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


    Hum reduction quest - solved !

    Share
    avatar
    Peter W.

    Posts : 436
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Hum reduction quest - solved !

    Post by Peter W. on Thu Aug 10, 2017 2:29 pm

    Glad you found it!

    And, it looks like you will need to rebuild the sub. It has been my experience that active subs tend to be minimally constructed. Even ones from 'good' manufacturers. And why it is that I will not keep one as a standing rule. I remember "Powered Advent" speakers from back in the day ($450 a pair when new). They were pretty wretched and blew up by the numbers. And very nearly impossible to repair. It is going to be caps - and overall, pretty easy to do, the hardest part being getting to the caps in the first place.

    For the record, I keep two AR sub-sat systems (Athena and 660) and one Revox Piccolo system. All very, very nice, but all passive.
    avatar
    deepee99

    Posts : 1646
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Hum reduction quest - solved !

    Post by deepee99 on Thu Aug 10, 2017 3:37 pm

    Good for you, Aulde Son. Do enough wrong things and eventually the right one crops up. Well done!
    avatar
    Bob Latino
    Admin

    Posts : 2543
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Hum reduction quest - solved !

    Post by Bob Latino on Thu Aug 10, 2017 3:41 pm

    LeGrace wrote:Found it! Sub and M125's not playing nice together.
    No more hum, I mean church mouse quiet!! Now I understand why yanking the RCA input before was so effective in getting rid of the the hum. Given the M125s connect directly to the sub removing this connection was breaking the circuit.

    Glad to hear that you found the issue ... The VTA M-125 amps (if built properly built) have about a 95 dB signal to noise ratio. Any noise from the amps is usually caused by either a noisy front driver tube or a ground loop. In your case it was a ground loop with your sub being on the same power strip as the amps..

    Bob
    avatar
    LeGrace

    Posts : 222
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: Hum reduction quest - solved !

    Post by LeGrace on Thu Aug 10, 2017 4:02 pm

    Bob they are totally silent now. sunny
    avatar
    wgallupe

    Posts : 115
    Join date : 2014-05-18
    Age : 63
    Location : Central Mass.

    Re: Hum reduction quest - solved !

    Post by wgallupe on Tue Aug 15, 2017 7:45 am

    LeGrace wrote:Signal path is through sub's high pass filter, not its crossover. The high pass is a fixed 80 hz cut off. Could be the high pass cap is a slow poke. Right now the way I have things the sub goes on and off along with the M125's. Maybe I should just be leaving it on.  Or as you suggest bypass entirely, certainly part of a process of elimination exercise.

    Really appreciate all the great suggestions.

    Hi Legrace, a 'crossover' in its simplest terms is a high pass filter together with a low pass filter. If you are sending everything above 80hz from the subwoofer to the M125 then that signal has to pass through a capacitor. To 'high pass' at a relatively low 80hz means a lot of capacitance is needed which leads to the assumption that an electrolytic type are most likely being used. Shocked

    In any event, glad to see that you solved the hum problem.
    avatar
    wgallupe

    Posts : 115
    Join date : 2014-05-18
    Age : 63
    Location : Central Mass.

    Re: Hum reduction quest - solved !

    Post by wgallupe on Tue Aug 15, 2017 7:57 am

    deepee99 wrote:
    wgallupe wrote:If your system is still hooked up as described in the link below, I would undo all of that and only run the pre outs from the Marantz to the 125s. Nothing else. Then see if the hum goes away.

    http://dynacotubeaudio.forumotion.com/t3276-tube-rolling-for-low-freq-spectrum#29578

    By the way, inserting a subwoofer's crossover into the line level signal path is something I would never do. Just saying...

    WG, I dunno about that. Dick Vandersteen's been doing it for years with great success. But spendy, for sure, and only for his powered subwoofs, which recover the lost low frequency signals with their own EQs. Saves the output tubes from heavy lifting. I don't care for the complexity, but it does work.

    Hi Dave, maybe Vandersteen are using high quality caps? Think about it this way: We go to great lengths to make sure the signal path in our amp and preamp are as perfect as we can (afford). In fact most of us with VTA amps/preamps have gone the extra mile to install the optional high quality $$$ output coupling caps. In my mind it would be a waste to send that signal on to a sub using sub-standard caps/parts (sorry for the pun) in it's filter.

    Anyway, I would at least want to know what quality of parts are in the sub's filter before I went that route.
    avatar
    corndog71

    Posts : 553
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Hum reduction quest - solved !

