First Kaiju: Slight hum and somewhat low volume

[Alex.podaru]

Hi,

I've just completed my first Kaiju kit and started using it to drive a pair of Harbeth SuperHL5 (not the most efficient @ 86dB). Even before connecting it to the the speakers I've noticed the power transformer making a slight hum during the voltage tests, is that normal? Once the speakers were connected the the hum balance was brought to a minimum there is still a relative low hum, not you noticeable while listening music unless there is a quiet passage.

The other thing I'm curious about is that the Kaiju doesn't seem to drive the speakers too loud (or as loud as I was expecting them to... would be the more accurate statement). I've previously built a S.E.X. 3.0 for my headphones but was pleasantly surprised to see that it could drive the Harbeth to decent levels, with crystal clear sound albeit lacking a bit of "oomf". Now the sound out of the Kaiju feels much richer and definitely has that "oomf" that the S.E.X. was lacking, but with its power rated at 8 times that of the S.E.X., I was expecting a little more loudness. I have both amps wired for 4ohms at the output transformers and they are very similar in term of loudness (with an ear test only). Is this normal or did I wire something wrong somewhere? Am I understanding the power rating wrong?

As you can probably tell I am quite new at this and would appreciate any input!

Thank you!

aPodz

 

[Paul Birkeland]

I would certainly speculate that something is amiss based on your description.  I'm going to assume the obvious that the trim pots are all the way up and that you've passed your voltage checks.  I'd probably go back and double check these to be sure! 

When I've run into issues like this, it has often times come from wiring mistakes on the output transformers which end up reducing the available output voltage.  I would check there first!

Beyond that, it's easy to check the amp by downloading a 60Hz tone onto your phone and playing it through your amp, then measuring a few AC voltages under those conditions.  I can help you do that if your DC voltage check is good and the output transformer wiring is correct. 

As far at the PT humming, I would recommend tightening down the hardware as much as possible.

-PB

 

[Alex.podaru]

Thank you for the quick reply Paul!
I've went through the instructions double checking the connections and it seems that things are wired correctly. I'll attach some pictures and hopefully your experienced eyes will catch something I've missed. Regarding voltages here's the information I've collected so far:
I live in the States, and the initial voltage I've measured was 123V AC, and so I've followed the instructions for "IF your voltage is GREATER than 115V AC and LESS than 130V AC".
On the secondary test: I remember getting normal values when I did the test. I redid it after all the components were installed (minus to 300B tubes as I am afraid of breaking them) and here is what I got: 195V between 7-8, 6.3 between all the other ones.
On the high voltage power supply test (again with all the components minus the the 300B tubes) I would get 256V @10U, 529V @14U and 267V @15U.
And finally I was getting 529V @IA and 297V @OA on both boards, with 32U and 46U dialed in to 175V on the board potentiometer.

I tightened all parts and changed the output to an 8Ω secondary and that has reduced the hum a little, but has not eliminated it. 

 

[Alex.podaru]

I've also uploaded some more pictures and a video at the following link: (https://www.dropbox.com/sh/rqdhxjshjnqn3xw/AACE71o6q6DwaUsyMegQcM9Fa?dl=0)

 

[Doc B]

If the amp is humming and the trim pots are not moved rewiring the amp from 4 ohms to 8 ohms should make the hum louder, not more quiet.

Does the hum go up and down with the level controls, or stay the same no matter what setting?

 

[Alex.podaru]

The hum stays the same irrespective of the position of the volume potentiometers. It might have gone quieter from the tightening of the screws securing the transformers I did at the same time as the re-wiring of the output transformers.

 

[Doc B]

Does it change if you disconnect the interconnect cables from the input jacks?

 

[Alex.podaru]

It stays about the same whether the input cable is in or out, and it stays the same whether i am inputing a phono stage or an headphone jack. 

 

[Doc B]

OK, we are narrowing down the possibilities. Does the hum start as soon as you turn the amp on, or after it warms up?

