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    Right channel does not sound nearly as loud as the left

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    xlr8
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    Right channel does not sound nearly as loud as the left

    Post by xlr8 on Sat Feb 06, 2010 5:57 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!!

    Bob Latino
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    Posts: 1821
    Join date: 2008-11-26
    Location: Massachusetts

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

    Post by Bob Latino on Sat Feb 06, 2010 8:06 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

    xlr8
    Guest

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

    Post by xlr8 on Sat Feb 06, 2010 8:50 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.

    Bob Latino
    Admin

    Posts: 1821
    Join date: 2008-11-26
    Location: Massachusetts

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

    Post by Bob Latino on Sun Feb 07, 2010 6:34 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

    xlr8
    Guest

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

    Post by xlr8 on Sun Feb 07, 2010 11:37 am

    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!

    xlr8
    Guest

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

    Post by xlr8 on Sun Feb 07, 2010 12:52 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.

    xlr8
    Guest

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

    Post by xlr8 on Sun Feb 07, 2010 1:08 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.

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

    Post by Bob Latino on Sun Feb 07, 2010 1:13 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

    xlr8
    Guest

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

    Post by xlr8 on Sun Feb 07, 2010 1:59 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!!

    xlr8
    Guest

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

    Post by xlr8 on Mon Feb 08, 2010 12:57 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?

    Bob Latino
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    Posts: 1821
    Join date: 2008-11-26
    Location: Massachusetts

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

    Post by Bob Latino on Mon Feb 08, 2010 1:30 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

    xlr8
    Guest

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

    Post by xlr8 on Mon Feb 08, 2010 8:15 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.

    Hewie

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    Join date: 2010-01-27

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

    Post by Hewie on Tue Feb 09, 2010 10:17 am

    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

    xlr8
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    Re: Right channel does not sound nearly as loud as the left

    Post by xlr8 on Tue Feb 09, 2010 11:13 am



    I can't seem to add the link to this post...

    xlr8

    Posts: 68
    Join date: 2010-02-09

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

    Post by xlr8 on Tue Feb 09, 2010 11:17 am

    http://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...

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