Tube with Power IC Output Stage - JLTi

[moamps]

1/2 POWER SUPPLY

[moamps]

2/2 AMP

[moamps]

TECHNICAL DATA

POWER SUPPLY
- transformer toroid 230V/8*12V/180VA
- output amps rails 2*32V DC(2*24V), two bridge with doubled diode BYW95C
caps Samsung 470uF/100V, four for each amp
- tube buffer rails 2*45V (half wave voltage doubler from 1*36Vac), two BYW95C, CLC network, 470uF Samsung +100mH+6800uF Panasonic
- tube heating 6V DC, 4xBYW26c, 2* 1000uF Nichicon, stabilized with 7806, 1*1000uF Nichicon

INPUT
usual gold plated cinches, Alps selector 2*1in3, Preh pot 2*10klog

TUBE BUFFER
tube E88CC (NOS Tesla CH), or ECC88 (OS Siemens from scopes)
resistors - usual metal film

OUTPUT AMP
LM 3875 - inverted setup - gain ca 30dB
input cap 2u2/250V ROE MKT, LPF 2*680pF ROE MKC, 2*47nF/160V ROE MKP
resistors - usual metal film
output DC offset about -5mV

POWER ON DELAY
relay 10A/30VDC on output

INPUT IMPEDANCE
10k

FREQUENCY RANGE
10Hz-20kHz (-1dB, -2dB)/1W/8ohm/THD=0,1%/IMD2=0,075%

OUTPUT POWER
36Vpp - 20W RMS (8ohm/both amps on/THD lower than 0.15% 100Hz-20kHz)
24Vpp - 18W RMS (4ohm/both amps on/THD lower than 0.25% 100Hz-20kHz)

NOISE FLOOR
-56dBV

DIMENSION
330*200*40mm

WEIGHT
about 5kg

[moamps]

THD graph shows decent absolute values of harmonics distortion at all output powers and frequencies. It's interesting that distortion falls off with the increase of power for frequencies above 200Hz and stays below 0.1%. My guess is that this happens because there is some kind of noise (100Hz) at the output, resulting from imperfect power supply and the star-grounding method used, which is included in measuring THD results (that's why the noise floor reads only -56dBV). But, the most important quality is, IMHO, that distortion is relatively constant throughout the entire frequency range, which ultimately gives very good sonic results.

[moamps]

Graph with the values of individual harmonics components reveals yet another good side of the amp (again, IMHO) - harmonics values drop uniformly as the factor 'n' increases and this ratio is quite constant for the entire frequency range, regardless of power or load.

[moamps]

THD/output signal amplitude ratio Graph, measured at 1kHz (with filters HP 400Hz, LP 80kHz), shows a constant distortion value for the amplitude range 2Vpp to ca 40Vpp (50mW to 20W on 8ohm).

Measurements were made with Neutrik 3337 analyzer (unfortunately, my plotter isn't working so I can't show the original diagrams - I had to draw the graphs myself, based on the results tables).


To be continued ...

Regards

[JOE DIRT®]

great Job on the amp....very neatly done and pro quality work....alot of you amaze me in these forums you take it up a step higher....congrats!!!

DIRT®

[Nuuk]

Yes, nice work Moamps! What I like about this hobby is that it doesn't work by just throwing money at it. Half the fun is getting results the cheapest way possible and that requires a bit of thought!

Your transformer screen is brilliant. I have often thought that I would like to live next to the local tip and be able to look through all the things that are thrown away every day. Then I could really build some wild hi-fi

[vuki]

Wonderfull work moamps!
According to the measurements the sound of your amp should be even better than the look. I'm eager to compare it to the "standard" inv. GC and my TDA7294 amp. Listening session ahead!

[protos]

It seems that His Holiness didn't manage to seriously distract the die-hard croatian audiophiles.