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Old 2nd October 2010, 07:16 PM   #1
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Default Voltage output issue with B1

My B1 is not outputting enough voltage to drive my amps to full output. I have a modded Teradak Chameleon with TX output and I measure 1.99v on the dac output with a Odb 1k tone. When I measure the output of the B1 at full volume it is only .597v. I'm losing 1.4v.

The TXs in the dac are Cinemag are CMOB-2L 600:600 and the pot in the B1 is a gigawork 20k. Is it possible I need a higher impedance pot? All parts in the B1 are the stock specified values with the exception of the two (per channel) in line resistors. These are, in order, 330 and 270.

I have exhausted my electronics knowledge; any help would be welcome.
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Old 2nd October 2010, 07:26 PM   #2
nar is offline nar
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If I recall the B1 has no Vgain so @ max you can output your source level from preamp, plus the gain of your power amp in the end at the speakers.
Changing the pot value won't do anything solving the fact there is not enough gain.
What are the precise resistors you altered (in value) ? You said "in line" resistors, which is not 100% clear.
Maybe you should try stock values to see if the output level is restored.
Have you checked correct pot; wiring too ?
If you stick to B1, then maybe use a higher gain power amp.
Or, you should change the line R values to give you no input attenuation at all.
Even with that, you could probably lack a little gain in the end ( with a 20dB diff. gain amp ).
26 dB could suit well.

Brds,

nAr
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Last edited by nar; 2nd October 2010 at 07:29 PM.
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Old 2nd October 2010, 07:33 PM   #3
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Yes, I thought it would output what I'm getting from the dac, 1.99v. But somehow 1.4v is disappearing. The resistors are 102, 202 (330r) and 104, 204 (270r).
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Old 3rd October 2010, 06:44 AM   #4
nar is offline nar
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Did you try same values for those 2 resistors ? And why did you change from orig. values ?
Maybe the pot. is mis-wired.

nAr
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Old 3rd October 2010, 11:23 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
when fed with that test signal:
What is the voltage at the input to the pot?
What is the voltage at the output of the pot?
Confirm that the output of the B1 is ~31% of the input voltage?
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Old 3rd October 2010, 04:40 PM   #6
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Quote:
Originally Posted by AndrewT View Post
Hi,
when fed with that test signal:
What is the voltage at the input to the pot?
What is the voltage at the output of the pot?
Confirm that the output of the B1 is ~31% of the input voltage?
Thanks for checking in with me.

The output is the same (1.9) at the input and output of the pot. Also the same (1.9) at input and output of R102, 202. At the input of C101, 201 the voltage has dropped to 1.38. It is 1.38 at the input to R104, 204 but at the output of R104, 204 the voltage has dropped to .6. R104, 204 is a 270R Riken 1 watt. WTF?
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Old 3rd October 2010, 04:57 PM   #7
AndrewT is offline AndrewT  Scotland
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are these AC or DC voltages?
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Old 3rd October 2010, 05:08 PM   #8
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Quote:
Originally Posted by AndrewT View Post
are these AC or DC voltages?
Sorry, AC.
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Old 3rd October 2010, 05:11 PM   #9
DougL is offline DougL  United States
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Just a guess, assuming AC voltages, is R105 and R205 221R?

Doug
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Old 3rd October 2010, 05:12 PM   #10
DougL is offline DougL  United States
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Also, is that loaded with the next stage or unloaded?
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