Ac15c1 Hissing problem « VOX | Discussion Forums

Member

I bought an AC15C1 a few weeks ago and ever since the things been constantly mucking up. The Top boost channel has cut out once or twice early on, but hasn't done so since a few weeks ago. Then, more recently, it has started hissing whenever i play a note, and not regular distortion hiss, more of a white noise type thing. I have taken it back to the store twice where they have played it and the thing has worked fine, so i have taken it back hoping it would just stop, but it always seems to much up again. I recorded the sound it makes, so could you guys have a listen and tell me what you think?

http://www.zshare.net/download/8581822209c32d66/

Note that you may have to turn it up a bit, and also that the noise is not the microphone buzzing, its what i was describing.

Posted 2 years ago

clydebillt

Member

Try swapping the valves out (always my first port of call in a valve amp).
If you haven't got any spare lying around then swap them around into different positions.
Check the connections at the speaker are tight enough.
After that I'm pretty much done.

I'm sure I've seen the top boost problem mentioned on here before, but can't remember too much else about it.

good luck

Posted 2 years ago

ktchaw

Member

the only problem i have with that is since it is so new, only about a month old, i'm debating whether or not to take it back under warranty, especially considering this is the first valve amp i've owned and ive never changed tubes before.

Posted 2 years ago

ac15er

Member

When I got my C1, the dealer said they would give a three month warranty on the valves if there where any duds in that time, that might have just been the dealer attempting to give me good service as I've spent a fair amount in the shop.

As I swapped them all out for better ones right away I don't recall if mine sounded like your sound clip or not, but swapping them around is a good idea to start with, then if there is no difference take it back for a checkup.

Changing the tubes is pretty easy, the hardest bit is getting the back off the amp.

cheers

Posted 2 years ago

cwicker

Member

Hey ktchaw, Did you ever resolve your problem? I downloaded your audio file and it exactly replicates the problems that I am having. It sounds like a slight buzz/sizzle/hiss toward the end of the note.

I guess I will try switching the valves around like clydebillt suggested.

I kinda feel bad that I've waited until I'm having problems before posting on the board because I've really been digging my Vox ac15c1!!

Posted 2 years ago

danelbaum

Member

Hey cwicker, did changing the valves help? I have had this happen to me on two new Ac15c1s, the second of which being new fresh out of the box.

Posted 2 years ago

cwicker

Member

I haven't changed the valves yet. A guitar show will be in town in a few weeks and I was planning on picking some up at that time. However, I have been tinkering with the amp and it seems like the slight buzz mostly happens when playing above the F note on the A string. I wonder if placing dampeners on the tubes may help.

Later!

Posted 2 years ago

simonnq

Member

I have dampers on all of my tube amps, I cannot say that it will totally fix your issue, but for me they are a god send, and SOOOOOOO cheap! I was noticing a sort of delay/reverb thing when playing loud stacato chords, this didn't sound very good as it sounded like rattles etc. After the dampers, absolutely no noises, no matter what volume. My amp is constantly run at maximum volume and I still have no strange noises what so ever. I have replaced tubes 3 times now with still no issues. of course as the tubes change the dampers are put right back on :).

Posted 2 years ago

cwicker

Member

EuroDampers ordered! I will report back when they are delivered and installed. simonnq finally beat it into my stubborn head ;)

Later!

Posted 2 years ago

simonnq

Member

Thees are the ones I use,

http://cgi.ebay.com.au/TUBE-AMP-PREAMP-DAMPERS-12AX7-12AU7-ECC83-EL84-6922-/370479270598?pt=Vintage_Electronics_R2&hash=item5642490ac6#ht_5164wt_1127

Very cheap and work well :). the same size fits the EF86, 12ax7 and the el84's.

Posted 2 years ago

ac15er

Member

^^I just ordered some dampers off ebay, but not those ones, do the spring retainers still fit OK around the tubes as they look quite fat?

cheers

Posted 2 years ago

simonnq

Member

They will stretch a little, but should fit fine. My dampers are not really that big and I have had no probs etc...

The biggest stretch for me was the retainer on the GZ34, the standard Sovtek is quite a small tube compared to the JJ !!!.

