My First Amplfier

[Bama Slamma]

Today, I finished building my first amplifier kit. The kit was from Future Kits. It's a stereo power amplifier kit. Basically it came with two identical modules. I finished building the amps today. I'm still waiting for the power supply components to get here. I bought a 35-0-35V, 300 VA EI type transformer from a local parts supplier. They had to order it from Hammond. I also bought a nice rack-mount chassis to put the finished amp in. I have two 19000 UF caps for the power supply. 19000 UF per rail seems like enough. Also I bought two 10K audio taper pots for volume controls.

Anyway, specs on the amps

type: Full complementary Class AB
power: 100w rms into 8 ohms.
distortion: 0.02% THD
Frequency response: 10 Hz to 100 KHz +-1 Db
rail voltage: +-50 VDC

Hopefully I can send out some photos of the completed amp.

[Gordy]

When undertaking the internal wiring:

1. As you have mains input, E-I transformer and high-ish current rectification in the direct environment consider using a screened cable from the line input socket to the volume control and then to circuit board.

2. As a starting point use reasonable gauge wire in the power supply, such as 14 awg.

3. Position your power supply filter capacitors close to the output transistors. If they are more than a couple of inches away then twist the positive and negative cables together to reduce inductance.


Good luck with your project.

[unclejed613]

at full load that will give you +/- 29.1V with 0.5V ripple and 46.4V with 0.2V ripple with a 200mA load.

[Bama Slamma]

As of now, the mains voltage is 120 volts right on the nose. The transformer's primary voltage is actually 115 volts. How much difference would that make on the output? To go from 115 to 70 volts is almost a 2 to 1 ratio, 4 to 1 on either side of the center tap. Five extra volts on the primary would probably bump the secondary up slightly.

[Piercarlo]

Originally posted by Bama Slamma
As of now, the mains voltage is 120 volts right on the nose. The transformer's primary voltage is actually 115 volts. How much difference would that make on the output? To go from 115 to 70 volts is almost a 2 to 1 ratio, 4 to 1 on either side of the center tap. Five extra volts on the primary would probably bump the secondary up slightly.

Don't worry. Mains tolerance should be accomodate variation of about +/- 20% on the nominal voltage. If your kit is well designed (i.e. equipped with component rated about 1.5 times the actual working voltages) this tolerance is not a concern at all.

Piercarlo

[Bama Slamma]

I got the transformer today and wired up the power supply. The transformer was actually a 30-0-30V transformer. With 120VAC input, it was reading 32-0-32V. The fully assembled supply measures +/-45VDC. I wired up one amp to the supply and powered it up. The amp was so quiet I didn't even think it was working until I touched the input with my finger, causing a buzz to come out of the speaker. I cannibalized a set of cheap headphones for the cord and used a Discman as the source. Upon hitting PLAY, a deafeningly loud, heavily clipped version of Tchaikovsky's 1812 Overture came out of the cheap speaker I was using to test the amp, followed by a puff of magic smoke from the speaker as it gave up the ghost (the speaker, not the amp). I hooked up a better speaker to the amp and reduced the volume on the CD player. Result: Beautiful Music! I hooked up the other amp and fed it with the other channel. Result: Beautiful Music In Stereo! With this success, I'm definitely addicted to building audio products. It looks jerry-rigged now, but I have a very nice chassis on the way to mount the amps in.

[CBS240]

Originally posted by Bama Slamma
... I'm definitely addicted to building audio products. It looks jerry-rigged now, but I have a very nice chassis on the way to mount the amps in.

DIYaudio hooks another victim...

[unclejed613]

COOL!!!! glad to hear that it works............ you've now been bit by the "bug"........... hifi has been about experimentation with technology ever since Edison first scratched "mary had a little lamb" into a wax cylinder.......

[Bama Slamma]

The chassis just arrived in the mail today. I'll mount up everything in it tomorrow. The chassis will mount in a standard 19" equipment rack. I'll have to plan everything out. It's easy to drill a hole but very difficult to fill one back in once a hole has been drilled in the wrong place. I'll post some pics once the amps are in the chassis.

[Bama Slamma]

Well I finally got my pictures ready. Apparently they were over the 104K limit for attachments, so I shrank 'em down. Well without further ado, the pics showing the amp both in the testing and completed stages. This shot is initial testing on the kitchen counter. The red towel is for insulation purposes.