The Dynaco Tube Audio Forum

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


    Is this speaker selector switch save with the VTA ST-120?

    Share

    almonds

    Posts : 5
    Join date : 2018-05-16

    Is this speaker selector switch save with the VTA ST-120?

    Post by almonds on Wed Jul 25, 2018 4:36 pm

    Does anyone know whether this type of speaker selector switch will be safe to use with the ST-120.

    My intended use is to have a solid state amp (Kenwood model 600) and the ST-120 hooked up and then a pair of JBL L100s and some JBL 4425s.  I never plan on having both amps on at the same time.  I would only switch the speakers and the amp switches when both amps were off.

    https://www.amazon.com/gp/product/B077JZFPR8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

    I have pics of the inside of the switch, but I'm trying to figure out how to upload them here.

    https://photos.app.goo.gl/duoGvZChnsvc9uP39
    https://photos.app.goo.gl/jCXpKftdfzv3hktK9
    https://photos.app.goo.gl/5t6pzTk4fPcWopoW7


    Last edited by almonds on Wed Jul 25, 2018 4:37 pm; edited 1 time in total (Reason for editing : added photo links)

    almonds

    Posts : 5
    Join date : 2018-05-16

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by almonds on Wed Jul 25, 2018 4:47 pm

    Here is the info provided by the manufacturer:

    Dear Jordan

    Wish you have a good day.
    We feel sorry to tell you that we can't provide you the circuit diagram.
    It is safe for most tube amplifiers without long time no-load operation.
    But MC202 is without false-load function.
    For some luxry tube amplifier with sepecial requirements ,it may not be very suitable.
    Thanks for your kind understanding.

    Best Regards
    Yours Douk Audio
    avatar
    peterh

    Posts : 1038
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by peterh on Wed Jul 25, 2018 5:02 pm

    almonds wrote:Does anyone know whether this type of speaker selector switch will be safe to use with the ST-120.

    My intended use is to have a solid state amp (Kenwood model 600) and the ST-120 hooked up and then a pair of JBL L100s and some JBL 4425s.  I never plan on having both amps on at the same time.  I would only switch the speakers and the amp switches when both amps were off.

    https://www.amazon.com/gp/product/B077JZFPR8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

    I have pics of the inside of the switch, but I'm trying to figure out how to upload them here.

    https://photos.app.goo.gl/duoGvZChnsvc9uP39
    https://photos.app.goo.gl/jCXpKftdfzv3hktK9
    https://photos.app.goo.gl/5t6pzTk4fPcWopoW7
    Tube amps does not like unloaded, transistor amps may die of shorted ( or to low impedance)
    Providing the amps are unpowered when switching and not selected it's safe.
    One may protect thetubeamp by permanently attatching a 100ohm resistor ( 5w ) across each 8ohm outlet, this will make sure tha amp is always somewhat loaded.
    avatar
    tubes4hifi
    Admin

    Posts : 1478
    Join date : 2008-11-30

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by tubes4hifi on Thu Jul 26, 2018 12:26 pm

    almond,
    just READING your question made me realize you need a simple DPDT toggle switch for the speakers.
    Also you need a DPDT toggle switch for the amplifiers (only to switch when both amps are off).
    So looking at the photos was no surprise. You are paying $86 for two $2 switches and a box with connectors on it.
    I"m going to assume without further research that the four 68 ohm resistors are there to protect the amplifier from having no load on it.
    No reason it shouldn't work as long as you realize the obvious precautions of only having one amp on at a time,
    and you don't mind paying $60 or so more than what you could make this for yourself.
    avatar
    Peter W.

    Posts : 924
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by Peter W. on Thu Jul 26, 2018 12:29 pm

    Cutting to the chase - all that switch is, is a switch. And a hard switch at that.

    a) If there are always speakers connected to each output then whichever amp is connected to whichever output will be fine.
    b) No amp likes input unloaded. Neither tube nor solid-state.
    c) Tube amps can tolerated low input unloaded - for short periods.
    d) Solid-state amps of current design and with good overload protection may (operative word - may) tolerate brief periods of time unloaded.
    e) Solid-state amps with input and left *UNLOADED* of vintage design will merrily reduce themselves to slag in short order.

    So, if you do all your switching with the active components turned off, you will be fine. If that is NOT your intention, there are proper A/B component switches that will cover these issues. They are considerably more expensive, and do have passive loading. Keeping in mind that Passive Loading when it has to do with amps is the functional equivalent of a Dummy Load - not a tiny resistor.

    https://www.amazon.com/Electronics-Salon-Audio-Amplifier-Non-inductive-Resistor/dp/B00N8QYMXO/ref=sr_1_3?ie=UTF8&qid=1532622481&sr=8-3&keywords=audio+dummy+load

    almonds

    Posts : 5
    Join date : 2018-05-16

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by almonds on Thu Jul 26, 2018 12:55 pm

    Ok, thanks guys.
    I'm totally new to tube amps (this is my first one, aside from my guitar amps)

    So I get the no load thing now, thank you.

    But a big question I have is:

    It seems to me by looking at the circuit and the switches that this device shares a ground. For the life of me (and I'm not really an expert, so I could be wrong) I can't figure out how to achieve what this box does without some sort of common ground. And I just want to make sure that the VTA ST-120 is compatible with this.

    Thanks!

    jimmeq

    Posts : 28
    Join date : 2017-02-24

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by jimmeq on Wed Aug 01, 2018 2:34 pm

    I have been using this https://www.amazon.com/gp/product/B00LNOAGZQ/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 for over a year. It's as near perfect as a amp/speaker selector switch can get. I have switched live between my ST-120 and a Sony STR-DA777ES and the switch operation is silent. The operation feels manual rather than electronic.

    Sponsored content

    Re: Is this speaker selector switch save with the VTA ST-120?

    Post by Sponsored content


      Current date/time is Mon Oct 15, 2018 8:49 pm