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Rod Elliot P3A build sounds too bright/harsh/agressive
Rod Elliot P3A build sounds too bright/harsh/agressive
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Old 22nd March 2016, 01:01 AM   #1
Ravenash is offline Ravenash  Austria
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Default Rod Elliot P3A build sounds too bright/harsh/agressive

Hi guys,

I have just finished building the P3A amplifier, following all the exceptional feedback on the web, and unfortunately the sound is below my expectations. I realize that this is because of some components are used, but I simply cannot identify them.

My main problem is that the sound is very bright, agressive. I am looking for a warm, natural sound. The amplifier at this point has excellent transparency of instruments, good control and is doing an excellent job with all the frequency range from deep, strong bass to crisp highs. HOWEVER, the sound is very "loud", very harsh, bright, agressive. It is very tiresome to listen to it. I think that the middle frequencies are being brought up in front too loud. ( I have noticed this behaviour on the powerful Pioneer A-878, the reason why I changed it for the very warm Onkyo 8670 ).

I have used the exact values for all components in the design. WIMA capacitors for the 100 pF, all resistors are 1% Welwyn, the finals are MJ21193/4, drivers BC139/140 and others BC546 as specified. All A/C capacitors are polypropylene. My main concern is C1. I have used a Vishay polyprop capacitor - 4.7uF at 150V.It is massive in size, and seems of very good quality, but I am worried it is the one giving me this agressive, screamy sound.

Can you please provide any info about how I can make the P3A sound warmer and more relaxing to listen to ?

( mention - I am using this without a preamplifier at the moment, directly from the sound card output, but I also do that with the Onkyo and the sound is much warmer - could a preamp solve this problem ? )

Thank you so much.
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Old 22nd March 2016, 08:04 AM   #2
basi is online now basi  Croatia
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Can u post picture of your work?
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Old 22nd March 2016, 10:31 AM   #3
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Ravenash View Post
could a preamp solve this problem ?
The amp has sufficient gain and sensitivity but the answer is yes.
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Old 22nd March 2016, 12:15 PM   #4
currentflow is offline currentflow  United Kingdom
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Quote:
Originally Posted by Ravenash View Post
My main problem is that the sound is very bright, agressive. I am looking for a warm, natural sound. The amplifier at this point has excellent transparency of instruments, good control and is doing an excellent job with all the frequency range from deep, strong bass to crisp highs. HOWEVER, the sound is very "loud", very harsh, bright, agressive. It is very tiresome to listen to it.
A harsh-sounding amplifier might be the result of instability. If you have an oscilloscope and a signal generator, this might help reveal the cause of the problem.
Quote:
I have used the exact values for all components in the design. WIMA capacitors for the 100 pF, all resistors are 1% Welwyn, the finals are MJ21193/4, drivers BC139/140 and others BC546 as specified. All A/C capacitors are polypropylene. My main concern is C1. I have used a Vishay polyprop capacitor - 4.7uF at 150V.It is massive in size, and seems of very good quality, but I am worried it is the one giving me this agressive, screamy sound.
I think you meant to say BD139/140 (not BCxxx) drivers. For C1, why not try a different type of capacitor?
Quote:
Can you please provide any info about how I can make the P3A sound warmer and more relaxing to listen to ?

( mention - I am using this without a preamplifier at the moment, directly from the sound card output, but I also do that with the Onkyo and the sound is much warmer - could a preamp solve this problem ? )
A well-designed amplifier should sound fine without a pre-amplifier, given sufficient line levels to drive the amplifier to its full output capability. The problem is more likely to be caused by instability.
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Old 22nd March 2016, 12:20 PM   #5
DF96 is offline DF96  England
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A physically large coupling cap gives extra scope for capacitive feedback and instability. Polypropylene caps tend to be large.
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Old 22nd March 2016, 12:27 PM   #6
Bigun is offline Bigun  Canada
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Rod Elliot P3A build sounds too bright/harsh/agressive
This is a proven good sounding amp, so the issue must be in the implementation - or you have nasty speakers. I have only limited experience, but I would suggest looking for oscillations as mentioned already. After that I would say the most likely issue is feedback compensation capacitor choice and choice of other capacitors. Compensation capacitors - try Silver Mica or ceramic np0. Some metallized foil caps sound a bit harsh to me.
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Old 22nd March 2016, 12:52 PM   #7
Ravenash is offline Ravenash  Austria
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The Speakers are Pioneer DSS-9 , they should not be an issue. I will attach some pictures in a minute maybe you can see something wrong there

Link 1Click the image to open in full size.

Link 2Click the image to open in full size.

Link 3Click the image to open in full size.

Last edited by Ravenash; 22nd March 2016 at 01:14 PM.
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Old 22nd March 2016, 01:18 PM   #8
DF96 is offline DF96  England
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Try using a normal cap for C1 (assuming that is the big green cap floating in the air). By 'normal' I mean small, cheap, possibly lower value. If this solves the problem then you almost certainly had oscillation. The problem is not that the cap is defective, but simply that it is large and hanging over the circuit.
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Old 22nd March 2016, 01:19 PM   #9
sgrossklass is offline sgrossklass  Germany
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That 47 is absolutely huge. Mind trying with a cute little electrolytic instead? (Ideally a bipolar, low-leakage type, or two back-to-back, but a single polar one should do for now.)
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Old 22nd March 2016, 01:25 PM   #10
Ravenash is offline Ravenash  Austria
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Yes, the big cap is C1. I will buy a small one and see what happens. Thanks. I have been told that I do not have power supply decoupling. Can anyone please explain to me a bit how this would affect sound and how to fix ?
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