The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


3 posters

    PAS3X Phono Pre-amp

    avatar
    radiojer


    Posts : 1
    Join date : 2022-01-04

    PAS3X Phono Pre-amp Empty PAS3X Phono Pre-amp

    Post by radiojer Wed Jan 05, 2022 12:07 pm

    I have two PAS3X pre-amps, one I built and one I bought off of EBay. Neither have Modifications. The one I bought had a gritty "clipped" sounding phono pre-amp. The other inputs sounded fine. I read some posts on a guitar blog that a 12AT7 tube could be substituted for the 12AX7. The pin-outs are the same, and the operating parameters are the similar, with the exception the 12AT7 has less gain, 60 as opposed the 100. I made the substitutions on the phono pre-amp. The result of the substitution was much improved audio, excellent mid range, and highs. Noise floor is very low. All the gritty clipped audio was gone. Yes, the gain was a bit less, as expected, but closer to the other inputs. I can find no downside to this substitution. Any comments?
    peterh
    peterh


    Posts : 1613
    Join date : 2012-12-25
    Location : gothenburg, sweden

    PAS3X Phono Pre-amp Empty Re: PAS3X Phono Pre-amp

    Post by peterh Wed Jan 05, 2022 12:41 pm

    radiojer wrote:I have two PAS3X pre-amps, one I built and one I bought off of EBay.  Neither have Modifications.  The one I bought had a gritty "clipped" sounding phono pre-amp.  The other inputs sounded fine.  I read some posts on a guitar blog that a 12AT7 tube could be substituted for the 12AX7.  The pin-outs are the same, and the operating parameters are the similar, with the exception the 12AT7 has less gain, 60 as opposed the 100.  I made the substitutions on the phono pre-amp.  The result of the substitution was much improved audio, excellent mid range, and highs.  Noise floor is very low.  All the gritty clipped audio was gone.  Yes, the gain was a bit less, as expected, but closer to the other inputs.  I can find no downside to this substitution.  Any comments?
    You have turned the PAS to something with more dist and less RIAA like.
    Get new 12AX7 and be done with it.
    audioregenesis
    audioregenesis


    Posts : 29
    Join date : 2008-12-30
    Location : Canada

    PAS3X Phono Pre-amp Empty Re: PAS3X Phono Pre-amp

    Post by audioregenesis Thu Jan 06, 2022 2:12 pm

    Proper low frequency response of the phono stage requires all of the gain the 12AX7 can provide as well as positive feedback. The 12AT7 will result in considerable loss of bass response.

    Sponsored content


    PAS3X Phono Pre-amp Empty Re: PAS3X Phono Pre-amp

    Post by Sponsored content


      Current date/time is Thu Jan 20, 2022 10:16 am