My new 3886 amp seems light on the highs. - diyAudio
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Old 7th February 2011, 08:24 PM   #1
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Default My new 3886 amp seems light on the highs.

Hi all.

I just finished my first chip amp using the stereo 3886 kit from chipamp.com, and a 200VA 22V x 2 transformer. It sounds really good, but I'm wondering if I'm missing the high end a little.

I used a 10K pot for the volume. I used 22g wires for all the signal hookups, and also for the outputs from the power board. Does anyone think the thin wires or my choice of pot could be stifling the highs? The other thing I'm thinking is that I'm using it with my ipod (AIFF files), so maybe the defect is in the DAC in the ipod.

Has anyone else had this issue? Is it a matter of modifying the kit components? Any thoughts would be most welcome. Thanks.

Josh
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Old 7th February 2011, 08:44 PM   #2
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Hi Josh, can I ask what you are comparing it with?

I run the chipamp boards in unmodified form and the balance is very good, the only difference I can see is that I am using a 50k Alps blue pot. Thin wires tend to affect the bass rather than the highs and I would be tempted to go with something a bit thicker for the outputs. Just give both the boards the once over to make sure everything is where it is supposed to be.

Good luck,

Ian
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Old 7th February 2011, 11:20 PM   #3
AndrewT is online now AndrewT  Scotland
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what filters have you fitted to your chipamp?
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Old 7th February 2011, 11:52 PM   #4
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Ian- I am comparing the chip amp to my old Onkyo receiver, and also to my c-moy amps with Grado SR80 or Shure 144 phones. The chip amp sounds better than the Onkyo, but I feel like it's missing a little sizzle.

Andrew- I made the stock 3886 stereo kit from chipamp.com, and being a newbie, I'm not sure which are the filter caps. Here are the included components with the kit:

Components for amplifier boards
2 LM3886TF
4 22 kohm 0.5w compact metal film resistors
2 10 kohm 0.5w compact metal film resistors
2 1 kohm 0.5w compact metal film resistors
2 680 ohm 0.5w compact metal film resistors
2 2.7 ohm 2w metal film resistors
6 100 uf 50v Panasonic FC
2 47 uf 50v Panasonic FC 60.1 uf film caps

and the schematic is on page 3 of this document:http://chipamp.com/docs/lm3886-manual.pdf

Now that I'm looking, he suggests a 25k pot. Does this make a difference?

I am planning to try it out with a CD player instead of iPod today.

Thanks again for your thoughts.

Last edited by jbernst5; 7th February 2011 at 11:55 PM.
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Old 8th February 2011, 05:25 AM   #5
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The pot shouldn't really make much difference.

In terms of your comparison we'll have to stick with the Onkyo, as the headphones introduce an additional variable into the equation. I would assume you are using the same speakers with both?

Are you using the chipamp power supply boards as well?

Also, do both channels have the tonal balance that you noted?
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Old 8th February 2011, 09:45 AM   #6
AndrewT is online now AndrewT  Scotland
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The two input filters are omitted from the p3 schematic.

It really requires an RF filter.
Add a small cap across R2, somewhere between 220pF and 680pF. The 680pF may just cut a tiny bit of treble. The 220pF filter is so high above audio you cannot possibly hear any treble cut.

There is no high pass filter. The high pass and it's other function, DC blocking, is I believe mandatory. At present you have mixed AC and DC coupling with the NFB cap defining the bass roll off.
Does your Source have a DC blocking capacitor? If it has then you don't need a second one in series with it. But you must ensure that all the sources that could be plugged in, ALL have DC blocking fitted.
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Last edited by AndrewT; 8th February 2011 at 09:48 AM.
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Old 8th February 2011, 01:04 PM   #7
Hubba is offline Hubba  Sweden
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Andrew,

Also being a newbie to LM3886 chipamp your reply cought my eye; The NFB cap is according to the build instructions "optional", so leaving it out means that one should ensure that there are DC blocking fitted to the source (in my case a CD). Is that correct or have I misunderstod you?

What's the best way of implementing a high pass filter to the chipamp.com schematics, and how will it effect the chipamp in lack of better a better word...

Regards,
Fredrik
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Old 8th February 2011, 03:58 PM   #8
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Please humor my ignorance...

As far as an RF filter goes, when I turn the amp on and turn it up all the way, it is dead silent. Would an RF filter be important in that case?

I don't know what an NFB cap is. Is that Ci in the diagram, which Brian GT describes as a "feedback cap," listed as optional in the assembly manual for the kit? Do other typical chip amp designs use a high pass filter?

How can I tell if my sources have DC blocking fitted? I'm using my iPod Classic headphone out now, but my my plan is to use a CD player, and then probably an Opus DAC and Ballsie Lite converted from Twisted Pear audio.

Very confused here.

Last edited by jbernst5; 8th February 2011 at 04:05 PM.
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Old 8th February 2011, 08:09 PM   #9
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RF interference is often intermittent in nature and often shows-up at the most inconvenient times. The world is rapidly becoming a very RFI noisy place. It's best to plan ahead.
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Old 9th February 2011, 03:38 PM   #10
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This AM I turned the iPod down and the amp all the way up. The sound came into focus. I'm guessing this points to the 10K pot stifling the highs. I think I'll change it out. Does this make sense?
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