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
 
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
 
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.
 
Official Court Jester
Joined 2003
Paid Member
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
 

Attachments

  • s150-300-500.png
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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!
 
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!

Mpmarino, thank you so much for your valuable hint, it seems that I have similar issue, as soon as possible I'll check those damn tantalums with the hope this fix the issue. My serial number says that my S500 II was built in 1986 so can't actually complain if sometingh start to show its age.
Luckly I'm able to replace them on my own, any suggestion about the best replacement I can use for these caps?
 
I read the above as it was the 420/470 uF e-cap that was the real problem so you should probably re-cap both types (e-caps and tantalums) so be sure amp will run without problems for the years to come…….

You are perfectly right! I'm going to replace all the capacitors present in my amp with the best I can find, I want make it really sings as it was designed for.
A part this functional issue the amp looks like new, (thirty four years old now!) cosmetically speaking.
I replaced all the original flimsy feet with more suitable and stronger rubber ones, considering its weight it had to be the oem choice even because the mechanical and electrical construction is top notch.
 
Mpmarino, just checked my caps, tantalums and some e-caps found dead!
Now I'm in the process to find the best caps on the market to replace them and bring back my S500 to life.
Can't wait for this work done and compare the Threshold to my other amp McCormack DNA-2 driving one of more bastard load you can meet, the Thiel CS 3.6 speakers, thing that the DNA-2 actually does with pleasant authority.
 
Mpmarino, just checked my caps, tantalums and some e-caps found dead!
Now I'm in the process to find the best caps on the market to replace them and bring back my S500 to life.
Can't wait for this work done and compare the Threshold to my other amp McCormack DNA-2 driving one of more bastard load you can meet, the Thiel CS 3.6 speakers, thing that the DNA-2 actually does with pleasant authority.

So what was the outcome of this? What caps did you end up going with?