Compu-Bias vs. Aiken Wombat

[iggs]

I have the Compu-Bias and it works great, just wondering if there is a difference between the two, and if it would be worth getting the Wombat as well. They look pretty identical on paper.

I do a lot of tube swapping so I wouldn't mind having both if it's worth it.

Thanks.

 

[reaiken]

Apologies if this comes across as spamming, but since you asked, they are far from identical. Here are a few differences:

Probe display: The Compu-bias can only display 2 tubes at once. The Wombat can display up to 4 tubes at once, so you can bias 100W amps without having to swap the probes around. The display alternates between probes 1/2 and 3/4 every couple of seconds, or, if you want to stay on one pair of tubes, you can simply unplug the other probe connector and the display will switch the two active probes and stay there. Both products display voltage, current, and power dissipation, so in that respect, they are functionally similar.

Basic accuracy: The Compu-bias is spec'd at +/-5% voltage, +/-5% current accuracy. The Wombat is spec'd at 1% for both voltage and current, although in some aspects the internal accuracy is higher - the voltage sense resistors in the probe are 0.1% tolerance, and the current sense resistor is 1%, and the ADCs (analog-to-digital converters) in the Wombat are 12-bit, so the voltage/current resolution is 1/4096 of the full-scale, so the ADC can internally resolve down to 0.24V and 122uA, but, of course, the overall accuracy is set by the probe resistor tolerance. The point is that the tolerance is set by the probe accuracy, it is not limited by an internal low-resolution 8 or 10-bit converter.

To put this into perspective, +/-5% accuracy on a 500V reading is a potential error of +/25V, whereas a 1% accuracy is an error of 5V, and 0.1% accuracy (the Wombat voltage resistor tolerance) is an error of 0.5V. For current, a 5% accuracy at 40mA is an error of 2mA, 1% accuracy is an error of 0.4mA.

Range: The Compu-bias displays up to 600V, 500mA. The Wombat will display up to 999V (although we spec it a 750V for a conservative safety margin), and 500mA.

Backlighting: The wombat is back-lit (white LED), for use on dark stages or darker benches. The Compu-bias has no backlight.

Batteries: The Compu-bias uses a single 9V, at 3-4mA (36mW). The Wombat uses 2-AA batteries at 36mA (108mW). Battery life of the Wombat will be shorter, in exchange for the convenience of the backlit display. Backlighting is not just for dark use, if you've ever used a calculator without a backlit display, you will know that it is sometimes difficult to read the display clearly without direct light shining on it. The backlight enhances the contrast in all light levels.

Probes: The Compu-bias has both octal and noval (9-pin) probes. The Wombat currently only has octal tubes available, although noval probes and a special dual-triode probe are in development, to be available shortly.

Additional features: The Compu-bias can be used to measure power, using the optional watt-probe, although it is not a true-RMS power reading. The Wombat does not have this feature, so if you need it, you'd be better off with the Compu-bias.

Regulatory compliance: The Wombat is RoHS-compliant, and hopefully will have the CE mark approval before too long (I'm currently working on testing), although the compliance testing is hideously expensive. The CE mark is required for sales to EU countries. As far as I know, the Compu-bias is not CE or RoHS-compliant. I have tested emissions on the Wombat up to 300MHz with a biconical EMC antenna (I'm currently working on getting a 2GHz biconilog antenna in for full-range EMC frequency testing), and there were no discernible RF emissions at all unless the unit was in actual physical contact with the antenna, so I don't think it will have any problem passing the 30MHz to 1GHz emissions requirements for CE.

Feng-Shui: The Wombat has a catchier name and the backlight is cool.



Summary: To be honest, both will do what you want, and even the basic 5% accuracy of the Compu-bias is good enough for amp work, so if you already have a Compu-bias, you would probably be wasting your money on the Wombat, unless the extra feature of biasing 4 tubes at once is desirable.

 

[iggs]

Thanks so much for detailed reply Randall ... you had me at: "4 tubes at once" ...

Do I just e-mail you for order?

 

[reaiken]

Thanks so much for detailed reply Randall ... you had me at: "4 tubes at once" ...

Do I just e-mail you for order?

Oh, you mean I wasted all that time typing?

Yes, just email me, but if you want to pay by credit card, don't email the numbers, because email is not secure, call with the numbers instead, or include your phone number in the email and I'll call you prior to shipping to get the payment details.

Thanks!

RA

 

[jellewelagen]

Randall, What's the max B+ with the Feng-Shui unit?

Edit, just found it...999V...nice!

