Test output transformers in my 2 stage only 845 amplifier

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Test output transformers in my 2 stage only 845 amplifier
Dec 25^st , 2008

There is an opened forum about this 845 with only two stages

In this test the power supply was 900V and 70mA bias.

COMPONENTS

Lundahl LL1620/90mA AM

Price: 350 euro each in Europe
410$ each in US

Declared specifications:

Turns ratio: 4 x 19.2 : 8 x 1

Static resistance of primary: : 308 ohm

Max. primary signal voltage r.m.s. at 30 Hz: 380v

with ALT_B secondaries connections:

- Max. Power at 30 Hz: 13W on 8ohm
- Max. Power at 30 Hz: 25W on 4ohm
- Primary Load Impedance: 11.5k on 8ohm

Dimension(mm): 110x85x78

Weight: 2.5Kg

Tango X-10S

Price: 1380$ for a pair in Japan
844 euro each in Europe

Declared specifications:

Primary Load Impedance: 10Kohm

Max. Power at 30Hz: 40W

Design/max current: 70/130mA

Dimension(mm): 125x125x180

Weight: 7.7Kg

MEASUREMENT TEST

Follows the comparation measurements on 8ohm resistive load.

I have used in all the measurements the Clio system by Audiomatica with the Transit by M-Audio to use the USB port of my portable pc (instead of the PCI audio board).

In the first frequency measurements I have found a strange negative peak at 12KHz relative to a capacitor of the LL1668, so for this new set of measurements I have separated the core-chassie of the LL1668 from the ground of amplifier.

Lundahl LL1620/90mA AM

The inductance measured is 40H as declared in the datasheet (If the 45mA type have 80H for the 90mA the value is L = 80H * 45mA / 90mA = 40H).
This 40H value, with the internal resistance of the 845 about 1700 ohm, should give a low cut-off of F = R/(2*3.14*L) = 1700 / (2*3.14*40) = 7Hz(-3db).

On the first two plot we can see that the distortion level change with the frequency so probably the 9.5Vrms are a little too much for this transformer (Pout=9.5*9.5/8=11.3W).

In the frequency band measurement there is a value about 20Hz at -3 db at the max power and 15Hz at -3db at lower level.
To get the best high frequency response is necessary use a 47ohm resistor to the output ground as in the schematic (see plot without the 47ohm).

The output level, so the voltage gain of the amplifier, using the LL1620 is little bit less because it is a 11K5 on 8ohm instead of 10K so the turn ratio is 38x and not 35x.
This mean a big advantage in the damping factor using Lundahl because with LL1620 the measured output impedance is only 1.77ohm.

Tango X-10S

The inductance measured is 90H.

The distortion is quite constant with the frequency.

It give a very good low frequency band 12Hz at -3db with a little peak at 30Hz.
The high frequency band follow the input stage response.

The output impedance is 2.26ohm.

The larger signal for a good distortion decay

The larger signal for a good distortion decay

Follows the measurement at 50Hz at the same level

Frequency response at the same output level

Frequency response at 6Vrms output level

SONIC PERFORMANCES TEST

Test System:

- Rega Planar 3
- Cartridge Denon DL103
- MC Step-up Sowter 9580 or Lundahl LL1931
- My Pre Phono 4
- SYNCHESTRA Reference nterconnect cables
- SYNCHESTRA SIGNATURE Speaker Cable
- Martin Logan AERIUS modified

In all my sonic performance tests I always search to be sure of an objective result using many persons and these with different experiences.
This mean that the result here is not my personal and it is not subjective like many other test published online.

Lundahl LL1620/90mA AM

The details in middle and high frequency band sometimes since to be better than Tango probably for the use of Amorphous core but the final result is compromised by a light low frequency band also in the reproduction of instruments like the piano.
Soon I will check the performances of a bigger core Lundahl model like the LL1688AM.

Tango X-10S

A very good result on any frequency band.