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Old 8th August 2008, 05:17 PM   #1
hadihf is offline hadihf  Pakistan
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Default 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?

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Farooq
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Old 8th August 2008, 10:03 PM   #2
lineup is offline lineup  Sweden
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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 ?
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Old 8th August 2008, 11:31 PM   #3
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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.
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Old 9th August 2008, 03:38 AM   #4
hadihf is offline hadihf  Pakistan
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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.

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Farooq
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Old 9th August 2008, 08:40 AM   #5
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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.
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Old 9th August 2008, 09:44 AM   #6
AndrewT is offline AndrewT  Scotland
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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.
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Old 9th August 2008, 09:59 AM   #7
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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.
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Old 9th August 2008, 01:58 PM   #8
hadihf is offline hadihf  Pakistan
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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
File Type: pdf talema2.pdf (53.3 KB, 282 views)
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Old 9th August 2008, 03:00 PM   #9
Tolu is offline Tolu  Germany
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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
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Old 9th August 2008, 04:42 PM   #10
Nordic is offline Nordic  South Africa
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P88 is ok, but not spectacular, rather try the Pedja Rogic buffer.
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