Posted 2 years ago

ac15er

Member

Yeah, I figured the retainers would either stretch a little or they could be adjusted a bit, they're only bent spring wire after all, I bought some chinese dampers pretty cheap with free delivery to Australia.

i don't really have a problem with my AC15, just suffering GAS.

cheers

Posted 2 years ago

simonnq

Member

Another Aussie :) I got mine from the states no issues , especially with our dollar at the moment :)

Posted 2 years ago

docd

Member

simonnq said: "Thees are the ones I use, http://cgi.ebay.com.au/TUBE-AMP-PREAMP-DAMPERS-12AX7-12AU7-ECC83-EL84-6922-/370479270598?pt=Vintage_Electronics_R2&hash=item5642490ac6#ht_5164wt_1127 Very cheap and work well :). the same size fits the EF86, 12ax7 and the el84's."

Simon - Did you try any other types of dampers, like http://herbiesaudiolab.net/rx.htm ? I have a VT40+ and, if you check the thread, you'll note that lots of us are having the "hiss" problem with the VT+ amps. I'm wondering if one type of damper will work better than another...if dampers are in fact what's need to fix this problem.

Posted 2 years ago

simonnq

Member

Dampers will not really fix any hiss per se', what they fix is the mechanical rattling sounds you hear with valves. This occurs when the valves are vibrated by the speakers. Some valves are worse than others, if you give a valve a gentle shake near you ear you can tell which ones will make more noise than others, I do mean a GENTLE shake! Then place the dampers on the same valve and shake again, you will notice quite a difference.

The VT40+ series of amps are very different from what I am used to, I have not had a lot to do with the hybrid types of technology. Valves are usually used to try and warm up a digital signal, the issue is that an analogue ( valve ) type of technology does not have the same noise floor as a digital one. To be honest I haven't really read the VT40 thread due to not knowing anything about that style of amp at all :(

Sorry mate I haven't even seem those dampers before, I did quite a bit of research before I purchased mine and there are literally hundreds of different designs out there. I went with the above for 2 reasons, first they were cheap!, second I can use as many on a tube as I like, I have found that if I place a damper at each point where the internal plates touch the outer glass that it has fixed all of the problems I was having.

Of course I only use good valves, no sovteks for me :) Currently I like JJ's.

Posted 2 years ago

danelbaum

Member

ktchaw,

I had a problem very similar to yours, and it happened in two different Ac15c1s. The first one I exchanged because it did it right when I got home. The second one started about a week after I got it

I then ordered some new JJ Tubes. Hoping for the best, I switched them out. When I turned the amp on, there was no more buzzing, and the amp sounded even better than before!

Coming from a newbie, changing the tubes was a lot easier than I expected. Taking the back off was a bit painstaking, but putting the tubes in was fine. I just used some electrical contact cleaner (DeoxIT) and worked the tube in and out a few times. The only problem I had was getting the old tube out of the socket covered by the cover.

Posted 2 years ago

cwicker

Member

Ok, Installed the dampners and it did not solve the problem. However, I changed out the pre-amp tubes and problem solved! I don't hear the slight buzz "afternotes" any more.

After replacing the tubes I realized that my amp had not been sounding as great as it had in the past. It sounds amazing once more!!

Posted 2 years ago

ktchaw

Member

Hey everyone, sorry havent checked up on this in a while.

So basically i ended up returning it under warranty, they had it for ages i only got it back about 3 weeks ago or so, and it has been working fine ever since it got back. However, since a bout a few days ago ive been noticing some completely different problems.

Every so often when i go to crank up the top boost itll sound muddy and wrong, unlike the old and fantastic drive sounds it was making, now it sometimes just reverts to some odd flubby sounding drive which is just wrong. Also another thing i've been noticing is an odd staticy type sound, which is much more prominent when turned up but which disappears when i touch anything metal on the guitar or amp, the switches on the amp or the volume/tone pots or strings on my guitar. I've tried it with both my tele with single coils and my jackson with humbuckers and its still there.

Anyone have any ideas? Think i should go for a new one or replace the tubes, or anything else you guys can think of?

Cheers

Posted 2 years ago