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ouimetnick 13th February 2013 02:54 AM

What Did I Break Now?
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So if you guys remember a thread that I made recently called Breaking a Hafler DH-101 into Sections? Well I did some stuff based off what I learned.

So tonight I did something. Didn't work. Let me explain. My amp is a DH-220. I use a powered subwoofer with my unit. So I clipped the following wires from the rca jack connectors (both left and right)


I connected the TUNER jacks straight to eyelets 4L and 4R. I was told (and schematic shows it) that these are line level jacks. So I can bypass the crappy source selector switches and go strain into the line level input. Now how would I connect a subwoofer with out an adapter? Well I took another wire and connected the TUNER jacks to the FROM jacks. So FROM and TUNER are connected in parallel. So I could connect the output of my iPod to the input of the preamp and the sub plate amp.

Thats ALL I did. I didn't disconnect any other wires. I noticed there are resistors R30 and R31 that lower the source line level to the tape outputs (sub used to be connected there and it worked) but I could plug my iPod into the sub directly and use the sub's volume control with out an issue, so I figured those resistors aren't needed.

Were R32, R33, and R34 suppose to be the reason it doesn't work? I connected this all up just a few minutes ago and got a LOUD noise (static, not hum) through the amp. LOUD as in full volume loud. I disconnected the sub incase it could be a grounding issue, and no dice.

I have pictures to show how I did this.

I still want the tone control switch in the circuit so I can switch them on and off.

I didn't disconnect anything else besides mentioned above, but cut the path shorter.

I did this because even cleaning the switches with deoxit only gets them good for 6 or so months. So I said screw that, I'll bypass them.

I can always buy a RadioShack source selector if needed.

Any ideas. Kinda annoyed at my self. Only preamp I have. :D

The video:

picowallspeaker 13th February 2013 04:01 AM

probably it was a faulty ground connection. Any magic smoke from the amp ?

ouimetnick 13th February 2013 04:02 AM

Didn't see anything. Amp still works fine.

picowallspeaker 13th February 2013 04:16 AM

It happened to me once ( or twice ?). When doing all the mess I do, the ground was the last thing I didn't check, and Murphy ('s law) punished me!
I'm wondering which kind of de-oxi are you using : if it is oily, that's no good.

ouimetnick 13th February 2013 11:14 AM

Deoxit D5
The red stuff

ouimetnick 14th February 2013 03:11 AM

Well I removed all the switch wiring and wired what I needed. The tone controls and obviously IN and OUT jacks.

Fixed the problem.. sorta.

Hafler DH-101 HUMM - YouTube

Its humming along nicely.. :( I know it wants to try to sing, and it can, but also hums too.

Wires are neat, and the hum is in both channels. The power supply has been recapped and the rectifier diodes replaced with UF4007 diodes a while back.

Is it a coincidence and maybe a regulator is acting up? Not sure why it is doing what it is doing, but it is.

Also, why are there 8 wires from the tone switch and what does that do? When those 8 wires aren't connected, the tone circuit is on by default, but when wired, and the switch is depressed, the tone controls are off. So I think it is a normally closed switch?

But why 8 wires? I can understand 4 wires Bass L&R and Tone L&R, but whats 8 of them for?

The tone button connects to eyelets 5L, 5R 6L, 6R, 7L, 7R, 8L, 8R


ouimetnick 15th February 2013 12:37 AM


ouimetnick 15th February 2013 02:13 AM

Well desoldering the 8 wires connecting the tone switch to PC-4 didn't make a difference, hum is still there.

I have the unit grounded with a third prong. The hum decreases, but is still there with out the grounding. The amp isn't grounded.

If it had to do with grounding the chassis, I would have heard this hum before I changed it all. As of now, I only have the power supply hooked up directly to the board. B+, B-, and Ground. And I have the input and output jacks connected as shown before. Those jacks ARE grounded like they are suppose to be. So perhaps I messed up something else, and it isn't a wiring issue? Could someone watch the video? Is it oscillating? The hum increases for a second after power has been cut (as caps drain)

Should I replace the voltage regulators in the power supply after? This hum is in both channels, and it louder when the TONE switch is pressed.

Not change in hum when the TONE switch is out or desoldered, so thats that.

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