Musical Fidelity Tubelog

[ktigerb]

Hi
Need help with Tubelog DAC .Anyone have any info please ?
turns on loghts show but no audio out not even noise

thanks
keith

[jean-paul]

First I can tell you no servicemanual/schematic exists of this model anymore. It uses Sanyo DAC and DIR chips which typenumbers have been removed. I had one too and it can sound wonderful when you give it some time/work. Mine sometimes had locking problems as I discovered just when I sold it. I liked it very much, sometimes even more than my non os DAC at that time. When you replace the I/V opamps you'll learn to appreciate it ! Do you have a rev. 1 or rev. 2 ?

Are you sure the tube section PSU is OK ? It should have + and - 24 V at the supply-transistors emitters.

Check the mute relay if it functions OK.

You can connect the I/V opamps outputs directly to the output ( same connector ) bypassing the tube stage. Try that too to see if the tube stage is OK.

Check all supply lines, the 7812 regulator becomes very, very hot and it might be broken. When it's broken a 5V supply line is dead too as they are connected in series.

Ground yourself and reseat the DIR and DAC chips gently and carefully in their sockets. When the Tubalog has been repaired please remove the sockets and solder the chips directly on the board.

Just some tips. Use the Search function on Tubalog as I described my mods in a thread.

[ktigerb]

Greetings Jean-Paul
Your reply much appreciated.
I started doing most of what you recommend but the seller had someone else who was pressing to take over the machine and I decided that he could sit with the problem instead.
I will build my own on similar lines using 6CW4 nuvistors (CJ MC pre-amp configuration minus Riaa) i.e. using the dacs I/V outs. with or without a buffer.(will see which is needed.)
I was thinking of using the above circuit with a switchable RIAA circuit so it could double up as a MC stage as well.

regards
keith birss

[hew128]

Hi Jean Paul,

I have a Tubalog with ISSUE 1 on the motherboards. Seems they have not remove the chip numbers on mine.

Saw your other thread about replacing the OPAMP(s). I have not done so but found replacing the Jamicon's on the tube board with Panasonic FC and the 2 glass capacitor with Wima's of the same values. Really opens up the tubalog after running it in for a few hours.