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Either the mic isn't picking it up or my ears are not sensitive to what you are hearing. They sound pretty much the same to me.
 

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Fiesta ST150
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Find someone with oscope
 

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Hi guys. Made a few videos showing A/B tests of my amp to demonstrate the problem with this amp of mine.
I assume that you have swapped sources and drivers to absolutely narrow down the problem to just the PPI amp?


Either the mic isn't picking it up or my ears are not sensitive to what you are hearing. They sound pretty much the same to me.
I thought the same thing halfway through the first video. I had the volume set to OP's voice. Turned the volume up/down for music/narrator and defiinitely heard the distortion. Side note, the PPI sounded slightly thinner than the Soundstream. Could be bass boost, eq, room boundary, etc, but definitely a different frequency response in the open room with PPI amp.

Find someone with oscope
Yes.
 

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I could be wrong but it kinda sounds like to me the RCA ground connections in the amp are broke. Have you tried turning the gain pot up and down while your feeding it a signal ? Dirty gain pot can do that too.
 

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Discussion Starter · #6 ·
Hey guys thanks a lot for replies. Yeah, I've tried changing the gain but not necessarily while feeding it signal. Could be worth a try although the amp is disconnected again now in favor of the A204.2 that sounds like goddamned heaven. This problem has actually been pursued since I first noticed it in late 2016. The A600.2 has been on a few different setups. I'm not just examining this problem on this setup with this set of RCA's, this PSU, this source, etc.

So, part of my purpose of putting this post together was to try to get some other big names in the repair game to view and hopefully help to offer.

There's one that did, so I'm shipping it off as soon as I can get a box to fit it.

Yeah, aside from the distortion, this A600.2 does sound thinner than the Soundstream. That Soundstream is just brilliant. But the PPI has it's own character that I really enjoy. Very crisp on mids and highs especially when connected to my Soundstream speakers rated for like 100WRMS.

Just wish it didn't have the distortion. After about 2 days, it becomes easier to hear and makes the amp basically unusable.
 

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Grab a bottle of deoxit d5 and give the pots and switches a small spray in the slots/cracks (you'll have to open the amp to do it effectively). Work them all back and forth many many times. Wait a few hours.. do it again.


See if it makes a difference, it often does :).
 

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Discussion Starter · #8 ·
Grab a bottle of deoxit d5 and give the pots and switches a small spray in the slots/cracks (you'll have to open the amp to do it effectively). Work them all back and forth many many times. Wait a few hours.. do it again.


See if it makes a difference, it often does :).
Right on thank you I'll give this a try.
 

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Grab a bottle of deoxit d5 and give the pots and switches a small spray in the slots/cracks (you'll have to open the amp to do it effectively). Work them all back and forth many many times. Wait a few hours.. do it again.


See if it makes a difference, it often does :).
This was going to be my suggestion too.
 

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Discussion Starter · #13 ·
I am not assuming that you are looking for this amplifier to be repaired but if you do Shawn King does amazing work. Sorry if you don't need this recommendation.
Yes I am. Thanks for the recommendation. I've gotten an offer from a well respected guy in the field who agreed to have a look. Will keep Shawn in mind though.
 

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Hey guys thanks a lot for replies. Yeah, I've tried changing the gain but not necessarily while feeding it signal. Could be worth a try although the amp is disconnected again now in favor of the A204.2 that sounds like goddamned heaven. This problem has actually been pursued since I first noticed it in late 2016. The A600.2 has been on a few different setups. I'm not just examining this problem on this setup with this set of RCA's, this PSU, this source, etc.

So, part of my purpose of putting this post together was to try to get some other big names in the repair game to view and hopefully help to offer.

There's one that did, so I'm shipping it off as soon as I can get a box to fit it.

Yeah, aside from the distortion, this A600.2 does sound thinner than the Soundstream. That Soundstream is just brilliant. But the PPI has it's own character that I really enjoy. Very crisp on mids and highs especially when connected to my Soundstream speakers rated for like 100WRMS.

Just wish it didn't have the distortion. After about 2 days, it becomes easier to hear and makes the amp basically unusable.
I believe Blessing God would be a much better approach than cursing Him 😊
 

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Discussion Starter · #15 ·
From Ray at Linear Power:


****
I got to do a detailed and comprehensive listen and test of your amp. You had two things wrong in this amp that I found both caused by past work to the amp. The caps had been replaced sometime in the past and someone had snipped the legs to two of the rectifier diodes and resoldered them back together. (or tried resoldering them back together) One leg wasn’t soldered well and was arcing across the poor connection, creating an arc creates an enormous amount of AC ripple current and RF noise. This in turn caused the rail caps associated with that rail voltage to have to filter large amounts of ripple current and noise. Those two caps exceeded their capability and were letting more noise through on the rail voltage that feeds the output devices as well as the step down voltage section for the preamp. All that being said, simply it damaged the two caps and you were getting dirty voltage into your audio stages from poor electronic work. I replaced ALL rail voltage caps as well as a few others and put a brand new set of 4 bridge rectifier diodes in the amp and it looks much cleaner on the O’scope and sounds much much cleaner.

Your amp is ready to come back to you. I will listen to it again in the morning one more time but this explains exactly what you were hearing.

Ray

PS I think the first time I listened to it the rectifier with the broken leg connection was actually stuck together and not arcing. When I disassembled the amp and was testing I heard a pop and then saw an arc. Looking closer I saw the solder gobbed on the legs and I touched it and it arced again. I replaced ALL the rectifier diodes with a matching set since two of the 4 had their legs cut and resoldered and the diodes were an off brand diode anyway. I put you all top notch Motorola diodes in it and like I said replaced all he rail voltage caps, not just the ones affected on that one side.


*

Can't wait to get the amp back later this week! It's been through a full workup by a legend xD
 

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So Oscope fixed it :D
 

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Discussion Starter · #18 ·
Yeah I should also mention that the guy from oldschoolcaraudiorestoration on facebook recommended Ray.

So yeah, 4yrs, 2 technicians, about 350 bucks in fees and shipping charges, and 1 proper engineer with an oscope.

Worth it though, I'm loving this xD
 
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