| Psychobiker |
Hey,
Well, first off, am I ever relieved!
I've been fiddling, and the best ripple I've found yet is 10V RMS, that's out of a 16uF->680R->220uF PI filter...any suggestions?
I'm thinking along the lines of - I'm well under the limit and it improves as per increase of filter cap size...so I'll pop a 45u in there.
Duncanamps PSUD gives millivolt-level ripple...but it fibs methinks.
I'm using GZ34.
L |
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| eduard |
| replace the 680 ohm with a choke with about the same resistance or add another cap and a choke so you will have cap choke cap res cap If it is for a preamp most of them will do because of the low current involved. |
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| Psychobiker |
I have a kinda-choke, an old toroidal transformer with 7.2H primary inductance. That said, I really ought to find a proper one.
I think I'll pop a larger initial cap in there and see what happens,
L |
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| eduard |
Hello,
I think replacing the 16 with a 45 will not do a lot . switching from resistor will change a 6db filter into a 12 db. It will not cost a great deal of money especially if you buy them i a surplus shop. A few euro did do the trick in the past. Try it greetings, Eduard |
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| AndrewT |
| what voltage and current are you working with? |
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| peranders |
| It seems to be very tube related :nod: |
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| AndrewT |
Hi,
Psud predicts mV of ripple and you are measuring 10V of ripple.
What common mode voltage is in with the ripple.
How much of that common mode voltage gets through to the AC measurement?
Have you got access to a scope?
Could you take your ripple measurement through a high voltage isolating cap? Make sure the turn over frequency of the cap and meter impedance is well below the mains frequency. |
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| Psychobiker |
| will measure on tuesday, when I can get at a scope |
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| Psychobiker |
NONCE MOMENT #2!!!
Don't leave your input floating :p. That makes 50Hz hum
Other than that we have good sounding music!!!
RE the ripple, that was on the filter cap. B+ has <10mV |
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| underwurlde |
LOL
I think everyone here had assumed you meant 10mV of ripple when you stated 10V....:xeye: |
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| AndrewT |
| quote: | Originally posted by underwurlde
LOL
I think everyone here had assumed you meant 10mV of ripple when you stated 10V....:xeye: |
no,
I read 10Vrms and assumed he meant 10Vrms. |
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| Psychobiker |
I replaced the original paper-in-oil caps (8uF each) with a larger polypropylene (30uF) one, brought ripple down to 5V. Granted, that is measuring from the initial filter cap. I will need to measure B+ ripple whenever. Either way, it's absolutely dead silent at full volume (currently no input attenuation).
Best results come from :
C(30uF)->680R->220uF->680R->B+->220uf->6.8KR->220uF->C+
I must substitute the inductor again for the first 680R, but...if it ain't broke...
I'm sorry for being such a moron. I just had a bad day :p
Measuring the wrong ripple, leaving my inputs floating (THAT's what caused the hum!!), you name it.
L |
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| ßart West-VL. |
| quote: | Originally posted by Psychobiker
... brought ripple down to 5V. ... |
Forums would be much better if everyone read there own posts before posting them...
Is it 5V now or 5mV? |
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| AndrewT |
Is B+ taken off before or after the 220uf? i.e. the second 220uF.
It would be instructive to see the results of measuring the ripple at each of the capacitors. |
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| Psychobiker |
Unfortunately to do that, requires turning the thing on its head, which I can't do. I can only read ripple at the B+ and C+ takeoff points.
5 VOLTS at the initial filter cap, when I have some more free time, I'll measure B+ and C+ ripple.
Bart, I won't omit mV if I actually mean mV.
Andrew, B+ is taken after the second 220uF, <1cm from its terminal
L |
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| AndrewT |
| post12 is wrong! B+ is shown before 220uf. |
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| Psychobiker |
I only realised that when I checked it last night, but damn editing facility here!!
30uF->680R->220uF->680R->220uF->B+->6.8KR->220uF-C+ |
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| eduard |
Hello psychobiker,
How much current is the circuit drawing in milliampere?
Can you change the power supply into a choke-input? That would mean a higher ac voltage to start with and the use of a bleeder resistance which is a good thing anyway to get the caps unloaded when there is no longer a tension at the heaters. The choke needed for a choke-input should have a minimum induction depending on the load and does have a harder life but for me it is the way to go. When you are on a budget usually a potted one and a relative big bleeder resistor will do the job. When using it further on in the power supply most of them will do fine. A pity Ireland doesn't have euro otherwise i would be pleased to send you one to give it a try.
The primary of a power supply transformer isn't the way to go.
The circuit that did inspire to use chokes was published in 1981 by Jean Hiraga to deliver a tension of 470 and 400 volts dc to a tube pre amplifier. I will give The values of the parts and the measured ripple.
25mf 20 henry 25mf 500-3000 ohm ( adjustable )25mf 1500 ohm 25 mf 1500 ohm 50mf 1500ohm 100mf 1500 ohm 1500 ohm 200mf 30000ohm 200mf .The first cap 7,5 volts after the choke 200mv. The first 200mf 0,1 mv the last 200mf 0,05 mv. The 2* 200mf were doubled both by 2mf paper in oil. All caps were electrolytics. I did copy this circuit using a 300B power transformer, using only non-electolytic caps, only chokes instead of the 1500 ohm. After a while i wanted to bring down the voltage by adding a resistor after the rectifier tube but i didn't have the right value so i did insert a choke having about the same value. This created a choke input supply so the voltage did drop a lot. But i had a higher voltage winding available at the 300b transformer so i did come very close to the voltage measured before so i did guess it would be okay to connect the pre amp again. I remember i was wondering what is caising this voltage drop. At that time ( early eighties) there wan't this huge load of information available about power supplies. Curious? Just try finding some surplus? chokes. Greetings, Eduard |
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| Psychobiker |
If it works, I'm sending it in for evaluation, and then when I get it back, start fiddling. Thanks for the suggestions - have definitely taken them on board!
L |
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| AndrewT |
Hi,
if Eduard's 25mF comes before the choke (20H inductor) then it is still a capacitor input filter.
A choke input filter starts with a choke.
for a choke input the DC output voltage is approx 0.9*Vac.
For a capacitor input filter the DC output voltage is approx 1.4*Vac.
BTW all Ed's mf (milli femto) are really micro farad (uF). |
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| eduard |
Hello Andrew and all the others,
The original from Jean Hiraga was indeed NOT a choke -input but i did eventually change it into a choke input like i did tell later on in the post.
AND the chokes values were henry and the cap values microfarad.
I remember that one of the chokes was 50 henry and the other ones were between 5 and 10 henry.
The ripple meaurements were stated in the circuits article.
Going from choke-input using a higher voltage available on the power transformer to compensate the voltage loss did still give a big improvement allthough there were all ready a big number of chokes involved. Greetings, Eduard |
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| eduard |
Hello,
Reed the hiraga 20 watt thread and all the links attached to get some additional information. Greetings, eduard |
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| Psychobiker |
The whole buzz turned out to be an ungrounded input
:angel: |
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