Thanks,

Jelle

 

[iggs]

Oh, you mean I wasted all that time typing?

Yes, just email me, but if you want to pay by credit card, don't email the numbers, because email is not secure, call with the numbers instead, or include your phone number in the email and I'll call you prior to shipping to get the payment details.

Thanks!

RA

LOL ... the other specs look pretty good to ...

Just e-mailed you.

One more question: is it "safe" to play through the amp with the probes attached and Wombat turned on or not? Compu-bias had a specific warning regarding this and noted a potential damage to the unit.

 

[TD_Madden]

My Wombat arrived last week....I did 4 amps very quickly....the only problem I had was in deciding whether to do them at 50% or 70% dissipation...

;-)

 

[reaiken]

One more question: is it "safe" to play through the amp with the probes attached and Wombat turned on or not? Compu-bias had a specific warning regarding this and noted a potential damage to the unit.

It is not recommended, because the plate voltage while playing could exceed the maximum voltage rating of the plate voltage sense resistors and arc over, which might damage the unit. The head unit has spike/ESD protection, so it would likely survive, but the probe itself may be damaged.

RA

 

[iggs]

It is not recommended, because the plate voltage while playing could exceed the maximum voltage rating of the plate voltage sense resistors and arc over, which might damage the unit. The head unit has spike/ESD protection, so it would likely survive, but the probe itself may be damaged.

RA

Great, thanks for the clarification.

 

[5er Driver]

The Wombat.......hopefully will have the CE mark before too long. The CE mark is required for sales to EU countries.

We need the Wombat in Europe. Specifically in Germany so I can bias 4 tubes at the same time!

 

[roadhog96]

Does the Wombat have a power down mode to conserve on battery life?
Does it have a on/off option for the backlight or is it on all the time?
How about Safety issures, any High Voltages at the ends of the plugs were they plug into the meter? Any chance on getting zapped etc.?
Is the Wombat capable of factory software updates through downloads like the Compu Bias?
Is there a owner/operator manual available for viewing like the Compu Bias, I'm interested in reading about all the specs that aren't listed on the web site?
I'd like to do a one on one comparison between the two. I'm really interested in this Wombat.

 

[reaiken]

Does the Wombat have a power down mode to conserve on battery life?

No, but the LED backlight is very low current (total unit current draw is only 36mA at 3V (fresh batteries), and 46mA at 2.5V), so the battery life is still plenty long enough for normal use. The typical discharge characteristics of an AA Duracell is around 110 hours at 36mA (the new 1.5V per cell battery current draw of the Wombat), and around 25 hours at 100mA (old 0.8V per cell depleted battery current draw), so, depending on battery type, the battery life should average around 40-80 hours of continuous operation, which is a long time with average use of a few minutes per bias. The unit has an internal regulated switching power supply that will function down to 1.1V (0.55V per AA cell), so the product will function down the last bit of energy left in the battery.

Does it have a on/off option for the backlight or is it on all the time?

No, it is on all the time for best contrast on the display in all lighting conditions. I can build you a special unit with no backlight if you prefer.

How about Safety issures, any High Voltages at the ends of the plugs were they plug into the meter? Any chance on getting zapped etc.?

No, only low voltages (less than 5V) are on the cables and in the display unit. All HV is contained inside the probe heads, so as long as you don't take them apart, you are okay.

Is the Wombat capable of factory software updates through downloads like the Compu Bias?

Hopefully there won't need to be any software updates, if I did my job correctly, but there is an internal header on the board for software update functionality. While it could be done by the customer, it would be recommended to do it at the factory, because a USB download cable would be required, which would have to be purchased by the customer ($35).

Is there a owner/operator manual available for viewing like the Compu Bias?

Yes, although I am still working on it, so it will be updated shortly with newer pictures and specs. The current pictures on the website show the old, non-backlit display and non-RoHS-compliant probes.

Here is a link to the preliminary manual: http://www.aikenamps.com/WombatManual.pdf

I'm trying to do a one on one comparison between the two. I'm really interested in this Wombat.

I think I outlined most of the differences in my previous post (#2). If you have any further questions, feel free to ask.

 

[roadhog96]

Not hung up on battereis, just like to know all the facts, don't want any supprises after the fact if you know what I mean.

Can the Wombat use Lithium or rechargable battieres?

Do you take Pay Pal?

The link to the Wombat preliminary manual not working.

Thanks so far for all your replies.

 

[reaiken]

Not hung up on battereis, Like to know all the facts, don't want any supprises after the fact if you know what I mean.

Understood. A well-educated consumer is the best customer.

