In 2012 Vox / Korg introduced the hand wired AC4hw1 which is a new model. Not a vintage re issue. I bought this amp used. Apart from tubes and general check up, has been modded for better bass and better sound in general.
And a recap w. some Rifa caps, a tropical fish cap is used to unleash the low end.
I sawed off the lower part of the back to make it more...'open' sounding. Matter of taste. The Greenback (though Chinese maufactured) works very well for me.
Furthermore I only use 4 screws for the back panel. Korg uses 15 (!)
A stupidity where marketing meets design I can live with. As follows: Vox says everywhere that the 'hot mode' bypasses tone circuit completely. Not true, because when the cool mode is being switched to hot, the treble pot suddenly becomes a kind of attenuator. So (most of the time it may be so) if treble is around 12 h. then the hot mode will not be so hot after all. Not cool i.m.h.o. Can live with it though. What to me is unacceptable, is the hum. It is a 50 hz (Netherlands) hum. So if playing to record and / or at low volume level this amp is useless. Hum is constant. Has nothing to do with input. So now I am going to (try to) get rid of this hum. Even if the so called 'Vox sound' will be altered. Dare say this, for it is a newly designed amp. And a nice small amp should be silent. A SE as well.
Anyone w. same problem to solve? Does anyone have the lay out? Vox / Korg of course -company policy- does not help. They do know about the hum. Probably they aim at the consumer market... not @ serious musicians who are bothered by this nagging hum-tone.
Vox / Korg AC4hw1 hum problem - lay out needed
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Stevem
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Re: Vox / Korg AC4hw1 hum problem - lay out needed
Low volume levels, the amp is only 4 watts as it is!
Like you where asked in your other posting on this site, please post us some pictures if you can and we can likely move you forward towards a resolve!
Like you where asked in your other posting on this site, please post us some pictures if you can and we can likely move you forward towards a resolve!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Vox / Korg AC4hw1 hum problem - lay out needed
Specs
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Re: Vox / Korg AC4hw1 hum problem - lay out needed
before after some mods
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Last edited by Luuc on Fri May 15, 2015 6:12 am, edited 4 times in total.
Re: Vox / Korg AC4hw1 hum problem - lay out needed
detail
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Re: Vox / Korg AC4hw1 hum problem - lay out needed
detail
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Re: Vox / Korg AC4hw1 hum problem - lay out needed
detail
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Re: Vox / Korg AC4hw1 hum problem - lay out needed
detail
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Re: Vox / Korg AC4hw1 hum problem - lay out needed
Hi Stevem NY,
4 w. from a tube amp w. a Greenback (only 98 db spl) - well: It might get loud:-) really. Again: when playing loud, this hum has vanished because is does not get any louder when amp has been cranked up.
My problem is, against other opinions, that a SE can be silent as well, hum free. Especially a smaller amp for studio / home use. That is what I am pursuing.
4 w. from a tube amp w. a Greenback (only 98 db spl) - well: It might get loud:-) really. Again: when playing loud, this hum has vanished because is does not get any louder when amp has been cranked up.
My problem is, against other opinions, that a SE can be silent as well, hum free. Especially a smaller amp for studio / home use. That is what I am pursuing.
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Stevem
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- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Vox / Korg AC4hw1 hum problem - lay out needed
Well first off none of the filament wires are not twisted, so redoing that with tightly twisted wire will make a big difference, but even right now with the way the amps sits if you just lift the preamp grid wires up off of the heater wiring I would bet you would hear a nice reduction in hum levels!
All wires carrying AC should be kept as far away from the first gain stage preamp section and tube as possible.
All the AC wiring both into and out of the PT should be very tightly twisted also and if you really want to take it to a extreme you can sheild the heater wires!
All wires carrying AC should be kept as far away from the first gain stage preamp section and tube as possible.
All the AC wiring both into and out of the PT should be very tightly twisted also and if you really want to take it to a extreme you can sheild the heater wires!
Last edited by Stevem on Fri May 15, 2015 2:56 pm, edited 1 time in total.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Vox / Korg AC4hw1 hum problem - lay out needed
Since I am not a tech, even I understand this. Q. remains: why didn't Korg / Vox do this in the first place? Why not, if you call it your Flag Ship series...
