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Old 17th September 2005, 07:48 PM   #1
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Default Amp1-B Terrible Bass Performance

I built an AMP1-B from 41Hz.com, and while the sound it generally nice (if perhaos overly polite), the bass performance is terrible. That is, there is no bass. Can anyone make suggestions as to what might help.

I built the amp stock except the 330uF electrolytic caps were replaced with 220uF of higher quailty. The 4.7uF electrolytic input caps were replaced with 4.7F Blackgates. The power supply is essentially this design. The 10000uF on each side is made up of 10 1000uF Panasonic FM caps. The transformer is a 160VAC with 18V secondaries (which rectiries as +/-25.5V.)

As this has burned in for a few hours, the bass has improved a bit, but it is still very weak.

Obvious places to start are with a bigger transformer, more rail capacitance, bigger film caps on the rails, replacing the 220uF's, or something else. Does anyone have any experience which would suggest which place is the best to start?

-d
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Old 17th September 2005, 08:16 PM   #2
Bgt is offline Bgt  Netherlands
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Quote:
The 4.7uF electrolytic input caps
Put 22uf caps here.
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Old 17th September 2005, 08:19 PM   #3
Nisbeth is offline Nisbeth  Denmark
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What's your reference for the comparison? Frequently class D amps are described as being "lean" or "bright" because the amp has much more control over the bass, making it sound as if there is less bass


/U.
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Old 17th September 2005, 08:30 PM   #4
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Quote:
Originally posted by Bgt

Put 22uf caps here.

Really? What is the input impedence that the caps need to be so large? The schematic has 3.3uF caps on the input which would suggest that everyone who builds these has worse bass than me, which I can't believe.

As a side question, my preamp has output caps. Is there really any reason for the input caps at all?

Quote:
Originally posted by Nisbeth
What's your reference for the comparison? Frequently class D amps are described as being "lean" or "bright" because the amp has much more control over the bass, making it sound as if there is less bass


/U.
No, this isn't lean. This is nothing audble below about 120Hz.

B/t/w, the midrange, compared to a chip amp, is really spectacular.
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Old 17th September 2005, 08:35 PM   #5
Bgt is offline Bgt  Netherlands
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Quote:
What is the input impedence that the caps need to be so large?
20k, I mean if you soldered in the proper value.
You should have the full spectrum than.
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Old 17th September 2005, 08:44 PM   #6
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Quote:
Originally posted by Bgt

20k, I mean if you soldered in the proper value.
This is probably a good thing to check first, though I think it is fine.

Using C = 1/(2 * pi * Hz * R), 4.7, or even 3.3uF is plenty.
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Old 17th September 2005, 09:02 PM   #7
Bgt is offline Bgt  Netherlands
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Maybe your input caps. are not ok. Take them out since you have them in the preamp. But watch the + level is on the proper side of the cap., I mean the highest + level. Otherwise this cap isn't happy. Or take take the cap out of the preamp.
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Old 18th September 2005, 12:28 AM   #8
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I replaced the 220uF rail caps with 470uF Nichicon Muse caps (whic no, do not fit on the board) and the bass is there.
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Old 18th September 2005, 01:55 AM   #9
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It's just a coupling cap like any other right? Keep the module from amplifying DC, that means if you're source has very low DC output you can do without them normally but I think the case of the Triphath chip amps you can't because you require a level conversion as well.

It takes alot more than a few hours for black gates to burn in, you're looking at weeks and months!

What if you tried a cheaper cap of same value, non black gate, let that burn in in a few hours and see how it sounds?

You could also experiment more with the values of the snubbers, see what difference that makes.
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Old 18th September 2005, 03:42 AM   #10
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I built an Amp-1B . Stock parts. Supply caps on board are 330uF Nichicon and input R is 20 K and input C is 3.3uF Panasonic.
Sounded good from the first day.
Now it sounds great and the bass has slightly less weight but is very taut.
For comparison I'm using a Creek 5350SE.
I think it is better than the Creek except for the slightly lighter bass. But that is noticeable only when compared. Played loud ( Mission 701 - 89db/watt ) it is really impressive and very clear and detailed. It's a great amp - great value for money.
I don't feel any loss of bass when listening to it on most music.

Supply is +/- 35 V with a 10 A bridge and 2x 10,000uF Samsung capacitors. No low value cap bypassing and no snubberising ! Maybe later on.
No special supply / speaker connecting cables either . All industry standard electrical hook-up wire and I think not very good !
Still sounds extremely good.
Cheers.
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