Problem: in Stereo mode, the L channel fuses on both amps blow on power up.
How did I get here?
The short version is for 5 years, I have run these amps in Mono Bridge mode ... I only used one in Stereo mode when I first got it and was trying out a few different amps. When I found a second HCA-1500, I just checked/adjusted bias and put them straight into Mono Bridge and never looked back. I did run that second amp in Stereo first, to make sure it was working. And it was.
Today, after reading some opinions that using stereo amps in mono bridge mode don't always have the sound quality as in Stereo ... just got me thinking. So I pulled the amps out of the racks, and got the first amp ready to try. Switched from Mono to Stereo BEFORE plugging in, and ... no L channel. R channel was fine. After fiddling around, I decided to try the other amp. Same thing. Opened them up and both F001, F002 fuses on the L channel for EACH amp were blown.
I figure maybe after only using the amps this way to drive Vandersteen 2C speakers for 2 years, and then my Vandersteen 3A's for the last 3 years ... maybe something happened???
For those first TWO years, I was driving Vandersteen 2C speakers. Lovely. For the last THREE years, I have really enjoyed powering my Vandersteen 3A speakers.
So here I sit with three possible paths:
Path #1 - get more fuses and just run amps in mono bridge mode.
Path #2 - get help to troubleshoot what problem might be.
Goofy idea #3 - use the B&K ST-202 Plus amp that I have working again, but it's not properly biased ...
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Additional info, in case it matters.
The HCA-1500's are two different runs. And by that, I mean the only difference I see is that "Amp 1" has 15,000 uF ps caps (four), and "Amp 2" has 20,000 uF ps caps (four). Based on that alone, I'm thinking that if I decide to use just one amp, maybe it should be the higher uF rated "Amp 2". I'd be curious on your thoughts. Both are 80V ps caps.
How did I get here?
The short version is for 5 years, I have run these amps in Mono Bridge mode ... I only used one in Stereo mode when I first got it and was trying out a few different amps. When I found a second HCA-1500, I just checked/adjusted bias and put them straight into Mono Bridge and never looked back. I did run that second amp in Stereo first, to make sure it was working. And it was.
Today, after reading some opinions that using stereo amps in mono bridge mode don't always have the sound quality as in Stereo ... just got me thinking. So I pulled the amps out of the racks, and got the first amp ready to try. Switched from Mono to Stereo BEFORE plugging in, and ... no L channel. R channel was fine. After fiddling around, I decided to try the other amp. Same thing. Opened them up and both F001, F002 fuses on the L channel for EACH amp were blown.
I figure maybe after only using the amps this way to drive Vandersteen 2C speakers for 2 years, and then my Vandersteen 3A's for the last 3 years ... maybe something happened???
For those first TWO years, I was driving Vandersteen 2C speakers. Lovely. For the last THREE years, I have really enjoyed powering my Vandersteen 3A speakers.
So here I sit with three possible paths:
Path #1 - get more fuses and just run amps in mono bridge mode.
Path #2 - get help to troubleshoot what problem might be.
Goofy idea #3 - use the B&K ST-202 Plus amp that I have working again, but it's not properly biased ...
---
Additional info, in case it matters.
The HCA-1500's are two different runs. And by that, I mean the only difference I see is that "Amp 1" has 15,000 uF ps caps (four), and "Amp 2" has 20,000 uF ps caps (four). Based on that alone, I'm thinking that if I decide to use just one amp, maybe it should be the higher uF rated "Amp 2". I'd be curious on your thoughts. Both are 80V ps caps.
Attachments
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Here is schematic.
I have run out of 6.3A, 250V fuses ... I don't see any locally and may have to order. What a PITA.
I have run out of 6.3A, 250V fuses ... I don't see any locally and may have to order. What a PITA.
I had issues with the selector switch and losing a channel.
Pulling out the switch and checking continuity both ways showed a dead throw
Opening it up and looking for a reason didnt show just why it failed other than cheap construction maybe..,.
Replaced it a CK quality switch and it worked perfectly
Regards
David
Pulling out the switch and checking continuity both ways showed a dead throw
Opening it up and looking for a reason didnt show just why it failed other than cheap construction maybe..,.
Replaced it a CK quality switch and it worked perfectly
Regards
David
Faulty switches would be my preferred cause. Sounds like the cheapest option. I already have too many projects and timing on this wasn't great. But it never is, eh? 🙂
I'll pull a switch tomorrow and check, unless it is possible to get a good reading with the switch in place. I bought a new switch from Parasound about one year ago. So the switches are far apart in age. Hmm.
I'll pull a switch tomorrow and check, unless it is possible to get a good reading with the switch in place. I bought a new switch from Parasound about one year ago. So the switches are far apart in age. Hmm.
