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Post by darkarn on Mar 5, 2021 18:45:56 GMT
As long as it is quiet when the potmeter is not moved it is no problem. Sorry that I took this long to reply, it took me a while to get more tubes and stuff to try to investigate. I will explain more in the next few posts
Actually I am not sure about this; it seems tube-dependant.
I am using the Ember 2.1 where there are four positions for bypassing the capacitor and/or resistor. I have already tried all four positions and can still hear the scratching sounds towards the end of the volpot
I have just had a similar problem with the vol pot on my Kameleon portable amp. My solution was to remove the knob from the vol pot.
Turn the amp to face upwards and spray a few squirts of alcohol down the spindle.
I waited a couple of minutes to let the alcohol penetrate the pot, then rapidly turned the vol pot from low to high a few times.
Wiped away any excess alcohol and put the knob back on.
Left the unit overnight and tried it next day.
The volume pot is now completely quiet
Hope this helps?
Sorry, this didn't work. Not sure if the volpot burnt out (not sure if there is such thing), or I simply can't get the alcohol to enter the right parts of the spindle
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Post by darkarn on Mar 5, 2021 19:04:42 GMT
Firstly, here's how I repaired my Project Ember. I just stuck the volpot upside down and rewired accordingly since I realised that I needed to spend far more to do the PCB through hole repairs.
The volpot is actually much quieter now but I still am unsure about the strange noise I am hearing only on the right channel whenever I change the volume by turning the volpot. I am also hearing a different noise mostly on the left channel at higher volume levels without touching the volpot. This is seen on the different 5670/396A/6SN7 tubes I have gotten over the months
Here are the samples that I have recorded and amplified further in Audacity for easier listening purposes:
Notably, the WE 396A is the most quiet, followed by the 6SN7GTB and then any of the GE 5670 tubes.
These are done with both capacitors and resistors bypassed. I noticed that only when the capacitors are bypassed would some of these noise would be lessened but most remain. Bypassing only the resistors do not help at all.
May I know what do all of these ultimately mean?
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solderdude
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Post by solderdude on Mar 6, 2021 9:22:13 GMT
Gain differs per tube, grid leakage differs per tube. The 'noise' you hear while adjusting is caused by the resistance of the volpot changing when adjusting and thus loading the tubegrid leakae current differently. capacitor coupled and series resistance added as well as the tube itself all have an impact. For this reason those tweaks are present to reduce the noise. Most noise will be heard with resistors and capacitors bypassed for this reason and is VERY tube dependent. One would need to buffer the input circuit of the tube stage to get rid of this (different amp design).
The amount and type of hum pickup is tube dependent and tube gain dependent. This all is as expected.
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Post by darkarn on Mar 6, 2021 16:39:54 GMT
Gain differs per tube, grid leakage differs per tube. The 'noise' you hear while adjusting is caused by the resistance of the volpot changing when adjusting and thus loading the tubegrid leakae current differently. capacitor coupled and series resistance added as well as the tube itself all have an impact. For this reason those tweaks are present to reduce the noise. Most noise will be heard with resistors and capacitors bypassed for this reason and is VERY tube dependent. One would need to buffer the input circuit of the tube stage to get rid of this (different amp design). The amount and type of hum pickup is tube dependent and tube gain dependent. This all is as expected.
Thanks, I see. I guess the initial 12AU7 tubes I have are much quieter than the current 5670/396A/6SN7 tubes, will use the tweaks and see how it goes
Am I right to say that it is normal for the noise to be only on one channel, since this is what I am hearing (right channel only when adjusting, left channel only when at maximum position)?
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solderdude
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Post by solderdude on Mar 6, 2021 16:51:18 GMT
I have often found differences between tube halves, maybe that's what causing differences. As long as it is not audible during usage.
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Post by darkarn on Mar 6, 2021 17:35:53 GMT
I have often found differences between tube halves, maybe that's what causing differences. As long as it is not audible during usage.
I notice this issue on all tubes tested so far though, even though I used both resistors and capacitors. Thankfully it appears that it is audible only when there is no other audio playing or at quiet passages of a song. It gets louder when I touch the bottom right post (the metal pole supporting the arcylic faceplate nearest to the volpot), so maybe it's a grounding issue?
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solderdude
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Post by solderdude on Mar 7, 2021 7:46:46 GMT
Hum alike issues that increase or decrease often is a grounding issue. Did you ground the metal part of the potmeter ?
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Post by deafear on Mar 7, 2021 21:35:24 GMT
Can my project ember be used as a record player preamp?
I have a really cheap turntable and want to upgrade. My good receiver is newer and doesn't have a phono input.
I've been considering getting a Uturn Orbit, but would need a preamp, which is extra. I was going to use my ember in the signal path anyway, so if I can use it would save me $70.
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Post by darkarn on Mar 8, 2021 2:18:43 GMT
Hum alike issues that increase or decrease often is a grounding issue. Did you ground the metal part of the potmeter ? I did so by soldering a piece of metal wire to that spot beside the potmeter and curling it around the potmeter's metal part
Come of think of it, that piece of metal wire started to look errr less silvery and starting to look more copper-ish? Feels unusually flimsy too compared to when I did that. Not sure how much of this matters but I thought I should raise it up
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Post by deafear on Mar 12, 2021 0:55:36 GMT
Can my project ember be used as a record player preamp? Never mind. I did some Google searching and the answer is no.
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solderdude
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Post by solderdude on Mar 12, 2021 13:17:20 GMT
Can my project ember be used as a record player preamp? I have a really cheap turntable and want to upgrade. My good receiver is newer and doesn't have a phono input. I've been considering getting a Uturn Orbit, but would need a preamp, which is extra. I was going to use my ember in the signal path anyway, so if I can use it would save me $70. Not possible alas, for a TT you will need an RIAA correction. Also the amp would be way too noise and have not enough gain. Something like the Schiit Mani is recommended.
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Post by darkarn on Apr 6, 2021 21:16:20 GMT
My grounding issue seems to be getting worse. I am now hearing a faint buzz on my left channel even without touching the volpot. Only when I touch the top left screw or the left capacitor would then the buzzing noise go away
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Post by solderdude on Apr 7, 2021 8:54:54 GMT
Grounding issues can be hard to solve.
With the amp stand-alone so only headphones connected do you get a hum that goes away when touching the amp ?
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Post by darkarn on Apr 7, 2021 9:14:01 GMT
Grounding issues can be hard to solve. With the amp stand-alone so only headphones connected do you get a hum that goes away when touching the amp ? Sounded more like a buzzing noise. It goes softer if I touch either of the large capacitors
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Post by solderdude on Apr 7, 2021 12:25:06 GMT
Looks like you need to run a wire from the RCA shield to ground. That can be safety ground, copper water piping or central heating with all metal piping.
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