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


    Preamp for ST70

    jeffjmr
    jeffjmr

    Posts : 15
    Join date : 2020-08-22

    Preamp for ST70 Empty Preamp for ST70

    Post by jeffjmr on Fri Sep 11, 2020 8:32 pm

    I think I have my ST70 dialed in now and would like to add a preamp. While it doesn’t HAVE to be a Dynaco, I like the affordability and I like to tinker so they seem to be a good choice.

    What I can’t seem to determine is the practical differences between the PAT4, PAS4, PAT5 etc. I don’t think I want another tube device like the PAS3 but I am open to suggestions if it makes a significantly better match for the ST70. I like the upgrades readily available for the PAT4.

    Any and all input will be appreciated.
    Jeff
    avatar
    Dale Stevens

    Posts : 150
    Join date : 2014-07-06
    Age : 71
    Location : Loris, SC

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by Dale Stevens on Sun Sep 13, 2020 1:48 pm

    Jeff, may depend on your speakers; What are they? Dale
    jeffjmr
    jeffjmr

    Posts : 15
    Join date : 2020-08-22

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by jeffjmr on Sun Sep 13, 2020 2:04 pm

    Dale Stevens wrote:Jeff, may depend on your speakers; What are they? Dale

    Thanks Dale. For a little while the ST70 is driving a pair of B&W DM605S2, which are 8 ohm nominal with a self-powered bass section. But the ST70 was purchased specifically to drive a pair of 16+ ohm Altec Lansing A5Xs which are nearing restoration completion.

    The ST70 is a “factory” built unit from Triode USA with a few insurance mods like the “yellow paper” diode mod to the rectifier tube and an inrush current limiter. All tubes are relatively new JJs. Since my house voltage averages 120 and on some days 123 I’ll be building a bucking transformer. Otherwise no additional mods are being considered until I actually hear the Altecs with this setup. I don’t care for the consumer grade Mitsubishi or Yamaha receivers I have with the ST70. Direct driving from an Apple Airport and a Sony Walkman are sounding better thus my interest in a standalone preamp.

    Thanks for any light you can shed on the subject.
    Jeff

    PeterCapo
    PeterCapo

    Posts : 892
    Join date : 2008-12-05

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by PeterCapo on Sun Sep 13, 2020 5:39 pm

    Provided that any given sample of the different vintage units you mentioned are functioning properly, I'd suggest doing as much reading as possible through different forums, and any other sources you can find, that talk about the sonic character of each one.  If a picture emerges from the noise, then I suppose I'd make a choice based on that.

    BTW, the best information anywhere on the PAS is found along the left-hand side of the following webpage: http://www.audioregenesis.com/
    jeffjmr
    jeffjmr

    Posts : 15
    Join date : 2020-08-22

    Preamp for ST70 Empty Preamp

    Post by jeffjmr on Mon Sep 14, 2020 10:58 pm

    I am sensitive to the highly subjective nature of audio system sound. A clear picture has not emerged. I was looking more for some comments about glaring issues and reliability, and any technical differences between the models that might be considered important. From what I have read so far, the PAT4 looks like the way to go, but would love to hear from folks who may have experience with more models.

    Thanks,
    Jeff
    peterh
    peterh

    Posts : 1403
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by peterh on Tue Sep 15, 2020 2:41 am

    jeffjmr wrote:I am sensitive to the highly subjective nature of audio system sound. A clear picture has not emerged. I was looking more for some comments about glaring issues and reliability, and any technical differences between the models that might be considered important. From what I have read so far, the PAT4 looks like the way to go, but would love to hear from folks who may have experience with more models.

    Thanks,
    Jeff
    An unmolested PAS3/3X is the preffered way. A PAT4 should have the final
    transistor replaced before considering. PAT4 is easiest to find in unmolested form.
    PeterCapo
    PeterCapo

    Posts : 892
    Join date : 2008-12-05

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by PeterCapo on Tue Sep 15, 2020 4:40 am

    PAT-4 needs to see 100KΩ or higher amplifier load. If it drops below that, the bass progressively rolls off. PAS can also be load sensitive, but the Audio Regenesis documents explain how to address it. Their tone control potentiometers may not be replaceable, so bypassing them may be the best option. If there are issues with their selector switches, then you've got a pretty significant problem to overcome. These are all old age issues, by the way, not design flaws.

    If you go with an aftermarket circuit replacement for them, then you've got an altogether different preamp.
    Bob Latino
    Bob Latino
    Admin

    Posts : 2942
    Join date : 2008-11-26
    Location : Massachusetts

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by Bob Latino on Tue Sep 15, 2020 8:27 am

    jeffjmr wrote:I think I have my ST70 dialed in now and would like to add a preamp. While it doesn’t HAVE to be a Dynaco, I like the affordability and I like to tinker so they seem to be a good choice.

    What I can’t seem to determine is the practical differences between the PAT4, PAS4, PAT5 etc. I don’t think I want another tube device like the PAS3 but I am open to suggestions if it makes a significantly better match for the ST70. I like the upgrades readily available for the PAT4.

    Any and all input will be appreciated.
    Jeff

    Check out Roy Mottram's VTA SP14 preamp (kit or wired) at the link below. This preamp can run with preamps costing in the $4K - $5K range .. Link below ..

