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


5 posters

    Right channel does not sound nearly as loud as the left

    xlr8
    avatar
    xlr8
    Guest


    • Post n°1

    Right channel does not sound nearly as loud as the left Empty Right channel does not sound nearly as loud as the left

    Post by xlr8 Sat Feb 06, 2010 7:57 pm

    Hello,

    I just completed my 2nd st-70 rebuild today and upon hooking it up to the system I've found that the right channel output is much less than the left. I'm using a replacement a-470s from triode electronics on the right channel and the older stock one on the left. I've tried swapping the output tubes from side to side with no difference. Same with the input tubes, no difference. The bias is solid on both channels and music comes through clean and clear with no audible distortion, it's just that the right channel is much quieter.

    I just need to be pointed in the right direction. Thanks in advance for the help!!
    • Back to top
    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3274
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°2

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Bob Latino Sat Feb 06, 2010 10:06 pm

    Hi,

    Did you change out the driver board ? If so - is it the stock Dynaco circuit or another replacement driver board ? OR is it still the original driver board in there ?

    Bob
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°3

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Sat Feb 06, 2010 10:50 pm

    I should have clarified, yes I did install the VTA driver board in this amp as well. I just finished going back through and re-flowing all of the solder joints I made on the board and the tubes. I've hooked it back up and set bias again, and still the same problem.
    • Back to top
    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3274
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°4

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Bob Latino Sun Feb 07, 2010 8:34 am

    xlr8 wrote:I should have clarified, yes I did install the VTA driver board in this amp as well. I just finished going back through and re-flowing all of the solder joints I made on the board and the tubes. I've hooked it back up and set bias again, and still the same problem.

    Hi,

    I am assuming that you already checked out your preamp for the problem by swapping the RCA input interconnects to eliminate your preamp as a source of the problem.

    First two things to try ...

    1. Check to see that right channel output transformer is grounded properly. Check for continuity from the "ground" terminal on the speaker strip to the chassis. You should get zero ohms or full continuity.

    2. Check the values across each resistor on the (good) left channel and compare it to its mirror resistor on the right channel. See if you can find any difference.

    See if you can post a photo of the inside wiring in this thread. Sometimes one of us may be able to pick up on something in the wiring that you have overlooked.

    Bob
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°5

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Sun Feb 07, 2010 1:37 pm

    Ok, I'll go through the things you mentioned later this evening and if everything checks out, I'll put up a photo. Thank you very much!
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°6

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Sun Feb 07, 2010 2:52 pm

    Ok, I just went through and measured each resistor on the board and I did find one major difference. From the input wires, the second resistor to the left and the second resistor to the right. With the meter set @ 200k, second resistor to the left flashes 175-180k and then nothing. The second resistor to the right side reads 41k. Everything else you mentioned seems to check out.
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°7

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Sun Feb 07, 2010 3:08 pm

    Update:

    I just tried measuring with a different meter and second resistor to the left reads 228k, second resistor to the right reads 47.7k.
    • Back to top
    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3274
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°8

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Bob Latino Sun Feb 07, 2010 3:13 pm

    Those two resistors are R3 and R4. Both should be 270K (270,000 ohm resistors). I think that you may have found your problem. Get two 270K resistors and place them in R3 and R4 and let us know if that solves the problem. Those two resistors set the input impedance or the input signal's reference to ground. Because you have only 47K on the RIGHT channel instead of 270K too much of the RIGHT channel's input signal is leaking to ground.

    Bob
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°9

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Sun Feb 07, 2010 3:59 pm

    You know, I really appreciate you making the learning process so easy for me. I am hoping that posting the issues I'm having will help someone else in the future so we can leave you alone LOL! Thank you for all of your help and especially your quick and accurate responses. I'll let you know what happens after I install the new resistors. Probably won't be until tommorow.

    Again, Thank you very much!!
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°10

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Mon Feb 08, 2010 2:57 pm

    Well, today I installed 2 new known good 270k resistors and I get close to the same readings. I tested them before I installed them and they were within their tolerances. I also tested the original ones after I pulled them and they are within specs as well, yet when installed in the amp, I get 238k on the left channel and 54k on the right. Could this indicate that there is something else wrong in the chain?
    • Back to top
    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3274
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°11

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Bob Latino Mon Feb 08, 2010 3:30 pm

    xlr8 wrote:Well, today I installed 2 new known good 270k resistors and I get close to the same readings. I tested them before I installed them and they were within their tolerances. I also tested the original ones after I pulled them and they are within specs as well, yet when installed in the amp, I get 238k on the left channel and 54k on the right. Could this indicate that there is something else wrong in the chain?

    Yes - You have some other issue going on there ... Other things to check ...

