Help Identifying / locating this part

[Kyrad777]

Hey everyone.  I'm trying to repair a studio reference amp, and to match the other amps in the system, I need to replace this with the exact same part ( if possible ).  SMD may be an acceptable alternative, but I would like to identify this ( exactly ) and exhaust all avenues before going that route.  The 2AR is what seems to be tripping me up.  I'm sure it's obvious, but im just not seeing it.

I've attached a picture of the part and its markings and the associated info from the service manual.

Searching for these in the usual places ( Digikey, Mouser ) isn't showing an exact replacement.  But then again, I could be missing it, since I don't source components full time.

Any help would be greatly appreciated. 

- edit - This is part of the power supply board, but the overall topology of the amp has the output from the amp section coming back onto this board, and I don't know if a different part will affect the sound.  I say this because I have several amps with different revisions of boards with different values here, and they sound drastically different.  Midrange stands out significantly and sounds a bit harsh, and the bass sounds boomier and starts rolling off around 60-70hz - ( the amp frequency response is  10 - 70,000, so the right parts are crucial to maintain that. )

Thanks!

[ataradov]

Can you show more of the schematic?

This is just a generic 100 nF capacitor. "2AR" is irrelevant, it is a date code or some other random stuff like this.

[Haenk]

The "C" in the schematic might hint at a 0.25% part.
The second row *does* have a meaning, however it's a manufacturer marking. And varies. So without having the manufacturer listed in the service manual, go with a reasonable part. Voltage would likely be 100V or less (check schematic), grab a small tolerance part to be safe, ignore tempco.

[Zenith]

The "C" in the schematic might hint at a 0.25% part.

Or "ceramic". More may understood by looking at the other caps on the schematic to see it there is a pattern. The manual may have a parts list stating exactly what this component is.

As said previously, this looks like a 100nF capacitor and the 2AR is most likely some manufacturing or QC code, representing the batch number or similar. In that case it would be of no meaning to anyone apart from the manufacturer. Tracking down a part with the same code would be very hard.

I find it hard to imagine that a ceramic capacitor in the power supply would have a drastic effect on sound quality. Given that it does, my solution would be to get a few lots of twenty or so similar capacitors and try them. Choose which sounds the best.

[wraper]

The "C" in the schematic might hint at a 0.25% part.

Zero chance for that. It's just some unstable garbage like Y5V.

[Gyro]

Ye, it's a very bog standard 100nF ceramic cap. It looks very small so the ceramic composition isn't going to be anything special, certainly not close tolerance or tempco. If it's not faulty (shorted or low value) I'd leave it. I really doubt it has any effect on sound quality unless in the signal path - which would be extremely unlikely in a 'studio reference amp'.

[wraper]

I need to replace this with the exact same part ( if possible ).

For what? I see zero valid reason to replace it so far.

[Zenith]

I need to replace this with the exact same part ( if possible ).

For what? I see zero valid reason to replace it so far.

I gather he's trying to match these amplifiers with different revisions of boards. This one sounds worse than the others, and this is a part that stands out as different. In my view he should look elsewhere for the differences in sound.

[Vovk_Z]

The "C" in the schematic might hint at a 0.25% part.

Zero chance for that. It's just some unstable garbage like Y5V.

+1.

I guess any 0.1uF capacitor which fits that place shoud do.

[tooki]

- edit - This is part of the power supply board, but the overall topology of the amp has the output from the amp section coming back onto this board, and I don't know if a different part will affect the sound.  I say this because I have several amps with different revisions of boards with different values here, and they sound drastically different.  Midrange stands out significantly and sounds a bit harsh, and the bass sounds boomier and starts rolling off around 60-70hz - ( the amp frequency response is  10 - 70,000, so the right parts are crucial to maintain that. )

If the other units’ caps also say “104” on the first line, then they have the same value cap. I would assume they’re just made with different batches of caps. (The 2AR is likely a lot code or date code.)

The real question is, is it in the audio signal path or not? (Any part of the power supply that has feedback from the amp section is, in a sense, part of the audio path.) The function that comes to mind is dynamic power supply voltage scaling, which uses the audio signal to modify the power supply voltage, allowing an amplifier to operate with less wasted energy during quieter passages.

Maybe you could do what I would have done from the start and provide basic information about the device, like the manufacturer and model, so that we can try and find service manuals or schematics or something.

[Haenk]

The "C" in the schematic might hint at a 0.25% part.

