Let me say straight away that maths isn't one of my strongpoints and what knowledge I have doesn't get used much!

I want to know the output impedance (Zout) of the 2P29L preamp I'm working on. The preamp is using the Bartola schematic with his (Ale's) Mu Follower 'Gyrator'.

https://www.bartola.co.uk/valves/2017/0 ... ht-preamp/

https://www.bartola.co.uk/valves/2016/0 ... l-pse-amp/

Ale has a blog post on his website about calculating Zout so I thought I would try and learn by following it.

https://www.bartola.co.uk/valves/2018/0 ... impedance/

I thought the obvious starting point was to verify my maths by working through the 'proof of the pudding' example so I created a little spreadsheet to input the variables and perform the calculation. Once I get that taped I can move on to substituting the relevant values for the 2P29L scenario. I've attached the 'proof of the pudding' equation example below - my problem is I don't get the 356ohm answer when I work though it - is it me?

## Zout Maths - is it me?

### #2 Re: Zout Maths - is it me?

works for me (100+1000)/(1+(100*20.9/1000)) = 359

https://www.google.com/search?client=ub ... 8&oe=utf-8

https://www.google.com/search?client=ub ... 8&oe=utf-8

Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.

### #3 Re: Zout Maths - is it me?

Cheers Nick. I was missing the division by 1000 after the 20.9 - I did say...

### #4 Re: Zout Maths - is it me?

I have my spreadsheet setup and working correctly now thanks to Nick's pointer - now I need to work out the values I need to input for my specific configuration.