Where to squeeze a 600ohm LCR riaa network

[Eric W]

Can a 600ohm LCR be sandwiched between two transformers at the input (for MC), such as:

2:1 - LCR - 600R - 10:1 followed by your favorite tubes for adequate gain.

That would make the build easier. Pro's and con's?

Still struggling to find a suitable drive for the 600ohm units, leaning towards a 7788 pentode approach.

Thanks a lot,

Eric

[dave slagle]

I'm not sure i follow. Did you mean 2:1 >> LCR >> 1:10 then into the gain?

If so the cartridge should have no problem driving the 600R without the 2:1 but then you run into problems.

The load seen by the cartridge will be "fixed" at 600 ohms
The source impedance presented from the LCR will be 600R making a stepup difficult.
The LCR will attenuate the already tiny signal from the MC cart substantially.

dave

[Eric W]

Thanks Dave,

What I meant was:

Step-up 1:2 into the 600R LCR, followed by another step-up transformer. The first xformer could be a typical line input transformer, 150:600, the second could be a 10K:40K (10 x may have been a little optimistic).

Just trying to figure out how to get direct coupling of the tube gain stages. I think I'll just try it with the stuff I have lying around.

Cheers, Eric

[dave slagle]

it is an interesting thought. The load the LCR puts on the cart is pretty flat. I would size the first step up to properly load your cartridge when terminated with 600R to get as much gain before the LCR as possible. Say you are using a 5 ohm cartridge that wants to see a 20 ohm load, then a 1:5.5 would keep your cartridge happy.

You still need to account for the 10X loss in the LCR so low impedance cartridges will be your friend. After the 600 ohm lcr, you will need a stepup that likes being driven with a 600 ohm source which is not a trivial task either.

I think it is an interesting idea and hope you give it a go!

[DowdyLama]

Yeah - I think it's an interesting approach - keep us posted!