[JN] CLC Filter Choke Choice

Philip Yates toobman57 at gmail.com
Tue Jun 4 12:33:45 CDT 2019


Well, 27 Hz and 22 uF implies 1.58 Hy, which could easily be the case when
an iron core inductor has current going through it. The resistance is
1/(2*pi*27) = 268 ohms. For the inductor, subtract the resistance of the
inductor from 268, and place the difference in series with the inductor.
Put a 268 ohm resistor in series with the cap, and you have a phase-zero
power supply. 268 ohms may be a little on the high side for a 300B amp,
maybe not. With a 3K output tranny, the output impedance is increased by a
factor of (3K + 268)/3K = 1.09. Of course, this impedance is constant over
the amp's frequency range, whereas in a normal LC supply, the output
impedance varies in both magnitude and phase over the frequency range.

In most cases, it LOOKS like the first stage should be either active --
basically an electronic inductor -- or a lower resistance (100 ohms or so)
stage with large caps, maybe even electrolytic caps, that has a low
resonant frequency (close to DC for the active inductor, maybe 2 to 5 Hz
with electrolytics). This is followed by a second LC stage, with an air
core inductor and a high quality cap that handles frequencies above 100 Hz
or so, I don't know where an audible difference would occur.

Phil

On Tue, Jun 4, 2019 at 9:07 AM Guido Tent via Sound <sound at soundlist.org>
wrote:

> hi,
>
> I was working on an SE 300b amp yesterday. It has local filtering, 4H+22uF
>
> Yes, that resonates around 27Hz where the HT showed max modulation :-)
>  The low frequency playback must suffer from that, I id not perform a
> listening test yet, will do.
>
> best,
> -
> Guido
>
>
>
>
>
>
> On May, 30, 2019, at 23:10, Joseph Levy via Sound <sound at soundlist.org>
> wrote:
>
> Greetings,
>
> I have several transformers and chokes on hand that were stripped off a
> collection of somewhat crudely built (by someone else) DIY 300B amps. They
> include a pair of Tango Permalloy SET OPTs and a pair of Tamura Permalloy
> PP OPTs.
>
> I also have several pairs of vintage filter chokes that meet or exceed the
> minimum specs for the designs I'm working from. The chokes have specs of:
>
> 10Hy @ 200mA, DCR = 90 ohms
> 8Hy @ 300mA, DCR = 80 ohms
> 5Hy @ 400mA, DCR = 45 ohms
>
> The rectifier is a 5AR4 / GZ34 followed by a 40uF cap, a choke, and then a
> higher value cap.
>
> Some time ago, one of my local audio buddies told me that a lower DCR is
> preferred in an SET design rather than a PP where it's not as critical, but
> I don't recall him explaining why. If I were to use one of those chokes
> with either the SET or PP designs, is there a preferred combination?
>
> Thanks!
> JL
> _______________________________________________
> Sound mailing list
> Sound at soundlist.org
> http://mailman.soundlist.org/mailman/listinfo/sound
>
>
>
> Guido Tent
> Managing director
>
> Guido at tentlabs.com
> www.tentlabs.com
> www.grimmaudio.com
>
> o u r    w e b s h o p
>
> www.tentlabsshop.com
>
> Egelstraat 2
> 5622 AK  Eindhoven
> The Netherlands
>
> P +31 (0)40 2130 186
> F +31 (0)40 2130 187
> M+31 (0)6 2466 5125
>
> *Where is my Marie Kondo book………..*
>
> _______________________________________________
> Sound mailing list
> Sound at soundlist.org
> http://mailman.soundlist.org/mailman/listinfo/sound
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.soundlist.org/pipermail/sound/attachments/20190604/9488d868/attachment.htm>


More information about the Sound mailing list