    Post by corndog71 on Tue Aug 15, 2017 9:17 am



    Here's one way to split the signal between 2 amps with a high pass for one output. (Photo from GR Research) I did something similar using 0.01uf caps for my ST120.
    avatar
    wgallupe

    Posts : 115
    Join date : 2014-05-18
    Age : 63
    Location : Central Mass.

    Re: Hum reduction quest - solved !

    Post by wgallupe on Tue Aug 15, 2017 11:01 am

    corndog71 wrote:

    Here's one way to split the signal between 2 amps with a high pass for one output.  (Photo from GR Research)  I did something similar using 0.01uf caps for my ST120.

    Hi corndog, Ah yes, I mis-spoke above about the need for an electrolytic capacitor. Was thinking of speaker level signal.Embarassed

    As you show, line level allows for a small high quality cap. I happen to like Sonicap Platinums too. Have them as coupling caps in my SP13 and high pass filter bypass caps in my GR Research OB-5s...Smile

    Wayne
    avatar
    LeGrace

    Posts : 222
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: Hum reduction quest - solved !

    Post by LeGrace Today at 6:31 am

    Just to close the loop on the grounding adapter. Finally came in the mail yesterday. I put the sub back the way it was before but this time using a single grounding adapter on the sub. Equally effective solution, heck I'd swear even a smidgen better then the separate receptacle approach. Apparently there are differing levels of quiet. This has been interesting learning. Thanks folks.
    avatar
    deepee99

    Posts : 1646
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Hum reduction quest - solved !

    Post by deepee99 Today at 11:13 am

    LeGrace wrote:Just to close the loop on the grounding adapter. Finally came in the mail yesterday. I put the sub back the way it was before but this time using a single grounding adapter on the sub. Equally effective solution, heck I'd swear even a smidgen better then the separate receptacle approach. Apparently there are differing levels of quiet. This has been interesting learning. Thanks folks.
    LeGrace, those cheater plugs are a diagnostic tool, not a solution, although a lot of people use them as such in older houses, they're asking for shock-hazard trouble.
    avatar
    jfine

    Posts : 58
    Join date : 2017-06-19

    Re: Hum reduction quest - solved !

    Post by jfine Today at 11:51 am

    deepee99 wrote:
    LeGrace, those cheater plugs are a diagnostic tool, not a solution, although a lot of people use them as such in older houses, they're asking for shock-hazard trouble.

    I dunno, there seems to be confusing opinions on that.

    If I have 2 M125's, and use cheaters on both, but the preamp uses a standard 3 prong, wouldn't the interconnects used between them find the ground to the 3 prong on the preamp hazard-wise?
    avatar
    LeGrace

    Posts : 222
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: Hum reduction quest - solved !

    Post by LeGrace Today at 12:04 pm

    Yes, some pretty explicit warnings on the packaging. But then my sub is inter-connected with multiple grounded devices, won't this reduce the risk?

    As an aside when I was moving cords around I was surprised to learn that my  Marantz amp has a 2 prong plug, not 3 prong as with the M125's. Never had cause to pay attention to this before. If sold today would it have to come with a 3 prong plug to satisfy present day safety standards?
    avatar
    deepee99

    Posts : 1646
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: Hum reduction quest - solved !

    Post by deepee99 Today at 12:05 pm

    jfine wrote:
    deepee99 wrote:
    LeGrace, those cheater plugs are a diagnostic tool, not a solution, although a lot of people use them as such in older houses, they're asking for shock-hazard trouble.

    I dunno, there seems to be confusing opinions on that.

    If I have 2 M125's, and use cheaters on both, but the preamp uses a standard 3 prong, wouldn't the interconnects used between them find the ground to the 3 prong on the preamp hazard-wise?

    Jeff, theoretically, yes. But why float the ground on both amps?
    I know PeterW has been sitting on his typing fingers on this subject but maybe it's time he weighed in. And if I recall, the SP-series pre-amps have internally-floated grounds and the interconnects are isolated from the chassis ground. Peter, HALLLLP!
    avatar
    Peter W.

    Posts : 436
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: Hum reduction quest - solved !

    Post by Peter W. Today at 12:29 pm

    I am in Texas at the moment on business. But, yes, cheaters are called such for a reason. Also killers. More later.

    Sponsored content

    Re: Hum reduction quest - solved !

    Post by Sponsored content


      Current date/time is Sat Aug 19, 2017 4:40 pm