Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Tube DIY Asylum ]

---

[ Alert Moderator ]

---

RE: Increase L in pi network

Posted by Triode_Kingdom (A) on September 22, 2017 at 21:01:56

In Reply to: RE: Increase L in pi network posted by Sidewinder on September 22, 2017 at 17:32:39:

Bear in mind I'm only advising regarding the supply. What you're asking of the amplifier may not be related to this. Many things can influence system dynamics, including components and phenomena external to the amplifier proper.

Based on a basic SPICE analysis, the supply you're using now exhibits a very smooth output impedance curve. There is only one resonance peak, and it is well below the audio band at 6 Hz. The plot is below:

I also plotted the supply with the 25H choke you're considering. That pushes the peak much lower in frequency (off the page in fact), but it does nothing to reduce impedance at 20 Hz and above. The best means to reduce the impedance in that area - and push the peak away at the same time - is to install a larger value at C2. The plot below represents impedance values using a 100uF cap:

My conclusion from these plots is that the 25H choke will not materially benefit your amplifier. I'll also say that although the additional capacitance in the second plot might appear beneficial, the reduction in impedance at low frequencies must be considered against the load presented by the output stage and the efficiency of the overall system. Because this is a SET, the output stage does not make the same dynamic current demands at low frequencies as push-pull AB1. Its loading on the supply is relatively constant regardless of output power and frequency. However, many SETs are driven into clipping at least occasionally during normal use, and a larger second cap can be helpful in dealing with that.

I have to disagree with Eli's comment regarding SS rectification in this case. Additional anode voltage might be beneficial if the amplifier is being regularly tasked beyond its limits. Otherwise, the natural characteristic of Class A to always draw the same average current renders the benefits of SS as it relates to push-pull designs irrelevant.

Edits: 09/22/17

This post is made possible by the generous support of people like you and our sponsors:

Parts Connexion

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---