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    first impression of my new to me ST70

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    rickelrod

    Posts : 7
    Join date : 2013-02-05
    Age : 50
    Location : Berryville,VA

    first impression of my new to me ST70

    Post by rickelrod on Wed Feb 13, 2013 8:47 am

    I set it up with a Hafler 915 preamp until the pas2 arrives. My source was an oppo 981 dvd/cd player using the internal dac. Speakers were my KG4s. First impression was that while warm, the bass seems muddy. That said any horns, strings, piano, and vocals were terrific. I also have a pair of Vandersteen 1c's to try. Did not spend much time on speaker placement etc.. I know the "sound" is there to find but am concerned about the bass issue. Wondering if the mods made to amp are an issue? PAS2 is due to arrive tomorrow. We will see what difference that will make.Will post the PAS2 build in another topic. Thanks for any input

    Rick

    GP49

    Posts : 733
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: first impression of my new to me ST70

    Post by GP49 on Wed Feb 13, 2013 11:49 am

    WHAT "bass issue?" Please clarify or explain.

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: first impression of my new to me ST70

    Post by tubes4hifi on Wed Feb 13, 2013 2:32 pm

    if this is a stock Dynaco from 50 years ago, yes, muddy bass.
    If this has our VTA mod in it, it should be full deep and tight.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: first impression of my new to me ST70

    Post by Bob Latino on Wed Feb 13, 2013 3:40 pm



    Rick,

    You have what appears to me to be a Triode Electronics driver board which is better than the stock board. The thing that bothers me is that the rebuilder of that amp has a "jury rigged" power supply that has so many (about 10?) smaller caps wired in there, it is possible that they are not wired to the power supply correctly. The rebuilder also put in triode/ultralinear switches in there which may or may not be wired into the amp correctly. Try flipping those two switches in the other direction and see if the bass picks up ?

    Bob

    GP49

    Posts : 733
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: first impression of my new to me ST70

    Post by GP49 on Wed Feb 13, 2013 3:44 pm

    That photo is a reminder that often, unless a recently-acquired Stereo 70 is box-stock, you really don't know WHAT you have.

    rickelrod

    Posts : 7
    Join date : 2013-02-05
    Age : 50
    Location : Berryville,VA

    Re: first impression of my new to me ST70

    Post by rickelrod on Wed Feb 13, 2013 5:48 pm

    GP49 wrote:WHAT "bass issue?" Please clarify or explain.

    First word that comes to mind is muddy.Like if you were to take an EQ and over use the 250hz slide (or there about)

    rickelrod

    Posts : 7
    Join date : 2013-02-05
    Age : 50
    Location : Berryville,VA

    Re: first impression of my new to me ST70

    Post by rickelrod on Wed Feb 13, 2013 5:50 pm

    Here is the description of the rebuild as described by seller.

    This is a ST-70 that I purchased a few years ago and discarded everything but the cases and transformers. The chrome has some pitting and some of the lettering has rubbed off over the years. But on the insides the original circuit board has been replaced with a Triode Electronics board that gets rid of the 7199 tubes and replaces them with 12AX7's & 12AU7's. I upgraded this board with metal film resistors, Aura coupling caps, ceramic & gold plated tube sockets. The output tube sockets are also ceramic and gold plated. The Multi-cap is still there but only for show. It's function has been replaced by banks of Nichicon 450V capacitors with at least doubling the stock capacitance rating on each amplification stage to give a more focused soundstage and stronger bass than a stock unit. The input and speaker jacks are Cardis and are wired to the 8 ohm taps. The amp also has switches on top to switch between triode and pentode mode. The internal signal wiring is teflon cover silver. The driver tubes are Electro-Harmonix and the output tubes are matched set of Sevelanta EL-34's.

    rickelrod

    Posts : 7
    Join date : 2013-02-05
    Age : 50
    Location : Berryville,VA

    Re: first impression of my new to me ST70

    Post by rickelrod on Wed Feb 13, 2013 5:53 pm

    Bob Latino wrote:

    Rick,

    You have what appears to me to be a Triode Electronics driver board which is better than the stock board. The thing that bothers me is that the rebuilder of that amp has a "jury rigged" power supply that has so many (about 10?) smaller caps wired in there, it is possible that they are not wired to the power supply correctly. The rebuilder also put in triode/ultralinear switches in there which may or may not be wired into the amp correctly. Try flipping those two switches in the other direction and see if the bass picks up ?

    Bob

    Bob,

    It seems you may be spot on with regards to the work done on the amp. I cant speak to the electronics but the asthetics of some of the mods ie. rca and speaker connection upgrades look less than stellar.

    rockinrob86

    Posts : 18
    Join date : 2012-03-26

    Re: first impression of my new to me ST70

    Post by rockinrob86 on Thu Feb 14, 2013 2:16 pm

    This amp has pretty bad build quality. I have a VTA modded ST-70 and thought I was having bass problems initially, but every single issue, including the bass one came down to me being cheap and not getting decent tubes. I tried to use the original ones, a lot of tubes I bought for cheap on Ebay, etc. I finally bought some EH 6CA7 tubes and haven't looked back. I can say for sure that a VTA modded ST-70 has fantastic bass.

    The power supply is incredibly important for adequate bass response, and it looks like corners were cut on the power supply with the amp you bought.


    Last edited by rockinrob86 on Fri Feb 15, 2013 9:15 am; edited 1 time in total

    charlief64

    Posts : 13
    Join date : 2012-12-21

    Re: first impression of my new to me ST70

    Post by charlief64 on Thu Feb 14, 2013 11:28 pm

    I agree. My VTA modded ST 70 has tight, clear bass and plenty of it. and Im using cheapo JJs in the output.
    charlie

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