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
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
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.
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.
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?
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!
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?
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.
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.
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