Stealth 8- Emotiva will no longer repair? Jan 8, 2021 15:40:37 GMT -5
Post by garbulky on Jan 8, 2021 15:40:37 GMT -5
If you have scratchy sounds from your Stealth 8's then, as you know, the amp is on the way out. Unfortunately if one of the amp's fails then there is a risk of getting pure DC rail voltage to one of your speakers. If it's the amp that powers the woofer it might survive but if it's the amp that powers the tweeter, it will most likely melt the tweeter.
If you ask Emotiva, they will send you the schematics for the Stealth 8. There is a good chance that one of the output transistors is failing. There is a PNP and NPN output transistor for each of the amps. These are readily available from many sources. If you are proficient with soldering, you can replace these yourself. If you're lucky this will solve your problems. In my case it did not help.
If replacing the output transistors does not fix the issue, then things become much more complicated. You could start moving upstream replacing components as you go but without the right test equipment this procedure is hit or miss and certainly not for the faint of heart.
After doing a post mortem on my amp, it became clear that the row of power transistors on the underside of the amp were no longer making good mechanical contact with the heat sink on the backside of the Stealth 8. The thermal paste that conducts the heat between the transistors and the heatsink had turned to a white dust and the amp slowly cooked itself over time.
Until my amp failed, I was happy with my Stealth 8's. Since I was unwilling to scrap a monitor with one dead amp, my solution was to order a 2 channel 125 watt per channel class D plate amplifier with an integrated DSP. Specifically I used a miniDSP PWR-ICE125 from Parts Express. I had considered going with a 250 watt per channel amp but I discovered that the existing Stealth 8 tweeters are only rated for 80 watts.
Replacing the amps and power supply with a plate amplifier is a straightforward procedure. In a nutshell, you remove the back of your Stealth 8. You disconnect the power LED, and the 4 wires that go to the speakers. Then you remove and discard all the amp components including the power supply and the rear heat sink. When you're done you have an empty back plate. Next you cut a really large hole in the back plate of the amp and bolt the plate amplifier in its place. After hooking up the speakers, you're mostly good to go. The only task that remains is to program the DSP. My DSP required a router and windows PC. All the programming is done via a P.C. From a functional point of view, the signal first goes to the DSP. The DSP processes the signal then sends the output to a dedicated amp for the woofer and a dedicated amp for the tweeter.
The only downside is that programming the DSP takes some effort if you want your newly fixed monitor to exactly match the characteristics of your un-doctored Stealth 8. I used a reference microphone to ascertain the frequency response of my remaining good Steath 8. Then I was able to program the DSP to set the crossover frequency and set gain to match.
And finally, the last option would be to purchase a passive crossover and simply use the dead Stealth 8 with an external amp. If both my Stealth 8's had died, I might have considered this option.
I hope this helps someone.
So you literally have to rebuild the electronics and related software from scratch?! Wow. Wouldn't it have been better to send the amp to a local repair store to replace the faild transistors and apply better thermal paste?