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Old 19th April 2005, 04:25 PM   #1
dgo is offline dgo  Netherlands
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Unhappy SI: popping behaviour

I've got two SI's here. One unmodded, and on one yesterday I
replaced the input caps (my first simple SI mod yoohoo )

Both however seem to pop on the right channel. The modded one started this after I replaced the input caps (thanks very much to panomaniac giving me advise and answering my questions !!)
the unmodded (100 hours+ playing time) one suddenly started this behaviour today for unknown reasons

The popping occurs not only when powering on/off, but also when unmuting/muting the source so also when the CD track changes. Needless to say this is pretty annoying.

My questions:

- Anyone else have these experiences?
- Could this be a result of me using a 13,8V PSU? The SI doesn't seem to have a problem with the higher voltage in any other way?
- What's causing this popping anyway? the input caps charging/decharging?

Can anyone tell me if the evoluation board has any popping issues? I'm really considering buying one of those for use as my main amp in art's chassis... (2024 or 2021b version, I'm not sure yet)

Thanks in advance!


PS My scepticism to the input cap replacement vaporated like snow before the sun while I'm testing the mod. Amazing difference in the bass dept! thanks everyone for all the info about this!
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Old 19th April 2005, 06:09 PM   #2
ohenry is offline ohenry  United States
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I have the TA2024 evaluation board and it does "thump" upon turning on, but not too badly through my 94db efficient speakers. It got a little worse when I doubled the PS caps value. I don't have any noise during other times, just turn on.

I'm not sure if the 13.8v power supply makes a difference, I have one manufactured by Pyramid but was afraid to try it with the 2024 chip. I use a battery (12 volt SLA) and I can live with the thump, no regrets.

Others can help you with those technical questions, I only have guesses to offer.

Oh, and that input cap benefit is significant. Good decision to give it a try...
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Old 19th April 2005, 06:47 PM   #3
BWRX is offline BWRX  United States
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i've experienced a similar periodic ticking coming through the speakers from a stock SI running on battery power. apparently, the ticking was due to the low supply voltage from the discharged batteries. fresh AA's fixed that right up. as far as your popping issue... are you positive it isn't from the cd player? what revision board is it? the first boards included no protection diodes, the second revision boards included the protection diodes and had the heat slug soldered to the board, the third revision also has the protection diodes but does not have the heat slug soldered to the board. i ask only because i think the latest amps can have overheating issues if driven hard enough. if you've been following the other threads, you know that i've been testing both a stock SI (with a 3rd revision board) and my modified SI (with a second revision board). well, last week while i was re-testing the frequency response of the stock SI, the output of both channels suddenly went dead on me. i made sure the amp wasn't overheating because it was warm from other testing but it was as hot as when i was testing THD at an output of 11W into 4ohms. anyway, i let it cool down for a few minutes and turned it back on. as i turned the volume knob up the output suddenly cut out again. this time when i turned the amp off and back on there was no output at all on either channel. i had 20W 8ohm load resistors on the outputs of both channels, was using a 1Vrms 1kHz sine wave input signal, and was powering the amp with a 12V rail from a DC bench supply. this is the same stock amp that has gone into its thermal protection mode twice on me so far. i have no idea why the amp died because my modified amp was subjected to the exact same tests, has never gone into thermal protection, and still sounds great. the new boards sure do look better, but i've been disappointed with them so far with regards to reliability
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Old 20th April 2005, 12:29 AM   #4
dgo is offline dgo  Netherlands
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Thanks both for your replies.

@ ohenry: I'm not really worried about a bit of a thump on turn
on/off as long as it's not too loud. My speakers are only 89 dB, so I
guess that'll be ok with the evo board. I ordered it tonight (both the
2024 and the 2021b version as my faith in my amp3 project gets
less every day and I'm really eager to hear the 2021b in a proper
setup.)

How's your 2024 evo board in comparison to your input modded SI
holding up?

