It was a half-hour job to mod my Mule preamp by swapping out the UX-120 and introducing the 01a (CX-301a in fact), add the resistor divider to deliver low gain on this preamp:
I set the valves at 115V/4mA. The Source Followers are running at 15mA and the resistor divider is actually 100KΩ/33KΩ (Kiwame) which is what I had at hand. It worked like a charm.
The 01a is driving my Slagle AVC into the 300B amplifier. I can say I can hear now the subtlety of the thoriated-tungsten filaments of the 01a with the extra level of gain I was hoping for. The amp sounds very dynamic at high level and with the clarity of the 01a.
This is indeed a clear winner. I will leave this preamp on my system for a while to confirm further impressions. For now, I just simply love it.
Hi Ale. I understand that you came back to the preamp after missing some of its qualities. If you would start with the 01a + AVC and end with the 300b, what would be your choice for the driver?
Not sure if I understand your question. Are you asking for a driver choice? If so, 47, 10Y/801a or a D3a would be my preferred ones.
Thanks Ale. I was thinking that your use of the 47 as driver lead you to use a low gain 01A pre. I was asking myself that if one uses the 01A with high gain perhaps other alternatives would be available between the 01A+AVC pre and the 300b output stage.
Yes, you can. Tone and overall sound will be different, you need to experiment. With full gain, you have the microphonic noise of the 01a which could become a problem or not.
Hi Ale,
With separate power supply chassis and signal chassis for the 01a preamp, do you ground the HT power supply board, do you use a ground lift switch for signal ground, or do you let signal ground float and only run chassis ground between the two chassis via the umbilical.
Regards,
Matt
Hi Matt
Currently I don’t have a ground lift switch, yet is useful in some situations. The key thing here is to have one ground connection point and at the input of the preamplifier. I run the earth from the mains (either HT or LT supply) into the main chassis. Then I have the earth and ground connection point at the input of the preamp. I made a small PCB to have a ground loop breaker which can be useful.
Cheers
Ale
I have this same setup, the AVC at output drives any cable with ease thanks to Dave! The setup can make a SS amp sound good…