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Feedback on These Two

heeman

Well-Known Member
Famous
Do any of you own one of these or have any experience with them?

Parasound HCA-750A 2 Channel Amplifier

ROTEL RB-980BX STEREO POWER AMPLIFIER
 

AndySTL

Well-Known Member
I think they would both be fine amplifiers. I used to have a couple of Parasound mono blocks. They were ok, but I needed a 5 channel amp at the time, so I sold them and picked up a Rotel RB-985. I think the Rotel you listed is from the same family. The Rotel was nice but it didn't have a 12v remote trigger which annoyed me since I had to switch it on manually every time. I sold that amp about a year ago because it was not being used. I regret that now...wish I still had it.

I don't think that Rotel you listed has a 12v trigger either. Not sure if that's important to you or not. There may be some work-around solutions in case you needed remote power on.
 

heeman

Well-Known Member
Famous
Thanks AndySTL.

I checked the Owners Manual and you are correct, no trigger for on/off.
 

heeman

Well-Known Member
Famous
Okay Soundhound, I am a little rusty on my basic electronic circuit skills.

How would you get this to interact with a remote?

Go For It, make me look STUPID!! :bow-blue:
 

Flint

Dog Faced Pony Soldier
Superstar
The preamp's 12v output is the trigger signal... so the preamp reacting to the remote is how it works. That how ALL 12v trigger inputs work.

I have the 750 and love it!
 

soundhound

Well-Known Member
heeman said:
Okay Soundhound, I am a little rusty on my basic electronic circuit skills.

How would you get this to interact with a remote?

Go For It, make me look STUPID!! :bow-blue:
The relay is meant to be powered by the trigger output of your preamp / receiver. A 1000 ohm 1/4 watt resistor would be inserted in series with pin #3 of the relay (the anode of the LED, which provides 10.8 milliamps to the LED inside the solid state relay). The other lead of the resistor would then be connected to the "hot" side of the 12VDC trigger of the preamp / receiver (tip of the 1/8" plug) and pin #4 of the relay (the cathode of the LED) would be connected to the "GND" side of the trigger output of the preamp / receiver (sleeve side of the 1/8" plug). Pins 1 and 2 of the relay would be connected in series with the "HOT" (black) lead of the 120VAC just as if the relay were a common wall switch. When the preamp triggers, the relay will turn on anything which is connected through the solid state relay. The solid state relay is rated at up to 240VAC and 12 amps.

All the 12 volt trigger of your preamp / receiver is doing is lighting a LED inside the solid state relay, which triggers a TRIAC, completing the AC circuit to the load. There is complete electrical isolation between the trigger signal and the AC load. For this reason, these types of relays are very popular in computer controlled (PLC controlled) automation systems to control anything from lights to huge motors.
 

heeman

Well-Known Member
Famous
Guys, I understand how the circuit works off of the 12 volt trigger.

It appears that the Onkyo TX NR708 only has a trigger on the Zone 2??

I don't have the unit yet to check it out, however my question was not clear, sorry.

If I have a 12 V trigger available I will be able accomplish this.

If there is no 12 V trigger available, I have to get my lazy ass off of the coach and turn the amps on..........wait, I can do that before I sit down!!! :scared-eek:
 

DIYer

Well-Known Member
Famous
AndySTL said:
Is the 750 the old model name for the current Z-Amp?
I don't think so. Zamp v.3 is
- 45 watts RMS x 2 @ 8 Ω
- 60 watts RMS x 2 @ 4 Ω
- 90 watts RMS x 1 @ 8 Ω (bridged mono)

where as HCA-750A is
- 75 watts RMS x 2 @ 8 Ω
- 125 watts RMS x 2 @ 4 Ω
- 250 watts RMS x 1 @ 8 Ω (bridged mono)
 

Batman

Well-Known Member
Staff member
Moderator
Famous
Interesting, I've been putting off an inexpensive way to add a trigger to my 2-ch Rotel...if I pursue it I will start another thread in the DIY section. SH, is there an inexpensive way to add a trigger to the power cable side of things to avoid opening an amp (provided I read the above instructions properly, I assume getting into the cabinet would be needed and in my case a bit of a pain) an external relay that the amp would plug into and then plug the relay into an outlet?
 

soundhound

Well-Known Member
Batman said:
Interesting, I've been putting off an inexpensive way to add a trigger to my 2-ch Rotel...if I pursue it I will start another thread in the DIY section. SH, is there an inexpensive way to add a trigger to the power cable side of things to avoid opening an amp (provided I read the above instructions properly, I assume getting into the cabinet would be needed and in my case a bit of a pain) an external relay that the amp would plug into and then plug the relay into an outlet?

The assumption was that the relay would be built external to the amp, probably in an inexpensive metal electrical outlet box with a power cord going in, a trigger signal going in (from the preamp) and an outlet to plug the controlled amp into.

Here's a solid state relay which can handle up to 16 amps. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=425-2414-ND
 

malsackj

Well-Known Member
I have used a 10 amp solution for some of my gear in a metal box with outlets, I used a 120 Volt switched outlet on the back of the pre/pro that turns on or off the relay.

http://www.parts-express.com/pe/showdet ... er=075-166
http://www.parts-express.com/pe/showdet ... er=075-100

http://www.parts-express.com/pe/showdet ... er=075-124
There is a separate mount for these models that I was not seeing.

If I spend a few extra dollars the relay will time delay !!!
I have a fuse in the front of the relay for 10 amps.
 

soundhound

Well-Known Member
malsackj said:
I have used a 10 amp solution for some of my gear in a metal box with outlets, I used a 120 Volt switched outlet on the back of the pre/pro that turns on or off the relay.

http://www.parts-express.com/pe/showdet ... er=075-166
http://www.parts-express.com/pe/showdet ... er=075-100

http://www.parts-express.com/pe/showdet ... er=075-124
There is a separate mount for these models that I was not seeing.

If I spend a few extra dollars the relay will time delay !!!
I have a fuse in the front of the relay for 10 amps.
While those relays will work, I would recommend a solid state relay. The reasons are that the coil of the relay draws a lot of current relatively at 75 milliamps, which could overload some trigger outputs or limit the number of components the trigger output can drive; the LED in a solid state relay only draws 10 milliamps. More importantly, if a reverse-biased diode (like a 1N4004) is not placed across the relay coil of a mechanical relay, back EMF is formed when the relay coil is energized and de-energized, and this spike of current can (probably will eventually) cause failure of the 12 VDC trigger circuitry in the preamp. The LED in a solid state relay is completely non-inductive.

Another reason is that this particular solid state relay is a zero crossing type which means that the relay kicks in at the exact point of zero volts AC in the cycle, providing a "soft start" for the attached gear; no mechanical relay can do this and depending on where in the AC cycle the contacts mate, there is the possibility of a spike of current which is harder on both the relay and the gear being powered.

A solid state relay never wears out; mechanical relays do because of contact pitting (see zero crossing above).

The solid state relay not only has higher current capability (16 amps), it is also cheaper when one factors in the cost of the socket for the mechanical relay. The solid state relay can simply be screwed to the metal box.

BTW, the data sheet for the 16 A solid state relay is here: http://media.digikey.com/pdf/Data Sheets/Sharp PDFs/S116,216S02.pdf
 
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