1200 vs 1500 differencs?

[stgdz]

Recently picked up a 1200 after looking for a HCA 1500 for awhile, curious as to what the differences were between the two The 1500 has a DC trigger on it i know that.

From the advertisement they look pretty close the same



Parasound HCA-1200II
205 watts RMS x 2, 20Hz-20kHz, 8 W, both channels driven
315 watts RMS x 2, 20Hz-20kHz, 4 W, both channels driven
Continuous Power Output - Mono
625 watts RMS, 20Hz-201kHz, 8 W
Frequency Response
8Hz-150kHz, +0/-3dB at 1 watt
Total Harmonic Distortion
0.06% at full power
0.03% typical levels
TIM
Unmeasurable
IM Distortion
0.04%
Dynamic Headroom
2dB
lnterchannel Crosstalk
80dB at 1kHz
63dB at 10kHz
lnput lmpedance
42kW
lnput Sensitivity
1.4V for rated output
1.0V for 28.28V output, THX reference level
S/N Ratio
110dB, input shorted, IHF A weighted
Damping Factor
600 at 20Hz


1500

http://www.parasound.com/vintage/hca1500a.php

[audioqueso]

I've owned the 1205A and the 1500A. Both had DC triggers. I know the 1200 series didn't have DC driggers. Then they made models listed as 12##A which DID have DC triggers.

Sound. They both sounded identical. I found the 1205A had a SLIGHTLY more opened soundstage. Aside from that, they sounded the same to me.

[stgdz]

What would make the amp go into stand by mode? I was watching master and commander last night and it was able to handle the canon scenes fine but almost a minute after the scene it went into standby mode. I will see if I can find some more info out tonight about the scene but my 1205 was able to keep up where the 1200 crapped out but turned back on.

[Peter Nielsen]

Overheating. (Do you have something stacked on top of the amp?)
Bad bias or DC offset adjustment.

[stgdz]

Overheating. (Do you have something stacked on top of the amp?)
Bad bias or DC offset adjustment.

Nothing is on top of the amp. How do I determine the bias or the dc offset?

Also the master and commander movie is the only movie so far that I have noticed that the amp turns off on. I was able to repeat the issue the 2nd time through. The amp was able to handle irene scene in black hawk down, thecrane scene in terminator 2, and all transformers movie. The amp just warm to the touch, no warmer then it normally is.

edit-left channel is toast, nothing but static out of it. Right channel appears to be fine but haven't pushed it hard I believe I heard a pop out of the channel though. The 1200 doesn't go to standby when there is static.

Hooked up the fronts to the 1205 and it didn't clip out.
Crap, so what is the best way to fix this now? I have access to a multimeter but not tonight, I don't know the condition of the fuse but it looks to be ok(its solid white).

[Peter Nielsen]

Nothing is on top of the amp. How do I determine the bias or the dc offset?

Service equipment and knowledge is required... Sounds like the left channel is burnt out. Probably need output transistor replacement. No easy fuse fix for sure...

Peter

[stgdz]

Service equipment and knowledge is required... Sounds like the left channel is burnt out. Probably need output transistor replacement. No easy fuse fix for sure...

Peter

Well I took it apart tonight and the 1200 is certainly harder to get at then the 1205. I noticed that all the transistors are on the bottom and had to remove a heck of a lot of screws to get at it. Also the left channel gives off sound but I have to drop the volume down really low. When I gradaully up it the sound starts to distort. Taking a thermal probe to the channel I get temeprature about 5 degree above room temp where the working right channel is 10-20 degrees above room temp. All of the transistors on the left channel read out to be at room temp.

I kinda have a hunch that it may be on the power supply board, would I be able to unplug the left channel and plug it into the right channel to verify this?

I am going to e-mail parasound service tomorrow to see if they can supply me a service manual. Any idea what the transistors are? I built a gainclone up once so it I may be able to trouble shoot my way out of this.

[Peter Nielsen]

If the channels are identical, swapping them is a good idea! No idea what the transistors are, but make sure you get genuine parts and not cheap counterfeits that fail prematurely: http://www.geocities.com/cdkands/counterfeits.html

[stgdz]

I plan on getting the replacement transistor from digikey or mouser. How can I tell what transitor failed?

I plan on replacing the fuses too, are they fast or slo blow?
edit-no luck on replacing the fuses. Also looks like I can't swap the channels.

[Peter Nielsen]

I plan on getting the replacement transistor from digikey or mouser. How can I tell what transitor failed?

If you don't know, don't attempt it. Do you even know for sure that it's the output transistors?

Also, it's possible that matched transistors are required to meet the specs...