Salas hotrodded blue DCB1 build

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AndrewT

R.I.P.
Joined 2004
johnwmclean said:
Andrew for typical 50VA single secondary 15V winding ~1.6A, does one typically half that value to calculate continuous DC output current for ~830mAdc?
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The way I have interpreted the manufacturers' datasheet on de-rating for a capacitor input filter, that is what I find.
That continuous DC current from a capacitor input filter ~= 50% of the AC current rating. This allows approximately 70% of the Power that the transformer is rated at and matches well with that de-rating factor I mentioned seeing in almost every transformer manufacturers' data.

A few Members disagree with my interpretation.
But if that de-rating factor is ignored and one tries to draw the full power rating on the DC side, then what effect does I^2R have on the heating of the transformer when feeding high current pulses into the windings? Short higher current pulses that have exactly the same energy as a sinusoidal waveform heat the winding more. That extra heat has to be accounted for. In my opinion that's why the Manufacturers apply the de-rating factor when the transformer is not supplying sinusoidal waveform currents.
 
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syklab

Member
Joined 2009
Hi,
I am try to gether components berfore the board arrive and noted the Vishay Z-foil resistor 220R is very hard to find and none in HK. Can anyone recommend a place to buy this from? Tried Michael Percy but close until October. Also found this Vishay Military Wirewound Resistor 24.3 Ohms 10W 1%, is that good for setting the CCS?

Thanks

Vishay Military Wirewound Resistor 24.3 Ohms 10W 1% | eBay
 
qusp

qusp

Member
Joined 2009
johnwmclean said:
Not a fan? Well the Buff32 may be better straight into the F5X, but I’m going to give this a crack and see what becomes... :)
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Hey John, nah its not that, love your work as always and the flames are a gas :rofl:, I assume this was tongue in cheek (and i certainly hope so now ive stuck my foot in it) i'm just not sure I see this as really being balanced, as its just 2 single ended circuits referenced to ground and fed a differential signal. i need to fire mine up (pretty much identical to yours and finally got the iron now, so just need the time for casework)

I will admit i'm a little uncertain of the need for it in your system (or mine thus my snails pace building schedule), but understand the compulsion to build build build and why not when you can produce such nice looking kit.

how are you finding the volumite, i'm interested to hear your thoughts on that after I really pushed it as an option for you. perhaps via email though.
 
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johnwmclean

Member
Joined 2009
Thanks Jeremy, that makes total sense.

I've been listening through the Beta22 with ears to the grill it's almost impossible to detect the dcb1 in the circuit (all very short cables), which is testament to it's fine transparency. At the moment I'm preferring the DCB1 in circuit, there seems to be an increase in energy, transients seem more relaxed. It's minor, I need more listening time, longer cable runs may pronounce a definite improvement I don't know yet. I'm eager for you to complete yours now, for your impression.
 
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cersepn

Member
Joined 2010
Thank you, Andrew.

From the amp manual,
"The A 21 is direct-coupled from its input jacks to its speaker terminals. This advanced circuitry never needs adjustment or maintenance. It operates outside the audio signal path to keep the DC offset at the output of the A 21 at a constant 0.00 Vdc."

and
"Each channel of the A 21 has a high-quality protection relay with gold-plated contacts for long-term reliability. These relays function to protect either the amplifier, the speakers, or both. When the A 21 is first powered on, these relays remain open for three seconds as the positive and negative power supplies stabilize and reach equilibrium ...

Specialized current-sensing transistors are connected to the output stages of the A 21 to constantly monitor the current flow through the output transistors. If the current drawn by this stage exceeds a predetermined safe level due to a load impedance below 1 ohm or a short circuit at the speaker terminals, the output relay will open immediately to prevent any of the output transistors or other parts from failing.

Each channel of the amplifier has a separate fuse for its positive and negative DC voltage rails. These fuses provide backup protection in case the over-current protection does not work in time, or if an internal part
fails. In the event of a part failure, these fuses halt operation to minimize damage to additional parts."

Not sure if it's only marketing fluff... with what the manual said, is it still advisable to use the DCB1 capless with the amp?
 
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