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[Quoting tomb]

Is there a difference between an xfmr with two secondaries and a CT xfmr wired for two separate secondaries?

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I hope the illustrations make it all clear.

For the CKIII, you must use a dual secondary transformer or two separate single-secondary transformers because of the double bridge rectifiers. The two secondaries must be completely independent.

[Edited by amb on 11-04-2006 at 07:45 AM.]

I am building walwarts with two completely separate leads and plugs to use on the SOHA, and it's good to know I can use them on this, too.

For general information, a complete BOM is available listing all components from Mouser. It uses 'plain' components nothing boutique which is obviously personal preference..dB

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[Quoting dBel84]

@ Tomb : Just to be clear, the SOHA uses a centre tapped secondary which is not the same as the CKIII - if you have dual secondaries and use the "wallwart" with 5 pin din out, 2 sets of "hot" and 1 ground - this would work.

For general information, a complete BOM is available listing all components from Mouser. It uses 'plain' components nothing boutique which is obviously personal preference..dB

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OK - I believe we are talking the same thing. Ala Batman, I am enclosing an Amveco toroid in a Jameco walwart enclosure, terminating in two separate sets of wire leads with 2.1mm plugs. The cold legs are not combined until they are wired from the panel sockets to the ground pads on the board.

I gave up on the DIN idea in favor of this - cheaper, with more compatibility. (As evidenced by this discussion, I think.)

One detail you mention seems important, though - I must not tie the house wall ground to the "cold" legs inside the walwart enclosure and still use it for the Cavalli-Kumisa - or can I?

[Edited by tomb on 11-04-2006 at 10:50 AM.]

And, as Tomb noted, the dual secondary toroids are probably the ideal transformer for this amp. You get both secondaries from one package and low radiation and noise.

If you use a toroid with a dual primary, then the schematic as drawn may not show the correct wiring of the primaries for different line (mains) voltages.

[Edited by runeight on 11-04-2006 at 12:38 PM.]

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[Quoting runeight]

dBel84 has suggested that I mod the PS schematic to reflect the line (mains) filtering that Benny originally used and that dBel used in his Kumisa. So, here it is. :)

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In fact, the CKIII should make a very good no-feedback linestage. Although, it could be simplified some for this purpose. The big output transistors could be eliminated from the design because you really don't need tens of mA for a linestage. And the variable bias can easily be replaced with a fixed bias adequate for a preamp.

However, the CKIII is a totally DC coupled amplifier. If you have a big SS power amp that will track to DC, you'll have to be very careful with turn on transients and with the possibility of DC appearing at the input of the CKIII because this will show up directly at the speaker terminals.

If anyone wants to pursue this idea, let me know. If not, we'll just let it pass for now.

hows the turn on thump on this version?
also i like the point of servo feedback.

any reason for 7815/7912's instead of 317/337's

allan

Turn-on transient is a potential problem for any preamp without output delay muting. The solution is either to add such a muting circuit, or to exercise proper turn on/off sequence (i.e., turn on preamp before the power amp, and turn off power amp befoer the preamp).

I think you need heatsinks on the output transistors. You may be able to get by without them but they are going to be red hot. The transistors I am using are smaller than TO-220 and I don't think would be able to dissipate the head on their own.

I also noticed the servo has changed slightly. Did you find any problems with how it was before (how it was with my prototype)?

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[Quoting Dave_M]

I think you need heatsinks on the output transistors. You may be able to get by without them but they are going to be red hot.

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Something that I had not mentioned before is that this amp needs a decent warm up time to sound its best. This warm up also applies to setting the bias. It is the first amp that I have listened to where this change in sound signature is that apparent..dB

dBel84, no turn on/off thump is good news.
Which one was the "penultimate configuration", feedback to input?

"20V rails just to prove it was stable . The servo will compensate for any difference between the regulator outputs which will rarely be equal"
I used 317's reg'd to adjust for +/-18v
Ended put servo feedback where Runeight has it now, but so many changes needed to make new pcb's and when thead highjacked, i lost interest.
will start again shortly, when time permits.
did have another thought on a version though, fets?

Dave_M, "I think you need heatsinks on the output transistors"
You could use the case for a heatsink.
eg, use a aluminium base and mount the trannies to it. (with silpads of cause)

allan

@ Steinchen .... in the interest of the greater community I upped the bias to 50mA real toasty now and I can merely feel the side of the chassis to decide whether it is powered up or not. No obvious initial changes but this is a delicate area of reviewing and assessing small changes in sonic character. This I will leave to others , in the meantime I will keep it running the higher bias and just enjoy the music. If anything becomes apparent, I will be sure to let you know..dB ( I had done this initally but not for an extended period ? who knows....)

[Edited by runeight on 11-07-2006 at 11:07 AM.]

@runeight
as for the servo, why did you go as low as 100k with the feedback resistor ? Do you think I'll run into trouble if I changed the 10uF electrolytics to 4.7uF polyester box caps and increased the 100k resistor to 200k ?

@amb
may you add some alternative pads for a more flexible part selection ? I'd like to suggest 5 / 7.5 / 10 mm leadspacing pads for C7 and C16, additional 5mm pads for C20 and C21 and maybe additional 5mm pads for TO-220 rectifier diodes.