Hafler DH-500 Question

[shinkamp]

Hello Knowledgeable Audioholics,

Due to a strange circumstance I came to look at my Hafler DH-500 amplifier today. I noticed that the front plate on the amplifier does not have an on/off switch. Almost all images of the DH-500 on the internet have an on/off switch with a red light on the front plate. I looked on the back and there is a small silver toggle switch by where the power cord comes out. I couldn't find any images of this on the internet. I toggled it up and down but the audio didn't seem to change. If the amp was shut off, would the audio continue to work? I don't have a preamp. My amplifier is wired to a high-end Yamaha RX-A3000 receiver. I guess I just assumed that there would be no sound when I toggled that switch. Can anyone shed some light on this for me?

Thanks.

shinkamp

 

[TLS Guy]

Hello Knowledgeable Audioholics,

Due to a strange circumstance I came to look at my Hafler DH-500 amplifier today. I noticed that the front plate on the amplifier does not have an on/off switch. Almost all images of the DH-500 on the internet have an on/off switch with a red light on the front plate. I looked on the back and there is a small silver toggle switch by where the power cord comes out. I couldn't find any images of this on the internet. I toggled it up and down but the audio didn't seem to change. If the amp was shut off, would the audio continue to work? I don't have a preamp. My amplifier is wired to a high-end Yamaha RX-A3000 receiver. I guess I just assumed that there would be no sound when I toggled that switch. Can anyone shed some light on this for me?

Thanks.

shinkamp

From what I can tell, Hafler made a PA version of that amp, which had no power switch. This is probably so it could get switched from a main control center, and they did not want the amp getting accidentally switched off. I have no idea what that rear switch is about, but I can be certain it is not a power switch.

 

[Trebdp83]

Perhaps a DIY mod? Here are some pics of something similar, though this unit is equipped with a switch on the front panel.

 

[TLS Guy]

Perhaps a DIY mod? Here are some pics of something similar, though this unit is equipped with a switch on the front panel.

View attachment 71804View attachment 71806
View attachment 71807

I have researched this further. He has the pro version which has no front switch and that toggle switch on the back changes the fan speed. So if the OP wants to use this amp, he needs to have an external switch unit.

 

[shinkamp]

Hello and thank you to those who replied to my first post. Your answers got me thinking and I decided to open up the DH-500 and see what's inside. The toggle switch is wired with 2 large green wires. One is grounded to the chassis and the other is soldered to the lowest (of the 3) spades where the female power cord pushes into the amp. I also noted that the amp has Nippon Chemi Con (18000 uF, 100 volt) caps and there are 2 (slightly longer than an inch) beige rectangular components which are shedding some white powder. They are labeled Colber 300 Ohm 10% 7W. I may get someone to "freshen up" this amp in the future so any insight into the toggle switch or better components would be greatly appreciated. Attached are some pictures. I'll try not to take up any more of your time after this and thank you very much..
shinkamp

 

[infoisthub]

Hello Knowledgeable Audioholics,

Due to a strange circumstance I came to look at my Hafler DH-500 amplifier today. I noticed that the front plate on the amplifier does not have an on/off switch. Almost all images of the DH-500 on the internet have an on/off switch with a red light on the front plate. I looked on the back and there is a small silver toggle switch by where the power cord comes out. I couldn't find any images of this on the internet. I toggled it up and down but the audio didn't seem to change. If the amp was shut off, would the audio continue to work? I don't have a preamp. My amplifier property is wired to a high-end Yamaha RX-A3000 receiver. I guess I just assumed that there would be no sound when I toggled that switch. Can anyone shed some light on this for me?

Thanks.

shinkamp

Your Hafler DH-500 amplifier typically has a power switch on the front panel. If yours doesn't, and instead has a silver toggle switch on the back, it might have been modified. If flipping this switch doesn't affect the sound, the amplifier could be getting power through your Yamaha RX-A3000 receiver. To understand this setup better, check how the amplifier is connected to the power source and consider consulting an audio technician.

 

[Eppie]

Hello and thank you to those who replied to my first post. Your answers got me thinking and I decided to open up the DH-500 and see what's inside. The toggle switch is wired with 2 large green wires. One is grounded to the chassis and the other is soldered to the lowest (of the 3) spades where the female power cord pushes into the amp. I also noted that the amp has Nippon Chemi Con (18000 uF, 100 volt) caps and there are 2 (slightly longer than an inch) beige rectangular components which are shedding some white powder. They are labeled Colber 300 Ohm 10% 7W. I may get someone to "freshen up" this amp in the future so any insight into the toggle switch or better components would be greatly appreciated. Attached are some pictures. I'll try not to take up any more of your time after this and thank you very much..
shinkamp

Thanks for posting the photos. That is not a power switch. It appears that the ground wire from the power jack connects to the toggle switch, which connect to the chassis. The black and white wires are the power lines which go right to the power supply, so the amp is always on. The toggle switch allows you to connect the chassis to earth ground (when on) or let the chassis float. Most likely to remove any ground loops that could cause hum. I will leave it to @TLS Guy as to whether that's a good design or not.

The white powder is from a cement resistor. If it is crumbling badly I would replace it. Luckily the values are still easy to read. 300 ohms, 10% tolerance, 7 watt power rating. Those should still be available and are easy to replace. I would replace both of them.

Maybe have them look at the circuit board left of the heat sinks as well for any ageing components. The two large blue filter capacitors should be ok, but that bright green capacitor near the speaker terminals does not look original, so maybe someone has already replaced some of the old electrolytic caps.

 

[TLS Guy]

Hello and thank you to those who replied to my first post. Your answers got me thinking and I decided to open up the DH-500 and see what's inside. The toggle switch is wired with 2 large green wires. One is grounded to the chassis and the other is soldered to the lowest (of the 3) spades where the female power cord pushes into the amp. I also noted that the amp has Nippon Chemi Con (18000 uF, 100 volt) caps and there are 2 (slightly longer than an inch) beige rectangular components which are shedding some white powder. They are labeled Colber 300 Ohm 10% 7W. I may get someone to "freshen up" this amp in the future so any insight into the toggle switch or better components would be greatly appreciated. Attached are some pictures. I'll try not to take up any more of your time after this and thank you very much..
shinkamp

That was a pro amp and not a domestic amp. The switch is a ground break which is common on pro amps, which are prone to ground loops because of constantly changing environments. It has not power switch so as not to cause error, as there would have been a master switch somewhere in the rig, likely on the main rack. That is pretty typical of that breed. So that amp has likely been used hard.