Question about KEF Audio Cresta 2 Speaker

1 Answer

Measuring mA with a DMM

I'm trying to bias a tube amplifier using a Sperry 350a digital multimeter.

I'm getting a negative reading when the amp is powered up (-65mA) as opposed to just 65mA.

Any idea as to why?

Posted by on


1 Answer

  • Level 1:

    An expert who has achieved level 1.


    An expert that hasĀ over 10 points.

    Problem Solver:

    An expert who has answered 5 questions.

  • Contributor
  • 10 Answers

The most obvious solution to your problem is that you may have the meter simply connected backwards. To make life easy, Groovetubes sells a thing called a bias probe that makes biasing tube amps a breeze.

Posted on Dec 27, 2007


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Why does my sperry DM6450 multimeter read "connect terminal" even when both are connected?

Are you connecting your leads to the proper terminals on the meter? There are, what, four of them? Easy to mix up.

If it still isn't working, then you might have a bad connector on your multimeter.

Nov 03, 2014 | Sperry Instruments DM6450 64 Series...

1 Answer

I purchased the velleman DVM850BL to check current drain from my vehicles batteries as I keep having to recharge my batteries pretty often. Since I am not an electrician or electronic tech, I would just...

To check the current, you'll have to set up your equipment to the mA (milliamp) position. It's located on the right side of the equipment, on the "A" section. The test leads should be positioned accordingly and it is: black in the middle connector (common) and red on the right connector (mA).
It's safe to start measuring the current in a higher scale. Safe for the equipment. So start measuring with the equipment set to the 10A scale and the red test lead on the left connector (which reads 10ADC or so) and check the reading to see if it's below 0.2A, which is the same equivalent of 200mA. If it is, then it is safe to start reading the milliamp (mA). Undo the leads to the mA port and change the equipment scale to 200mA. If you don't observe this and you try read a current higher than 200mA, your equipment might burnout.
But wait: to measure current, you have to open up the circuit that you pretend to do the reading. You can only measure voltage (not current) with the circuit "closed" (also be careful to not try to measure voltage while the equipment is set to measure Amps. Leads will meltdown!!).
To do this, remove one of the batteries terminal. Doesn't matter if it is positive or negative. Then, with the equipment already set to the scale you want, connect one lead to the terminal and the other to the cable or wire that you just disconnected. This will provide continuance of the circuit, having the current going through the DVM and displaying the actual current through that circuit.

Nov 22, 2013 | Velleman DVM850BL Digital Multimeter

1 Answer

How to set mastech multimeter to read small batteries

Set the multimeter to a DC voltage range that includes the voltage you wish to test. Connect the probes with the correct polarity and observe the reading

Mar 16, 2013 | Mastech 19-range Digital Multimeter Dmm...

2 Answers

Hi Thanks for your help, One year old Sony mini

sir i think ypur unit is ok and run correctly... try to check your speaker maybe your speaker got open or burnt... you can test it by swapping your speaker to another unit or you can test your speaker using multitester...just point your selector at resistance test a speaker has 8ohms reading....

the speaker has a two terminal.. a positive terminal and a negative terminal... your multitester has a two lead.. red lead which is a positive and a black lead which is negative..
measure-speaker-impedance-1.1-800x800.jpg Multimeter probe sockets (NL Graphics) Insert the probes of a digital multimeter in the correct sockets of the multimeter. There may be several different sockets for the probes depending on what parameters you're measuring. Look for the sockets marked "impedance" or displaying the ohm symbol. Different models and brands of multimeters will vary in their labeling, so check your multimeter's manual if you're not certain about which one to use.

  • 2 Select the range for the multimeter. Since you'll be measuring fairly low resistance levels with a speaker, choose a range that will encompass readings in the 2-16 ohm range. It's extremely rare to find speakers that will have an impedance outside of that range.
  • 3 Touch one probe to each of the speaker terminals and check the reading. This will be the impedance of the speaker. Record the measurement, and when you're done, turn off the multimeter to preserve the batteries for the next time you need the multimeter.

  • Read more: How to Measure Speaker Impedance '
    if you think this help please rate me thanks...

    Jun 10, 2011 | Sony CMT-HPZ9 Shelf System

    1 Answer

    Do 4-10 devilles need to have the bias adjusted when replacing tubes?

    When replacing the two output tubes you should check the voltage at TP26 or either cathode pin of the power output tubes to ground. Set the bias by adjusting pot R82 to 60mv which is 60 ma across the 1 ohm metering resistor. This coresponds to 30 ma per tube. Changing other tubes requires NO adjustment.

    Apr 12, 2011 | Fender Hot Rod Deluxe Guitar Combo...

    2 Answers

    Car won't start. replaced battery. ok for 3-4 days. Problem reoccurred. dealership can't find what is draining power. Replaced battery second time. cycle started over again.

    If you have some electrical know how you can try to trace the draw yourself. You will need a multimeter capable of measuring amps.

    First dis-connect the negative terminal, and make sure your dome light and everything else is turned off.

    Next connect the multimeter in between the terminal and battery connection basically completing the circuit, and make sure the meter is set to amperage.