As my SI's running without any problems on the 13,8V regulated
PSU, I'm confident enough to use this psu on the evo board. For the
2021b its not a problem at all..

due to this popping problem I haven't been able to listen properly to
my newly mod SI unfortunately. But I will tomorrow! (read below)
The first impression on the bass is, however, I'm stunned by the
difference


@BWRX:

Thank you 1000x for your remark about the cd player!!! You made
my day

It would've taken me probably a few more days to have figured this
out.... It would've been my latest guess probably with the SI already
popping slightly after my mod..

pfew... I've never been so happy with something breaking down!
That damn Yamaha player (although sounding good) was annoying
me anyway the last few weeks with refusing cd's and other
drive/laser related problems! And at leasts it's not my babies, my
SI's (I feel I have a personal relationship with both now as they
sound different ) I can happily revert back to listening again

(After I buy a new player tomorrow
thinking about a NAD C542, hearing good things about that player)

As for the revision o/t board: I've got the board without the solder
heatsink but I'm not sure about the protection diodes though.. How
can I tell? What do they protect by the way?

and Yes, I read your thread about your testing. Interesting stuff. Did
you have those ebay extra heatsinks installed? I wouldn't be
surprised by the way about production differences (read
weaknesses) causing that different behaviour..

btw, I'd be interested in a graph of the bass response of a modded
SI , or evo board, do you make any?
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Old 20th April 2005, 04:21 AM   #5
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by dgo
Thanks both for your replies.

@ ohenry: I'm not really worried about a bit of a thump on turn
on/off as long as it's not too loud. My speakers are only 89 dB, so I
guess that'll be ok with the evo board. I ordered it tonight (both the
2024 and the 2021b version as my faith in my amp3 project gets
less every day and I'm really eager to hear the 2021b in a proper
setup.)

How's your 2024 evo board in comparison to your input modded SI
holding up?

As my SI's running without any problems on the 13,8V regulated
PSU, I'm confident enough to use this psu on the evo board. For the
2021b its not a problem at all..

due to this popping problem I haven't been able to listen properly to
my newly mod SI unfortunately. But I will tomorrow! (read below)
The first impression on the bass is, however, I'm stunned by the
difference


@BWRX:

Thank you 1000x for your remark about the cd player!!! You made
my day

It would've taken me probably a few more days to have figured this
out.... It would've been my latest guess probably with the SI already
popping slightly after my mod..

pfew... I've never been so happy with something breaking down!
That damn Yamaha player (although sounding good) was annoying
me anyway the last few weeks with refusing cd's and other
drive/laser related problems! And at leasts it's not my babies, my
SI's (I feel I have a personal relationship with both now as they
sound different ) I can happily revert back to listening again

(After I buy a new player tomorrow
thinking about a NAD C542, hearing good things about that player)

As for the revision o/t board: I've got the board without the solder
heatsink but I'm not sure about the protection diodes though.. How
can I tell? What do they protect by the way?

and Yes, I read your thread about your testing. Interesting stuff. Did
you have those ebay extra heatsinks installed? I wouldn't be
surprised by the way about production differences (read
weaknesses) causing that different behaviour..

btw, I'd be interested in a graph of the bass response of a modded
SI , or evo board, do you make any?

popping smells like DC offset issues. Is there a DC offset at the output of the amp after turn on?

Gertjan
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Old 20th April 2005, 04:52 AM   #6
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Default Offset

All have dc offset. There is no circuit for controlling it, and no caps in line on the outputs either. All have been under 150 mv that I have tried.

George
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Old 20th April 2005, 01:39 PM   #7
ohenry is offline ohenry  United States
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Quote:
Originally posted by dgo
Thanks both for your replies.

@ ohenry:
How's your 2024 evo board in comparison to your input modded SI holding up?
The evaluation board sounds better out of the box, IMO, largely due to higher PS and input signal cap ratings. I did different mods on the SI and the evaluation board, so no credible comparison can be done (I have better parts on the evaluation board).
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