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Old 6th June 2003, 11:50 AM   #31
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by overmind

1. Remove the wima bypassing caps to the 1000uF electrolytic
Yes. Bypassing is a dicey game. I know people who routinely use just a single bypass. If your "lwo-Z" Electrolytic cap has a "normal" parasitic inductance (say 300nH - gives 180mOhm @ 100KHz and you a 470nF bypass you get a high Q resonant circuit at around 420KHz, quite possibly in a region where it can add to the instability o the circuit.

Quote:
Originally posted by overmind

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.
Yup. BTW, this basic suggested snubber can be much improved upon, I suggest the late John "Buddah" Camilles article in Sound Practices on "Reducing Diode Noise" for a really comprehensive treatment how to kill the various rectificaion noise sources....

Quote:
Originally posted by overmind

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.
Yup.

Quote:
Originally posted by overmind

7. By pass the input 4.7uF cap.
As before, beware of "Bypassing". It is a good tool to be applied correctly, but failure to do so can often make things worse.

Quote:
Originally posted by overmind

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.
Meggit resistors and chassis will be fine.

Quote:
Originally posted by overmind

9. Upgrade Transformer to 400 or 500VA, +/-24Vac
I would strongly suggest to go for four separate lower power transformers. That way you can operate them in the "low flux" connection (1/2 rated primary voltage), plus I'd suggest adding the DC killer circuit. Using fully separate supplies per channel comes highly recommended too. Using the right mechanical arrangement for the transformers can in addition minimise any leakage from the mains into the actual circuit, by the expedient of in effect "bucking out" the leakage components.

Quote:
Originally posted by overmind

I will also try the sunbber circuit suggested by mikelm.
The type of snubber Mike suggests as well as the even more extensive ones by John Camille need to be accuratly calculated for the given mains transformer - they are NOT universal. Getting them wrong is worse than not having them.

The simple CRC PI Filter recommended above is nowhere near as effective, yet it is much less critical and close to "universal". You could try using a large value capacitor on the "rectifier" side of this CRC circuit, have a listen.

Sayonara
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Old 6th June 2003, 09:02 PM   #32
mikelm is offline mikelm  England
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Default where can I find this article

Quote:
Originally posted by Kuei Yang Wang

I suggest the late John "Buddah" Camilles article in Sound Practices on "Reducing Diode Noise" for a really comprehensive treatment how to kill the various rectificaion noise sources....
I would like to read this. I could not find it on the sound practices site / back issues.

do you or anyone know where I can find it ?

Mike

p.s. Now, if Kuei Yang Wang is chinese, Kuei would be your family name and Yang Wang your given names ( or something similar. ) So should I be calling you 'Mr Kuei or Yang Wang or just Wang ? Hope you don't mind me asking
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Old 7th June 2003, 10:58 AM   #33
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: where can I find this article

Koinichiwa,

Quote:
Originally posted by mikelm


I would like to read this. I could not find it on the sound practices site / back issues.

do you or anyone know where I can find it ?
It's in issue 7. But do buy the CD-Rom - it is worth having, printing out and reading....

Quote:
Originally posted by mikelm


p.s. Now, if Kuei Yang Wang is chinese, Kuei would be your family name and Yang Wang your given names ( or something similar. ) So should I be calling you 'Mr Kuei or Yang Wang or just Wang ? Hope you don't mind me asking

Non of the above. Please see:

http://www.sazan.net/digest/sazguide.shtml#Kaiyanwang

Kuei Yang Wang is another possible rendering of the name of the "Demon-Eye King".

Sayonara
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Old 8th June 2003, 04:23 AM   #34
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Quote:
Originally posted by Kuei Yang Wang
Koinichiwa,

Yes. Bypassing is a dicey game. I know people who routinely use just a single bypass. If your "lwo-Z" Electrolytic cap has a "normal" parasitic inductance (say 300nH - gives 180mOhm @ 100KHz and you a 470nF bypass you get a high Q resonant circuit at around 420KHz, quite possibly in a region where it can add to the instability o the circuit.


Yup. BTW, this basic suggested snubber can be much improved upon, I suggest the late John "Buddah" Camilles article in Sound Practices on "Reducing Diode Noise" for a really comprehensive treatment how to kill the various rectificaion noise sources....


I think I have a lot to read up. Thanks for pointing to the link/source.



Quote:

Meggit resistors and chassis will be fine.
I bought some 1 ohm carbon film resistors, 1 watt rating, together with the white coffin resistors. I intend to parallel 5 pieces of the 1 ohm resistors to achieve 0.2ohm.

If the purpose of using Film Power resistor is for it's non inductiveness, then would carbon film fit in as well? Paralleling them would further reduce the overall inductance.


Quote:

I would strongly suggest to go for four separate lower power transformers. That way you can operate them in the "low flux" connection (1/2 rated primary voltage), plus I'd suggest adding the DC killer circuit. Using fully separate supplies per channel comes highly recommended too. Using the right mechanical arrangement for the transformers can in addition minimise any leakage from the mains into the actual circuit, by the expedient of in effect "bucking out" the leakage components.
Four transformers would much costly than one large transformer. I have the schematic of your inverted Gainclone, the verison with 4 transformers for one channel.

