Great to hear it's Alive!
Yesterday I removed the 1500 from a bi- amp system and set it up solo. I did bypass all of the pots/switch/clip connection on the input. I have biased both channels at around 19mv. I feel the messy input circuit bypassed results in a cleaner high end. I was surprised how warm (soft) sounding this amp is in my system. The warmest amp I have owned. I would like to hear from others if that is their experience. I will next bypass the output relay next. It might be responsible for a bit of, I call it, shoutyness in some voices.
More listening time today....
Also, a question for owners. Is the transition from standby to full on a fast click. Mine sort of moseys through that step.
Yesterday I removed the 1500 from a bi- amp system and set it up solo. I did bypass all of the pots/switch/clip connection on the input. I have biased both channels at around 19mv. I feel the messy input circuit bypassed results in a cleaner high end. I was surprised how warm (soft) sounding this amp is in my system. The warmest amp I have owned. I would like to hear from others if that is their experience. I will next bypass the output relay next. It might be responsible for a bit of, I call it, shoutyness in some voices.
More listening time today....
Also, a question for owners. Is the transition from standby to full on a fast click. Mine sort of moseys through that step.
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Not an owner but just looking at the schematic it should come out of standby instantly if using the front panel switch. If it's taking seconds to activate then either the switch contacts are getting a high resistance or the relay is slow to pull in. My money is on the switch.I've had faulty switches that the contact resistance is high on them right after they're switched and then the resistance drops over a few second period. This sounds like what may be happening to your amp.
An easy way to check if it's the switch is to put the amp in standby and jump across the JP2A connector where the switch is connected to the board to see if the amp comes out of standby more quickly with the jumper than with the switch. This should be low voltage DC on the switch. The schematic doesn't say but 24vdc or less based on the start circuit filter cap rating.
I can confirm we have good audio. Lots of new caps and I think some break-in time my not be a bad thing. I really want to find an HCA-3500 now .....
For anyone coming to this thread later, researching this amp, I've updated all the parts, notes, photos, docs, etc in the Google sheet that was in the first post on this thread. Along with everyone's help comments on this thread, someone else should be able to get pretty far along:
Parasound HCA-1500 Google Sheets
My takeaway lessons and reminders on this one:
Filippo
For anyone coming to this thread later, researching this amp, I've updated all the parts, notes, photos, docs, etc in the Google sheet that was in the first post on this thread. Along with everyone's help comments on this thread, someone else should be able to get pretty far along:
Parasound HCA-1500 Google Sheets
My takeaway lessons and reminders on this one:
- Troubleshoot first, don't succumb to the possibility of solving the problem through upgrades.
- DBT was great for initial soft start, but after that a full sized Variac or straight wall power as not enough current with the DBT.
- Nothing beats learning with something broken.
Filippo
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Interesting. I just tried the link in incognito mode and it worked. As an alternative, I've created a PDF with content. Attached.
Filippo
Spent several hours listening to the 1500. I did use foil film resistors to make an attenuation input to bypass the normal factory system and match the gain of my preamp. This amps has a very pleasant sound. I could live with it. I still think there is still more potential to be found. More to come....
The best mod I have found so far that really wakes this amp up is doing something that was done on the 3500. Bypass R110/111, R210/211 with a 100uf cap. I use a silmic II, 100uf 16v. There is 9v DC across these resistors. Be very careful and observe polarity, or poof goes the magic smoke. Have only a few hours on this change. Really brings out the detail, and Dynamics. You may like the warmer original sound. If you try this Watch Out....
The next mod completed yesterday was two fold. I changed the value/type resistors in the input attenuator and the feedback resistors. The input now has a TX2375 and the feedback has S102k. The most obvious change was apparent in the high frequencies. The sibilance reduced and went from a sh as in sash to a pronounced Ssss. My bad as I did those two changes at the same time, so not sure if both contributed to the change.
All these mods have been on a temporary bases, as see in the picture. These will be done under the board as there s plenty of space to better accommodate them. When this is done the earlier mentioned beefing up of the power supply traces will be done.
All these changes have very much increased my pleasure in listening to music. Additionally, those mods have increased the space if you will, between poor, medium and well recorded music. It becomes very evident, what is a good recording, and what is not.
All these mods have been on a temporary bases, as see in the picture. These will be done under the board as there s plenty of space to better accommodate them. When this is done the earlier mentioned beefing up of the power supply traces will be done.
All these changes have very much increased my pleasure in listening to music. Additionally, those mods have increased the space if you will, between poor, medium and well recorded music. It becomes very evident, what is a good recording, and what is not.
Attachments
I have completed most of my planned mods. I didn't bypass the output relay due to speaker protection. The two must do mods to improve the sound of this amp are, one bypass the input pots/switch and install a attenuator. One could also replace R102/202 with a 10-50k resistor and connect the input to R101/201. Second, bypass R110/111 and R210/211 with both 100uf and .01 film(KS, PP). Watch carefully the polarity of the electrolytic caps. These get you much improvement. If you believe resistors sound different, change R101/201 and R112/212 for additional improvement. These will make the biggest bang for the effort. With a reasonably revealing system, these mods will be quite evident.
You could soldered the crimp output connection or increase the size of those wires.
You could soldered the crimp output connection or increase the size of those wires.
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Hi, do you want to try the higher driver current mod, it can be reversed easily if you don't like.
"remove two 100R resistors R119,R120 and replace a 47R 2W connect between two driver transistors. After mod reset bias."
Former owner here, over 10 years. At various times I used it in stereo, bridged and for biamping. FWIW I never would have described it as "warm" or "soft." I always felt it's biggest weakness was what I perceived as congestion in complex passages at high volume.
Overall it's a nice vintage solid state amp if you can find one. Have fun!!!
Bypassing the cascode divider resistors R110/111/210/211 with a large value cap may induce a thump at start up. This would be masked by the delayed speaker protect relay engagement. But if you bypass the SP relay you may find you have a nasty thump. It's hard to see that added cap having any benefit due to the voltage regulator on the front end PS that Parasound put on there.
WBS, I am having lots of fun during the shelter in place. I completely concur, a better description than my "warm". Maybe I should of used mushy. It really cleans up with the suggested mods. The congestion is now vastly reduced, but I know what you mean. Chamberman, if you have one of these give it a try. The delay in the output relay must protect against the thump, none here. The R110-211 bypass is done on the 3500 with a similar overall layout, so I decided to do the same. It did amazing things to mine. I also decide that bypassing the output relay wasn't a good idea with rails of 72v. YMMV, but you'll never hear the potential until these mods are done.
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Okay, now I understand and agree completely!
Enjoy it, stay safe and stay healthy!!!
I have been hesitant to comment on sound characteristics - first because everything was new and I felt some break-in would be good. Second because pairing to speakers seems to have so much to do, even beyond the differences one hears versus another.
Loud "mushy" middle is something I think I can relate. The klipsch setup tends to have very forward treble presence from my experience. Some people may find that a bit harsh. YMMV. But I believe the mushy middle may describe a weakness I notice. I'll need to go back and give a listen again, and read back through the posts from the past week or so.
Thanks for posting and continuing to compile information on this amp, folks!
Filippo
Loud "mushy" middle is something I think I can relate. The klipsch setup tends to have very forward treble presence from my experience. Some people may find that a bit harsh. YMMV. But I believe the mushy middle may describe a weakness I notice. I'll need to go back and give a listen again, and read back through the posts from the past week or so.
Thanks for posting and continuing to compile information on this amp, folks!
Filippo