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Old 4th June 2003, 08:50 PM   #21
mikelm is offline mikelm  England
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Quote:
Originally posted by Nuuk
When building prototypes, don't just leave everything just sitting there. Screw the transformer onto a chunky pice of timber, the rectifier bridge too and even fix some of the cables down.

Yes - after some recent mods I was left with a bit of a lash up. odd bits of cheap wire here & there... I thought it was sounding good until I did it all properly this w/e with careful layout, earthing etc with cat 5. The improvement was suprising ( noticed immediately by my other 1/2 ! )

cheers

mike
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Old 5th June 2003, 11:02 AM   #22
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Default weak transformer

For me, athough it may not be the only responsible for the sound you have, your transformer is very weak.
You could get another one and use two, one for each channel.

Hey Kwei, nice to see you here.
I wonder what you use as a power amp...
If it's the same league as your preamp, it has to be something special.
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Old 5th June 2003, 04:30 PM   #23
mikelm is offline mikelm  England
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Default Re: Re: Help!! Irritating sound of my GainKlone

Quote:
Originally posted by Kuei Yang Wang


Finally, the two parallel capacitors before and after the bridge rectifier are SERIOUSLY bad news in my view. remove the 0.47uF Cap and place it after the Bridge to not loose it's use.

Sayoanra
For many years I put a cap like this ( often upto 4.7u !!! ) in this position and without really knowing what it was doing I noticed a HUGE improvement in the sound. ( Also the transformer warmed up a bit !!! )

Having done some spice research on this recently, I now realise that this cap has the effect of drastically reducing the frequency, but not the amplitute and lenght, of the ringing in low resistance secondaries.

My current idea is to keep the 4.7uF with 100ohm in series and .47uF across them both. This stops the ringing and removes and fast transients that might create any RF nasties.

I hope this does not sound too wacky

If it does here is the test cct I used - try it and see what you think

cheers

mike

PS the voltage source is 18V AC
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Old 5th June 2003, 05:40 PM   #24
tiroth is offline tiroth  United States
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I think you are hard at work on reproducing Calculating Optimum Snubbers.
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Old 5th June 2003, 06:36 PM   #25
mikelm is offline mikelm  England
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Quote:
Originally posted by tiroth
I think you are hard at work on reproducing Calculating Optimum Snubbers.
Yes - this was my starting point, but as you can see it was not my finnishing point

based on my previous experience I think the bigger value caps will sound better. If the 1st cap is about 10 times smaller than the second its is quite easy to find a resistor value that will stop the ringing.

with 10uF & 100uF+10ohms the tendency for ringing simply merges into the next mains cycle - this is probably going a bit too far but who knows it may sound best of all as it is also quite a powerful mains noise filter !

cheers

mike

to see what is going on put a current meter in between the snubber cct and the TR coil and a voltmeter between ground & snubber caps.
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Old 5th June 2003, 11:45 PM   #26
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Default Re: weak transformer

Koinichiwa,

Quote:
Originally posted by carlosfm

I wonder what you use as a power amp...
If it's the same league as your preamp, it has to be something special.
You can see the whole system here:

http://www.arduman.com/aa/Sayfalar/t...n/thorsten.htm

I do think the Poweramps are in the same league as my Pre. But that is just my opinion. A look inside:

Click the image to open in full size.

A look from above:

Click the image to open in full size.

And a schematic for those who like that sort of thing:

Click the image to open in full size.

Sayonara
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Old 6th June 2003, 04:49 AM   #27
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Letís see what I am going to do

1. Remove the wima bypassing caps to the 1000uF electrolytic
2. Move the RifaX2 caps after the bridge rectifier
3. Add 0.22ohm white coffin wire wound resistors between the transformer and the bridge rectifier. Insert two Wima 10nF cap before and after the wire wound resistors.
4. Improve the wiring + arrangement (nail them on a board), transformer upgrade at later stage.
5. CONVERT to inverting configuration. HALILUYA!!!
6. Lowering the value of the resistors used in the amp circuit.
7. By pass the input 4.7uF cap.
8. Add 0.22 ohm Power film after the out pin and the binding post. I think I need a heat sink for this resistor or I have to attach it to the chassis of the amp. So far I can only find Meggritt MPR20 with this value in my country.
9. Upgrade Transformer to 400 or 500VA, +/-24Vac

I will also try the sunbber circuit suggested by mikelm.

I start off with the most cost effective change.

So far I had removed the bypassing wima caps and one set of RifaX2+FKP1 combo before the bridge rectifier, the other combo is still in the circuit. The effect: the bass region of the sound clear up quite bit. Previously, I perceived the bass to be good, but a little on the face, too up front. Now the bass have cleaned up, the on the face feeling is gone, the music is more relax and at ease, but still not quite there yet. Another thing I have noticed, with the bass cleaned up, the mid and the high are also clearer, the high is also more extended and slightly more prominent. I would say the sound before the removal of the caps is more muffle. The improvement is positive.

Kueiís diagnosis is spot on. Alikato! Kuei San.

Again thank you everyone. I will feedback the effect of each change once I have done them.


Regards,
SW Yeo
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Old 6th June 2003, 06:03 AM   #28
mikelm is offline mikelm  England
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Letís see what I am going to do

>3. Add 0.22ohm white coffin wire wound resistors between the transformer and the bridge rectifier. Insert two Wima 10nF cap before and after the wire wound resistors.

>5. CONVERT to inverting configuration. HALILUYA!!!
>6. Lowering the value of the resistors used in the amp circuit.

If you change to inverting mode the input resistor IS the i/p resistance so if you lower your values you will have to be sure that our preamp can drive this value. For inverting mode many of us get great results with 10K/220K

>8. Add 0.22 ohm Power film after the out pin and the binding post. I think I need a heat sink for this resistor or I have to attach it to the chassis of the amp. So far I can only find Meggritt MPR20 with this value in my country.

should be ok without the sink - but might sound good on it

>I will also try the snubber circuit suggested by mikelm.

you will need this OR coffins & caps ( point 3 ), not both !

Sounds like you will end up will a great sounding amp - good luck

mike
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Old 6th June 2003, 08:27 AM   #29
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Default Re: Re: weak transformer

Quote:
Originally posted by Kuei Yang Wang
Koinichiwa,

You can see the whole system here:

http://www.arduman.com/aa/Sayfalar/t...n/thorsten.htm

I do think the Poweramps are in the same league as my Pre. But that is just my opinion. A look inside:

Click the image to open in full size.

A look from above:

Click the image to open in full size.

And a schematic for those who like that sort of thing:

Click the image to open in full size.

Sayonara

This guy is fantastic.
Kuei, I'm making an ultra-high-end preamp.
Not in the same league as yours, that's outer-space high-end.
Reports soon.
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Old 6th June 2003, 09:13 AM   #30
fedde is offline fedde  Netherlands
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Yesterday, I replaced my 220 k feedback resistor with 330 k. Also I use that value on the + input. (DC <0.7 mV !)

I had quite some stability issues recently after some changes. But the amp seems to be fully stable now again and also sounds better. More dynamic, better defined and more gain. Everything better

Fedde
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