    VTA SP14 preamp

    Bob

    jeffjmr
    jeffjmr

    Posts : 15
    Join date : 2020-08-22

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by jeffjmr on Tue Sep 15, 2020 10:42 pm

    Thank you Bob.

    That looks like a top notch unit, but is above my budget at the moment.

    Also, thanks for this great forum. It has been most informative and helpful.

    Jeff
    avatar
    Dale Stevens

    Posts : 150
    Join date : 2014-07-06
    Age : 71
    Location : Loris, SC

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by Dale Stevens on Wed Sep 16, 2020 10:35 am

    Jeff, very nice speakers with high efficiency. If you don't want a tube pre then here's what I have;
    A Dynaco PAT5 , solid state, with all new boards and jack strips from UPDATEMYDYNACO. Input to the pre is a dedicated Dell laptop running windows 10 and Spotify then out at the usb port to a Dragon Fly red Dac. The Pat5 is then driving a VTA ST-120 to Klipsch horns. Amazing sound. The laptop also serves as cd player. I'm satisfied so much with this system that no further upgrades are being considered ( at this time , of course ) Dale
    PeterCapo
    PeterCapo

    Posts : 892
    Join date : 2008-12-05

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by PeterCapo on Wed Sep 16, 2020 1:30 pm

    This preamp is from the UpdateMyDynaco guy, and it's available assembled: https://www.akitika.com/PR102.html

    Here are a couple of other possibilities, but unless you want to build the kit, you'd want to contact them and ask if they sell them fully assembled, plug-and-play:

    https://www.transcendentsound.com/fixer.html
    https://www.transcendentsound.com/slider.html
    jeffjmr
    jeffjmr

    Posts : 15
    Join date : 2020-08-22

    Preamp for ST70 Empty Pat4

    Post by jeffjmr on Wed Sep 16, 2020 2:43 pm

    PeterCapo wrote:PAT-4 needs to see 100KΩ or higher amplifier load.  If it drops below that, the bass progressively rolls off.  PAS can also be load sensitive, but the Audio Regenesis documents explain how to address it.  Their tone control potentiometers may not be replaceable, so bypassing them may be the best option.  If there are issues with their selector switches, then you've got a pretty significant problem to overcome.  These are all old age issues, by the way, not design flaws.

    If you go with an aftermarket circuit replacement for them, then you've got an altogether different preamp.

    Thanks, Peter.

    Definitely not interested in any bass rolloff. Already a bit worried that I’m gonna need a sub with the Altecs. Loving my B&Ws with their built-in sub in my bedroom which is significantly smaller than the family room which is where the Altecs are going to be.

    So will the ST70 provide the appropriate load to a PAT4? Will installing most or all of the suggested mods to the PAT4 or the PAS3 address that issue? Also, not sure I won’t wish I had tone control in the larger room.

    Coincidentally I had seen the Akitika and like it. A bit more even in kit form than I think a fully modded/updated PAS3 or PAT4 would run but intriguing nonetheless.

    Jeff
    jeffjmr
    jeffjmr

    Posts : 15
    Join date : 2020-08-22

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by jeffjmr on Wed Sep 16, 2020 2:58 pm

    peterh wrote:
    An unmolested PAS3/3X is the preffered way. A PAT4 should have the final
    transistor replaced before considering. PAT4 is easiest to find in unmolested form.

    Hmmm.  Unmolested PAS3s are not plentiful. Does that mean you suggest no upgrades to the original?

    Same question for PAT4, which are easier to find.

    Jeff
    PeterCapo
    PeterCapo

    Posts : 892
    Join date : 2008-12-05

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by PeterCapo on Wed Sep 16, 2020 3:20 pm

    Assuming your Stereo 70 is working to its original design goals, there should be no problem with bass roll-off, again, assuming everything is working as it should in both the amp and the preamp.  No mods are necessary with the possible exception of adding a DC blocking capacitor to the outputs of non-X PAS units.

    However, original PAS and PAT units are old.  Depending on your level of electronics knowledge and also your electro-mechanical rework abilities, they may or may not be a practical choice.  There are potential - even likely - pitfalls due to their age, as would be the case with any vintage gear from that era.

    The Akitika PR102 assembled and tested appears to be listed for $659 plus shipping.  That's going to be tough to beat.

    Roy also sells his SP-8 for less than $1,000 http://www.tubes4hifi.com/pre11.htm#SP8

    Dr. Lloyd Peppard's Line 2CRM is also under $1,000 https://www.mapletreeaudio.com/index.html#Preamplifiers
    peterh
    peterh

    Posts : 1403
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by peterh on Wed Sep 16, 2020 3:33 pm

    jeffjmr wrote:
    peterh wrote:
    An unmolested PAS3/3X is the preffered way. A PAT4 should have the final
    transistor replaced before considering. PAT4 is easiest to find in unmolested form.

    Hmmm.  Unmolested PAS3s are not plentiful. Does that mean you suggest no upgrades to the original?

    Same question for PAT4, which are easier to find.

    Jeff
    By unmolested i mean needed replacements ( tubes pots etc, possibly power supply)
    Observe that heavily modified PAS might be upgraded to original configuration
    as boards are available that conforms to the original schematic.

    Both PAS3 and PAT4/5 will be perfectly fine to use for a ST70.

    Sponsored content

    Preamp for ST70 Empty Re: Preamp for ST70

    Post by Sponsored content


      Current date/time is Thu Sep 24, 2020 2:09 pm