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

[alex0]

What judgement on the amplifier, the scheme which one was published in the " ELEKTOR ELECTRONICS" ¹4 2001 p36-45?

[Eccu]

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?

Thanks!

[Helix]

use the 53 v ones, the amp has SOAR protection

[UrSv]

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).

/UrSv

[Eccu]

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...

[wuffwaff]

you can use an LF411CN instead of the OP77

william

[Helix]

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






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

[Eccu]

are you sure wuffwaff (william) ?
LF411CN have Input Offset Voltage about typical 0,8 mV and Max 2,0 mV when OP77GP have Input Offset Voltage -values typical 50uV(micro V) and Max 100uV?

Nice amp, Helix.

[wuffwaff]

eccu,

sure 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.

william

[Eccu]

thanks wuffwaff... )

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).