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Pre preamp problem
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GrahamD View Drop Down
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Joined: 13 Feb 2015
Location: Auckland NZ
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    Posted: 27 Jun 2017 at 10:22pm
Just for fun I recently built a Pre Preamp kit from Boozhound Labs for use with a LOMC cartridge but experienced a strange problem.
When I connected this to my ProJect Phonobox SE II ( using the MM mode  and 47k ohms ) it would barely make a sound.
I double and triple checked my assembly of the circuit and could find nothing wrong.
When I connected it to my Graham Slee Gram Amp II it worked perfectly !!
It is a complete mystery to me but there must be something in the ProJect circuit that is not compatible with this pre preamp.
The LOMC cartridge works fine straight into the ProJect MC stage or via a vintage Ortofon T-10 SUT into MM mode.
Has any one experienced this or have some suggestion as to why this should be happening.
Cheers
Graham Confused
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Graham Slee View Drop Down
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Joined: 11 Jan 2008
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2017 at 7:49am
Strange.

It's not a case of you using the phonobox power supply for both duties? If one derived a 3 rail supply from it, and the other being two rail, could semi-short a rail to ground thus defeating its abilities.

I took a look at the pre-pre's schematic. Such a shame that so many small signal FETs are becoming obsolete.
That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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GrahamD View Drop Down
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Points: 34 		Post Options Post Options   Thanks (0) Thanks(0)   Quote GrahamD Quote  Post ReplyReply Direct Link To This Post Posted: 28 Jun 2017 at 9:47am
Hi Graham.
No, I was running the pre-preamp on a 12volt SLA battery.
It's really strange. It does sound very nice into your Gram Amp.
I liked the idea of such a simple circuit and it gets rave reviews from other users.
It just doesn't like the ProJec tpreamp !!
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