Leak Delta 70 with MOSFET output stage

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I found my old pcb which is a partially cloned Leak Delta 70 circuit.
I looked at the old threads on the Leak Delta 70 and there were several. This one was about what I had planned to do. Main difference was a CCS on the emitter of the input transistor ( 2SA970), Filtered supply to the input stage, and a Darlington VAS ( 2SC1854 and KSP42 ).
It used to work long ago ! Not sure if it does now. The output power Tr are 2x IRF250 and drivers are 2SD669 and 2SB649.
The spade lugs seem oxidised and so I plan to solder the speaker wires to the board. The board has an on board power supply and dc protection relay. Can't find the files on it so I had to check out the board physically to see what I had done. Hope it works. Trouble shooting will be a pain due to lack of time !:)

Wonder if anyone made a clone of the Leak Delta 70 or a modified version like I did.
Powered up the board up with a 30-0-30 Vac transformer.

Can't play it loud now. Sounds quite nice at low volume. Bass is very good however HF may sound slightly soft compared to another amp. But midrange is very nice. The amp sounds nice .
The 'soft' HF could be due to the input capacitor which is a no name polyester cap !Chinese I assume. Will change it tomorrow and see what happens. Low level sounds are wonderful. Very clear. Will compare it with a Beyer DT990 ! May not be fair as the phones have no acoustic reflections to deal with . The DAC has a headphone output.
Should be able to do some testing today...I hope !
The circuit is attached. Semiconductors as listed earlier but seem to be different from what I had planned to use . However it works. As it stands there is no heat sink on the drivers. The bias transistor BD139 is on the main heat sink with the power transistors. Will try to post a picture later.

Note that there is no capacitor from base to collector on the input transistor. The original circuit would oscillate without that ! There was also some talk about the Baxandall mod which was a diode and resistor in the emitter leg of the pnp driver transistor. ( you can add it vertically if you want !) The original Leak Delta 70 didn't have it and I didn't use it either. However the sound is quite smooth at low volume and so I guess it isn't required ! Lets see what the test results are like.
The drivers are quite warm. So I will add a small aluminum heat sink on them. Need to check what the drift is like. R3 and R15 are 1 K multi turn presets. R3 is set to control the dc offset output voltage.
Not sure what I did with the dc protection circuit. Will have to draw it out again. Don't seem to have the original drawings. The gain might be too low for some applications. Will set it for 0dBm for full output and see how it fares. Depends on how much free time I have today !........Also need to change the input capacitor !


  • Leak D70.jpg
    Leak D70.jpg
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I've been trying to get a FFT of the amp. There is a ground loop somewhere which is picking up power supply harmonics below about -60dB. However I can't hear any hum or noise while playing music or not.
Spent a lot of time trying to get rid of it and looks like I did but later it reappeared ! No point wasting time over it. The amp does sound very nice. Distortion seems to be about 0.06% at 1 watt into 4 ohms. Nothing great. Very nice midrange. It appears to be stable but there is a slight lift in HF of less than a dB just beyond 20KHz and then it rolls off. Shouldn't be there. Will check it when I have time.
All this with the no name polyester 0.47uF input capacitor. Will be trying a Solen polyprop cap next. Plan to run the amp everyday for a few days and see if anything changes. After that will compare it with maybe a Creek 5350 ? Maybe the bass will not be as good as the Creek ?
Bias current of the output stage is about 75mA and offset was set at 0.00V and drifted to less than -10mV after a couple of hours of playing music at average levels.

Can also compare it with a TDA7294 chip amp and a few others too ! Also a LM1875 !:) I like that small amp. Very nice ! Closing shop for the day. Lots of other matters to attend to !:D
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All the details are already in the posts put up earlier.
The pcb isn't good so I don't plan to put it up. Besides I don't have the original files. So you might have to make your own layout.
Note that it isn't perfect yet. All mentioned in the earlier posts. However it does sound good.....But then so many other amps on the forum also sound good !:D
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