Zero chance for that. It's just some unstable garbage like Y5V.

That's what I assume as well. But you never know, unless there is a schematic available. Maybe someone did some voodoo in there...

[TimFox]

Since a ceramic capacitor in that value and physical size cannot be C0G/NP0, a tight tolerance such as 0.25% would be impossible due to the various co-efficients of the non-linear dielectrics that could fit in that package.
If it were so, the proper label would be "104C".
A C0G/NP0 code might read "102K" for 1 nF, 10% tolerance, or "102J" for 5% tolerance.

[DavidAlfa]

You only need precision / stability if being part of the signal path. Are you sure it's not doing simple power decoupling?
Edit: So it's part of the PSU. Then it doesn't.
What model is it? Posting a screenshot of three lines and a cap doesn't help at all!

[TimFox]

Back to the original post.
You reported differences in the frequency response between units:  "Midrange stands out significantly and sounds a bit harsh, and the bass sounds boomier and starts rolling off around 60-70hz - ( the amp frequency response is  10 - 70,000, so the right parts are crucial to maintain that.)"
Have you measured the frequency response of the amplifiers themselves?
Perhaps the perceived differences are in the loudspeakers, etc.

[Zenith]

Yes, I'd have more faith in Bode plots comparing these amplifiers, than the subjective evaluation that with one, the bass was boomy and the mid-range stood out and was harsh.

[Kyrad777]

Hey everyone, thank you all for the great responses.  I'm going to try and answer some of the questions posed and give more information that was requested.

One important note.  I just discovered that there are several different revisions of power supply boards.  This could account for the very different sound between units.  I tried swapping one board from one amp to another ( thinking... ASSUMING they were all the same ) and it didn't go well.  There was an electrical "buzzing" sound from the amp, and the heat sinks got rather warm from being on for 15 seconds. ( these amps run at room temp unless you are really driving them hard ).   So apparently im not 100% sure the schematic I posted is for this particular amp revision.

I do have the service manual that I have attached below.  I purposely didn't list the name of the amp because most people see the manufacture and dismiss it as junk.  This particular amp was designed by a different company and then rebadged by Alesis when it bought out the company in the 90's.  It was made specifically for the monitor Two speakers ( not the monitor one MK2, The monitor Two, a three way speaker - Pic below.  ). It is for a Alesis RA500.


The part I am trying to replace actually blew during a very heavy bass passage.  ( pic below )  It also took out the woofer on that side ( voice coil came loose and is now rubbing against the magnet structure. ). I have 4 of these amps, and only one sounds what I would describe as "transparent".  All the others have a differing "Tonality" to them.  As for the comment that it was "different speakers", I replaced the blown woofer with a spare before I discovered the amp had a problem. It sounded the same as it did before.  I have been doing sound for almost 40 years ( studio, live and recording ) so I have a very good ear for hearing subtle changes.  But honestly, anyone that would A/B these would easily notice the difference.  With the replacement amp, the midrange went from "existing, open and revealing" to "harsh, screechy and bright".  Not a subtle difference at all.  The Bass now is very "Boxy" sounding, not going much below 80hz.  All sources, A/D converters and such are exactly the same.  The amp is the only difference.  So I get the skepticism, but trust me when I say it's the replacement amp that is making the difference.  I do plan on pulling the "bad sounding one" apart after the main amp is back up and seeing if someone changed the output transistors with "Bob's Brand" parts. I can still get the original transistors, so I am planning on rebuilding the second amp when I can.  Anyway,  I'm guessing that is where the difference is.  Honestly, the listening experience went from "Holy crap, I can hear something ive never heard in that classic recording before" to more of a "Big annoying cheap boom box" type of sound, just from switching the amps. 

Anywho, I got on a bit of a tangent there.  I thought at first the big caps had started leaking and that shorted the part out ( you can see something on the board in the photo ).  Turns out one of the neighborhood stray cats had snuck in the studio and marked the rack above the amp, and that had dripped down on the board and apparently shorted it out during loud passages.  Initially, ( before I knew about the cat ) I was thinking it was a cap leaking.  I removed the caps planning on replacing them and realized there was no electrolytic under them.  The white glue had sealed the underside, and there was no "pee" under them.  Using a powerful infrared light source the "Goo" floresed brightly.  Luckily all the traces are on the backside, so no corrosion damage.  The caps tested well within spec, so those are going back in. 

