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 mine

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

[IMGDEAD]http://www.ohmslaw.co.uk/pre-power.jpg[/IMGDEAD]
[IMGDEAD]http://www.ohmslaw.co.uk/overview.jpg[/IMGDEAD]
[IMGDEAD]http://www.ohmslaw.co.uk/ps.jpg[/IMGDEAD]
[IMGDEAD]http://www.ohmslaw.co.uk/amp.jpg[/IMGDEAD]

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).

 

[Eccu]

oops! weird smiley

 

[rikkitikkitavi]

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.

/rickard

 

[rickpt]

I also built an elektor amplifier that has a dc servo. I changed the original lf411 for an opa604 and it gave very good sonic results.

I hope this help’s

Regards

Ricardo

 

[Eccu]

thanks for everyone... I think that I try first OP07... because I´m stingy...
maybe I upgrade some day it to OP77EP or something, when my audition take some practice...



Happy listening for everyone

 

[swede]

So, where did you guys find the output transistors?

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

Regards,
//magnus

 

[rikkitikkitavi]

the output transistors for the millenium cresendo are sold by ELFA:

check out page 796-797 in the new catalouge under "ersättningshalvledare" but they are quite expensive.

www.elfa.se

/rickard

 

[Eccu]

So, where did you guys find the output transistors?

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

Regards,
//magnus

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

But I think that in Elfa has too these Fet´s.
2SJ201
2SK537 (equiv. 2SK2733)
2SK1530




I hope you understand my Enlgish

 

[UrSv]

Swede,

I have 50 closely matched pairs of the 2SJ201/2SK1530 set. How many do you need?

/UrSv (Sweden)

 

[Eccu]

Swede,

I have 50 closely matched pairs of the 2SJ201/2SK1530 set. How many do you need?

/UrSv (Sweden)

Hey UrSv. How do you perform Fet matching?
Can you explain something or is there some www page?

 

[Eccu]

my amp. Rendered in Blender.