LSK pre - BAF 2013

[Samuel Jayaraj]

Haven't powered it up yet because I am not too sure of the 200 ohm trimpot settings (minimum or maximum value) at start up. Juma said it sounds 'velvety'!!

 

[e_fortier]

If I were you I would set it up 1/2 way at 100ohm and install a light bulb in series with mains power.

 

[stoN_Cold]

Haven't powered it up yet because I am not too sure of the 200 ohm trimpot settings (minimum or maximum value) at start up.

Look schematic, 200Ω/ 40%.

 

[Samuel Jayaraj]

Thanks zeonrider, I saw 40% on schematic already. But just wanted to slowly ramp up bias, just in case..... Since Juma might be busy and has not chimed in here, I will set the trimpots to about 50% and then see which way to turn. Juma said 1.2A in post #118. Thanks again.

 

[e_fortier]

Make sure to let us know how it sounds ;-)

 

[Samuel Jayaraj]

Sure - tomorrow. Thanks everyone for the tips and help.

 

[juma]

Juma, I have assembled the board for the amp shown below. Would like to know whether 200R trimpots are to be set at minimum for setting bias of 0.7Amps?

Boards for the attached preamp is also ready but not yet assembled. Thanks.

Yes, pots to minimum resistance before turning the amp on.
I'll be slow in answering in next week or two - moving to another country...

 

[Samuel Jayaraj]

Thanks a million Juma. You're contributions here have been second to none; you have come up with so many innovative and great sounding designs. Hope you settle down quickly in your new country and continue to contribute and support in the way that you have thus far. Thank you again on behalf of the DIYaudio community.

 

[dobrivoje]

Thanks a million Juma. You're contributions here have been second to none; you have come up with so many innovative and great sounding designs. Hope you settle down quickly in your new country and continue to contribute and support in the way that you have thus far. Thank you again on behalf of the DIYaudio community.

+1

 

[WalterW]

+2

 

[didiet78]

+3

Didiet

 

[Soundhappy]

Thanks a million Juma. You're contributions here have been second to none; you have come up with so many innovative and great sounding designs. Hope you settle down quickly in your new country and continue to contribute and support in the way that you have thus far. Thank you again on behalf of the DIYaudio community.

+4
Thanks Juma
Best regards
Christophe

 

[juma]

Thanks guys - I hope I'll have more time for the forum in about week or two...

 

[pidesd]

juma,

i am curious to know what is the reason to choose a resistor value of 220 for r7 ( on the schematic post number 1).

wouldnt a higher value give less distortion? is it aquestion of dc offset?

regards,

-py

 

[Samuel Jayaraj]

Well, I have assembled a single channel of Juma's Amp at post @118, schematic of which is attached herein.

It is fabulous. I will reserve my further comments until I complete the other channel and get it all tidy in an enclosure.

In the meantime, I have a question since I can hear audible noise/hiss through my 94db Fostex speakers even with PSU caps totalling 22,500uF per rail (CRC) and front end supplied through diode and filtered with 3300uF per rail.

I want to use a capacitance multiplier capable of atleast 2 Amps current and low noise (100uV or lesser) for the output section.

I am also attaching a schematic of a PSU to multiply and regulate supply for the front end.

My question is, what should be the value of R21, 22 to make it suitable for the front end of Juma's Amp?

 

[dobrivoje]

Sam,

I think that Juma is still busy, so you can try this PSU.
It's also Juma's design.

 

[Samuel Jayaraj]

Thanks dobrivoje, that is also a capacitance multiplier but it needs about 4-6 volts headroom. I am thinking of using a BJT series pass which needs 2.5 volts of headroom for the output stage.

My question is regarding the cap multiplier-regulated supply for the front-end, tapped off the same main transformer. I measured Juma amp front-end and IIRC it draws a little over 120mA!

 

[Samuel Jayaraj]

Well, I have assembled a single channel of Juma's Amp at post @118, schematic of which is attached herein.

I am also attaching a schematic of a PSU to multiply and regulate supply for the front end.

My question is, what should be the value of R21, 22 to make it suitable for the front end of Juma's Amp?

Any help? Thanks.

 

[jarkaa]

Any help? Thanks.

Hi,

Those resistor are not necessary. The circuit will work well without those.

I am using the same circuit with 10ohm resistors and it works great.

J

 

[prakit]

My take on the LSK-Juma Linestage.
K170GR/J74GR-input at 5mA, BJT C3421/A1358-Cascode at 20mA.
The sound is addicting.
Kudos is due to NP and Juma!