No, I had some in my bin. Just pull it out and check the throws with a DVM
It has been a few years since I fixed mine
Seeing how they are not used very often, I spent a considerable time looking at everything else only to sit there and suspect the switch in the end and that was it on mine
Hope thats all it is on yours
3a,s are awsome speakers BTW
Regards
David
It has been a few years since I fixed mine
Seeing how they are not used very often, I spent a considerable time looking at everything else only to sit there and suspect the switch in the end and that was it on mine
Hope thats all it is on yours
3a,s are awsome speakers BTW
Regards
David
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Heard from Parasound this morning. I have the wrong fuses. It's odd to me that the two different previous owners put the exact same fuses in.
The AC back panels both had 12A 250V ceramic fuses ... should be 6.3A.
All other fuses in both amps were Fast Blo ... ALL fuses in the amp should be SLO BLO.
Ordering fuses today ... hope to get in about 4 days so I can test. I'm getting double quantities, but will power up on variac/dbt just in case ... in case there is another issue.
The AC back panels both had 12A 250V ceramic fuses ... should be 6.3A.
All other fuses in both amps were Fast Blo ... ALL fuses in the amp should be SLO BLO.
Ordering fuses today ... hope to get in about 4 days so I can test. I'm getting double quantities, but will power up on variac/dbt just in case ... in case there is another issue.
Fuses arrived and are in both amps.
Powering up on variac/dbt and I notice the same thing on both amps. Maybe this is normal for this topology?
The relay located at the front left behind the faceplate on both amps starts clicking on/off when my (cheap) variac gets to 70V ... I have tried on both amps, and in Stereo and Mono Bridge mode. So either something strange is happening on both, which is coincidental in my mind, or there is something about how this amp is designed that explains why the relay is clicking on/off without stopping as the dim bulb tester gets brighter. I'm using a 100w bulb. Nothing is connected to the amp.
I'm powering up this way since I don't want to start blowing fuses if there is something wrong that would be detected by what is normally my first step.
Thoughts? I was told I should hear back from Parasound today, maybe later, to talk to Tony.
Powering up on variac/dbt and I notice the same thing on both amps. Maybe this is normal for this topology?
The relay located at the front left behind the faceplate on both amps starts clicking on/off when my (cheap) variac gets to 70V ... I have tried on both amps, and in Stereo and Mono Bridge mode. So either something strange is happening on both, which is coincidental in my mind, or there is something about how this amp is designed that explains why the relay is clicking on/off without stopping as the dim bulb tester gets brighter. I'm using a 100w bulb. Nothing is connected to the amp.
I'm powering up this way since I don't want to start blowing fuses if there is something wrong that would be detected by what is normally my first step.
Thoughts? I was told I should hear back from Parasound today, maybe later, to talk to Tony.
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As I went to sleep last night I had an idea.
I removed the fuses on the L channel (F001, F002) for both amps. Powered up on variac / dbt (100w bulb) and the relay clicks back and forth until I get to full power (120v) and a few seconds later, as normal, amp comes out of power protect with green AC Line and amber Normal lights come on.
What did we learn?
By stopping the flow of current across one or both of these fuses on the L channel, the amp is fine.
Questions.
1) Should I test with one of the two L channel fuses in place to see if it's down to one fuseholder, or a component in between? Then swap fuse positions? Or is that pointless?
2) Based on the R channel being fine, is there a reason to suspect the mono/stereo switch? I'm thinking if there was a problem with the switch, it would be on both channels.
I removed the fuses on the L channel (F001, F002) for both amps. Powered up on variac / dbt (100w bulb) and the relay clicks back and forth until I get to full power (120v) and a few seconds later, as normal, amp comes out of power protect with green AC Line and amber Normal lights come on.
What did we learn?
By stopping the flow of current across one or both of these fuses on the L channel, the amp is fine.
Questions.
1) Should I test with one of the two L channel fuses in place to see if it's down to one fuseholder, or a component in between? Then swap fuse positions? Or is that pointless?
2) Based on the R channel being fine, is there a reason to suspect the mono/stereo switch? I'm thinking if there was a problem with the switch, it would be on both channels.
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Amp #1 (older)
Serial no. # 251330
60,000uF as in product info on Parasound site ...
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Amp #2 (newer)
Serial no. 7 91004 20003 4 (01250) ... this is a UPC sticker
80,000 uF ... more than posted specs, so I assume later version.
Note film caps replacing C215, C216 (C115, C116 on schematic)
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I am optimistic that the fix on this will be affordable, once we figure out what the problem is. In the end, I will possibly want to just run one amp with my Vandersteen 3A's ... right now while these are out of commission, I'm using a B&K ST-202 Plus that is not biased correctly (underbiased since I don't have equipment for input signal and dummy load) ... but it sounds pretty darn good.
So I'm hoping that if these amps have had a blown L channel fuse for years, maybe I haven't heard them as good as they can be, which is hard to believe since they have sounded great up to this point.
