Preamplifier tube upgrades

[adam8290]

Hi All,

Have any of you upgraded the tube(s) in your microphone preamplifiers? If so, how did you choose the tube? I have found several sites that sell tubes, some specifically for mic preamps, but I can't tell how to know whether a $189 tube will sound better than a $7 tube. What tube(s) did you buy, who did you buy from, and did you experience an improvement?

In my specific case I just bought an ART MPA gold. I have found many web posts suggesting that this pre can rival much more expensive units, and that upgrading the stock 12AX7A tubes with just about any other tubes immediately improves the sound quality if the unit. Also, I don't really understand what kind of tubes I can replace the 12AX7As with. Better quality 12AX7A's only, or may I choose from tubes with other designations?

Thanks for any thoughts. I also just bought an AKG Perception 100 to start off with. I've been using an SM57, so I should notice a big improvement with the new pre/mic combination all the way around.

Thanks,

--Adam

Dell Inspiron 6000, Edirol UA-1EX (until I get the Firebox), Evolution E-Keys 49, Shure SM-57 (& Beta 58A sometimes), Live 6 & Reason 3, glyph Porta gig.

[terragong]

maybe this is helpfull
http://www.tubeampdoctor.com/index.php?language=en

[adam8290]

Thanks Terragong,

This site is similar to many others I have found, with listings of many different tubes to purchase, but no guidance about what tubes are good in microphone preamplifiers. I guess this requires that somebody has done some subjective A/B comparisons, but I would think that there would be agreement about broad classes of tubes as not so good, medium good, and excellent. I guess, for starters, I am looking for that, along with info on which tubes fit into the slot currently occupied by the 12AX7As in the MPA Gold. Again thanks for trying.

--Adam

[adam8290]

Hi All,

I did a bit more research and found a site called Eurotubes. A websearch on that name gets you there. Eddie, the site manager, helped me alot. The site also has very good info on the benefits of cleaning tube sockets before putting new ones in. I have not found this kind of basic info anywhere on the net, so I am posting this with hopes it will help. If you got this far and are trying to upgrade tubes, Eddie might be able to help you. Here is the email exchange with my questions and his answers:


To: eurotubes@cnnw.net
Subject: Replacing the 12AX7As in my Art MPA Gold

Hi,

I have an ART MPA Gold 2 channel preamp coming in the mail. It comes
stock with two 12AX7A tubes. I've read several posts across the web
which recommend that upgrading the tubes can make this unit rival mic
preamps that are far far more expensive. I am very new to tubes and
fairly new to pre-amps and condenser mics as well (just bought an
AKG Perception 100 for starters) . Your site has the best
explanations I've found by far about tubes, but I want to be sure I am
in the right place. If you are able to answer these questions I am
probably in the position to buy a set or two of tubes from you:

* Your site seems to focus on guitar amps. Are the tubes listed for
sale on your site appropriate for mic preamps, too?

* Do the numbers (12AX7, 12AT7, 6DJ8, etc.) represent types of tubes
that each only fit into certain types of equipment? For example, will
only 12AX7 tubes fit into my MPA Gold or will tubes with other number
designations also fit?

* There seem to be several types of 12AX7s: standard, triode matched,
balanced, balanced and matched, and high gain, increasing in price as
the list progresses. Do you have any ideas about which of these would
be best for the MPA? At the prices listed, price is not an issue. Does
each have different qualities that may be valuable for certain uses
(like mics, electric guitar direct in, etc.)? Is it better for the
electronics of this 2-channel unit that the tubes be matched? If not,
do some owners of two channel units like to have one channel with a
hotter (producing greater distortion or just different character) tube
than the other? If you are not familiar with the MPA, it is a variable
impedance pre with 75db total gain (including a 20db gain button that
seems important to the tube conversation, though I don't know exactly
why).

* The MPA is not a high-end unit. Would more expensive tubes than the
ones you list improve the performance of this pre even more? Is there a
point when the improvement gained by replacing the tubes is not matched
by what I am assuming is the mid-level quality of the rest of the
electronics?

Thanks again and thanks for the only site I've found so far that even
tries to explain tube issues in an organized way,

--Adam

Eurotubes wrote:

Hi Adam,

The tubes we offer can definitely be used in mic pre amp situations.
We test all of our pre amp tubes very rigorously for noise and
microphonics so they will perform flawlessly in hifi and mic pre amp
applications.

There are a lot of tubes that are interchangeable but there are also a
lot that aren't. All 12AX7's (ECC83), 5751's, 12AT7's (ECC81), 12AY7's
and 12AU7's (ECC82) are pretty much interchangeable. The biggest
difference between those listed is there amplification factor. I
listed them in descending order with the ECC83 having the highest
amplification factor and the ECC82 with the lowest.

Sometimes it can be beneficial to sub tubes with lower or higher
amplification factors but we usually don't recommend this in mic pre's
or hifi applications.

The ART MPA Gold preamp uses two 12AX7’s so I would recommend using a matched triode ECC83S's to get a warmer and smoother sound with better
definition. These run 10.50 a tube.

You can also use the Gold Pin ECC83S’s. The main difference with them
is that they are smoother in the top end and a little richer in the
mids. They are however expensive, the ECC83S matched triode Gold Pin
tubes run 21.50 each.

A pair of either can be shipped by Priority mail for 7.50 with a 3 day
delivery.

Tubes can only reproduce what the circuit has to offer. Of course
different brands and types of tubes have different sonic properties
but I would say in a mic pre that tubes really only make up about
10-15% of it’s over all tone. So there is certainly an audible
improvement to be had and whether or not that 10-15% percent is worth
more to you then 30 bucks is hard to say.