I do need to replace both smaller caps so they match, but after reading some of the responses i'm thinking I may have been over concerned about how this may affect the sound.  On high end amps, it's common practice to put a smaller cap across the main filter caps to increase high frequency capability ( Ive heard this from multiple high end amp designers on several podcasts ).  Im guessing it may have some truth to it?  Being the amp tops out at 70,000 HZ ( my cat can attest that it goes higher that 20K ) I'm leaning toward the possibility that this cap matters.  It may not, but I don't want to loose the way the highs sounded before. 

Side note, I get that I may be overthinking this or coming off as an audio snob, ( im definitely not, I have Alesis equipment )  but every single person that listens to these speakers on that amp spends at least 15 minutes pulling up classic recordings, then sits there with their mouths open and eyes wide.  They always make the following two comments " I've never heard that before" and "The hairs on my neck and arms are standing up".  These aren't the best speakers ever made, heck, I have 4 pairs of them and only one pair sound even remotely good ( I got all them used ).  But for what they are, they are remarkable, and I don't have 4 grand to replace them with something comparable.   Hence, why I am so passionate to repair the amp to its original performance.  Thats why I am asking the professional community what you all think.  It's very possible I am completely missing something, or overcomplicating a simple solution.



Thanks everyone. 

[Kyrad777]

Service manual isn't showing up as being attached for me, so here is a capture of the schematic.

[ataradov]

"transparent" is not a meaningful description. Stop describing sound with that audiophool terminology and start measuring it.

But apart from that, if some random capacitor in the power supply affects your equipment, then your equipment is shit.

We don't care about the name, we just want more of the schematic to judge how important it is to anything. Chances are - it is not important at all.

[ataradov]

LOL. This is just a random cap on the output of the rectifier. It quite literally does not matter.

[fzabkar]

104/M -> mylar ?
104/C -> ceramic ?

[fzabkar]

LOL. This is just a random cap on the output of the rectifier. It quite literally does not matter.

I can't believe that I've just read an entire thread about this stupid "hi-fidelity" cap. ROTFLMAO.

[TimFox]

"transparent" is not a meaningful description. Stop describing sound with that audiophool terminology and start measuring it.

But apart from that, if some random capacitor in the power supply affects your equipment, then your equipment is shit.

We don't care about the name, we just want more of the schematic to judge how important it is to anything. Chances are - it is not important at all.

To be fair, if that component in the power supply is defective (possibly internal arcing) it might well screw up the sound.

[ataradov]

Well, ok it may lead to bad power rails. But in no way it would make sound more "transparent" or make "midrange stand out". It will just make it distorted.

And yes, given the use of "104/M", it would make sense that they are mylar capacitors. Although I have no clue why they needed C03.

[fzabkar]

"transparent" is not a meaningful description. Stop describing sound with that audiophool terminology and start measuring it.

But apart from that, if some random capacitor in the power supply affects your equipment, then your equipment is shit.

We don't care about the name, we just want more of the schematic to judge how important it is to anything. Chances are - it is not important at all.

To be fair, if that component in the power supply is defective (possibly internal arcing) it might well screw up the sound.

My understanding was that the OP wanted to replace this capacitor, and they were concerned that the replacement may not have the same sound fidelity as the original.

[Kyrad777]

EDIT - Apologies if this comes off snarky.  Its been quite a day.


I said nothing about this cap drastically changing the sound.  I said the replacement amp I am using sounds drastically different. 

I want the good amp back that sounds like you are in front of the band, and not listening through speakers.  Not the crappy one I am using now that sounds awful.

For those of you that only understand measurements,  the "bad amp" is outputting a very different signal than the input signal at certain frequencies ( mostly the upper midrange frequencies), plus it is rolling off the bass frequencies below 80 HZ and emphasizing 100-120 hz.  This can probably be attributed to the cheap replacement transistors someone put in it.  The "Good" amp output is darn near flat from 10 - 70,000.

In an amp that is capable of going far past a typical frequency response of 20 - 20,000, parts might matter, maybe not.  And the way the power supply behaves at high power levels might become important. Maybe not.  Who knows.   If this was a consumer amp, I could care less what I replaced it with.  But this amp is important for mixing songs in a studio environment, and therefore important for generating income.  Hence why I am asking the pro's. 

ALSO, in my follow up post, I even said this part probably wouldn't make that much difference, but I wanted to keep it as close to factory as possible.  That is all. 

Thank you to those of you that took this seriously and gave me some good leads.