Modulus-86 build thread

[hunterst]

Is anyone else here experiencing buzzing from the transformer? I'm using the Hammond 1182N22 and it is making a very annoying buzz whenever the amp is turned on.

[tomchr]

It could be because of DC on the mains. That can happen when the mains voltage is distorted. It would be an even-order harmonic distortion then, but it doesn't sound good.

Solution: Mains DC and Transformers
See fig. 8:


The rectifier bridge could be a KBPC3510 or KBPC2510. The caps don't need to be fancy. They should be able to handle some ripple current, though. At least as much as the expected primary current, but more is better.

Tom

[hunterst]

Thanks Tom, that looks like a quick and easy build. I'll give it a try.

[BrianL]

There are, or at least were, some simple commercial products with essentially this circuit inside. I think Emotiva has/had one. The price was reasonable. It may be an option if you don't want to do the building.

[Halauhula]

Originally Posted by BrianL

There are, or at least were, some simple commercial products with essentially this circuit inside. I think Emotiva has/had one. The price was reasonable. It may be an option if you don't want to do the building.

I believe the Emotiva product is a very different animal: it is to safely break a ground loop while allowing shorts to conduct to safety ground. The ground loop breaker usually consists of a large bridge rectifier or a low value (around 2-10 ohms) large wattage, heat-sinked resistor inserted between signal ground and safety ground.


Tom's suggestion, by contrast, is intended to prevent "effective DC" from entering the amplifier' power supply via the AC line. Effective DC, as I understand it, can result where another load on the isle does not place demands on the hot and neutral lines, or where there is an imbalance of loads on each side of the 220 line (110+110=220). The link that Tom has provided provides a discussion of this problem, but there are other sources available on the web which discuss this issue of DC on AC power lines.

[tomchr]

I've seen both in commercial amps, actually.

Tom

[BrianL]

Look at Emotiva CMX2 - It looks like the DC blocker plus a ground missing/fault detector (similar to one of those plug-in tester gizmos with 3 Neon bulbs that electricians use) plus some noise filtering.