Crescendo Millenium amplifier (ELEKTOR magazine ¹4 2001 p.36-45)?

And I have questions about operating voltage of Cresendo ME.
In schematic recommend 45-50 VDC (about 35 VAC) so can I use lower or higher voltages?
I can get transformers with 30 VAC (about 42VDC) or 38 VAC (about 53 VDC).
Which one is better? And do I have make some modifications in schema if I use lower or higher voltages?



2002-01-31 5:48 pm
The 2*38 VAC secondary will give you about 2-4 volts lower than 53 VDC after losses in the rectifier and elsewhere so I would go with the higher voltage. I haven't read the new Elektor Crescendo article (I still have the originals from the 80's though...) and I don't know what the class or bias is but remember that the 38 VAC is UNDER LOAD and that if bias is low the voltage may be a few to maybe even 10 % higher. General rule according to me is to use the highest capacity transformer you can find/afford since the power supply will be tougher and the difference between no load and load voltages decrease with higher capacity (all that internal resistance of secondary windings I think).

I have other question now about Crescendo ME.
Can I replace OP77GP with OP07CP, OP27GP or OP37GP. This OP77GP are used in a sort of Offset compensation.
Because I can´t get this OP77GP.

OP77GP Input Offset Voltage -values typical 50yV(micro V) and Max 100yV.
OP07CP Input Offset Voltage -values typical 60yV and Max 150yV.
OP27GP and OP37GP Input Offset Voltage -values typical 30yV and Max 100yV.

Sorry my very bad English...
Here is mine

Here is my elector amp, oh and the 4 channel pre-amp i made:


it has 4*22,000uF rifa's
500W transformer

sure:cool: the LF411 was used very often by Elektor for dc-servo´s. A few power amps used them and I still use it in the phono section of my preamp. I changed it for a OP77 in my power amp when I rebuild this.
I think it´s not so important if the power amp has 0,1 or 2mv (or even 20mV) offset as long as it´s below say 50-100mV. The difference in input offset voltage between the op77 and the LF411 will only cause the amp to have 1 or 2 mV more offset.

thanks wuffwaff... :eek:)

but can I still use OP07 or OP27... ?
OP77 datasheet shows that it is Next generation OP07... so I think that OP07 is better combatible with OP77GP than LF411...

So which one is best choice, because I can get these:
OP07CP costs about 1,6 € (Euros),
OP27GP costs about 3,8 € (Euros) and
LF411CN costs about 1,9 € (Euros).
OP 77, OP177 and OP277 (and OP-97) are all upgrades of the standard OP-07, so they can all replace OP-07 in a DC-servo, basically any pin compatible modern op with low-offset , low bias can replace OP-07 in this circuit. (the higher number ,the better op)

OP-27 have much higher bandwidth and slew rate than the OP-07, but used in a DC-servo, this shouldnt matter since the servo loop is bandwidthlimited to about 1 Hertz or so. It could probably be used in a DC-servo circuit.

OP-37 is NOT unity gain stable (min gain 5 ) so I dont think it can be used in a DC-servo circuit.

swede said:
So, where did you guys find the output transistors?

Here in Sweden, they are kind of hard to find. Any european supplier will do.


In Finland / Oulu (Uleåborg)... there is an electronics shop named spelektroniikka ( only in finnish)...

But I think that in Elfa has too these Fet´s.
2SK537 (equiv. 2SK2733)

I hope you understand my Enlgish :)
my amp. Rendered in Blender.


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