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May 24, 2019, 12:20:06 pm

Author Topic: Reduction (+ Integration) Build Feedback Hum Problem [resolved]  (Read 789 times)

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Offline fullheadofnothing

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Re: Reduction (+ Integration) Build Feedback Hum Problem
« Reply #15 on: February 19, 2018, 10:18:54 am »
The fact that it changes when you move it suggests that it is an environmental issue. Can you post pictures of your setup?
Joshua Harris

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Offline Pflugshaupt

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Re: Reduction (+ Integration) Build Feedback Hum Problem
« Reply #16 on: February 26, 2018, 01:13:36 am »
Moving around does help a bit, but doesn't solve the hum completely. Overall I came to the conclusion that what I'm hearing is just the normal noise coming from the power supply. I concluded this after reading through lots of forum posts here and reading about the experience of others. At reasonable levels the hum is not audible or maybe no longer audible since I moved the wires around internally to get as much distance as possible for the signal paths to anything else.

What's messing with me is that my crack is so amazingly quiet. Even at max volume I hear just nothing besides very little tube hiss. On the crack I replaced the diodes with cree diodes and replaced the first 270 ohm resistor with a choke. Would maybe using cree diodes on the 135V rectifier + a 1kohm choke for the reduction help to lower the noise? Or am I better off replacing as much as possible of the signal path with shielded cable?

Offline fullheadofnothing

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Re: Reduction (+ Integration) Build Feedback Hum Problem
« Reply #17 on: February 26, 2018, 06:48:55 am »
Can you post pictures of your setup?

Also the wiring of the Reduction might be helpful.
Joshua Harris

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Offline Paul Birkeland

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Re: Reduction (+ Integration) Build Feedback Hum Problem
« Reply #18 on: February 26, 2018, 07:35:47 am »
The shunt regulator in the integration eliminates the benefits of different diodes or a choke in the power supply.  Additionally, power supply noise is 120Hz, which is commonly described as a buzz rather than a hum.  Hum is almost always ground related, and won't be eliminated by adding fancy parts to the Reduction (though you could potentially make it worse with these efforts).

The Crack is a low gain circuit fairly far up the chain in terms of signal level.  There's generally at least 100 times the signal coming into a Crack compared to a Reduction, so the comparison of noise floors between the two components is not particularly helpful.

Paul "PB" Birkeland

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Offline Doc B.

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Re: Reduction (+ Integration) Build Feedback Hum Problem
« Reply #19 on: February 26, 2018, 08:05:02 am »
The AT440Mlb is a hair on the low side output-wise at 4mV, and that will have some effect on the perceived noise floor. We spec the Reduction with Integration as being useful with cartridges down to 3mV, but of course the higher the output the better the S/N. The more common 5mV output level seems to be a sweet spot.

Different tubes will have different levels of noise as well. Finding a super quiet pair is pretty much a matter of plug it in and see.
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Offline Pflugshaupt

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Re: Reduction (+ Integration) Build Feedback Hum Problem
« Reply #20 on: February 27, 2018, 08:22:28 am »
Problem solved! In the end it was the same thing I read many times on this forum. I had a bad solder connection on one ground connection.

This is how I figured it out: I connected the reduction with an audio interface because I wanted to measure the hum to show it here. I made some rca plugs to short the inputs. While I set up everything to do a frequency plot I noted there was no hum when I had just the left channel connected to the audio interface. Then I tried connecting only the right channel and I got a crazy loud hum. With both channels I got hum on left and right, but more on the right as I wrote before. So I thought something was wrong with grounding just on the right channel and did a reflow of all solder joints on the right part. This has eliminated the hum completely and now I just hear faint tube hiss which I'm more than happy to have. As the problem was not extreme to begin with I guess one of my solder joints was not fully conductive. I believe it probably was the one where the three caps and the black twisted wire going to the right output are connected. Or maybe the difficult to solder ground post connection (Even with the post totally disassembled I had some troubles getting a good temp and flow there).

Finally things are as awesome as I hoped when I bought the kit and now I need to go and listen to some records! Thanks for all the help!
« Last Edit: February 27, 2018, 10:48:09 am by Pflugshaupt »