    1. Turn the amp on and measure the negative DC voltage on either pin 5 or 6 of the two output tubes on the channel with the low sound. You should get something like -28 to - 40 volts DC on both tubes of that channel.

    2. Turn the amp OFF

    A. Check the value of the 1000 ohm resistor between pins 5 and 6 on the two output tubes on the bad channel

    B. Check that there is NO continuity across either coupling caps on that channel. If you get any resistance across either cap, the cap with the resistance is no good and must be replaced.

    Since you got the tranformer that gives you the lower level sound from Triode Electronics you may want to give them a call and tell them about the problem. It could be a bad output transformer. If you want to make a quick test of your output transformer then check this sticky thread above > Testing Dynaco A-470 output transformers

    Bob
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°12

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Mon Feb 08, 2010 10:15 pm

    Ok, The 1000ohm resistors all check out as well as -48v on pins 5 and 6 of both tubes. I do not get resistance readings on any of the coupling caps, but I do get 2.8k on C2. I checked the transformer, but did not check all combinations, so I'll finish that tomorrow and post what I find.
    • Back to top
    Hewie
    avatar
    Hewie


    Posts : 3
    Join date : 2010-01-27
    • Post n°13

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Hewie Tue Feb 09, 2010 12:17 pm

    xlr8 wrote:...I get 238k on the left channel and 54k on the right. Could this indicate that there is something else wrong in the chain?
    If this is with driver tubes removed, there is something wrong with your input + or - wiring. Since there should not be any resistive elements in parallel to R3/R4 to ground, the readings of these resistors in and out of circuit should not appreciably change. Can you post a picture of the bottom of your amp?
    Dave
    • Back to top
    xlr8
    avatar
    xlr8
    Guest


    • Post n°14

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Tue Feb 09, 2010 1:13 pm



    I can't seem to add the link to this post...
    • Back to top
    xlr8
    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09
    • Post n°15

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Tue Feb 09, 2010 1:17 pm

    https://www.facebook.com/album.php?aid=45894&id=1562170391&saved#!/album.php?aid=45894&id=1562170391

    Ok, check these out. Hopefully someone will notice something I'm not...
    • Back to top
    GP49
    avatar
    GP49


    Posts : 792
    Join date : 2009-04-30
    Location : East of the sun and west of the moon
    • Post n°16

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by GP49 Tue Feb 09, 2010 6:25 pm

    You may wish to post the image to a hosting site such as Flickr or Photobucket.

    Those who are not members of Facebook (I do not wish to join ANY such social networking sites) can't see your photo.
    • Back to top
    xlr8
    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09
    • Post n°17

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Tue Feb 09, 2010 6:39 pm

    Sorry about that. It was the quickest thing I could think of.

    I have to go out of town for work and have left my amp in the hands of a good friend while I'm gone. He knows much more about this than I do. Actually, he was the one that encouraged me to dive into one of these amps before I ever purchased the 2 I have now. If he figures out what's wrong before I get back, I will surely let you all know.
    • Back to top
    xlr8
    avatar
    xlr8


    Posts : 68
    Join date : 2010-02-09
    • Post n°18

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 Fri Feb 19, 2010 3:59 pm

    update:

    Turns out, capacitor C-2 was the culprit. Replaced that cap and the amp sounds great! The problem amp is now driving a pair of maggie mg3a ribbon tweeters and it's brother is driving a line array of 12 5.25 inch units.

    Thank you folks very much for your patience and advice. I will not complain one bit about a bad cap coming in one of my amps because the troubleshooting experience has been invaluable. I should have bought a cap tester before I started! Embarassed
    • Back to top
    tubenutr
    tubenutr
    tubenutr


    Posts : 78
    Join date : 2015-01-25
    Age : 67
    Location : Northern Ontario
    • Post n°19

    Right channel does not sound nearly as loud as the left Empty VTA 70 hum

    Post by tubenutr Tue Oct 13, 2015 2:27 pm

    I thought I had seen this discussed before, but can't find it.

    My '70 has developed a hum on both channels. With an ear about 6 to 8 inches away its very noticeable.

    Can anyone help point me in the correct direction?

    PS - Nothing has been changed, tubes, power bar, etc..................

    • Back to top
    Bob Latino
    Bob Latino
    Bob Latino
    Admin


    Posts : 3274
    Join date : 2008-11-26
    Location : Massachusetts
    • Post n°20

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Bob Latino Tue Oct 13, 2015 2:43 pm

    If this is a stock ST-70, it is possible that the quad cap might need to be replaced ..

    Bob
    • Back to top
    Sponsored content

    Sponsored content


    • Post n°21

    Right channel does not sound nearly as loud as the left Empty Re: Right channel does not sound nearly as loud as the left

    Post by Sponsored content

    • Back to top
      Current date/time is Mon Nov 18, 2024 1:47 pm