 

[Alex.podaru]

I'd say it's pretty instantaneous, within 1-2 seconds of turning it on. At some point it didn't do it if the 300B tubes weren't in, but I haven't tested it without them in since then, if that information helps some.

 

[fullheadofnothing]

How much hum are you measuring?

 

[Alex.podaru]

I unfortunately don't have a multimeter that measures AC low voltage. I did the hum balance test by ear only, by standing a few feet away from the speaker and adjusting the hum balance. I'll can get a better multimeter if you really need a value. 

 

[fullheadofnothing]

If you have excessive hum, that would be a sign of a problem with your amp. It's impossible to say if the hum is excessive or not without knowing how much is there.

Cheapo meters work fine most of the time (the one shown in the manual is a super old RadioShack meter, and the meter that HarborFreight gives away is up to the task as well). What does your meter do when you try to measure low voltages?

 

[Paul Birkeland]

I'd second Josh's recommendation.  The cheap meters do suck at measuring low AC voltages, but if you get the $25 meter at Harbor Freight, it will resolve AC mV just well enough to do the job. 

If you'd like to check the gain of the amplifier, having a meter that resolves mV will be convenient as well.

-PB

 

[Alex.podaru]

Ok, I've been using this cheap one to get me through the build: (https://smile.amazon.com/AstroAI-Digital-Multimeter-Voltage-Tester/dp/B01ISAMUA6/ref=sr_1_4?s=hi&ie=UTF8&qid=1513026654&sr=1-4&keywords=AstroAI+Digital+Multimeter) and when I put it on 200 ~V i get a 0.00 reading.

I'll go get a better tool and come back to you guys with some values.

 

[Alex.podaru]

Ok, I've upgraded!! hehe

The reading at maximum hum on both channels was around 0.160V and I managed to get it down to 0.006V with the hum pot adjustment. I guess that would be within norm right?! I guess the hum was a little bothersome as I was comparing it to the S.E.X. which is dead quiet. Would that be due to the smaller transformers?

 

[Alex.podaru]

Oh and regarding the volume, maybe some objective measurements might help. I've downloaded an SPL tool on my phone and in my 11'x13'x9' room, with a random test tone of 650Hz generated with my laptop at max volume (on both the laptop and the amplifier), I was getting ~95dB at max volume on the Kaiju and ~96dB with the S.E.X.

 

[Doc B]

Yes, the 6mV you now measure is much more in line for 300B AC filaments than 160mV you had before. The S.E.X. amp has a DC heater supply for its indirectly heated 6DN7/6FJ7. To get that same level of quiet from the directly heated 300Bs of the Kaiju you can install the DC filament supply upgrade. We leave it optional because some users don't have a problem with AC heaters and their low efficiency speakers. Others may want to add it for more sensitive setups. I was just listening to a nice system with 104dB sensitive Lowther drivers last week, and a Kaiju with the DC filament supply is dead quiet on them.

Unfortunately without knowing what the measured signal voltage level from the laptop is, it's not really possible for us to say much more than that the SPL measurements you got show the gain of the S.E.X amp is a little bit higher than that of the Kaiju. It might simply be that the signal level from the maxed out laptop is not high enough to drive the Kaiju to full output.

Since you have a working AC meter now the next step would be to measure that max signal level from the laptop.

 

[Alex.podaru]

I had a tough time recording a max voltage with that same 650Hz tone, but while outputing music, the Max voltage I was recording was ~250mV.

 

[Paul Birkeland]

OK, here's how to gain test the amp.  First of all, you'll want a 60Hz tone, just to keep the meter accurate. 

The first measurement will be AC millivolts (maybe volts with a strong source) from the center pin of the RCA jack on the Kaiju to ground.

The second measurement will be AC millivolts from the center lug of the trim pot to ground.

The third measurement (you will need the amp on now) will be AC volts from pin 3 on each 4 pin socket to ground (likely no longer millivolt).

The fourth measurement will be the AC voltage across each pair of speaker posts (not referenced to ground here).

6mV of hum isn't unreasonable when the DC filament supply isn't installed.

-PB