Hey,
My AES K502 kit came about 2 weeks ago, and I assembled it last week. I've been testing it for the past few days. Right now, I have it hooked up to a pair of headphones (without anything to attenuate the headphones or change the impedance). I'd hook it up to my speakers, but I don't have them with me.
There's a lot of hum in my amp, and I was wondering what the best solutions for this were. I've been to Voltsecond's site, and have read the threads on a few forums about reducing the hum. So far, I've only applied Voltsecond's .01uF transformer HV mod, and I plan on bypassing the etchings to the filament that run under the tubes with hookup wire.
Has anyone modded the amp to DC tube heating? Would this get rid of the hum completely? Thanks.
also, i noticed that when I touch the potentiometer with my finger, the hum increases dramatically. i plan on upgrading to an ALPS pot, but why does the hum increase?
My AES K502 kit came about 2 weeks ago, and I assembled it last week. I've been testing it for the past few days. Right now, I have it hooked up to a pair of headphones (without anything to attenuate the headphones or change the impedance). I'd hook it up to my speakers, but I don't have them with me.
There's a lot of hum in my amp, and I was wondering what the best solutions for this were. I've been to Voltsecond's site, and have read the threads on a few forums about reducing the hum. So far, I've only applied Voltsecond's .01uF transformer HV mod, and I plan on bypassing the etchings to the filament that run under the tubes with hookup wire.
Has anyone modded the amp to DC tube heating? Would this get rid of the hum completely? Thanks.
also, i noticed that when I touch the potentiometer with my finger, the hum increases dramatically. i plan on upgrading to an ALPS pot, but why does the hum increase?
Make sure that the body of the volume pot is grounded. This isn't usually a problem if you have it mounted in a metal chassis but if you have it on the piece of wood then it can be an issue. You can use a spade lug type connector or just loop a wire around the front of the pot and tighten the nut on it. Take the other end of the wire to either the ground point near the pot (if your kit has one) or to one of the input grounds.
I have one of these amps that I build a few years ago and it is quiet. AC heaters are perfectly fine.
I have one of these amps that I build a few years ago and it is quiet. AC heaters are perfectly fine.
Hey,
thanks for the replies. I checked most of the ground connections on the board, and my kit did come with the ground lug on the pot. when I checked the connection between the lug to the yellow ground on the transformer, its showed a lot of resistance. but looking at the PCB, the hole for the ground lug on the PCB doesn't connect directly to ground.
I hooked up a 22awg wire from the lug to the ground on one of the inputs (the outside of the input?), but the hum wasn't reduced at all. and for some reason, when I tried hooking up the lug ground to the input while music was playing, the music on the left channel would dissappear.
I read on another forum that an ALPS blue velvet pot does wonders for the hum and LR balance on this amp, and I think im going to try that out as soon as I get a real enclosure for this thing.
If I want to mount it in a metal enclosure, would I have to desolder all the caps and metal-oxide resistors, and resolder on the reverse side? or could I mount the PCB on the bottom of the enclosure and buy new tube sockets that mount on the surface of the enclosure and connect them to the PCB with hookup wire? Thanks
thanks for the replies. I checked most of the ground connections on the board, and my kit did come with the ground lug on the pot. when I checked the connection between the lug to the yellow ground on the transformer, its showed a lot of resistance. but looking at the PCB, the hole for the ground lug on the PCB doesn't connect directly to ground.
I hooked up a 22awg wire from the lug to the ground on one of the inputs (the outside of the input?), but the hum wasn't reduced at all. and for some reason, when I tried hooking up the lug ground to the input while music was playing, the music on the left channel would dissappear.
I read on another forum that an ALPS blue velvet pot does wonders for the hum and LR balance on this amp, and I think im going to try that out as soon as I get a real enclosure for this thing.
If I want to mount it in a metal enclosure, would I have to desolder all the caps and metal-oxide resistors, and resolder on the reverse side? or could I mount the PCB on the bottom of the enclosure and buy new tube sockets that mount on the surface of the enclosure and connect them to the PCB with hookup wire? Thanks
update
ok, I hooked up the amp to my speakers today (~88db/w efficiency)
the hum is no where as noticeable on real speakers as on headphones. It almost dissappears, but I can still hear it when the music stops.
Music quality:
I only have a Yamaha RX596 commercial amp to compare it with. The K502 has a smoother sound than my Yamaha, but I feel like it doesn't have as much clarity as my Yamaha. I can't believe how loud this thing can go on only 8 watts per channel with such a simple design, but I felt it lacked the bass that my RX596 can produce (out of my 6" speakers). Cymbals don't sound as good on this tube amp either. It doesn't have that sharp clear wack that I get from my yamaha. However, the soundstage is more forward with this amp. I was shocked at how well the amp played a really poor quality MP3 of Scott Mckenzie's San Francisco. The drums and guitars sound much clearer on the K502.