Thanks,

Eddie

[Nogi]

Hi All,

Have any of you upgraded the tube(s) in your microphone preamplifiers? If so, how did you choose the tube? I have found several sites that sell tubes, some specifically for mic preamps, but I can't tell how to know whether a $189 tube will sound better than a $7 tube. What tube(s) did you buy, who did you buy from, and did you experience an improvement?

In my specific case I just bought an ART MPA gold. I have found many web posts suggesting that this pre can rival much more expensive units, and that upgrading the stock 12AX7A tubes with just about any other tubes immediately improves the sound quality if the unit. Also, I don't really understand what kind of tubes I can replace the 12AX7As with. Better quality 12AX7A's only, or may I choose from tubes with other designations?

Thanks for any thoughts. I also just bought an AKG Perception 100 to start off with. I've been using an SM57, so I should notice a big improvement with the new pre/mic combination all the way around.

Thanks,

--Adam

Dell Inspiron 6000, Edirol UA-1EX (until I get the Firebox), Evolution E-Keys 49, Shure SM-57 (& Beta 58A sometimes), Live 6 & Reason 3, glyph Porta gig.

Though you have many 'pin equivalent' options, you shouldn't modify the limited gain structure of that device so stick with a 12AX7. Unlike a guitar preamp where distortion characteristics are key, you are primarily looking for something with a low noise floor and smooth, balanced sound throughout the gain range. For this, I'd recommend the reissue Tung Sol 12AX7 or the Sovtek 12AX7 LPS. Either should be available online for under $20.

Please post your results.

[mauve]

Any news on the upgrade? Results?

[Tarekith]

My Korg EMX came with 12ax7's, and I just replaced them with JJ ECC83S's and it was a huge difference. I even did a comparison of the two, and while it won't directly apply, perhaps it will help you some:

-----------------

I wanted to create a quick and simple test to see how much of an audible difference replacing the tubes in my new Korg EMX-1 would make. After looking into what tubes to replace the stock 12AX7 tubes with, I decided on a pair of matched triode JJ ECC83S which I bought from Eurotubes.com:

https://ssl.eurotubes.com/cart/index.ph ... gory_id=12

I wanted to see how much difference there would be in level (volume) between the tube types, as well how much the distortion varied as well. The first thing I did was create a simple 1 bar pattern with a held sine wav to measure the output of the EMX using the stock tubes. The EMX-1 main outs were then routed to the inputs of my MOTU Ultralite soundcard, and I used Ableton Live 7.07 and the plug in Inspector XL from EAS to measure the levels. Inspector XL was set to use the K-14 meter scale, which is my preferred metering scale. I recorded the RMS meter readings at 5 difference positions of the Tube Gain knob on the EMX-1, based on the picture below:



Here are the readings I obtained with the stock Korg tubes:

Knob Position 0 = -11.30dB
Knob Position 2 = -9.50dB
Knob Position Half = -0.55dB
Knob Position 8 = 3.67dB
Knob Position Full = 3.93dB

Here are the readings I obtained with the JJ ECC83S tubes after the swap:

Knob Position 0 = -17.20dB
Knob Position 2 = -15.80dB
Knob Position Half = -6.49dB
Knob Position 8 = -2.22dB
Knob Position Full = -2.00dB

As you can see, the JJ tubes are quieter by roughly 5-6dB at all knob positions. Next to the tubes in the EMX-1 are pots to adjust the output levels of each tube, but there was not enough range to successfully match the levels of the two tube types, so be aware that swapping your tubes will potentially lower the output level of your EMX-1.

My next step was to record audio examples of the two tubes in action so people could hear the differences with a more real-world example. For this test, I used an 8 bar EMX-1 pattern from my last song, "Puled" which you can read about here:

http://www.korgforums.com/forum/phpBB2/ ... b9714a869b

I recorded 8 bars of audio from the EMX-1 into Ableton Live 7.07 using the same Tube Gain settings listed above. Live was set to record 24bit/44.1kHz wav files, and these were then converted to 320kbps MP3's once I was done to save on traffic on my site. I think even the MP3's make the differences plain to hear, so likely nothing would have been gained anyway by posting wav file formats. Here's the audio examples:

Knob Position 0:

http://tarekith.com/mp3s/01_Stock_Tubes_0.mp3

http://tarekith.com/mp3s/02_ECC83S_Tubes_0.mp3

Knob Position 2:

http://tarekith.com/mp3s/03_Stock_Tubes_2.mp3

http://tarekith.com/mp3s/04_ECC83S_Tubes_2.mp3

Knob Position Half:

http://tarekith.com/mp3s/05_Stock_Tubes_Half.mp3

http://tarekith.com/mp3s/06_ECC83S_Tubes_Half.mp3

Knob Position 8:

http://tarekith.com/mp3s/07_Stock_Tubes_8.mp3

http://tarekith.com/mp3s/08_ECC83S_Tubes_8.mp3

Knob Position Full:

http://tarekith.com/mp3s/09_Stock_Tubes_Full.mp3

http://tarekith.com/mp3s/10_ECC83S_Tubes_Full.mp3

As you can hear, not only are the stock tubes louder, but they also distort much more at higher Tube Gain settings on the EMX-1. As to which tube type is better, I'll leave that for you to decide, as it really depends on how you use the tubes and the sound you personally prefer.

Hope this was helpful to people. Thanks for taking the time to listen, and feel free to let me know if you have any questions on the testing I did.

[hill56871]

Thanks Tarekith, for that incredibly cool comparison! I too am amazed at how much distortion was imparted by your stock tubes, and was impressed by the smoothness of the replacements. Now that I have been using the MPA Gold for a bit, I do hear distortion that I have to work to tame. I have not yet bought replacement tubes (both of my ipods died and needed $), but will do so with more confidence now. I'll post when I get 'em.

--Adam