Hewlett Packard HP Model 334A Distortion Analyzer 1 of 2.MOV

Hewlett Packard (HP) Model 334A Distortion Analyzer Instructional Video

[@CovertCulvert]

Thank you! That was the clearest explanation of the three vids I've seen.

[@69mercurycyclone44]

Thank you for this video! Was shying away from these units because I didn't know how to use it. Love you're videos!

[@ElPasoTubeAmps]

I am really pleased to hear that it helped you and helped preserve another beautiful vintage instrument. Thank you for your comment.

[@ElPasoTubeAmps]

The output of the amp connects to the 8 ohm resistor. The distortion analyzer connects directly across the 8 ohm resistor and not the input of the amplifier. The 334A instrument can be switched between the voltmeter position and the distortion measurement position. In the voltmeter position the voltage is read and the value squared and divided by the value of the load resistor (8 ohms) to determine RMS power in watts. So, both power and THD can be measured with this instrument.

[@HansDelbruck53]

Actually, you're supposed to use Manual mode till you get your lowest distortion reading on the scale, then flip the lever to Automatic. After that, the reading will sometimes settle to an even lower (more accurate) reading. Do not start your measurement in Automatic mode. Used these, and repaired them (as well as the Tektronix test equipment you're using), for many years as a calibration technician in the army back in the Seventies. Brings back a lot of memories.

[@ElPasoTubeAmps]

Thank you. It is always good to add real experience to these videos so that when someone gets a "new" one, they can learn how to use it best as possible.

[@HansDelbruck53]

@@ElPasoTubeAmps You're welcome. It's been decades since I actually used a 334A, so I had to exercise my memory muscles to recall as much as I did. There are probably a few steps I've forgotten by now. I didn't know if there would be still a user manual available for old HP test equipment somewhere on the Internet or not, but I was able to find one. The Hewlett Packard corporation became Agilent, then that became Keysight. Here's a link to the Keysight operation and service manual for the 334A. It includes instructions for measuring distortion: literature.cdn.keysight.com/litweb/pdf/00333-90008.pdf?id=811981

[@ElPasoTubeAmps]

It is interesting you comment on skill level. I am also an EE and 61 years old and have seen a lot of change. I remember when grafting equations was total drudgery (almost masochistic for equations over 3rd degree) whereas nowadays we take it for granted on our calculators and PC's. Nowadays we can concentrate on solving the “larger problem” instead of spending so much time on the details. I guess that’s good but, does quality suffer? I don’t know. Thanks for your comments.

[@ElPasoTubeAmps]

Measuring the THD of an integrated amp can be done easily by putting the input (sine wave) signal from your generator into any of the aux (high level) inputs. The CD player would need some low distortion reference CD that I am not familiar with or know where to get. The 475A scope is certainly very capable of good display at audio frequencies. 50 ohm coax is a good choice as there are many connectors and adapters available. Good luck with your test setup.

[@120ohm]

I'm also wondering what exactly distortion is and why you need to measure it??? I acquired that same HP unit a few years back from a friend but it's just been setting on my bench... I mean it looks cool! All them knobs and stuff! LOL But I would love to be able to put it to use! I think it's REALLY neat how you have to know all the steps involved!!! All this new fancy computer controlled stuff takes the skill out of the trade... :( (2nd year Electrical Engineering Technology student at Purdue)

[@ElPasoTubeAmps]

@451mnu The equipment stack as you mentioned is purchased separately and you can expect to pay in the area of 1000-1500 dollars (or more) for all the components. The HP is just as good at accurate measurement but the Tektronix digital equipment requires no nulling and makes multiple measurements so easy whereas the HP has to be constantly "tweeked". Thank you for your comments.

[@ElPasoTubeAmps]

You have some very nice equipment. From looking at the 339A, it appears to be very similar to the 334A. The objective is to adjust the meter full scale with some input (say 1KHz) then null the fundamental frequency with adjustments. The remaining signal components are the distortion products. I don't know the CFG253 but I suggest you research it and find it's distortion limits for a sine wave and that way you can compare what is expected with what you measure on your 339A.

[@ElPasoTubeAmps]

I has been my experience that the original "bumble-bee" caps are most likely still OK. Some may disagree with me. All of my amp is original including the electrolytics and the selenium bias rectifiere. Replacing the caps may decrease its resell value. I would think about it long and hard before wholesale replacing the caps. It it works properly, enjoy it as it is.

[@philhemenway3503]

Excellent videos. For the novices in the viewing audience explain what kind of cable you are using for interconnects. Thanks.

[@ElPasoTubeAmps]

My distortion analyzer in the videos is the Tektronix AA501. It works in the TM500 series mainframes or it will work in the TM5000 series mainframes. There is also a model AA5001 that only works in the TM5000 series mainframes. The ultra-low distortion signal generators are the Tek SG505 modules that you may want to get to go along with the analyzer.