I still prefer my commercial SS amp over the K502. It just doesn't have the bass I like. The difference between the 2 amps reminds me of the difference between silk dome tweeters and metal dome tweeters.
ok, I hooked up the amp to my speakers today (~88db/w efficiency)
the hum is no where as noticeable on real speakers as on headphones. It almost dissappears, but I can still hear it when the music stops.
Music quality:
I only have a Yamaha RX596 commercial amp to compare it with. The K502 has a smoother sound than my Yamaha, but I feel like it doesn't have as much clarity as my Yamaha. I can't believe how loud this thing can go on only 8 watts per channel with such a simple design, but I felt it lacked the bass that my RX596 can produce (out of my 6" speakers). Cymbals don't sound as good on this tube amp either. It doesn't have that sharp clear wack that I get from my yamaha. However, the soundstage is more forward with this amp. I was shocked at how well the amp played a really poor quality MP3 of Scott Mckenzie's San Francisco. The drums and guitars sound much clearer on the K502.
I still prefer my commercial SS amp over the K502. It just doesn't have the bass I like. The difference between the 2 amps reminds me of the difference between silk dome tweeters and metal dome tweeters.
SYS847,
I also recently bought and assembled the kit. When I had it on the "breadboard" and the lug connected between the pot and ground hold near the pot I still had a hum in my left channel. I called up S5 Electronics and he suggested I sand off more from the underside of the stock Transformers which also did nothing for me. I then bought a Hammond chassis but while moving parts to the underside of the PCB I must have damaged the pot so I ordered another pot but that was twice the size and 1/2 watt, not sure if the original is that value as well. I have not had a chance to attach it yet but when I did try it out in my Hammond I still had the hum.
I also got two output Transformers (Hammond 1609) and that also did not help the hum. I also tried to use the two black wires that are supposed to be connected to the underside of the transformer and connected them directly to the Ground connection in the IEC receptacle but this also did not resolve it.
Keep us posted ...
I also recently bought and assembled the kit. When I had it on the "breadboard" and the lug connected between the pot and ground hold near the pot I still had a hum in my left channel. I called up S5 Electronics and he suggested I sand off more from the underside of the stock Transformers which also did nothing for me. I then bought a Hammond chassis but while moving parts to the underside of the PCB I must have damaged the pot so I ordered another pot but that was twice the size and 1/2 watt, not sure if the original is that value as well. I have not had a chance to attach it yet but when I did try it out in my Hammond I still had the hum.
I also got two output Transformers (Hammond 1609) and that also did not help the hum. I also tried to use the two black wires that are supposed to be connected to the underside of the transformer and connected them directly to the Ground connection in the IEC receptacle but this also did not resolve it.
Keep us posted ...
I'm thinking of moving the power supply off the board when I have time, and rectifiying the tube heaters. I'm also going to beef up the power supply caps.
If i don't rectify the tube heaters, I'll try something I saw on another forum where someone recommended covering the heater wires with copper mesh.
Im busy with school now so I won't get these changes done for a while but I figure these will isolate the amp from AC hum.
If i don't rectify the tube heaters, I'll try something I saw on another forum where someone recommended covering the heater wires with copper mesh.
Im busy with school now so I won't get these changes done for a while but I figure these will isolate the amp from AC hum.
lost left channel
I noticed you said that you lost the left channel. I had trouble with the pot as well and decided to replace it (after turning it on only one time). I replaced the pot with a radio shack A100KX2. Its a 100kOhm .5W Dual pot. I grounded it with the lug. I turned on the amp and had lost the left channel totally, except that it still pops when powered up. All tubes glow. I replaced the pot with an exact match to the B100K that it came with. Still the left channel is missing.
I got out the multimeter and tested every resistor and cap. I think the multimeter is bad (its a chinese cheapy from ebay). It read many caps and resistors but some of them it would not read AT ALL. I figure a bad cap will still give some reading and a bad resistor should still have some resistance.
I have yet to hook it up to the transformers.
So far, any suggestions? Has anyone dealt with this before?
I noticed you said that you lost the left channel. I had trouble with the pot as well and decided to replace it (after turning it on only one time). I replaced the pot with a radio shack A100KX2. Its a 100kOhm .5W Dual pot. I grounded it with the lug. I turned on the amp and had lost the left channel totally, except that it still pops when powered up. All tubes glow. I replaced the pot with an exact match to the B100K that it came with. Still the left channel is missing.
I got out the multimeter and tested every resistor and cap. I think the multimeter is bad (its a chinese cheapy from ebay). It read many caps and resistors but some of them it would not read AT ALL. I figure a bad cap will still give some reading and a bad resistor should still have some resistance.
I have yet to hook it up to the transformers.
So far, any suggestions? Has anyone dealt with this before?