Can the Wombat use Lithium or rechargable battieres?

Yes, anything in an AA size, Alkaline, NiCad, or NiMH. The cell voltage is not critical, due to the internal voltage regulator and calibrated ADC reference that maintain accurate measurements at any battery voltage within operating range.

Note that all batteries are not alike - NiCads range from 500mAH to 1100mAH, NiMH range from 1550mAH to 2300mAH, and alkaline range from 2700mAH to 3125mAH. Higher mAH ratings typically give longer life, although different battery chemistries have different discharge profiles, so you will get varying lifespans. You can estimate the lifetime by dividing the mAH rating by the current draw in mA of the Wombat - 36mA at 3V, 46mA at 2.5V, 100mA at 1.6V (voltages are for two batteries in series, so each cell voltage is half that).

You'll know when your batteries are dead by the display shutting off. It will maintain accurate measurements up to the point where it dies completely.

Also, when powered off, the unit draws no current from the battery (the power switch completely disconnects the battery), so there is no "standby" current.

Do you take Pay Pal?

No, just Visa, MC, AMEX, or check.

The link to the Wombat preliminary manual not working.

It works for me...???

BTW, I just added a "Frequently-asked questions" section to the manual with all of your questions. Thanks for helping me make a better manual.

Thanks so far for all your replies.

You're welcome!

 

[roadhog96]

Link to Wombat manual working now, don't know why it didn't first time.

Nice job on manual so far.

Question about the section on Biasing an amplifier with the Wombat.
Isn't it advisable to also have the speaker/s connected when Biasing? I didn't see anything about this in the manual only mentioned the guitar cord and volume control.[FONT=Arial,Bold][FONT=Arial,Bold]
[/FONT][/FONT]

 

[reaiken]

Link to Wombat manual working now, don't know why it didn't first time.

Nice job on manual so far.

Question about the section on Biasing an amplifier with the Wombat.
Isn't it advisable to also have the speaker/s connected when Biasing? I didn't see anything about this in the manual only mentioned the guitar cord and volume control.[FONT=Arial,Bold][FONT=Arial,Bold]
[/FONT][/FONT]

Why, it's right there in the second paragraph on page 8...

RA

 

[roadhog96]

I'm not trying to be a smart A$$ but I was refering to Biasing with a load on the output transformer. Isn't it advisable to have the speaker/s connected when Biasing?

I didn't see anything about this in the manual so I checked the manual again, maybe I'm missing something, wouldn't be the first time.

This is the second paragraph on page 8 from the manual;

Unplug any guitar cords going into the input jack. Turn the volume controls all the way down
(other control positions don’t matter). Turn the Wombat on, then turn the amplifier power switch
on, wait a minute or so for the tubes to warm up, then turn on the standby switch. Wait a few more
minutes for the tubes to reach their stable operating point.​

.

 

[reaiken]

I'm not trying to be a smart A$$ but I was refering to Biasing with a load on the output transformer. Isn't it advisable to have the speaker/s connected when Biasing?

I didn't see anything about this in the manual so I checked the manual again, maybe I'm missing something, wouldn't be the first time.

This is the second paragraph on page 8 from the manual;

Unplug any guitar cords going into the input jack. Turn the volume controls all the way down
(other control positions don’t matter). Turn the Wombat on, then turn the amplifier power switch
on, wait a minute or so for the tubes to warm up, then turn on the standby switch. Wait a few more
minutes for the tubes to reach their stable operating point.​

.

I guess you missed the joke (probably due to my lame attempt at humor) - I added it to the manual after you posted the comment... Download the manual again and you will see the corrected version...

RA

 

[rockon1]

Well all I can say is that the Wombat appears to be a well thought out,superior product! Bob

 

[roadhog96]

Generally as a rule of thumb, my advise to anyone including myself is, when it comes to new models, what ever it may be, that it's a good idea to wait a while, to give them a enough time to work any bugs out. Seems like many newly designed products have overlooked design flaws that have to be remedied after their release for sale.

However, there are always exceptions to this rule.

The Wombat does seem to have all bases covered. It appears a lot of thought has gone into it's design and functions. I'm very intrigued with this unit, from all the specifications I have read, to the in depth technical data reaiken has provided on this Forum.

The Wombat Biasing Meter could very well be the best value available on the today's market. I have done my fair share of research on other Biasing Meters and this one by far, exceeds them all, hands down.

Hey reaiken, what kind of warrantee comes with the Wombat...just in case? This question seems to be very appropriate at this time. A touch of my own lame humor.