Attenuator calculations. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Electronpusher0 · 2nd Jul 2019, 10:16 pm

Thinking about it my offering in the post above is probably no good as I think you said you had a 2 pole 50 way switch and the system I suggested uses 2 poles per channel, 4 pole in total. David & Lucien's solution only uses 1 pole per channel (at the expence of a long chain of resistors).

Peter

Radio Wrangler · 2nd Jul 2019, 11:43 pm

No, no, it comes out more easily as a tapped series string of resistors. You don't have to make 48 completely independent 2-resistor attenuators.

1) it only needs half as many resistors
2) it avoids tolerancing of resistor values causing exaggerated jumps at some steps.

So a string of resistors. top stud to input signal 12k resistor to next stud, from that 12k resistor to next stud

then10k
9.1k
7.5k
6.8k
5.6k
4.7k
4.2k
3.6k
3.3k
2.7k
2.2k
2k
1.8k
1.5k
1.2k
1.2k
1k
910
750
680
560
470
420
360
270
220
200
180
150
120
120
100
91
75
68
56
47
42
36
33
27
22
20
18
15
and the last step is a big jump to complete attenuation, 100 ohms to the bottom (grounded) stud.

This gives you a 98.89k pot! and steps of about 1.12 to 1.32dB

David

Radio Wrangler · 2nd Jul 2019, 11:51 pm

Well, I had an excuse for slow typing on that last one.

Other preferred values exist. Just pick the nearest. No one will really notice the difference. That's the advantage of the resistor string. The separate attenuator approach would force you into needing quite accurate resistors to keep the steps sane.

I've just spent a day at work followed by schooling a somewhat green and nappy Belgian Draught horse and a 30 mile drive home. I'm bushed and I'm turning in for today!

David

Electronpusher0 · 3rd Jul 2019, 7:08 am

Thats what I love about this forum, I am continually learning. Until now I had not considered using a tapped series string of resistors.
I feel a new Excel spread sheet coming on for calculating tapped series resistors.......

Peter

2nd Jul 2019, 10:16 pm	#21
Electronpusher0 Nonode Join Date: Jun 2016 Location: Bognor Regis, West Sussex, UK. Posts: 2,296	Re: Attenuator calculations. Thinking about it my offering in the post above is probably no good as I think you said you had a 2 pole 50 way switch and the system I suggested uses 2 poles per channel, 4 pole in total. David & Lucien's solution only uses 1 pole per channel (at the expence of a long chain of resistors). Peter

2nd Jul 2019, 11:43 pm	#22
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	Re: Attenuator calculations. No, no, it comes out more easily as a tapped series string of resistors. You don't have to make 48 completely independent 2-resistor attenuators. 1) it only needs half as many resistors 2) it avoids tolerancing of resistor values causing exaggerated jumps at some steps. So a string of resistors. top stud to input signal 12k resistor to next stud, from that 12k resistor to next stud then10k 9.1k 7.5k 6.8k 5.6k 4.7k 4.2k 3.6k 3.3k 2.7k 2.2k 2k 1.8k 1.5k 1.2k 1.2k 1k 910 750 680 560 470 420 360 270 220 200 180 150 120 120 100 91 75 68 56 47 42 36 33 27 22 20 18 15 and the last step is a big jump to complete attenuation, 100 ohms to the bottom (grounded) stud. This gives you a 98.89k pot! and steps of about 1.12 to 1.32dB David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

2nd Jul 2019, 11:51 pm	#23
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,867	Re: Attenuator calculations. Well, I had an excuse for slow typing on that last one. Other preferred values exist. Just pick the nearest. No one will really notice the difference. That's the advantage of the resistor string. The separate attenuator approach would force you into needing quite accurate resistors to keep the steps sane. I've just spent a day at work followed by schooling a somewhat green and nappy Belgian Draught horse and a 30 mile drive home. I'm bushed and I'm turning in for today! David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

3rd Jul 2019, 7:08 am	#24
Electronpusher0 Nonode Join Date: Jun 2016 Location: Bognor Regis, West Sussex, UK. Posts: 2,296	Re: Attenuator calculations. Thats what I love about this forum, I am continually learning. Until now I had not considered using a tapped series string of resistors. I feel a new Excel spread sheet coming on for calculating tapped series resistors....... Peter