    You should get a reading somewhere around 14-25 milliamps depending on how old or new the vehicle is. If you have a reading of say 200 milliamps then you have a draw somewhere.

    Now once you get a clear level reading start by removing individual fuses and seeing if the reading goes down. Once you find the fuse that drops the reading down to an acceptable level you found the circuit that has the problem.

    At this point you would have to trace individual parts of the circuit to find the specific draw which requires a fair bit of know how, and should be done by someone with this knowledge.

    Jan 12, 2011 | Lincoln LS Cars & Trucks

    1 Answer

    I have a crunch p1500.1 amp and it turns on and lights up but no sound comes out of the subbs and the protect light isnt on

    There a few different issues that could be troubling you.

    1. The Amplifier's outputs are no longer working
    - To test this, connect the negative probe of a digital multimeter (DMM) to the negative (-) terminal of the amps speaker output. Connect the positive probe of the DMM to the (+) terminal of the amps speaker output. The output terminals you are referencing should be the output to the same speaker. Set the DMM to AC Voltage/lowest setting. If you read AC voltage than the outputs are ok. If you show no reading then the outputs are bad. Stop here and get the amp repaired or use as a paperweight.

    2. Check the RCA connections behind the radio. They may have come undone. If so, re-connect and dance for joy as you once again enjoy music in your car.

    3. Confirm that your RCA connections to your amp are plugged into the INPUT and not OUTPUT or THROUGHPUT. If in the output or throughput then move to the input. refer to the last sentence in #2 above.

    4. Your RCA connections/or RCA cables are bad. Use the above mentioned DMM to check for continuity in the RCA's to ensuyre they are in working condition. You can also use the DMM set to ACC voltage like in #1 above to check to see if voltage (speaker signal) is being sent to your amp.

    5. Make sure the amplifier's gain setting is not turned all the way down. If so, adjust accordingly.

    If none of these solve your issue then most likely your amp is beyond the do-it-yourself repairs.

    Dec 22, 2010 | Crunch Car Audio & Video

    1 Answer

    Checking batteries

    I assume a "DM-350a" is some kind of a digital multimeter. I Googled and found it might be a "A.W. Sperry DM350A 5 Function 17 Range Digital Multimeter" and looking at the ranges available on that meter, you can't really thest the battery "under load" the only reasonable way to test small batteries. the DC current only goes up to 200 milli amperes. A "C" or "D" size flashlight battery puts out 1 to 4 amps depending on conditions. That's 5 to 20 times the current readable by that meter. The volts on one of those batteries is probably 1.6 volts to 1.3 volts etc. If you live in the United States, I'd say go to Radio Shack and spend $5 to $15 and buy a battery tester like "Enercell Analog 9-Range Battery Checker, $14.99, Model 22-156, catalog # 22-156"
    Then you and anyone in your family can read the instructions and test 8 or 9 different type batteries. Battery types: 1.5V button-cells, "AAA"/"N"/"AA"/"C"/"D", 6V, 9V, 12V, 15V and 22.5V..
    This is not supposed to be an advertizement, and I have no interest in RadioShack,... but it's supposed to be instructional.

    Small price, Good instruction to anyone who can read, and if anyone forgets, they can re-read. Testing a lot of batteries in a sitting goes very fast with these.

    Differently, with the sperry, or any voltmeter, you'd have to select a resistor small enough to draw the current, and large enough not to overheat or burn, connect it and measure the loaded voltage drop, compare the voltage and current of the loaded battery, and compare it to that of a new battery, and a battery you might consider too weak for your application.. Voltage equals amps times resistance, and power equals amps squared times resistance... Really, buy a battery tester.
    Regards --- GooseBay_Camper

    Sep 26, 2009 | Sperry Instruments HST401 Voltage...

    3 Answers

    I just brought a sperry dm-350A to test the switches on my dryer I thought they would come with instructions on how to use it but it didn't. Is there a place where I can go and learn what the symbols...

    Just got mine from home depot. Stick the black wire into the COM port and the red wire in the V port on the right. The red wire is the positive and the black is the ground. Touch the red tip to the positive and the black one to a ground. Turn the dial clockwise to the right and you are measuring your voltage(i left it on 200).

    Jul 11, 2009 | Measuring Tools & Sensors

    1 Answer

    Checking batteries AA D cel with a sperry DM 350A digital multimeter

    dc .... no lower then the voltage range of the highest voltage of the battery.

    Sep 06, 2008 | Measuring Tools & Sensors

    Not finding what you are looking for?
    KEF Audio Cresta 2 Speaker Logo

    Related Topics:

    191 people viewed this question

    Ask a Question

    Usually answered in minutes!

    Top KEF Audio Audio Players & Recorders Experts


    Level 3 Expert

    5554 Answers


    Level 3 Expert

    3289 Answers

    Vernon Taylor

    Level 3 Expert

    4685 Answers

    Are you a KEF Audio Audio Player and Recorder Expert? Answer questions, earn points and help others

    Answer questions

    Manuals & User Guides