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DQ828  
#1 Posted : Sunday, November 11, 2018 7:36:19 AM(UTC)
DQ828

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I made my TP Blll DAC some years back but recently I had an fault that ended up leading to this question.

While I was fixing the fault I connected my Squeezebox Touch (SBT)directly to my ASP Crossover and in doing that I noticed that the gain coming from the SBT was considerably higher than when run via the Blll IVY lll combo. At that point I ddin't measure the output but simply changed the Secondary Gain resistors (R13-16) from 180-Ohm to 250-Ohm to theoretically increase the output. Once the Blll was going again (bad PSU for the Arduino Mega) there didn't seem to be any real improvement on the gain stakes so I thought I do some measuring and also check that R1-4 were 750 Ohm as required. R1-4 are 750 Ohm.

For the testing I connected the SE output from the SBT and then the IVY lll to my multimeter and read the output voltage at full volume while playing various tones and the results are below;

SBT @ Full Volume:
100 Hz tone = 1.440v
250 Hz tone = 1.441v
440 Hz tone = 1.441v
1000 Hz tone = 1.441v
10000 Hz tone = 1.174v

SBT @ Full Volume to Blll @ Full Volume: R13-16 = 250 Ohms

100 Hz tone = 1.239v
250 Hz tone = 1.239v
440 Hz tone = 1.240v
1000 Hz tone = 1.234v
10000 Hz tone = 0.989v

The next measurements probably dont mean much but I thought they were interesting :)

SBT @ 70:
100 Hz tone = 0.261v
250 Hz tone = 0.261v
440 Hz tone = 0.261v
1000 Hz tone = 0.261v
10000 Hz tone = 0.211v

SBT @ Full Volume to Blll @ 70: R13-16 = 250 Ohms

100 Hz tone = 0.042v
250 Hz tone = 0.042v
440 Hz tone = 0.041v
1000 Hz tone = 0.040v
10000 Hz tone = 0.031v

So the question is, why is the output from the Blll lower than the SBT?

Edited by user Sunday, November 11, 2018 11:05:06 AM(UTC)  | Reason: Not specified

Brian Donegan  
#2 Posted : Sunday, November 11, 2018 7:02:06 PM(UTC)
Brian Donegan

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The output stage on the SBT has more gain.
DQ828  
#3 Posted : Monday, November 12, 2018 6:54:58 AM(UTC)
DQ828

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Hmmm, not exactly what I expected :)

So to get the 2Vrms output with the 750ohm/180ohm resister combo you reference for the Blll/Ivy lll, what sort of input do you have to feed the Blll?

They say "Measured at its RCA output jacks, the Squeezebox Touch's maximum output level at 1kHz was 2.06V, which meets the CD standard."

Theoretically they should give the same output in similar situations?

Edited by user Monday, November 12, 2018 10:36:35 AM(UTC)  | Reason: Not specified

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