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Old 24th April 2003, 10:14 PM   #1
Zldz is offline Zldz  Italy
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Default New gainclone schematic

From the Amp Chip DIY Forum:
http://home.attbi.com/~greggbaker/Inv_chip_amp.gif
This should be an evolution of Thorsten's inverted GC schematic.
I understand all the changes in the amp , but....the power supply is a little strange.
Any ideas?
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Old 24th April 2003, 10:34 PM   #2
mlloyd1 is offline mlloyd1  United States
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what's strange in the power supply- the series caps and paralleled rects? They are there to block DC and keep the transformers quiet.

mlloyd1
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Old 24th April 2003, 10:58 PM   #3
Zldz is offline Zldz  Italy
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Ok, but the question would be: is the improvement real? To justify the use FOUR transformers instead of two?
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Old 26th April 2003, 03:22 PM   #4
Previously: Kuei Yang Wang
 
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Koinichiwa,

Quote:
Originally posted by Zldz
Ok, but the question would be: is the improvement real? To justify the use FOUR transformers instead of two?
Well, I don't know if you did follow the "What makes a good audio power transformer?" Thread:

What makes a good audio power transformer?

In there I give the rationale for the dual transformer approach, the DC blocking and so on.

Something I have not drawn in is a high current, low resistance common mode choke with the associated X & Y Capacitors, such filters are controversial. It tend to use them more often than not though.

I would say that if you could get a suitable custom made unit with twice the primary turns, a small airgao to handle DC on the mains and fully symmetrical primary and secondary windings, with multiple electrostatic screens and with enough secondaries to power 2 Channels (that would mean 4pcs 30...48CT secondaries) you would have something as good or better than the approach using 4pcs of transformers.

It would likely have a long delivery time and be hideously expensive. Using multiple transformers, DC Blockers, field cancelling arrangements of windings et al will give you however 99% of the performance, if you buy surplus transformers it will be dead cheap too.

In cases where I have used powersupplies DC blocked, "low flux" connection and with leakage cancellation the results have been extremely pleasing.

Sayonara
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Old 27th April 2003, 06:25 PM   #5
Zldz is offline Zldz  Italy
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Many thanks for the explainations. I think I'll try if I'll found cheap xformers. Surplus, what a sweet sounding word.... we in Italy have no Apex Jr... unfortunately here there is no REAL surplus market....

Ciao
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Old 27th April 2003, 07:50 PM   #6
goskers is offline goskers  United States
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Default Is this correct then?

If I am understanding this correctly then, if you use the PS configuration on the latest schematics then you can use cheap trannies (EI) type?
If this is true then significant savings can be made over toroidal type.

Thanks
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Old 27th April 2003, 08:32 PM   #7
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Default Re: Is this correct then?

Koinichiwa,

Quote:
Originally posted by goskers
If I am understanding this correctly then, if you use the PS configuration on the latest schematics then you can use cheap trannies (EI) type?
Funnily enough, in Europe decent EI Types are the more expensive ones!

But yes, the PSU as shown makes the whole shooting match less less suceptible to transformer quality. We'd still like reasonably high power ratings....

Sayonara
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Old 27th April 2003, 08:50 PM   #8
Nielsio is offline Nielsio  Netherlands
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Kuei,

Any thoughts on Joe Rasmussen's newly posted material?
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Old 27th April 2003, 09:37 PM   #9
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Koinichiwa,

Quote:
Originally posted by Nielsio

Any thoughts on Joe Rasmussen's newly posted material?
Well, for one.

If Joe moved his point "G" to where the two PSU Capacitors join (as I always recommended) the sensitivity of his circuit to the wire between G and the join of two PSU Capacitors.... ;-)

If he used two bridges with good quality rectifiers and kept the rectifier returns separated I suspect the sound would clean up no end.

As for the bandwidth limiting, sure. It may help, much will depend upon the system. If the grounding is optimal, the recent revised schematic is employed in a suitably shielded enclosure and the bandwidth of the source is sufficiently narrow (like nothing wider bandwidth than SACD or DVD-A) I doubt it is neccesary.

Alternatively a pair of capacitors can be connected, one of 22pF Silver Mica between output and negative chip input and one of 220pF Silver Mica between negative chip input and ground. This should keep things stable, puts the -3db rolloff point where Joe likes it and makes the rollof absolutely stable without buffer.

I personally would probably put the rolloff much higher, I'd use 4.7pF/47pF I guess, but thats a matter of taste. Buffering? Not strictly needed, but if you like to, sure. I prefer the conceptual simplicity of not adding things that can be done without.

But in the end it's like cooking. No two chefs cook the same dish the same way. And no two of those eating these dishes will have exactly the same reaction to these.

I still prefer my ridiculously expensive (DIY) 300B SE Amplifers to anything else I came across (including gainclones - if not build by myself). Others may differ.

Sayonara
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