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Threshold S500 II volume  issue.
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Old 11th January 2020, 07:17 PM   #1
Silvanik is offline Silvanik  Italy
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Default Threshold S500 II volume issue.

Hello everybody fellow enthusiast,
I need some help for my recent purchase, a long time dreamed Threshold S500 series II (not a optical bias version).
Actually it works, or better, can properly switch on but the maximum volume is very low driving a pair of Tuscanini Idillia speakers that are almost a full resistive load of around 6 ohm and 85 db of sensitivity. The difference using my other amplifier, a McCormack DNA-2, is huge (same source, same pre amp).
This issue is present since my first use, I have had this amplifier for just one month.
Now, I'm aware that the DNA-2 has 300w/ch at 8 ohm, gain 30db, input sensistivity 1,5Vrms against 250 w/ch for the S500, gain 26,6db, I don't know the sensitivity, but all above considered for sure something in the S500 is wrong.
I checked all fuses and are ok.
Any suggestion to fix this issue will be very appreciated.
Maybe Nelson Pass could intervene here?

Thank you in advance to everyone that can help me
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Old 11th January 2020, 08:06 PM   #2
Norgaard is online now Norgaard  Denmark
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Hi,

Can you quantify: "volume is very low"
Measured output voltage RMS or peak?

"The usual health questions":
Have you measured or could you measure the DC voltage on the outputs
Are the heat sinks at the typical 50C or close ?
Any humming in the speakers at idle?
Has the power supply been re-capped?

If it indeed is very low - I expect it to be something else
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Old 11th January 2020, 09:08 PM   #3
Zen Mod is online now Zen Mod  Serbia
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Threshold S500 II volume  issue.
using RCA input , but forgot to put jumpers from 1-3 in XLR ?

edit - or , if there is switch for same thing, you forgot to switch it?
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Last edited by Zen Mod; 11th January 2020 at 09:11 PM.
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Old 11th January 2020, 11:10 PM   #4
Silvanik is offline Silvanik  Italy
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Quote:
Originally Posted by Norgaard View Post
Hi,

Can you quantify: "volume is very low"
Measured output voltage RMS or peak?

"The usual health questions":
Have you measured or could you measure the DC voltage on the outputs
Are the heat sinks at the typical 50C or close ?
Any humming in the speakers at idle?
Has the power supply been re-capped?

If it indeed is very low - I expect it to be something else
Norgaard, thank you so much for your answer.
The voltage output measurement is something I'm going to do tomorrow, and I can say that the heat sinks temperature remain all the time around the environmental one, would say 16/17C even after one hour, I measured the bias voltage and found it 30mV on right and 25mV on left: I know it's too low but it shouldn't affect the utmost volume, isn't it?
I haven't no kind of hum at any level.
The amplifier hasn't been re-capped but also this aspect shouldn't matter in the volume issue.
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Old 11th January 2020, 11:19 PM   #5
Silvanik is offline Silvanik  Italy
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Quote:
Originally Posted by Zen Mod View Post
using RCA input , but forgot to put jumpers from 1-3 in XLR ?

edit - or , if there is switch for same thing, you forgot to switch it?
Hi Zen Mod,
my S500 II only has RCA inputs, I had a look to the inside but didn't see any jumpers or selectors.
The only possible setting seems to be the pot for the bias on each driver board.
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Old 11th January 2020, 11:54 PM   #6
Zen Mod is online now Zen Mod  Serbia
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Threshold S500 II volume  issue.
can you dig anything from this - compare is it the same?
Attached Files
File Type: pdf s150-300-500.pdf (94.7 KB, 24 views)
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Old 12th January 2020, 12:13 AM   #7
Silvanik is offline Silvanik  Italy
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Quote:
Originally Posted by Zen Mod View Post
can you dig anything from this - compare is it the same?
Thank you for the schematic! Yes, I've this circuit, so I should find 76V as rails voltage.
I wonder what can furthermore affect the maximum volume? What check in the driver boards is recommended to be done in order to be sure the gain is right?
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Old 12th January 2020, 09:15 AM   #8
Silvanik is offline Silvanik  Italy
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Mr Nelson Pass,
could you give some hints to help me to fix the max volume issue?
Can a wrong (I mean very low) bias value affect the max volume output on Stasis topology?
Any words by you will be greatly appreciated.
Greetings from an italian Nelson Pass fan.
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Old 12th January 2020, 09:39 AM   #9
Zen Mod is online now Zen Mod  Serbia
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Threshold S500 II volume  issue.
post pictures

also , use some graphical editor (with file I'm attaching again) , and do some measurements and write them down , either clearly as text or clearly in schmtc itself

as you can see from schematic , Iq you measured is in specs

check function of S1 on board
Attached Images
File Type: png s150-300-500.png (116.8 KB, 82 views)
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Old 12th January 2020, 01:30 PM   #10
mpmarino is offline mpmarino  United States
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The S/500 I purchased had low or no gain in one channel.

Of course I knew the electro caps were past their life, and that the
tantalums were risky.

When I replaced the 420uf (470?) electro cap the gain was back. Subsequent testing of the old cap showed it was dead. The 420uf (470?) on the still working channel tested OK. (replaced anyway of course). Then replaced the tants with film.

I would start there, get it working and then worry about the bias - Unless it's too high right now!
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