Yes I am going to take it to a 'whatever it takes' extreme. I am not going to buid another amp though:-) And not obsessed. Just see ho far I can get.
An amp tech will do the work properly. I am going to make a checlist. Then we are getting to it.
R.I.P Blues Boy ! aged 89 years
Yes I am going to take it to a 'whatever it takes' extreme. I am not going to buid another amp though:-) And not obsessed. Just see ho far I can get.
An amp tech will do the work properly. I am going to make a checlist. Then we are getting to it.
R.I.P Blues Boy ! aged 89 years
-
Stevem
- Posts: 4570
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Vox / Korg AC4hw1 hum problem - lay out needed
I do not know, send Korg / Vox a email !
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Vox / Korg AC4hw1 hum problem - lay out needed
'Been there' so to speak: Already did this. They respond like a robot: 'get in touch with your local distributor.' Well I did…more than once I am not going to wait any longer, as you probably understand.
I called Vox. The guy at Tech Support couldn't help me. Company Policy* I did get through to him though. He confirmed that there are a lot of remarks / complaints on the hum. He confirmed that measures are to be taken, talked about shielding. As we discuss here.
*Korg is a very large company. If they officially would admit there is something not right in a model (of their Flagship Series!) they would be forced to do something about it. Compare this to Toyota models and their brake problems. 'All cars have to go back to a dealer to be fixed…'
Korg will not do this. Their response for now is: 'This is normal, it is part of the Vox sound.' And they get away with it as it seems.
If they would make these amps a little more expensive, it would be possible to make it hum 'free' at least...
Well: I do not go down that road, no Vox bashing, no crusade or whatever. Facts: yes. Furthermore I see Vox aiming more and more at the consumer market. That is just a sorry sight observation, not a fact.
I called Vox. The guy at Tech Support couldn't help me. Company Policy* I did get through to him though. He confirmed that there are a lot of remarks / complaints on the hum. He confirmed that measures are to be taken, talked about shielding. As we discuss here.
*Korg is a very large company. If they officially would admit there is something not right in a model (of their Flagship Series!) they would be forced to do something about it. Compare this to Toyota models and their brake problems. 'All cars have to go back to a dealer to be fixed…'
Korg will not do this. Their response for now is: 'This is normal, it is part of the Vox sound.' And they get away with it as it seems.
If they would make these amps a little more expensive, it would be possible to make it hum 'free' at least...
Well: I do not go down that road, no Vox bashing, no crusade or whatever. Facts: yes. Furthermore I see Vox aiming more and more at the consumer market. That is just a sorry sight observation, not a fact.
Re: Vox / Korg AC4hw1 hum problem - lay out needed
From your photos, it is now clear since the modding the lead dress not as precise as it was when it left the factory.
The heater /filament wires to the EL84 output tube are indeed not twisted.
As I mentioned in your other thread, the filament wires towards the preamp are very tightly twisted but are not ideal at the sockets. This could be directing your 50Hz AC noise right to the signal wires. Read this article, lower down the page "Layout / Lead Dress" http://www.valvewizard.co.uk/heater.html
It is still a mystery how the heater /filament circuit is referenced. Stevem asked that in your first thread. On the other thread BillyZ suggested elevating the filaments. Two threads about the issue on the same amp is too much for me. I'm done here. Good luck.
The heater /filament wires to the EL84 output tube are indeed not twisted.
As I mentioned in your other thread, the filament wires towards the preamp are very tightly twisted but are not ideal at the sockets. This could be directing your 50Hz AC noise right to the signal wires. Read this article, lower down the page "Layout / Lead Dress" http://www.valvewizard.co.uk/heater.html
It is still a mystery how the heater /filament circuit is referenced. Stevem asked that in your first thread. On the other thread BillyZ suggested elevating the filaments. Two threads about the issue on the same amp is too much for me. I'm done here. Good luck.
Re: Vox / Korg AC4hw1 hum problem - lay out needed
thank u, couln't agree more:-) this is why I am working on it from scratch. One morte thing: these pics are made after taking apart the amp. Modding just was about a recap and a choke done by a pro. tech.