[@slide4417]

Does the signal generator connect directly to the amps' input? And how do you measure the output of the amp? I suspect the amp connects to a BIG 8 ohm resistor, but how do you sample, or "pick off" to go into the distortion analyzer? Thanks!

[@stereopolice]

Thanks for the video; it really helped. Brian

[@ElPasoTubeAmps]

Thanks, Brian - I am glad it helped - there is a second one if you need to view it.

[@JesusIsLordofMybeing]

Love the video!! Can you use this same meter for performing IMD tests?? Thanks

[@ElPasoTubeAmps]

I don't think so. IMD takes two tones at different levels and this instrument doesn't do that.

[@flagshipaudio]

I just picked up a vintage mc275 and what to know what caps I should keep original? Thank you!

[@stereopolice]

I bought one based on your video, in order to measure my custom tube amp modifications. This model is probably the best value on the used market for those on a tight budget. Anyway, one question: I noticed you had the high pass filter "in" during this measurement. Is that a requirement?

[@ElPasoTubeAmps]

You should probably watch the second video I have on this unit - the high pass filter in will not allow you to measure frequencies below 1 KHz so you do have to be careful with it - please see part 2 of 2 where I do a much better job with this unit and thank you for your comments.

[@stereopolice]

ElPaso TubeAmps Thank you sir. I did watch the second video. But ... unfortunately, the darn distortion tester I bought is defective, can't get the meter to settle down and even give me an accurate voltage reading, seems to be a problem with the "range" selecting switch, so I'm back to dealing with ebay again. But I'll get this straight someday ... Thanks for the reply.

[@slide4417]

OK..I am working on acquiring all that I need to make these tests....just for fun! I have an old tube-type audio oscillator, plus a modern HP and brand new BK Precision function generator (I hear they have more distortion than the audio oscillators). A 100 Mhz Hitachi scope, and a nice digital Tektronix scope. Also a very nice Kenwood distortion analyzer (similar operation to the HP 334A) So, I just need to get a few big 8 ohm loads, and the 600 ohm BNC load, and I should be in good shape????

[@gbowne1]

I love the Tektronix TM500 type module mainframe instruments

[@babybearkill1]

Great video.. thanks

[@slide4417]

Can you tell me the model of that Tek digital distortion analyzer?

[@ElPasoTubeAmps]

@jjcarniel I have recently made another video with me fumbling and tinkering with the 334A that might help.

[@jimcastillo8950]

what is a distortion analzyer used for? what applications?

[@ElPasoTubeAmps]

It measures the difference between a perfect input sine wave and the actual sine wave coming out of the audio amplifier. It is used to evaluate the performance of the amplifier to accurately reproduce the input signal in relation to the output signal. In a perfect amplifier, the output signal would be exactly the same as the input signal but of a higher power (or voltage) level. In a quality HiFi amplifier the difference between the input signal and output signal should be typically only about 1% different. The difference is usually measured in Total Harmonic Distortion (THD) percent. The way a distortion analyzer works is by completely filtering out the frequency of the input test signal and measuring any small differences that are left in the output signal of the amplifier. If the input signal is pure and it passes thru the amplifier and remains pure, there would be no remnants of the signal and the output meter of the distortion analyzer would measure zero. Even in a very high quality amplifier there are distortion products in the form of harmonics which are integer multiples of the test frequency, that are actually created by the imperfections of the amplifier itself. High quality solid state amplifiers can measure very low values of harmonic distortion in the order of 0.01%. Very high quality vacuum tube amplifiers can have distortion figures usually around 0.1% at low volume levels and up to 1% or a little more at full volume and still be considered very high quality. It is my opinion from working with audio equipment for many years that we seem to like a little bit of harmonic distortion in the output of an amplifier and I would guess that is one reason why some people like vacuum tube amplifiers even today. In a guitar amplifier, typically the power level advertised by the manufacturer is only obtainable at about 10% distortion but that is the way guitar amplifiers are expected to sound. Adding a fuzz-box into the line from the guitar to the input of the guitar amplifier causes the signal to become essentially a square wave and distortion levels reach 100% but in some cases that is the sound we like. Harmonic distortion in a vacuum tube amplifier generally makes the signal somewhat out-of-shape (and distorted) as observed on an oscilloscope but the edges of the distorted signal are smooth and our ears are not offended by this type of distortion. A solid state amplifier, when over-driven, tends to distort the signal and make it have sharp corners on the distorted wave (rather than the smooth rounded corners of the vacuum tube amplifier) and these sharp transitions sound very harsh to our ears and we find it annoying and tire of the sound quickly. That is in my opinion, why the vacuum tube amplifier remains so popular to this day. Hope this helps...

[@m2m259]

par que serve isso?

[@gbowne1]

Not everybody understands the Root Mean Square voltage scale.

[@jimmyc451]

get it out of automatic when nothing is connected pls and change yiiur arrange as you null

[@jimmyc451]

the 334A is better btw