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    vta and bottlehead 3 preamp hummm mm

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    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 53
    Location : athens

    vta and bottlehead 3 preamp hummm mm

    Post by kost on Mon Dec 13, 2010 7:55 pm

    Hey Bob

    My Bottlehead preamp hums when it is used with my VTA ST-70. Any idea about the problem?

    cheers

    kost

    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: vta and bottlehead 3 preamp hummm mm

    Post by Bob Latino on Mon Dec 13, 2010 8:22 pm

    Hi Kost,

    I don't mean to knock the Bottlehead preamp but the one that I used one time (IMHO) had too much gain. It was equipped with two 11 step attenuators (way too few steps !) and you only had about 4 or 5 steps before the amp was pretty loud. I don't even know why they would sell a preamp with only 11 steps of volume ? Maybe your Bottlehead preamp has different attenuators or maybe they have changed the volume attenuators in more recent Foreplay's.

    One other issue might be that the VTA ST-70 with the standard gain board with 12AT7 driver tubes does have a little more gain than the average tube amp. If the VTA ST-70 doesn't hum with another preamp then it's not the amp. If the Foreplay works OK with another amp and does not hum, then maybe it is the interaction of the two that is the problem. The VTA ST-70 and ST-120 have a 270,000 ohm input impedance and work well with virtually any preamp.

    If they won't work together properly, then my choice would be to sell your Bottlehead Foreplay and consider in its place the PAS-3 Clone preamp KIT which IMHO is a much better preamp with significantly better bottom end response than the Foreplay.

    VTA PAS-3 clone preamp kit

    Bob

    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 53
    Location : athens

    Re: vta and bottlehead 3 preamp hummm mm

    Post by kost on Wed Dec 15, 2010 6:05 am

    Hi Bob

    Thank you for your response.
    Do you think that with the 12au7 vta version things will
    be better?

    regards

    kost


    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: vta and bottlehead 3 preamp hummm mm

    Post by Bob Latino on Wed Dec 15, 2010 11:01 am

    Hi Kost,

    The standard gain board with 12AT7 tubes is a good fit for most music systems with preamps having a normal gain structure. The lower gain version of the VTA driver board is normally used if your speakers are very efficient - maybe 93 dB efficient or higher. Going to the lower gain version of the VTA driver board might help but IMHO the issue is with your preamp having too much gain.

    Bob

    defec

    Posts : 8
    Join date : 2010-12-19

    Re: vta and bottlehead 3 preamp hummm mm

    Post by defec on Sun Dec 19, 2010 8:39 pm

    Hi Kost, I have a FP II that I had to mod the hell out of to get to work with everything without noise. I don't know if the same mods are around for the III but I had to install filament snubbers on the tubes, some people just go DC for the heaters instead, and converted the preamp to unity gain. 1:1 gain seemed like plenty for everything. I now can even use a extra half of the 12au7 for a buffered tape loop that I'll get to someday. I did some power supply mods also. The preamp sounded way better after all this. They can probably help you over at the Bottlehead forums. Voltsecond has a page up but unfortunately it's for the older Foreplays

    http://www.siteswithstyle.com/VoltSecond/

    Bob, I ditched the terrible Bottlehead attenuators. Thankfully plenty of stuff can be scored no ebay to replace them and be far more functional.

    I was very interested in a preamp that Roy had up on his page with tone controls a bit ago but it seems to have disappeared in fair of just a pass rebuild.

    Anyway good luck.

    vegaseddoc

    Posts : 15
    Join date : 2009-11-21

    Re: vta and bottlehead 3 preamp hummm mm

    Post by vegaseddoc on Fri Dec 31, 2010 1:15 pm

    Kost,

    I have an FP3 and it works just fine with some minor modifications. The attenuators on the Bottlehead are junk. I replaced mine with goldpoints with 250k resistance, but a cheaper fix would be to place a small stepped attenuator on the ST70. I bought one from Bob to place on my ST120 with a 12AT7 VTA board. The combination works great with zero hum. You can then leave the FP3 attenuators on a very low setting by using the ST70 attenuator for volume control. The other option (I tried it and it sounds good) is to use a source selector switch and run your sources directly into the ST70 using the same attenuator from Bob.

    Happy New Year
    Jason

    howardnair

    Posts : 21
    Join date : 2010-05-31

    Re: vta and bottlehead 3 preamp hummm mm

    Post by howardnair on Sun Jan 02, 2011 4:33 pm

    kost--i have a bottlehead foreplay--i agree that the attenuators could be better-i have goldpoints in mine -prior to installing them i had no problems-the foreplay is a good product-i have upgraded mine several ways which is the idea behind bottlehead--regardless you should not be having problems-ck with the bottlehead forum

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