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 hadihf 8th August 2008 05:17 PM

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

 lineup 8th August 2008 10:03 PM

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 ?

 analog_sa 8th August 2008 11:31 PM

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.

 hadihf 9th August 2008 03:38 AM

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

 analog_sa 9th August 2008 08:40 AM

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.

 AndrewT 9th August 2008 09:44 AM

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.

 analog_sa 9th August 2008 09:59 AM

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.

 hadihf 9th August 2008 01:58 PM

2 Attachment(s)
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

 Tolu 9th August 2008 03:00 PM

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

 Nordic 9th August 2008 04:42 PM

P88 is ok, but not spectacular, rather try the Pedja Rogic buffer.

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