First Kaiju: Slight hum and somewhat low volume

[aPodz]

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?

[aPodz]

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.

[aPodz]

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

[aPodz]

Ok, so I hope I did this right... I fed in a 60hz tone (from http://www.szynalski.com/tone-generator/) from my laptop into the Kaiju and with the Kaiju powered off i took the following measurements for max AC voltage (i only did this on the left channel as both channels seem to behave identically at this point).
From the middle of the left input to the ground tab next to E: 1025mV
From the middle lug of the left trim pot (with the trim pot in its lowest position) to the ground tab next to E: 170mV
With the Kaiju powered on from B3 to he ground tab next to E: 403V
In the speaker terminals with the trim pot in its lowest position: 8mV
In the speaker terminals with the trim pot in its highest position: 6.28V

[Doc B.]

OK, this helps. 1.025Vrms of signal in is quite a bit less than the 1.56Vrms the Kaiju needs to see for full output power of 8W. Assuming 8 ohm output transformer secondary wiring into an 8ohm speaker, 6.28Vrms output is only about 5 watts output. So a preamp to boost that input signal a bit may be the best solution to get the Kaiju cookin'. Even a Quickie would do the job.

[Paul Birkeland]

From the middle of the left input to the ground tab next to E: 1025mV
From the middle lug of the left trim pot (with the trim pot in its lowest position) to the ground tab next to E: 170mV

You've lost 20dB through your trim pot, are you sure it's all the way up?

With the Kaiju powered on from B3 to he ground tab next to E: 403V
In the speaker terminals with the trim pot in its lowest position: 8mV
In the speaker terminals with the trim pot in its highest position: 6.28V

Yeah, turn the trim pot all the way up and start again.

[aPodz]

OK, this helps. 1.025Vrms of signal in is quite a bit less than the 1.56Vrms the Kaiju needs to see for full output power of 8W. Assuming 8 ohm output transformer secondary wiring into an 8ohm speaker, 6.28Vrms output is only about 5 watts output. So a preamp to boost that input signal a bit may be the best solution to get the Kaiju cookin'. Even a Quickie would do the job.

So, if I'm understanding this correctly, the Kaiju is working within norms, I just have to increase the input.

You've lost 20dB through your trim pot, are you sure it's all the way up?

Can you explain to me, if it's not too complicated or time consuming, how you've obtained the 20dB value? I will run those tests again with the trim pots all the way up.

[aPodz]

You've lost 20dB through your trim pot, are you sure it's all the way up?
Yeah, turn the trim pot all the way up and start again.

Tried it again with the trim pot all the way up and was getting near 1mV between RCA and middle lug of trim pot.

[aPodz]

Alright!! So I tried running the Kaiju through my Emotiva UMC 1 and boy can it get loud!! Still crystal clear and with its natural warmness and cohesion.

I couldn't help but to do the same with the S.E.X and I was again amaze how loud it got before showing signs of distortion. It really is a great little amp! 

[Paul Birkeland]

You reported about 1000mV of signal at the RCA jack, but only 100mV at the middle lug of the trim pot.  This would indicate a measuring error or that the pot isn't turned all the way up.  If the pot is all the way up, the middle lug of the pot and the center pin of the RCA jack will show the same AC voltage. (With the remote possibility of a wiring error, but I looked over your photo and couldn't see anything)

-PB

[aPodz]

My apologies! I was measuring the wrong thing. The reading i gave you of near 0mV was from RCA input to middle lug on trim pot. From trim pot to ground I am getting 1,009mV (with and RCA to ground of 1,010mV).

[Paul Birkeland]

Try pin 3 on each 4 pin socket again.  With 1V (1000mV) of signal coming into the amp, you should see more like 20-30V on pin 3.

[aPodz]

Ok, i’m getting 29V and 29.9v in the left and right channels respectively