Zout Maths - is it me?

We all start somewhere
Post Reply
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#1 Zout Maths - is it me?

Post by Ray P »

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?

Capture.PNG
Capture.PNG (2.49 KiB) Viewed 7571 times
Sorry, I couldn't resist!
User avatar
Nick
Site Admin
Posts: 15706
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#2 Re: Zout Maths - is it me?

Post by Nick »

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

https://www.google.com/search?client=ub ... 8&oe=utf-8
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#3 Re: Zout Maths - is it me?

Post by Ray P »

Cheers Nick. I was missing the division by 1000 after the 20.9 - I did say...
Sorry, I couldn't resist!
User avatar
Ray P
No idea why I do this anymore
Posts: 6294
Joined: Thu Nov 22, 2007 5:18 pm
Location: Somerset

#4 Re: Zout Maths - is it me?

Post by Ray P »

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.
Sorry, I couldn't resist!
Post Reply