Substituting silicon for an input transformer

Hi all 

I'm in the process of building a simple hi fi (not studio) preamp that calls for an input transformer, which has a specified voltage gain of 1:5.

Given that the recommended transformer is rather pricey and I don't need balanced input, is it as simple as substituting a good quality op-amp with the relevant gain setting?

I've read a lot in the various transformerless topics here, but nothing I've seen has quite answered my question. And my head is getting muddied!

Many thanks!

Headlab said:

Hi all 

I'm in the process of building a simple hi fi (not studio) preamp amp that calls for an input transformer, which has a specified voltage gain of 1:5.

Given that the recommended transformer is rather pricey and I don't need balanced input, is it as simple as substituting a good quality op-amp with the relevant gain setting?

Click to expand...

Should be fine, although what's the application? Mind your source impedance.

You might wish to look into something like an INA163 mic preamp chip, or just low noise opamp.

Headlab said:

Hi all 

I'm in the process of building a simple hi fi (not studio) preamp amp that calls for an input transformer, which has a specified voltage gain of 1:5.

Given that the recommended transformer is rather pricey and I don't need balanced input, is it as simple as substituting a good quality op-amp with the relevant gain setting?

I've read a lot in the various transformerless topics here, but nothing I've seen has quite answered my question. And my head is getting muddied!

Many thanks!

Click to expand...

A general purpose op amp may not give you S/N performance equivalent to a decent transformer preamp (what Andy was hinting about impedance)... BUT they make off the shelf dedicated mic preamp ICs that will work just fine, several IC makers sell them (THAT corp and others).

A transformer front end that steps up the voltage 5x steps up the impedance 25x.

JR

Thanks a ton for the information guys  ;D. I've had a look at several mic preamp ICs on your recommendation, but they're all balanced input. I'll be dealing with single ended only, so I reckon a good op amp like the OPA627 or AD797 will do the job.

My application is simple home stereo. Impedances in this realm are pretty much confined to "high input Z = good, low output Z = good". All the gear I'll have upstream from this preamp has an output Z of less than 100 ohms, and usually much less than that.

Impedance seems to be far more critical in the studio environment, and from what I've seen begins to look akin to black magic 

If you connect line level equipment to the preamp, you'll need a line preamp. Or maybe a mic preamp with modified input stage
Could you post a link to schematic?

Headlab said:

Thanks a ton for the information guys  ;D. I've had a look at several mic preamp ICs on your recommendation, but they're all balanced input. I'll be dealing with single ended only, so I reckon a good op amp like the OPA627 or AD797 will do the job.

Click to expand...

You can always use a single ended signal into a balanced input, but you can't effectively process balanced signals with unbalanced gear.  If you need a mic preamps, use a mic preamp... for line level signals an op amp should work. 

My application is simple home stereo. Impedances in this realm are pretty much confined to "high input Z = good, low output Z = good". All the gear I'll have upstream from this preamp has an output Z of less than 100 ohms, and usually much less than that.

Impedance seems to be far more critical in the studio environment, and from what I've seen begins to look akin to black magic 

Click to expand...

Home stereo are generally line level... 500mV or so.

JR

The only common hi-fi preamp which wants an input transformer is Moving Coil phono cartridge preamp.

This is a very specialized case of super low impedance. Lower than is hiss-optimum for Silicon. The transformer is an electronically elegant solution, but hard on the wallet.

There are gobs of transformerless MC preamp plans around. By the nature of phono, preamp hiss is not necessarily the limiting factor.