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PostPosted: Mon Jul 23, 2012 11:08 pm 
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Bottle Rocket

Joined: Mon Jul 23, 2012 9:13 pm
Posts: 2
New member here, and just bought a USED TA-15. Love the tones this amp provides, but noticed I'm having a noise issue on channel 1. Wondering if any of the other TA-15 owners out there can help me troubleshoot this problem.

FWIW, I did some searching around on the forum (read "TA-15 Hiss", and "TA-15 Noise in higher gain modes?", etc...) but nobody mentioned my exact issue.

THE TA-15 NOISE PROBLEM 30 SEC. SOUND CLIP:
The examples in the clip were recorded with an SM57 to Cloudlifter to Audiofire 4 into Cubase, NO processing. The amp WAS NOT receiving any input signal (no gtr plugged in) and the speaker cable from the head to my Mini Recto Cab is Brand New.

The amp was in Channel One, Normal Mode, with all knobs at zero, and cut/master pushed in.
Clip 1: In Standby
Clip 2: @ 5w (sounded fine)
Clip 3: @ 15w (constant buzz noise)
Clip 4: @ 25w (constant buzz/tone noise)

http://soundcloud.com/rstudio78/ta-15-troubleshooting

All settings on Channel 2 of the amp sound fine.

1. Does this sound like a bad preamp tube? power tube?

2. Do other TA-15 owners experience significant noise on Channel 1 in 15w & 25w with all knobs at zero???

Thanks for all the help!!!


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PostPosted: Wed Jul 25, 2012 2:36 pm 
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Mark I

Joined: Sun Oct 19, 2008 4:48 pm
Posts: 49
Location: England
This is way more mains hum than I get on my TA-15 and I assume that ch2 is ok so I would say definately something up here. First thing to try is to change the ch1 12ax7 tube - this is shown in the mesa manual. If you don't have a spare tube try swapping the ch1 and ch2 tubes (after fully disconnecting the power chord and allowing to cool of course) to see if the problem goes away. Otherwise if the hum is too loud to tollerate when you are playing then it's probably a job for an amp tech to sort:-(.

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PostPosted: Mon Jul 30, 2012 10:04 am 
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Mark II

Joined: Fri Jan 20, 2006 1:39 pm
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I talked to mesa about the same thing, and the reply I got was that the design of the TA-15 gives a specific kind of tone, but that design results in a bit of noise. When you have the cut control pressed in, you in essence have the master volume turned all the way up, so any noise is significantly increased. Supposedly you won't notice this at gigging volume. I found the TA-15 to be a noisy amp in general, but the tones are good, and when put in a mix the noise disappears completely.

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PostPosted: Mon Aug 06, 2012 11:58 am 
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Bottle Rocket

Joined: Mon Jul 23, 2012 9:13 pm
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markblasco wrote:
I talked to mesa about the same thing, and the reply I got was that the design of the TA-15 gives a specific kind of tone, but that design results in a bit of noise. When you have the cut control pressed in, you in essence have the master volume turned all the way up, so any noise is significantly increased. Supposedly you won't notice this at gigging volume. I found the TA-15 to be a noisy amp in general, but the tones are good, and when put in a mix the noise disappears completely.


That's exactly it. When the cut is active the noise is significant. Although in all other modes/channels I find it to be a relatively quiet amp.

I wanted to get to the bottom of this to find out if it was just "my" amp, or "the" amp in general. I sent my email to Mesa Boogie and they said "it sounds like a bad 12AX7 tube - the V1 position." So I swapped out the V1 tube with a "Mesa Boogie SPAX7" (which has low sensitivity to microphonic noise). This made no difference at all. Then I went to 2 different Guitar Centers in my area and fired up a TA-15 and a TA-30 in each store. All 4 of them had the same noise issue as my amp. The TA-30 noise seemed louder, to my ears. Because of all the background noise at Guitar Center you could easily miss it until you roll the amp into a quiet room, say a recording studio. But sure enough if you put your ear up to the speaker you will certainly hear the noise.

Nevertheless, this amp has so many configurations and features that I can overlook this one flaw. Especially since the other settings are much quieter. So for now, I'm keeping the amp and overall pretty happy with it. Thanks for the responses and if anyone else has questions about my findings or the sound clip please feel free to post or PM me.


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PostPosted: Thu Aug 09, 2012 9:36 am 
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Mark II

Joined: Fri Jan 20, 2006 1:39 pm
Posts: 54
rstudio78 wrote:
markblasco wrote:
I talked to mesa about the same thing, and the reply I got was that the design of the TA-15 gives a specific kind of tone, but that design results in a bit of noise. When you have the cut control pressed in, you in essence have the master volume turned all the way up, so any noise is significantly increased. Supposedly you won't notice this at gigging volume. I found the TA-15 to be a noisy amp in general, but the tones are good, and when put in a mix the noise disappears completely.


