L2 inductor choice

Design and use of Chokes for PS, anode and filament use.
Post Reply
bravi
Posts: 7
Joined: Fri May 07, 2010 11:09 pm

L2 inductor choice

Post by bravi »

Hi Dave,

I am doing an upgrade of Marantz 7 pre ( probably for the 7th time!) and am keen to get your advise for the combination for the best sound. My current plan is to use:

L2 (4.2H) inductor close to the anode resistor, with decoupling capacitor of 5uf using Audio note capacitor.

I estimate the current through each stage is 0.3ma and for 4 triode sections (2 valves) it will be around 1.2 ma.

Any advise on inductor value of L2 and the capacitor value for best sound?

Cheers!

Ravi
dave slagle
Posts: 2037
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

Hey,

there are a couple of things going on here. First the original 7 does not have any chokes in the PS and uses 1/2 wave rectification so just replacing a resistor with a choke will shift the B+ values around.

The decoupling cap after the choke will probably need to be bigger than 5µf in order to push the LC resonance down below the audio band. 4.2hy and 5µf give a resonant frequency of 35hz and this number should be well below 20hz.
Going to 50µf would do nicely and if you want to keep the cap in the 5µf range the choke could be upped to 40hy to push the resonant frequency down a decade.

dave
Get Your Fix
www.hifiheroin.com
bravi
Posts: 7
Joined: Fri May 07, 2010 11:09 pm

Post by bravi »

Thanks Dave. My idea of considering the inductor is a kind of experiment to push the boundaries in this preamp. The voltages to the sections are based on RC sections to arrive at the specified voltages- hence no issues here.

I wanted to stay with the std values you have in your web page and not wedded to the 4 Hy value. I can definitely go for higher values of caps with size being the constraint. If I use 22uf cap, can u pl check if the 10hy inductor will be ok?

Also can you pl p.m me the cost if I wish to consider 40Hy inductor. I need a pair.

Cheers!

Ravi
dave slagle
Posts: 2037
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Post by dave slagle »

The 20 or 40hy inductor will be the same price as the 4hy unit. Same core size just smaller wire and a smaller gap.

since this will be replacing a resistor and you are only drawing a few ma max, going for the 40hy makes sense to me. A crude way to determine comparable combinations is to use the LC product. Lets assume the 5µ 40hy combo is an acceptable choice. The LC product is 5*40 or 200. This means that 5hy 40µ, 10hy 20µ and 100hy 2µ will all have the same LC resonant frequency which is just over 11Hz. The actual number is not critical but the general consensus is it should be below 20hz.

googling power supply LC resonance should turn you up lots of opinions on this. I don't follow any hard fast rules just make sue the frequency of the last LC section is below 20hz and that if there are multiple LC sections to make sure they have different resonant frequencies.

dave
Get Your Fix
www.hifiheroin.com
Post Reply