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"WHAMMY" Pass DIY headphone amp guide
"WHAMMY" Pass DIY headphone amp guide
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Old 21st February 2019, 06:35 PM   #1171
6L6 is offline 6L6  United States
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Old 21st February 2019, 07:44 PM   #1172
RafaPolit is offline RafaPolit  Ecuador
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Well, now it has been repeatedly stated that, in order to get RCA outputs, it's best to have 25 to 100 Ohm resistors between the switched headphone jack and the outputs.

I have not yet done so (this was not as clear when I built my kit). I have it straight to the ACA inputs. I have not noticed or heard any oscillations: is there a way I could know or measure such oscillations? If I can't hear any clear issues, could there be really high frequency oscillations that are beyond hearing ranges that are harmful?

So, basic question: would it merit to take things apart and solder those resistors or, if things are sounding good, am I ok leaving the output with a much lower impedance?

Thanks as always (really enjoying the Whammy!)
Rafa.
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Old 21st February 2019, 08:37 PM   #1173
ahess is offline ahess  United States
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I'm not planning on having the output go to the amp. I'm going to wire the two sets of RCA inputs together, so with the amp off the preamp signal will go straight to the amp.
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Old 21st February 2019, 10:01 PM   #1174
wayne is offline wayne  United States
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The resistors may not be needed it is really kind of a safety thing.
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Old 21st February 2019, 10:45 PM   #1175
rich1051414 is offline rich1051414
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Quote:
Originally Posted by RafaPolit View Post
Well, now it has been repeatedly stated that, in order to get RCA outputs, it's best to have 25 to 100 Ohm resistors between the switched headphone jack and the outputs.

I have not yet done so (this was not as clear when I built my kit). I have it straight to the ACA inputs. I have not noticed or heard any oscillations: is there a way I could know or measure such oscillations? If I can't hear any clear issues, could there be really high frequency oscillations that are beyond hearing ranges that are harmful?

So, basic question: would it merit to take things apart and solder those resistors or, if things are sounding good, am I ok leaving the output with a much lower impedance?

Thanks as always (really enjoying the Whammy!)
Rafa.
There is an expectation that the line out will be relatively high impedance. It probably won't cause problems, though, simply supply more current than is necessary :P Where you could run into problems is if the line out is too hot, which is more likely to cause problems. Too hot could cause clipping.

Last edited by rich1051414; 21st February 2019 at 10:47 PM.
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Old 22nd February 2019, 08:52 PM   #1176
ahess is offline ahess  United States
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Well, another WHAMMY has become a WHAMMM. It took most of the day, but I'm happy with the results. It's dead silent even at full volume (oh, wait, it was off...that's better. No, still silent). The biggest change to the music is that the bass is much, much more defined. Before there was often a bass-cloud that bled into everything. Now the bass is tighter, and you get more of a sense of an instrument playing it. I think there is also more dynamics overall, but I need time to listen more.

Click the image to open in full size.

Thanks, Wayne, and everyone here who chipped in with ideas.

Gotta go listen to music...
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Old 22nd February 2019, 10:47 PM   #1177
ahess is offline ahess  United States
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Hmm...if I'm checking the DC offset right--measuring right/left headphone terminals and headphone ground, then I'm getting 23mV. That's high, right? Is there something I can do about that?

Also, checking the input the same way I got 0mV. Assuming I'm doing it correctly, does that mean that I could take out C1 and C5? Wouldn't that clean up the signal path a bit?

I'm worried about that 23 mV.
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Old 22nd February 2019, 10:53 PM   #1178
silasmellor is offline silasmellor  Denmark
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Anything connected?
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Old 23rd February 2019, 12:41 AM   #1179
ahess is offline ahess  United States
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The preamp is connected but off.
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Old 23rd February 2019, 01:55 AM   #1180
6L6 is offline 6L6  United States
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Quote:
Originally Posted by ahess View Post

I'm worried about that 23 mV.
Don't be.

Assuming you had really low resistance headphones like my Denons at 25ohm, your 0.023v of a volt will give a standing DC current of 0.00092A (0.92 milliamp), loading your headphones with a dissipation of 0.00002W

(Go back and count the zeroes after the decimals)

With higher impedance, there's even less to worry about.
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