Power supply chokes

[pre65]

Hi-i have been reading MJ with regard to choke input supplies and he says

"as a sweeping statement,chokes for HT choke input supplies generally need to be,equal to or greater than 15H,otherwise the AC current becomes crippling"

So is there a "rule of thumb" as to how big a choke needs to be to get "optimum" smoothing ?

As a practical example,for the mono power supply on ECL82 Doddington monoblocks would say,20H,be much better than 15H,or perhaps two 10H ?

[Nick]

So is there a "rule of thumb" as to how big a choke needs to be to get "optimum" smoothing ?

I think there are at least two bits of string that need measuring there.

Out of interest, what do you mean by optimum?

[pre65]

So is there a "rule of thumb" as to how big a choke needs to be to get "optimum" smoothing ?

I think there are at least two bits of string that need measuring there.

Out of interest, what do you mean by optimum?

Hi Nick-what i am trying to establish is that if a 15H choke is considered to be the minimum for reasonable ripple rejection how much better would be a bigger choke (say 20H) or two smaller chokes (say 2x10H) and is there a maximum value beyond which the cost negates any supposed gains.

I see Hammond do a 30H 100ma choke as used in Vox guitar amps and these are available in the USA for about $38

[Darren]

Hi Philip,

You need to also consider that the Henry rating of a choke is not fixed.

That is, the more current you draw the less the H. ( this can diminish rapidly) Less ma can sometimes mean more H than the stated rating. (but not usually)

Also, from experience, it's rare to actually get the rated Henries from the manufactures specks.

Nobody can tell you what to use, it depends on the circuit. Though experience will help you to get started.

I suggest you try several scenarios and measure the resultant AC left on the DC line.

You'll need less bits that you'd think. (from experience)

I once built an 6B4G SE amp with two 10uf caps and one 7h choke and it was fine. It started with 3 chokes and several caps some at 100uf. I removed them one by one and measured along the way.

You could say I had a surprise.

But, this may work for one circuit, it may not work so well for another.

[Nick]

Yes, the problm is (like everthing seems to be in audio) its not just about one parameter. If the only goal was low ripple, then huge chokes and huge caps would do it. But is not that simple, big caps and big chokes makes a supply that responds slowly to change in load, so the dynamic regulation is worst. And the Q of the various LC stages may be such that you get overshoot and ringing. Possibly more damaging than ripple. Also bigger chokes in terms of H will often have a higher DCR, and that will also reduce the regulation of the supply.

As Darren says, there is no better solution than to experiment and find what works for you. I know its getting boring now, but that is the BIG advantage to breadboarding, you CAN change things and find out what you prefer. You won't learn that by just recreating existing published circuits.

[Cressy Snr]

As Darren says, there is no better solution than to experiment and find what works for you. I know its getting boring now, but that is the BIG advantage to breadboarding, you CAN change things and find out what you prefer. You won't learn that by just recreating existing published circuits.

Hi Philip
I would concur with what Nick and Darren say here. I learned an incredible amount of useful stuff by designing, building and refining the 6AS7 push-pull amp from scratch. OK it is derivative in that it employs some of Olsen and Dahl's methods as used in the the Amity and also the choke-tail pairs used in the driver stages were nicked from somewhere else. But I had to blend everything together myself with the panel's help of course.

The upshot is that I have gained a great deal of satisfaction from this build because it was done from the ground up. Breadboarding up the DHT tubes as a first stage then hacking them into the amp proved that what I had was good and would really need a complete redesign to improve it. It's very hard to find these things out without clip leads and and a bit of MDF.

I would really try and have a go at an original SE design and get to grips with a few loadlines etc as I believe you are at the stage where you have learned all you are going to learn by building published ccts. It's time to take the next step.
The freedom and creativity a bit of board and some clip leads give you is quite addictive and the gains in confidence you will experience are well worth a bit of initial pointing and sniggering from the panel at your first efforts

Steve

[pre65]

Hi-been reading MJ again !

Todays subject is choke snubbing capacitors.

MJ is in favour of two 220nF (0.22uF) caps across the choke with the other ends commoned to 0v.

Now we dont seem to mention choke snubbers,and the majority of circuit diagrams i have dont show any so,are they worthwhile ?

If so the most cost effective i can find (not cheapest !) are WD Soniqs 0.22uF
630v @ £2.06 each,or 600v orange drops @ £2.50 each.

ps.or Russian PIO 100v for about the same price

[Paul Bannister]

I looked at an interesting Dutch website of 'DHTRob' where ther was a comparison of AE and Tribute chokes. Tribute was a name I had heard of but know nothing about - has anyone any experience of Tribute?

[Nick]

Phil: I always fit MJ type snubbers when using choke input. I suspect if you see circuits that use choke input, then there wil have eventually been snubbers, but (I have done it myself) its easy to draw up a circuit, and miss out adding things like that, because you know they will be there, but when someone else builds from that circuit, they don;t know what the author took for granted.

I must admit, its this sort of problem thats why I often don't post any circuits. Also by the time its been drawn out its out of date.

Paul: I don't have any tribute TX's, but I met Peiter (sp) once, and he is a very nice and knowing chap. But I know a couple of others here have some of his iron, so maybe they will comment.

AFAIK, biggest problem with Tribute, is it makes ordering from AE seem like buying off the shelf.

I must read what the comparison between the two say.

[pre65]

If so the most cost effective i can find (not cheapest !) are WD Soniqs 0.22uF
630v @ £2.06 each,or 600v orange drops @ £2.50 each.

ps.or Russian PIO 100v for about the same price

Hi-is the cap type important ?

I found these on e-bay and 20 would cost nearly the same as 8 WD Soniqs.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :IT&ih=020

[Andrew]

I use a generic polyprop of a suitable rating usually 650v 220nF orange drop.

cheers,

-- Andrew

[andrew Ivimey]

you really don't need anything fancy here. Its the one use I can think of for all those very cheap russian military pios that are very cheap but not very good for audio, actually.

[Nick]

For higher voltage use, the yellow RS ones are very good as well.

[pre65]

Hi-in the PT15 and the ECL82 amps designed by James D there is a 10H choke in the amp circuit (not power supply).

Do chokes in this position need "snubbing" ?

And what about the six 150H chokes in the ECL82 design ?

[Lee S]

Wouldn't have thought so Phil. I think you only need to snub PS chokes. I could be wrong though. Maybe someone else will give you a definitive answer. Chassis are looking good. Let's hope you like the sound of it when it's all finished after all the hard work. Well done !!