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"WHAMMY" Pass DIY headphone amp guide
"WHAMMY" Pass DIY headphone amp guide
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Old 29th May 2019, 05:57 PM   #1431
6L6 is online now 6L6  United States
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Or a switch...?



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Old 30th May 2019, 08:15 PM   #1432
Alfetta87 is offline Alfetta87  France
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Quote:
Originally Posted by rich1051414 View Post
I would really like a way to have a primary input, then a secondary, which automatically switches to the secondary if it has a signal, but I am not sure if doing such a thing would be feasible. I may use an auto-sensing A/V switch behind it instead of trying to merge it.
Not sure it's a good idea, as "something" has to sense the input signal. And this could occur into distorsions, which we don't want. Why not a good old switch as
6L6 suggests. They exist in gold plated, rhodium, palladium and any other fancy metal to ensure best connectivity.
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Old 2nd June 2019, 07:24 AM   #1433
bk856er is offline bk856er  United States
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Finished mine today. No headphone jack, just RCA in/out at the back. Squeezed in an inlet filter and power switch. Scavenged some Canare mic cable.

Sounds really great so far! Feeding my M2 from a phono stage.

BK
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Old 2nd June 2019, 04:51 PM   #1434
RafaPolit is offline RafaPolit  Ecuador
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Looks great! I see that you, like me, did not add the 25 ~ 75 Ohm resistors suggested by Wayne on the output RCAs when using it as a PRE. Maybe if it's just a pre, it would make sense.

It was reported to help with possible oscillations.

If you have a way to measure them, it would be interesting to know if there is actually any.

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Rafa.
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Old 2nd June 2019, 07:00 PM   #1435
bk856er is offline bk856er  United States
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Quote:
Originally Posted by RafaPolit View Post
Looks great! I see that you, like me, did not add the 25 ~ 75 Ohm resistors suggested by Wayne on the output RCAs when using it as a PRE. Maybe if it's just a pre, it would make sense.

It was reported to help with possible oscillations.

If you have a way to measure them, it would be interesting to know if there is actually any.

Best,
Rafa.
My impression was that recommendation was for setups with RCA-out paralleled off the headphone jack for better isolation and not strictly necessary. If it's generally more suitable for preamp-only duty to decrease the possibility of oscillation I'll definitely consider it, but the cramped rear panel has already become very tedious to work with!

BK
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Old 3rd June 2019, 06:00 AM   #1436
RafaPolit is offline RafaPolit  Ecuador
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My take was that output impedance is kept very low in order to drive 15 Ohm headphones with ease. For PRE duty where AMPs have 10K + Ohm input impedance, the usual value from manufacturers is around 100 Ohms.

My probable approach was to have them be soldered directly at or very near to RCA hot pin of the OUT RCAs (inside) so as to no clutter more space.

Perhaps I'm completely mistaken in the reasoning behind this resistors?

Best regards,
Rafa.
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Old 5th June 2019, 03:50 PM   #1437
mistahMax is offline mistahMax  United States
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The resisters in series with the output is to limit the current if the RCA terminals get accidentally shorted while the preamp is powered on - they act as a load. "A safety thing." At least, this is my understanding.
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Old 5th June 2019, 09:28 PM   #1438
wayne is offline wayne  United States
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You are correct it offers some short protection and stability into possible strange loads.
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Old 9th June 2019, 10:41 PM   #1439
bk856er is offline bk856er  United States
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Added some ventilation. 148 holes the hard way - oh my aching neck!

BK
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Old 10th June 2019, 09:44 PM   #1440
wayne is offline wayne  United States
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Nice job on the ventilation. I would have messed that up on the second to last hole.
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