Elektor's "Ulti Amp"

[Piersma]

The required additional low power supply for the main board.

[Piersma]

Replacing the VAS transistors MJE15031 (T12) and MJE15030 (T13) with transistors 2SA1209 and 2SC2911.

To remain stability with Sanyo 2SA/SC transistors place a 47pF styroflex cap from base to collector for both semiconductors and replace the feedback 220pF cap Cfb for a 100pF styroflex or silvered mica cap.

Lower the idling VAS current to 12mA, by replacing the emitters resistors (R31…) . New resistor value 33 Ohms.

Lower the idling current in the second differential stage to 10mA, this comes down to 5mA per transistor leg.

Replace R51, 100E resistor by a 10E resistor and remove the short to power-ground.

[Piersma]

for your information the 2SA1209/2SC2922 datasheet.

[Piersma]

Original matched dual transistors in this Elektor can be obtained (online) in Germany. Supplier is DSI who still offering the BFX36 and 2N914.

GES GmbH - www.Electronicpool.de - abgekündigte und schwer beschaffbare elektronische Bauteile

regards,
Piersma

[arothfr]

Hello "Piersma"
You seems to be the ULTI- specialist! Especially when I see how long you ingaged in this topic. I plan to start with this project in autumn this year. Before starting I would like to have solved all changes and improvements in the circuit and the bom.
At the moment I am just preparing a real pre-amp ( no caps in the signal line) with
proven design. If you are interested I would like to send you a pdf.-file for information. The only problem is, the paper`s language is german. I would be very pleased, if I could get any informations about your ULTI build phase. arothfr

[Piersma]

Arothfr, please sent a private message for more information.

[arothfr]

Hi Piersma,
thank you very much for your quick reaction. Yes, I plan to build the ULTI-Amp!
When I read the ELECTOR pages, I decided for many years, this should be the right one. For the professional out looking, it shouuld fit into a YAMAHA- case of the M50 amp. My first steps will be to check are all part I need available, next must be what kind of issues are known. Here I would like to contact you; what experience did you
make, What are your next projects ? Regards : arothfr

[Piersma]

Till this current day i still use the Ulti Amp as one of my preferred audio amplifiers. Ten years ago I a got a lot of emails from German builders who ran into trouble with this Elektor Amplifier, due to issues not mentioned (experienced) by Elektor. You should read this threat very carefully if you plan to build this "beast". You probably will run into problems sourcing the original parts by Elektor. Cross reference parts are still available.

Latest amplifier builds were Elvee's Circlophone and Roender's RFC-100.

[Piersma]

For your information.

[arothfr]

Hello Piersma,

here some interesting information for your next project " the ULTI pre-amp".
Name and quality of sound fits together; this one is real professional!
Have a look at the circuit ( Done with LT1028AP, OPA 637BP,OPA 627BP ), open this link............, Regards arothfrhttp://www.huennebeck-online.de/dy/pre-1/pre-1.pdf