So I had it finished. Sounded really nice except a high pitch "fuzz" on top of all higher frequency sounds. So I did many voltsecond mods. Put .01uf on HV lines. Put snubber on same lines and then rectifier diode after rectifier. Twisted pair of wires between pins 4 and 5 of outermost tubes and added 1uf caps to each of the tubes on pins 4 and 5. Also removed 33pf ceramics and replaced with copper wire. Shielded all transformers and twisted all wire from transformers.
I had a B100K stereo pot wired up to it but it had a metal tab that inhibited mounting it flush onto the case. When I bent the tab in I damaged the pot. I have 4 more of the same so just popped a new one in.
I had not tested it at all after the mods til last night.
The volume goes up a little but not much. I get squelching and a whooping sound that increases in pitch and then begins again over and over. If I turn it up higher the squelch and whooping goes away but then for a good half turn on the pot I get no increase in volume.
I hope this is all because of the pot. I will be replacing it today with another of the same type of pot. Hope that works. I have my doubts though because of the whooping sound. Anybody think that for some reason I am hearing a cap charge and discharge? Just a guess. When this happens it is not loud but the speaker flexes in and out slowly but it moves about 5mm. Very odd.
Suggestions?
I will update when I try other pot.
Uriah
I had a B100K stereo pot wired up to it but it had a metal tab that inhibited mounting it flush onto the case. When I bent the tab in I damaged the pot. I have 4 more of the same so just popped a new one in.
I had not tested it at all after the mods til last night.
The volume goes up a little but not much. I get squelching and a whooping sound that increases in pitch and then begins again over and over. If I turn it up higher the squelch and whooping goes away but then for a good half turn on the pot I get no increase in volume.
I hope this is all because of the pot. I will be replacing it today with another of the same type of pot. Hope that works. I have my doubts though because of the whooping sound. Anybody think that for some reason I am hearing a cap charge and discharge? Just a guess. When this happens it is not loud but the speaker flexes in and out slowly but it moves about 5mm. Very odd.
Suggestions?
I will update when I try other pot.
Uriah
Well, Tried a different pot. Still squelching. Now over most of the turn of the pot, but no whooping. However there is something similar to the whooping. When the music is sustained. For instance when Ben Folds holds a note it seems to overload and then it clips. I think you would call it clipping. Anyway what happens is that the sustained note cuts into squelching and the speaker flexes again. Then after a split second everything is normal for a short time until another sustain or complex line of music. Then same thing all over. So while it may be a crappy pot, I dont think thats the whole problem. I think I will remove the snubber and associated diode since they are probably the easiest to remove and replace.
Let me know if anyone has suggestions.
Uriah
Let me know if anyone has suggestions.
Uriah
nhuwar said:
Are you talking about the problem this guy is having?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=123511&highlight=
Might be my issue. I think I will remove all my mods and then work on this if you think that I have same problem as the guy in the link.
edit:
I checked all wires from and to transformers and they are all in the correct place.
Son of a gun. I removed all my mods and still have the issue.
okay what next?
I uploaded a video to youtube so that you could hear it.
http://www.youtube.com/watch?v=fKq1FjhX7f4
okay what next?
I uploaded a video to youtube so that you could hear it.
http://www.youtube.com/watch?v=fKq1FjhX7f4
SO, removed all mods except 33pf caps that are replaced with copper wire. I really dont think these are the problem. But what do I know.
Since the mention of oscillation I checked my instructions again for mentions of oscillation and it says check OPT leads to see if they are miswired. They are fine. IT also mentions that oscillation happens if faulty ground connection from board to the OPT housing. So I am working on that. We will see.
http://picasaweb.google.com/udailey/K502
Since the mention of oscillation I checked my instructions again for mentions of oscillation and it says check OPT leads to see if they are miswired. They are fine. IT also mentions that oscillation happens if faulty ground connection from board to the OPT housing. So I am working on that. We will see.
http://picasaweb.google.com/udailey/K502
Okay I removed all paint from the pads of the Transformers. I grounded from each pad to the PCB. Same issue exists.
Here is a link. Watch what happens to the outer right tube. This does not happen to the other tubes.....
http://www.youtube.com/watch?v=IMDraS1Ft_Q
You can also hear my daughter talking about "take a picture"
She just turned 2 on the 10th.
Here is a link. Watch what happens to the outer right tube. This does not happen to the other tubes.....
http://www.youtube.com/watch?v=IMDraS1Ft_Q
You can also hear my daughter talking about "take a picture"
She just turned 2 on the 10th.I moved that tube over one spot to the left. Same problem in the same tube. Its NOT happening in the tube to the farthest right. The glowing pulsing followed the tube when I moved it. By the way one other weird thing is that the amp will oscillate and make weird noise with no input turned on but the glowing pulse doesnt happen. When I turn on the music then it pulses and still makes the weird noise you can hear in the video. So maybe its not JUST the tube. What do you think?
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