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 Chip Amps Amplifiers based on integrated circuits

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 8th August 2008, 04:17 PM #1 diyAudio Member   Join Date: Mar 2007 High End Preamplifier Hi, This seems to be stupid but I odered the wrong tranformers for the high end preamplifier project published in Elektor April/May2004. Question, would a 5VA transformer work in place of 10VA for this project? Regards Farooq
 8th August 2008, 09:03 PM #2 diyAudio Member     Join Date: Dec 2005 Location: the north for a preamplifier 5 VA can be good depends a bit on the type of amplifier Is it Class A? How much is the voltage. +V and -V ? __________________ lineup
diyAudio Member

Join Date: Aug 2002
Location: Cascais
Quote:
 Originally posted by lineup Is it Class A?
Not quite.

It's hardly a preamp - just a PGA2311. 5VA would be pretty marginal in most cases but here probably doesn't matter much.

 9th August 2008, 02:38 AM #4 diyAudio Member   Join Date: Mar 2007 There are two power supplies, one digital and on analogue. The digital is +-5V for PGA2311. The other is for the PIC, and relay board and is +5V. If I roughly divide the current consumption for the analogue one, PIC = 10mA LCD+Backlight = 50mA IR sensor = 5mA Relay board (2 Relay on) = 75 mA misc = 60mA It sums up = 200 mA The analogue supply is parallel that means total current capacity@5V = 500mA. That should be sufficient. Please somebody correct me if I am wrong. Regards Farooq
 9th August 2008, 07:40 AM #5 diyAudio Member     Join Date: Aug 2002 Location: Cascais You are correct and it will indeed work. Of course any preamp with "high end" pretensions is expected to have appropriately oversized power supply - something like 50VA for the PGA would probably be average.
 9th August 2008, 08:44 AM #6 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders 500mA of DC after the capacitor input filter requires the AC rating of the transformer to be 1A. For a 5Vdc supply you would need at least 6Vac to supply the regulators. That comes out at a minimum of 12VA. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
 9th August 2008, 08:59 AM #7 diyAudio Member     Join Date: Aug 2002 Location: Cascais Andrew The Elektor design uses separate transformers: one for the PGA and another for everything else. The PGA hardly draws more than 20mA. I assume Farook has repalced each of the 10VA transformers with a 5VA.
diyAudio Member

Join Date: Mar 2007
That is correct. I am using two separate tramsformers. Attached is the datasheet. 70040 is origional, 70020 is required to be used.
Somebody constructed already constructed it? How does it sound?

Regards

Farooq
Attached Files
 talema2.pdf (53.3 KB, 290 views)

 9th August 2008, 02:00 PM #9 diyAudio Member     Join Date: Mar 2007 Hi Farooq a colleague of a german DIY forum has built that preamp and after two hours critical listening the preamp rests on top of his cupboard and gets dusty. I would eventually propose another preamp. Do you know the P88 from Rod Elliot of Australia? That is more High End! Elektor Preamp
 9th August 2008, 03:42 PM #10 diyAudio Member     Join Date: Sep 2005 P88 is ok, but not spectacular, rather try the Pedja Rogic buffer.

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