1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Dave Slagle Monoblock Transformer Volume Control Build

Discussion in 'DIY' started by SET12, Feb 7, 2016.

  1. SET12

    SET12 Super Member

    Messages:
    1,841
    Location:
    Appleton,WI
    I looked up the schematic of the 100B and I saw it is using a 12AX7 in its audio output circuit.

    You can easily substitute a 5751 which has a Mu of 70 vs the 12AX7's Mu of 100 so it will give less gain. You have to be careful with finding 5751's as many were simply re-branded 12AX7s. Going to a 5751 will reduce the output impedance of the 100b which is a good thing. Another thing I would consider is changing the 100K plate resistors to 47K this will further reduce the gain. Further since the tuner uses the 12AX7 pin out it allows other tubes to be used as well like the 12AU7 but I would change the plate resistors for that one. The 12AT7 is also a candidate but there again I would change the plate resistors. But for sure drop in a 5751 its a low noise tube to begin with and as I said it will reduce the gain without and resistor modification.

    Another option is to sell the TVC and go for an AVC which will give you an additional 10 db of attenuation. http://www.intactaudio.com/atten.html

    I know he is working on some new attenuators that may give even more attenuation. And you have the option of him custom making something that will work for you.

    SET12
     

     

    Please register to disable this ad.

  2. rogerfederer

    rogerfederer AK Subscriber Subscriber

    Messages:
    3,362
    Location:
    Northern VA
    Set12,
    I love your 5751 suggestion; will look for some; elegant solution!
     
  3. enginedr

    enginedr Well-Known Member

    Messages:
    885
    Location:
    nyc
    I had to have a remote . Took 2 weekends to build . Bent TAP modules
     

    Attached Files:

  4. SET12

    SET12 Super Member

    Messages:
    1,841
    Location:
    Appleton,WI
    How did you manage the Bent Tap Modules?

    Going here to his site it says they are no longer supplying them to us DIYers http://www.bentaudio.com/index2.html

    Otherwise I would of bought them!
     
  5. Redboy

    Redboy a few good watts Subscriber

    Messages:
    11,042
    Location:
    Twin Cities, MN
    I bet he bought them before John stopped selling to us regular schmoes... :)
     
  6. rogerfederer

    rogerfederer AK Subscriber Subscriber

    Messages:
    3,362
    Location:
    Northern VA
    here is an update for this thread. just installed the 5751s i got from jaymanaa (RCA triple plates) in my fisher 100b tuner. so far they sound fine. i was nervous about switching out the 12ax7 in the mpx unit but i'm not hearing any distortion. i may check w/ larry derouin and dave gillespie, just to make sure there is no problem i'm missing. the volume has only dropped slightly. however, i am so enjoying the sound improvement i got when i put the TVC in this system there is NO way i'd take it out. if i have to reduce the volume on the tuner i can always use the output pots on the back panel of the tuner.

    thanks again to SET12 for starting the thread and giving me the encouragement to go TVC.

    btw, i'm also very impressed with the stereo coffee LDR (which i'm using in a different system). it has a slightly different flavor, maybe very slightly less revealing, but still has really improved that rig -- which was already really good sounding.

    UPDATE: decided it was easiest to rotate my tuners; now i have a kenwood kt8300 in this rig -- output is a lot lower than the fisher and it sounds great; fisher went to the living room where it is happy
     
    Last edited: Jun 26, 2016

     

    Please register to disable this ad.

  7. mkane

    mkane AK Subscriber Subscriber

    Messages:
    6,217
    Location:
    103 miles N. of S.F.
    Diggin our's also. May add another set of input's so I can stop pulling interconnects.
     
  8. rogerfederer

    rogerfederer AK Subscriber Subscriber

    Messages:
    3,362
    Location:
    Northern VA
    OK, this is probably crazy...but any idea whether these would work for preamps/volume control:

    https://www.amazon.com/250W-Stereo-Autoformer-Control-Plate/dp/B0159XPD6I
    http://www.pimfg.com/Product-Detail/TTA-1019

    they are intended for use between a receiver and speakers (see http://www.pimfg.com/Product-Detail/TTA-1019 ) so its unclear how they would work as a preamp. only 30 db attenuation max, so that would be an issue.

    UPDATE: here is a mono version, so could do dual monos for better volume control: https://www.firefold.com/mono-autoformer-volume-control-avc-wall-plate-250w-peak-white

    UPDATE 2: i ordered 2 of the mono versions; will see how they sound
     
    Last edited: Jul 10, 2016
  9. mkane

    mkane AK Subscriber Subscriber

    Messages:
    6,217
    Location:
    103 miles N. of S.F.
    What will they think of next
     
  10. Tillerman

    Tillerman Active Member

    Messages:
    261
    Location:
    Southern Minnesota
    Old thread reboot.

    Dan,
    Can you recommend a source for the switches to use for 2 inputs with grounds switched as well? Also, I see there are some new listings at Intact audio for a TVC module. Is the one you based your build on still the best option today? Also, could you post an interior shot of your built unit showing the switch wiring more closely?

    I am still considering building the pair of mono boxes like you did, and using them between either my tuner or DAC as source inputs and the Aux input on my preamp. Another possibility would be to insert the TVC on my tape loop with the same preamp, as you have done.

    Thanks,
    Scott
     

Share This Page