High End Preamplifier

[hadihf]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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

 

[Ted205]

have you compared them ?

 

[analog_sa]

P88 is ok, but not spectacular

Sir, you are too kind

 

[Nordic]

Yes I have, which is why I recommended something that sounds 10 times better.

Here is my old one, collecting dust in an icecream tub.

I have one installed in an amp I gave to my mom in law.

 

[Ted205]

which opamp did you use ? Also why 2 ? unity gain ?

 

[Tolu]

If you use the original P88 PCB with two LM4562, you have nice stuff that isn't to beat so easy.

 

[Juergen Knoop]

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.

the Elektor circuit is sensitive against highlevel sources, DC, RF and cable capacitance
just the naked chip between input selector and output connectors
highend! no evil passive parts!
regards