That's exactly it. When the cut is active the noise is significant. Although in all other modes/channels I find it to be a relatively quiet amp.

I wanted to get to the bottom of this to find out if it was just "my" amp, or "the" amp in general. I sent my email to Mesa Boogie and they said "it sounds like a bad 12AX7 tube - the V1 position." So I swapped out the V1 tube with a "Mesa Boogie SPAX7" (which has low sensitivity to microphonic noise). This made no difference at all. Then I went to 2 different Guitar Centers in my area and fired up a TA-15 and a TA-30 in each store. All 4 of them had the same noise issue as my amp. The TA-30 noise seemed louder, to my ears. Because of all the background noise at Guitar Center you could easily miss it until you roll the amp into a quiet room, say a recording studio. But sure enough if you put your ear up to the speaker you will certainly hear the noise.

Nevertheless, this amp has so many configurations and features that I can overlook this one flaw. Especially since the other settings are much quieter. So for now, I'm keeping the amp and overall pretty happy with it. Thanks for the responses and if anyone else has questions about my findings or the sound clip please feel free to post or PM me.


Well, what I've been doing with the amp is using channel 2 for clean, and channel 1 for dirty sounds (to an extent, this amp doesn't leave the studio, so I do a lot of tweaking). I find that channel 1 with the gain all the way up makes for a great distorted sound, and channel 2 is a much cleaner less noisy sound.

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PostPosted: Mon Aug 11, 2014 2:10 pm 
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Bottle Rocket

Joined: Tue Apr 22, 2014 12:36 pm
Posts: 6
I just bought a brand new factory sealed TA-15 and having the same problem with the hum in green channel with the master volume /cut pressed in ( cut mode).
The worst modes are top boost at 15 and 25 watt. It's pretty silent in 5 watt mode as desribed above.

I dont have ground in my electrical outlet and im suspecting that this amp maybe is more prone to the hum without ground prong connected?

Would be interesting if others with at TA-15 would chime in and put in the thread if they have this same issue so we can maybe come to the conslusion that they all do it like i suspect. also let us know if the amp is grounded or not and if its running on 110 (US) or 230 volt(EU).


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PostPosted: Tue Aug 19, 2014 8:09 am 
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Mark III
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Joined: Mon Mar 18, 2013 7:34 pm
Posts: 159
Noize wrote:
...I dont have ground in my electrical outlet and im suspecting that this amp maybe is more prone to the hum without ground prong connected?...


Not only noise, but ground is for safety. Without a ground on the electrical outlet, you can be injured or killed. I would take care of proper grounding before I worried about noise. :wink:


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PostPosted: Sun Sep 07, 2014 8:09 pm 
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Bottle Rocket

Joined: Sun Sep 07, 2014 6:17 pm
Posts: 3
My TA-15 has the same issue. You'll also notice it with the red channel master cranked.

The noise is "normal" and expected. I took it up to Petaluma and had them look at it. A TA-15 new and fresh out of the box had the same noise (slightly louder, even). Mesa said that it's part of the amp's design.

My guess is that there's a circuit layout limitation given the small size of the chassis. The noise starts somewhere between V3 and V4, so perhaps the heaters are running close to something too sensitive. But if you've seen the TA-15 board, it's a little hard to know what's what/where. ;-/

It's true that with any significant guitar volume the buzz is near the noise floor -- noise wainscoting! But it can be a bit distracting, especially if you wonder if the amp has an issue.

FWIW!


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PostPosted: Mon Sep 22, 2014 9:49 am 
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Mark I
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Joined: Fri Aug 30, 2013 5:29 pm
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Location: Mtlk. Terrace Washington
Shouldn't be noise....that's why I took mine back....every TA-15 and TA-30 I tried had the same issue....Lynnwood, Kirkland and Seattle GC's had these last year....huge sale....everyone had noise. Should be a recall on them all....just my opinion.

Unlike my old Mesa Tremoverb....quiet as can be.

You'd think the lower watt and newer amp would be the same or better....I found the noise to be unacceptable and would have thought the same way about any amp....but I so desperately wanted to like this little amp....really cool looking.

Love Mesa, it's my favorite by far Amp and Cab maker....that's why I have a Tremoverb, two 4x12 Rectifier cabs and a 1x12 Lonestar cab, but I must say the TA -15 and 30 were unexpected let downs for me.

