The GU50 that I've been building for 4-5 months works great connected to a dummy load. But when connected to a speaker, the higher frequencies (10K and up
), at higher volumes, turn into ugly triangles. Get the same thing with feedback connected or not.
Here's the new schematic:
I forgot to fix, the filaments are all AC.
GU50 PP has a triangle at higher frequencies.
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GU50 PP has a triangle at higher frequencies.
by DeathRex » Sat Mar 02, 2013 1:27 pm
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DeathRex - KT88
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Re: GU50 PP has a triangle at higher frequencies.
by Geek » Sat Mar 02, 2013 7:10 pm
Heya,
This is a non-issue for several reasons:
- This is normal as a speaker is a complex LCR load.
- This is normal as a speaker has finite frequency response.
- This is moot as there is no way the ear can hear harmonics up there. What is heard is the complex wave structures (as in cymbals) which are retained regardless of frequency response.
- This is moot because ears, not test equipment, listen to amplifiers.
Cheers!
But when connected to a speaker, the higher frequencies (10K and up
), at higher volumes, turn into ugly triangles.
This is a non-issue for several reasons:
- This is normal as a speaker is a complex LCR load.
- This is normal as a speaker has finite frequency response.
- This is moot as there is no way the ear can hear harmonics up there. What is heard is the complex wave structures (as in cymbals) which are retained regardless of frequency response.
- This is moot because ears, not test equipment, listen to amplifiers.
Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Re: GU50 PP has a triangle at higher frequencies.
by DeathRex » Sat Mar 02, 2013 7:17 pm
OK thanks Gregg. I'll have to play something loud when everyone is away and see how it sounds.
BTW the speakers are Infinity RS-5Bs.
On another note, how do you figure how much feedback you need? I have the global path on a 100K pot so I can adjust it. It seems good somewhere between 14K and 25K.
BTW the speakers are Infinity RS-5Bs.
On another note, how do you figure how much feedback you need? I have the global path on a 100K pot so I can adjust it. It seems good somewhere between 14K and 25K.
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DeathRex - KT88
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Re: GU50 PP has a triangle at higher frequencies.
by Geek » Sat Mar 02, 2013 9:48 pm
Hi,
You have your NFB resistor in the area of 14-25K, so now you should sub a fixed value for it.
There are six standard 5% values in that range... 15K, 16K, 18K, 20K, 22K and 24K. A local Radio Shack might carry of that, 15K and 22K (they still seem to think resistors are 20% tolerance, LOL!) I suggest you tack in each resistor and do a few critical listening songs you're very familiar with and permanently add in the one that sounds best to you.
If you want to know how much NFB you have, use an analog AC meter with a dB scale. Set to 0dBm with a 1KHz sine wave. Remove the resistor and see what it shoots up to... that's your dB of gNFB!
Cheers!
You have your NFB resistor in the area of 14-25K, so now you should sub a fixed value for it.
There are six standard 5% values in that range... 15K, 16K, 18K, 20K, 22K and 24K. A local Radio Shack might carry of that, 15K and 22K (they still seem to think resistors are 20% tolerance, LOL!) I suggest you tack in each resistor and do a few critical listening songs you're very familiar with and permanently add in the one that sounds best to you.
If you want to know how much NFB you have, use an analog AC meter with a dB scale. Set to 0dBm with a 1KHz sine wave. Remove the resistor and see what it shoots up to... that's your dB of gNFB!
Cheers!
-= Gregg =-
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
Fine wine comes in glass bottles, not plastic sacks. Therefore the finer electrons are also found in glass bottles.
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Geek - KT88
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Re: GU50 PP has a triangle at higher frequencies.
by DeathRex » Sun Mar 03, 2013 8:39 am
Geek wrote:Hi,
If you want to know how much NFB you have, use an analog AC meter with a dB scale. Set to 0dBm with a 1KHz sine wave. Remove the resistor and see what it shoots up to... that's your dB of gNFB!
Cheers!
I've been searching everywhere for that.
Thanks Gregg.
At first I wanted to be a ET. Now I are one.
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DeathRex - KT88
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Re: GU50 PP has a triangle at higher frequencies.
by EWBrown » Mon Mar 04, 2013 9:51 am
IIRC, (it's been an all-too-long time since I learned about this), triangle waves are the summation of even order harmonics (2nd, 4th, etc),
and square waves are the summation of odd-order harmonics (3rd, 5th, 7th, etc).
/ed B
and square waves are the summation of odd-order harmonics (3rd, 5th, 7th, etc).
/ed B
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