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Low volume problem. (Read 2189 times)
timh
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Low volume problem.
01/22/12 at 01:45:30
 
Hello,
I'm new to electronics and this is my first amp build.  I've gotten all the way through, hooked it up to my speakers and my CD player and it works but the volume is very low.  I can't even hear it until the volume knob is up halfway.  I am driving Audio Nirvana speakers with 95 dB sensitivity so I should be alright there.  Is this a voltage problem or polarity?
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Lon
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Re: Low volume problem.
Reply #1 - 01/22/12 at 14:14:00
 
Like you, I would expect more with 95 db speakers. I think the best thing to do is to call and talk to Steve. He is most easily reached by phone, and he would probably know in seconds where to look to find the cure. . . .
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dank
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Re: Low volume problem.
Reply #2 - 01/22/12 at 22:46:56
 
Timh

Audio Nirvanas work well with the Zkit1.  I've run 6.5", 8", and 12" over the years.  Should be no problem driving them.

Is the volume coming out of the speakers the same on both the L and R channels?  Try placing your head between the speakers and adjusting the volume control from 0 to full.  Does the balance seem to stay constant with the left side being about the same volume as the right side?  If so, I'd guess that your source is too low and there is nothing wrong with the Zkit1.  Can you try a different source?

An amps gain is set so it will put out full power when the line level input is a certain value.  This value seems to keep creeping up, use to be about 1 volt rms (I think), not its more like 2volts.  Its defined somewhere, anyway...lets say its 1 volt.  If you had a 300 watt amp you would need a gain of 50 (1 v in makes 50v out and 50v into 8 ohms is 50*50/8=312 watts).  So your source would need to supply 1v for full power, but to get 2watts out (like your Zkit) you only need the source to supply 80 millivolts (80/1000 volts).  .080 * 50 = 4 v out, 4v into 8 ohms = 4*4/8 = 2 watts.  Now your Zkit1 gain should be around 4 (1 v in makes 4 v out, 4v into 8 ohms = 4*4/8 = 2 watts) so your source now needs to supply 1volt to get 2 watts out.  If your source can't do that you will get "low volume" when a higher power amp seems to work just fine.


Dan
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timh
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Re: Low volume problem.
Reply #3 - 01/23/12 at 02:48:21
 
Dan,
Thanks for the response and info.  I've got a lot to learn but I'm glad to have the help.  I checked the output voltage from my source (a Sherwood CD player) and it was 1.8 volts per side, so I'm assuming that is not the problem.  The sound is nicely balanced between both speakers also, confirming it is not likely the input.  So, I'm not sure where to go next.  I did have a problem with the volume pot.  I put the pot on the wrong side of the board and had to move it to the other.  In the process, I damaged the board where one of the legs from the RCA came in and had to bypass the board with a wire and connect it directly.  With that fix, It shouldn't be a problem I would think.  Any other ideas would be appreciated.  Thanks Dan and Lon for the suggestions.
Tim
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dank
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Re: Low volume problem.
Reply #4 - 01/23/12 at 13:20:32
 
Timh

If you can measure your source (and get 1.8v), then just measure after the volume control with the volume control turned all the way up (should get 1.8v) and then measure at the speaker (should get around 4v).  

If the voltage after the volume control is low, you could try jumpering it out for a test...just solder a wire from the wiper lug to the input lug...that should give you full volume.


Dan
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timh
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Re: Low volume problem.
Reply #5 - 01/24/12 at 03:50:08
 
I tested the after the volume pot and it was at 1.8vac.  But the speakers were below 1.5vac with full volume.
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dank
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Re: Low volume problem.
Reply #6 - 01/24/12 at 13:23:10
 
I assume you have measured the 4 test points A, B, C, and D and have good readings (A=345 vdc, B=310 vdc, C=10 vdc, D=2.5 vdc)

Take 3 voltage readings for me (be careful, these are high voltages):
1)  with no input, meter on dc volts (hundreds), measure from ground to both primary wires on the output transformer.  Expect 345 vdc on the wire connected to test point A, expect a few volts less from the wire that connects to the plate of the output tube.
2)  with source playing at full volume, meter on AC volts (hundreds), measure the AC voltage across the primary of the output transformer.  You should be getting somewhere between 200-250, but I suspect you are getting around 100.

Also, what tubes are you using and do you have any other tubes?  You might want to look at pin 6 of your output tubes.  What is connected to this pin?  Is it open?  Some output tubes (6BQ5) have this pin internally connected to the cathode (pin 3), but others (6p15p) do not.  On the 6p15p type tubes, a 0.1 uf cap between pin 6 and pin 3 is the CCE mod...however leaving pin  6 open can result in really poor preformance.  If your pin 6 is open and your output tubes don't have pin 6 internally connected to pin 3 try adding a wire from pin 6 to pin 3 (or try adding a .1uf 400v poly cap from pin 6 to pin 3 to implement the CCE mod).  This would need to be done on both the right and left side.

Dan
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timh
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Re: Low volume problem.
Reply #7 - 01/25/12 at 06:56:01
 
Dan,
Okay, here are my numbers:
A.  347 VDC
B.  280 VDC
C.  0.5 V on the leg of the 5W 150 ohm resistor
D.  0.3 V on pin 8 and 9.5V on pin 3 ( I'm using a EC88 Miniwatt tube)

Primary output wires (red): 348V and 347V
Blue plate wires: 348V and 342V
I'm using the SV83's and the 3-6 CCE mod already.    

Lesson learned here:  "The voltage never lies"  But, my question now is: are the low voltages the problem here and why are they low?
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dank
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Re: Low volume problem.
Reply #8 - 01/25/12 at 11:31:44
 
Timh

I think you have an incompatible input tube there.  Pull up the data sheet and compare it to one of the recomended input tubes like the 6n1p.
http://tubedata.itchurch.org/sheetsE.html  is a good place to find tube data sheets.

While the pin out of the two tubes seems compatible, the plate characteristics graphs are very different.  -2v grid and 200v plate on a 6n1p produce a 10 ma plate current, while they produce 60 ma on the ecc88.  

Try one of the recommended input tubes.  6922, 6dj8, or my favorite the 6n1p and see if that helps get the "D" and "B" numbers right.  There still may be a problem, but a known compatible input tube needs to be the next step.


Dan
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Kaloyanr
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Re: Low volume problem.
Reply #9 - 01/26/12 at 00:27:21
 
Does the tube heating work well?

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timh
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Re: Low volume problem.
Reply #10 - 01/26/12 at 03:32:36
 
Dan,
I changed out the tube and it worked.  It sounds amazing!!!  Thanks for the help in figuring this out, I really appreciate it.  
Cheers,
Tim
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