Author Topic: Unit gain & calibration issues

June 16, 2022, 11:09:28 pm
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tspirer

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(Copy/paste from email sent to JP for help and hoping to get response via here)

Hi JP,
 
I have the 2 of the TS500’s bought ~1.5 months apart.
 
I have not been able to get them both to behave the same in terms of output and VAC/db measures even with continuous recalibrations of both.
 
In short and before I dive into all the results and steps – the first question I need help answered is on the following test condition I did:
 
ConditionsSwitch position             Output voltage (VAC)Output voltage (VAC)
input signal = sine 1kHz, 1VAC   Units out of 500 Lunchbox
1.001
1.003
input signal = sine 1kHz, 1 VAC   Units installed in 500. TS500 is OFF* Levels are ~-1.0db differenece without units being switched to ON
0.861
0.959
 
 
As you see, without any unit being installed in my 500 Rack (Cranborne 500ADAT slots 13 & 14 in this case), for the same Sine wave I get nearly identical output VAC and db in my DAW with a negligible difference on the right side.
However, where I am stomped is – even when the units are in OFF position, with DRIVE on 0 just in case (I know it’s not supposed to affect when in OFF), and OUTPUT on 10 – I am getting a large difference out of the box already between L & R units.
 
Need some guidance as to what would cause this as I thought these are “true bypass” and yet I am getting this difference. 
 
Thank you in advance. 
 

June 18, 2022, 09:40:15 am
Reply #1

JPK

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The TS500 doesn't have a true bypass.
When in OFF position, the signal goes through the input transformer, R1, the output stage and the output transformer. So there are many possibilities of gain difference.
This doesn't explain the difference between out and in the lunchbox though.
How to you do the measurements when out of the lunchbox? Could the difference be caused by input or output loading?
JPK

June 22, 2022, 05:41:13 pm
Reply #2

tspirer

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The TS500 doesn't have a true bypass.
When in OFF position, the signal goes through the input transformer, R1, the output stage and the output transformer. So there are many possibilities of gain difference.
This doesn't explain the difference between out and in the lunchbox though.
How to you do the measurements when out of the lunchbox? Could the difference be caused by input or output loading?

Hi - I ran the measurements with the usual test oscillator in Logic Pro and checking voltages on XLR outputs.
Nothing changed in Logic or chassis in terms of settings/levels/gain/etc - I only literally paused test sound, turned off chasis, inserted TS500's, and restarted sound test.
Hope this answers your question.

June 23, 2022, 03:21:22 pm
Reply #3

JPK

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What is the setup when you test out of the lunchbox. Are you using an extender connected to the lunchbox, or an external PSU?
JPK

June 23, 2022, 04:04:58 pm
Reply #4

tspirer

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Not for this scenario but not sure I understand the relevance/question?

I literally ran the first test mentioned with both units out of 500.
Then I put them in (without XT) and placed them both in bypass with output/input same, to receive the results mentioned.

Let me know if you need to measure any TP's with the specific test conditions and flows and I can do so. 

Thanks

June 27, 2022, 03:43:04 pm
Reply #5

JPK

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For stereo use you need to adjust the input pots by looking at the meters because there can be small gain differences between units, mainly due to pots tolerances.
The output levels must also be matched by ear or in the DAW for the same reason.
JPK