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PostPosted: Tue Jul 25, 2017 10:13 am 
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Bottle Rocket

Joined: Thu Jul 20, 2017 9:07 am
Posts: 4
Hi all,

I know this is an old thread but I want to share my expirience with the TA-15.
I bought it second hand and it had the same hum problem.
Putted an osciloscope and I saw a 60Hz signal (actually 50Hz in my country), so I started with tube swapping ... The hum remained the same. Google-ing I saw this thread and others so I figured out wasn't only my amp but all of them.

Ok, so I started further test.
First, I opened heater wiring from PT and putted a DPDT switch in order to momentary break the heater circuit when amp was running and the hum went away (for a few seconds, while the heaters remains hot, the amp works ok and with no hum).
Next step was to connect a DC supply to the heater to confirm that noise came from heater. I did it with a 12 V battery and a simple regulator to deliver 6,3 VDC and again the amp worked great without hum.

So, I assume hum is related with heater path (a mix of wiring and PCB traces) so now I have 2 options:

- Re-wire the heater
- Convert the heater from AC to DC

Both are challenging but i'll give it a try!


Ok, if someone is still intersted in improving this little amp, let me know and I'll post futher information, thoughts and (hopefully) a happy ending!

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PostPosted: Thu Jul 27, 2017 8:50 am 
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Bottle Rocket

Joined: Thu Jul 27, 2017 8:38 am
Posts: 1
Hi everybody,

Just found this Thread, and believe i've got the same Probs.

Living in munich, Germany, 230v, 50hz.

Today i changed my el84s against a brandnew pair of matched ones from Tube Amp Doctor.

But the Problem persists :-(


@andresbianco
I am very interested in further Informations.


Cheers
Stefan

PS:
It seems to me, that the power Transformer gets extremely hot !


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PostPosted: Mon Aug 07, 2017 7:13 am 
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Bottle Rocket

Joined: Thu Jul 20, 2017 9:07 am
Posts: 4
Sorry for the delay, I'm quite busy these days. I have some outcomes to share with you but I need a couple of days in order to compile the info.

Andrés

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PostPosted: Mon Aug 14, 2017 9:25 pm 
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Bottle Rocket

Joined: Thu Jul 20, 2017 9:07 am
Posts: 4
Hello everyone,

I was busy these days.

To return to the question of noise, I did the following tests:

I used an external transformer (from an old Fender Twin Reverb) to supply the heaters. The noise remains the same.
Also, putted a DC positive reference to heater and nothing changes.

Then, I did the following mods and comparison:

1- Amp original
2- New preamplifier heater wiring (external), original AC wiring on power tubes 
3- Same as point 1 with V1 in DC (battery)
4- All preamplifier tubes in DC (from battery), original AC wiring on power tubes 
5- All tubes in DC from the battery
6- All tubes in DC from SMPS

Each of the following audio files you will find the same sequence, from config 1 to 6 (as mentioned above) with no guitar connected, recorded with a SM58, Channel 1, 15 watts and with this settings:

Audio 1: Volume min, bass and treble at 12 o'clock and master wide open (master knob pushed and cut in 0) 

Audio 2: Volume max, bass and treble at 12 o'clock, master wide open (master knob pushed and cut in 0) 

Audio 3: Volume max, bass max, treble min, master wide open (master knob pushed and cut in 0) 

https://soundcloud.com/andr-s-bianco/se ... lantic-hum


Listening all configurations, I chose to convert only the preamp tubes.
More current is needed in DC than AC, so rectifying AC would exceed the nominal transformer current. So, an extra transformer could do the job. I picked a SMPS transformer. I was little worry about switching noise but after some tests, no extra noise was injected. SMPS works at 40kHz, beyond audible frequencies. Also, I had to modify the SMPS to reduce the voltage from 12 to 6.3V.

Now the hum is way way less audible, just a background hum from the (low) HT filtering for screen and center tap of OT, only 30uF in this case and the fact that there is no balancing bias pot.

The HISS is another story, could be inherent to the design (Hi gain), plate resistors (if they were made of carbon compound).

I'm really (almost) satisfied, but if you could help me, I I would like to try to reduce hiss a little bit. Maybe changing to metal film resistor in 1st stage plate.

Also, I'm sharing the schematic here (Mesa boogie sent it to me.. .maybe because in not longer in production): https://drive.google.com/file/d/0B2Thi0 ... sp=sharing

You could see that there are 2 parallel triodes for the input stage with 220k as plate load.

DO YOU THINK CHANGING PLATE RESISTOR TO A METAL FILM COULD REDUCE THE HISS NOISE?

I'm including some pictures here: https://goo.gl/photos/BKgw2A2zXhQxX4jZ9

If someone wants to make this conversion, I could provide procedure instructions.

Thanks,
Andrés

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