Could I compromise by having all four set windings (4 x primary:230V + secondary:24V) into a transformer or I have to keep them as four individual transformers?



Quote:

The type of snubber Mike suggests as well as the even more extensive ones by John Camille need to be accuratly calculated for the given mains transformer - they are NOT universal. Getting them wrong is worse than not having them.

The simple CRC PI Filter recommended above is nowhere near as effective, yet it is much less critical and close to "universal". You could try using a large value capacitor on the "rectifier" side of this CRC circuit, have a listen.

Sayonara

I have inplemented the CRC PI filter. With the 10watt 0.22ohm white coffin + 10nF 1.6kV FKP1. The effect is positive, thus music becomes more relaxing, less harsh and more enjoyable.

It is possible to go for CRCRC, 10 watt, 0.1 ohm +10nF?


Thank You
Yeo
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Old 8th June 2003, 11:03 AM   #35
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by overmind

I bought some 1 ohm carbon film resistors, 1 watt rating, together with the white coffin resistors. I intend to parallel 5 pieces of the 1 ohm resistors to achieve 0.2ohm.

If the purpose of using Film Power resistor is for it's non inductiveness, then would carbon film fit in as well? Paralleling them would further reduce the overall inductance.
The purpose is actually for non-magnetic resistors. The "Powerfilm" types I have tried where all non-magnetic.

Quote:
Originally posted by overmind

Four transformers would much costly than one large transformer.
True, but not that much. If you start to go looking for Surplus Transformers you might find something easily.

Quote:
Originally posted by overmind

I have the schematic of your inverted Gainclone, the verison with 4 transformers for one channel.
Two transformers for one channel, actually.

Quote:
Originally posted by overmind

Could I compromise by having all four set windings (4 x primary:230V + secondary:24V) into a transformer or I have to keep them as four individual transformers?
The fundamental idea of having the windings in series is to halve the peak flux in the Transformer core. This helps making the transformer quieter and allows in the better power transfer despite the doubled DCR.

If you have Transformers custom wound you can have them made with more primary turns (at least 30% more)to reduce the flux and have a small airgap designed into the transformer, this would achieve pretty much the same.

If you get something custom made it's also worth asking for fully symmetrical primary and secondary windings (which suggests a C-Core or R-Core type transformer) and electrostatic screens.

Quote:
Originally posted by overmind

I have inplemented the CRC PI filter. With the 10watt 0.22ohm white coffin + 10nF 1.6kV FKP1. The effect is positive, thus music becomes more relaxing, less harsh and more enjoyable.

It is possible to go for CRCRC, 10 watt, 0.1 ohm +10nF?
Sure. You can do that, or you could place a second CRC after the rectifier. Also, by all means experiemnt with the value of the second capacitor in each CRC Filter (looking from the transforer to the output).

Sayonara
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Old 8th June 2003, 11:30 AM   #36
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Hi Quei

I am sure you have explained this before but wouldn't just two transformers (not centre-tapped), primaries and secondaries wired in series not achieve the low core flux? What is the advantage of having 4 separate windings? Reduction of external flux? Do you have to observe particular relative positioning of the transformers? Would that work with EI cores? Just interesting if you have actually listened to these effects and would care to share.
And last question. Is it possible to use split bobins (on EI)? Would the reduction in capacitance between primary and secondary be beneficial?


thanks

peter
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Old 8th June 2003, 11:54 AM   #37
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by analog_sa

I am sure you have explained this before but wouldn't just two transformers (not centre-tapped), primaries and secondaries wired in series not achieve the low core flux?
Sure.

Quote:
Originally posted by analog_sa

What is the advantage of having 4 separate windings?
The ability to use standard off the shelf Mains transformers? All the better Torrids I know come from the factury with 115V+115V primaries and xxV+xxV secondaries. That is just how they are being made.

Quote:
Originally posted by analog_sa

Do you have to observe particular relative positioning of the transformers?
If you wish to use two seperate transformers with opposite phase connections of the primaries to cancel the "leakage" into chassis and secondaries (as I suggest), you must ensure the transformers are arranged as symmetrical as possible.

I also suggest using non-metallic fixings if you use metallic chassis. You can simply place the transformer o a suitably thick piece of rubber, place a large nylon screw (or several for heavy transformers) well but thinly covered with that special seperation grease and then poor a suitable acrylic resin or the like (fairly thick consistency) into the transformer center. The result - a transformer center solidly gooped together with screw theread(s) for your nylon screw(s).

Quote:
Originally posted by analog_sa

Would that work with EI cores?
Sure. Both low flux and killing DC works for EI transformers. Cancelling the electrostatic leakage is much more difficult though.

Quote:
Originally posted by analog_sa

And last question. Is it possible to use split bobins (on EI)?

Of course.

Quote:
Originally posted by analog_sa

Would the reduction in capacitance between primary and secondary be beneficial?
Maybe. This will depend upon a few other issues as well, with EI Transformers often the leakage to the core (which has to be then grounded) causes the larger share of the problem.

Sayonara
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Old 8th June 2003, 12:26 PM   #38
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Kuei

Many thanks for your reply. I am about to order a few transformers with a local winder. Decided against toroids based on negative past experience with the sound. Otoh, i didn't use any form of dc cancellation.

cheers
peter
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