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I would rather buy local but not when they are ripping me off for cables and adapters.
I bit the bullet ten years ago and bought 4 of every adapter I could think of, even BNC to RCA in both flavors. Sometimes I need to series them like differential BNC to XLR.
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