@vkung
Hi Victor, just following up here since I got no response at the above mentioned email address. is info@vkmusic.ca correct?
Hi Victor, just following up here since I got no response at the above mentioned email address. is info@vkmusic.ca correct?
Hello all!
I finished my build a week ago and it is sounding great so far.
Today I noticed in the right channel a very slight 120hz hum. I can only hear it with my ear next to the speaker so it's not a huge deal, but the left channel is dead silent. I'd love to get rid of the hum if at all possible. My speakers are Zu Soul VI which are very sensitive at around 100db. The hum is not volume dependent and is present no matter where the volume pot is set.
To troubleshoot, here is what I have done so far.
1) voltage checks - all ok and within spec
2)swapped tubes left to right - checking for a faulty tube, but the hum stayed on the right channel
3) disconnected inputs - hum stayed present
4) Tried twisting transformer wires and routing them well away from each other - did not make a difference
5)Tightened speaker outputs - no change
6) changed coupling caps to stock - no difference
As I understand it 120Hz hum is typically indicative of a ground loop.
Any advice on what to check next would be appreciated.
Thanks!
I finished my build a week ago and it is sounding great so far.
Today I noticed in the right channel a very slight 120hz hum. I can only hear it with my ear next to the speaker so it's not a huge deal, but the left channel is dead silent. I'd love to get rid of the hum if at all possible. My speakers are Zu Soul VI which are very sensitive at around 100db. The hum is not volume dependent and is present no matter where the volume pot is set.
To troubleshoot, here is what I have done so far.
1) voltage checks - all ok and within spec
2)swapped tubes left to right - checking for a faulty tube, but the hum stayed on the right channel
3) disconnected inputs - hum stayed present
4) Tried twisting transformer wires and routing them well away from each other - did not make a difference
5)Tightened speaker outputs - no change
6) changed coupling caps to stock - no difference
As I understand it 120Hz hum is typically indicative of a ground loop.
Any advice on what to check next would be appreciated.
Thanks!
Here are my voltages with 2A3 tubes:
1 - 1.98
2 - 1.90
3 - 53.36
4 - 51.53
5 - 56.2
6 - 54.36
7 - 140.5
8 - 142.9
9 - 18mV
10 - 12mV
11 - 40.18
12 - 39.95
13 - 42.90
14 - 42.44
15 - 278
16 - 277.4
17 - 283.3
18 - 282.6
19 - 223
20 - 223
21 - 310.4
22 - 310.3
23 - 6.4 (12AU7)
1 - 1.98
2 - 1.90
3 - 53.36
4 - 51.53
5 - 56.2
6 - 54.36
7 - 140.5
8 - 142.9
9 - 18mV
10 - 12mV
11 - 40.18
12 - 39.95
13 - 42.90
14 - 42.44
15 - 278
16 - 277.4
17 - 283.3
18 - 282.6
19 - 223
20 - 223
21 - 310.4
22 - 310.3
23 - 6.4 (12AU7)
Hi Victor,
Here is what I have done so far.
I have verified that the hex sockets are indeed tight. I have continuity to ground on those screws attached to the hex sockets.
I also verified continuity to ground from those screws to the pins on the header labelled ground.
Verified continuity between the pot ground points and the ground points on the RCA jacks.
I verified continuity from the RCA jack to the RI pin on the pot header
Verified continuity from the RO pin header to R201.
I have not yet pulled out the boards and re-soldered anything yet.
I did try to short the right input jack and that made no difference.
I tried disabling negative feedback and that made the hum louder.
One observation is that the hum is initially louder when the amp is first powered on and then quiets down after being on for 15-30 seconds
So far the hum is still present in all scenarios.
Another observation - I am using the Spectroid frequency analyzer app on my phone and it appears as if there is both 60 Hz and 120Hz hum on the right channel. This is with my phone mic right inside the speaker cone.
Here is what I have done so far.
I have verified that the hex sockets are indeed tight. I have continuity to ground on those screws attached to the hex sockets.
I also verified continuity to ground from those screws to the pins on the header labelled ground.
Verified continuity between the pot ground points and the ground points on the RCA jacks.
I verified continuity from the RCA jack to the RI pin on the pot header
Verified continuity from the RO pin header to R201.
I have not yet pulled out the boards and re-soldered anything yet.
I did try to short the right input jack and that made no difference.
I tried disabling negative feedback and that made the hum louder.
One observation is that the hum is initially louder when the amp is first powered on and then quiets down after being on for 15-30 seconds
So far the hum is still present in all scenarios.
Another observation - I am using the Spectroid frequency analyzer app on my phone and it appears as if there is both 60 Hz and 120Hz hum on the right channel. This is with my phone mic right inside the speaker cone.
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For sure there is something wrong. It should be dead quiet .
Do you want to send for me to check for you?
If yes I need the bottom chassis with the PCB.. NO power Rack and Output transformer
You take care the both ways shipping.
Do you want to send for me to check for you?
If yes I need the bottom chassis with the PCB.. NO power Rack and Output transformer
You take care the both ways shipping.
Thanks Victor. Very kind of you to offer.
I agree the left channel is dead silent as are both channels on my TU-8600.
I will keep working on it and see if I can determine what is wrong for now
If you have any other ideas of things to check I am all ears.
I agree the left channel is dead silent as are both channels on my TU-8600.
I will keep working on it and see if I can determine what is wrong for now
If you have any other ideas of things to check I am all ears.
Success!!
I added the spacer to the tkd pot but more importantly found a cold solder joint on one of the electrolytic caps. Just got it back together and it is dead silent on both channels. Sounding great now!!!
I added the spacer to the tkd pot but more importantly found a cold solder joint on one of the electrolytic caps. Just got it back together and it is dead silent on both channels. Sounding great now!!!
Just completed a kit over the course of the last two days. As a complete beginner I couldn’t have asked for a more thorough and well thought out instruction guide. My solder skills were completely lacking when I started, but by the time I finished the pcb and transformers, I was able to solder joints with ease. The amp already sounds great, even with only about 2 or so hours on it.
After assembling the TU-8900 & listening for 8 hours…. I can say with confidence that this amp trumps my 8200R & 8600S. All (3) amps have lundahl opt & upgraded caps. The TU-8900 sound pulls you in…. It’s a non-fatigue, 3dimensional sound. The non-nfb setting is spooky good with no need for a preamp. In my opinion, the 8200R with lundahl has a closer sound to the TU8900 with lundahl & upgraded caps.
I finally found my forever amp ! The only thing I dislike on the 8900 is the PMJ8900 auto-bias board with surface mount components. Very difficult to repair & there’s no schematic for that board. Yes Elekit will replace that board if it malfunctions, but what happens down the road when the TU-8900 is eventually discontinued?
I finally found my forever amp ! The only thing I dislike on the 8900 is the PMJ8900 auto-bias board with surface mount components. Very difficult to repair & there’s no schematic for that board. Yes Elekit will replace that board if it malfunctions, but what happens down the road when the TU-8900 is eventually discontinued?
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Since the release of TU-8900 in September 2022, there is no single power pcb required to return to Elekit for repair.
TU-8233 is the ealier version 2A3/300b AMP (6-7YEARS AGO). Agian, there is no signle malfuction power pcb.
TU-8233 is the ealier version 2A3/300b AMP (6-7YEARS AGO). Agian, there is no signle malfuction power pcb.
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