The other thing is Vandersteen 3 (with A update) are 4 ohms. Hmm. Okay, so maybe this is a contributing factor. I didn't read the FAQ on the Parasound site with the statement to ONLY run 8 ohm speakers when using mono bridge. Lesson learned. But does this help point to the problem going on?
Serial no. # 251330
60,000uF as in product info on Parasound site ...
---
Amp #2 (newer)
Serial no. 7 91004 20003 4 (01250) ... this is a UPC sticker
80,000 uF ... more than posted specs, so I assume later version.
Note film caps replacing C215, C216 (C115, C116 on schematic)
---
I am optimistic that the fix on this will be affordable, once we figure out what the problem is. In the end, I will possibly want to just run one amp with my Vandersteen 3A's ... right now while these are out of commission, I'm using a B&K ST-202 Plus that is not biased correctly (underbiased since I don't have equipment for input signal and dummy load) ... but it sounds pretty darn good.
So I'm hoping that if these amps have had a blown L channel fuse for years, maybe I haven't heard them as good as they can be, which is hard to believe since they have sounded great up to this point.
The other thing is Vandersteen 3 (with A update) are 4 ohms. Hmm. Okay, so maybe this is a contributing factor. I didn't read the FAQ on the Parasound site with the statement to ONLY run 8 ohm speakers when using mono bridge. Lesson learned. But does this help point to the problem going on?
Attachments
Parasound FAQ on this amp.
Will these amps handle a four ohm speaker while the two channels are bridged to MONO?
No. Remember amps bridged to mono will "see" half the impedance the speaker is actually presenting. Sustained 2 Ohm loads are not advisable with any Parasound amplifier.
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Question...
In the context of my 4 ohm speakers ... and the amp running just the R channel, which is still good ... how would the L channel have a problem if it is not running? Or am I seeing this incorrectly?
Will these amps handle a four ohm speaker while the two channels are bridged to MONO?
No. Remember amps bridged to mono will "see" half the impedance the speaker is actually presenting. Sustained 2 Ohm loads are not advisable with any Parasound amplifier.
------------------------------
Question...
In the context of my 4 ohm speakers ... and the amp running just the R channel, which is still good ... how would the L channel have a problem if it is not running? Or am I seeing this incorrectly?
I have the option to send either or both amps back to Parasound. There is no warranty, but I'm not confident at this time it's worth the cost, versus selling for what I can get. I'll see if I can find a tech willing to take this on.
Update ... I left one of these amps with Classic Audio Restorations and I'm shipping the other to him now that we know the problem is in the L channel output / drivers ... might as well recap smaller electrolytics.
My model has Elna ps caps (80,000uF) which are 20,000uF higher than the specs on the Parasound site.
John, if you see this, are there any obvious (to you) changes in values or cap types in this amp? Maybe even current driver options for the Mosfets/Jfets? I'd like it to last a few more years before I can jump up to the JC line.
These amps are a fantastic value!!!
My model has Elna ps caps (80,000uF) which are 20,000uF higher than the specs on the Parasound site.
John, if you see this, are there any obvious (to you) changes in values or cap types in this amp? Maybe even current driver options for the Mosfets/Jfets? I'd like it to last a few more years before I can jump up to the JC line.
These amps are a fantastic value!!!
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I picked up my amp yesterday. Wow! I'm glad I decided to keep the amp and have Dan Horton, of Classic Audio Restoration, work on this.
It turns out that aside from the obvious shorted output devices on the left channel, from my stupidity, some of the output devices on the good side were measuring way below spec.
After just a day of running, I can say I don't miss running my Vandersteen 3A's with one amp, rather than the two in mono bridge.
One benefit of Dan's work was wpc output before clipping is higher than the spec'd 205 wpc ... it's now about 242 wpc. What helped this is that my amp must have been at some point, maybe later, in the production run where the power supply jumped from 60,000uF to 80,000uF.
I'm hoping Dan will jump in with more details. All I can say is that if you have a Parasound amp getting long in the tooth, or (partially) shorted out like mine, it is worth getting it fixed. IMHO these are great bang for the buck amps.
It turns out that aside from the obvious shorted output devices on the left channel, from my stupidity, some of the output devices on the good side were measuring way below spec.
After just a day of running, I can say I don't miss running my Vandersteen 3A's with one amp, rather than the two in mono bridge.
One benefit of Dan's work was wpc output before clipping is higher than the spec'd 205 wpc ... it's now about 242 wpc. What helped this is that my amp must have been at some point, maybe later, in the production run where the power supply jumped from 60,000uF to 80,000uF.
I'm hoping Dan will jump in with more details. All I can say is that if you have a Parasound amp getting long in the tooth, or (partially) shorted out like mine, it is worth getting it fixed. IMHO these are great bang for the buck amps.
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Another big thing is at powering up. Both amps used to make a little physical buzz/hum noise in the transformer at power up. Now, it's dead quiet. I have to look to make sure the amp came on. Dan must have replaced parts that fixed that since I'm sure (now) it was not normal.