Built my first amp ! (Randy Slone Design 4) But it is humming...

[jpnascim]

Last one, back panel. Very simple, to quickly get some music playing

 

[destroyer X]

Nice job Nascim.......by the way...tell me using E mail

What really happened with your Legacy that crashed 747-800 over Amazon jungle....or was crashed by...maybe.

Hummmm..... there's something strange.... is the Legacy made with Carbon fiber?

Go direct to my mail please.

Nice Gradiente Model 1450 Knob João Pedro...hehe

nanabrother@yahoo.com

regards,

Carlos

 

[drowranger]

Well, after some time I’ve managed to construct my first audio amplifier! It is an amplifier from Randy G. Slone. For those familiar with the book it is the design 4 contained in the book High Power Audio Amplifier Construction Manual. I saw many threads here in this forum regarding the OPTIMOS which is the flagship of Randy Slone’s designs but I haven’t seen many about this design I built. So I thought it would be nice to share my experience.
Here are the characteristics:

- BJT differential input (2N5551 and 2N5401)
- Darlignton VAS
- BJT OPS output
- It has OPS output protection (V-I Limiter)
- 300 VA E-I transformer (couldn’t get a hand on a toroidal)
- 2 x 10.000 uF capacitors in the PSU
- Volume adjustment and no tone controls
- Rated at 100 W rms (8 ohm).

I’ve made some parts modifications:

- Output transistors are MJL1302/MJL3281 from On instead of the Toshibas which are hard to find

- VAS and some other transistors are the KSA1220 and KSA 2690 form Fairchild instead of the 2SB649/2SD669 from Hitachi which are rare and not manufactured anymore as far as I know.

Unfortunately I don’t have a digital cam to send some pictures but I’ll try…


I haven’t had the opportunity to listen to many high end amplifiers in my life but I can say that this amplifier is excellent! The sound is pure, not exaggerated, precise and very pleasant to listen to (even though my pair of speakers is not Hi-Fi)

I feel great ! I thought I wouldn’t manage to do it since I am a newbie. It worked right at the first time (lucky me !) but I still have one minor problem that I ask you guys to help me: it is humming. From what I’ve read the problem has to do with improper grounding.

Well, attached is the wiring diagram of my amp. I hope it is clear for everyone. One problem that I’ve identified after reading a lot of star grounding posts here is that the signal input ground (shield of the cable) is connected to the rail decoupling and feedback ground in the PCB board (left and right pwr ground – see figure). So I guess I am mixing dirty and clean grounds. Besides that, anything wrong ??

Thank you,

João Pedro

just in case you still have problem in humming.try isolate the input connectors from the chassis.usually commercial amps have plastic isolators wrap around the female rca connectors to prevent it from touching the chassis.connect the ground terminal to high quality ground or star grounding.