Are you sure the usher is a clone of the stasis amp?
I know cosmetically it is very similar, but can anyone confirm whether the amp circuit is a clone of the stasis amp?
I would have thought they would need to pay licensing fees to Nelson, as I think that amp has components that are still under patent (could be wrong).
I know cosmetically it is very similar, but can anyone confirm whether the amp circuit is a clone of the stasis amp?
I would have thought they would need to pay licensing fees to Nelson, as I think that amp has components that are still under patent (could be wrong).
Melon Head
I really don't know. been googling around and found the clone story line til you brought up the validation question. did some more googling and found someone who worked on both and said they look identical but are internally different. even when so far as to say the usher line are at half bias of the threshold line.
so now more complexities.
I have 70 ma bias at 8 ohm
that will probally jump to 140 ma at 4 ohm
but our expert withness says usher bias is half of threshold bias
so it sounds like i should bias at 35ma at 8 ohms and 70ma at 4 ohms.
which is not a bad thing.
will think about it for a day....probally use a 4 ohm load resistor to do the final lock down bias adjustment.
I think that will keep me in the play it safe zone.
I really don't know. been googling around and found the clone story line til you brought up the validation question. did some more googling and found someone who worked on both and said they look identical but are internally different. even when so far as to say the usher line are at half bias of the threshold line.
so now more complexities.
I have 70 ma bias at 8 ohm
that will probally jump to 140 ma at 4 ohm
but our expert withness says usher bias is half of threshold bias
so it sounds like i should bias at 35ma at 8 ohms and 70ma at 4 ohms.
which is not a bad thing.
will think about it for a day....probally use a 4 ohm load resistor to do the final lock down bias adjustment.
I think that will keep me in the play it safe zone.
@speakerfritz - .7 is 700mA, not 70. Where is this measurement being taken - instead of the rail fuse?
The R1.5 is/was marketed as a 150W/ch Class A amp, though I'm not sure all of those are in Class A, maybe the first 5-10W only. Also it seems you have a very old version of the amplifier, the new one uses a horizontally mounted (and larger) transformer, plus some of the bits look very different. The heatsinks OTOH are almost exactly the same in the newer versions.
The R1.5 is/was marketed as a 150W/ch Class A amp, though I'm not sure all of those are in Class A, maybe the first 5-10W only. Also it seems you have a very old version of the amplifier, the new one uses a horizontally mounted (and larger) transformer, plus some of the bits look very different. The heatsinks OTOH are almost exactly the same in the newer versions.
With plus and minus 80 volts it cannot be class A.
If the ouput reach plus and minus 75 volts ( leaving only 5 volts below saturation )
If the load is 8 ohms current will be 9.37 amps at the speaker
peak power will reach 700W ( 75* 9.37 = 700w ) , then RMS or average power will be 300 W ( 50 % of peak power )
To have this power in class A ( purely class A ) bias shoul be set at 9.37 amps per chanel , with a total voltage of 160 volts this means 1.5 kW per chanel ( 160* 9.37 = 1499.2 ) then for both chanel you get 3kW , heatsink assembly as big as a coffin and power transformer should weight 150 pounds.
It must be class AB but a very powerfull amp 300 watts RMS per chanel in 8 ohms !
If the ouput reach plus and minus 75 volts ( leaving only 5 volts below saturation )
If the load is 8 ohms current will be 9.37 amps at the speaker
peak power will reach 700W ( 75* 9.37 = 700w ) , then RMS or average power will be 300 W ( 50 % of peak power )
To have this power in class A ( purely class A ) bias shoul be set at 9.37 amps per chanel , with a total voltage of 160 volts this means 1.5 kW per chanel ( 160* 9.37 = 1499.2 ) then for both chanel you get 3kW , heatsink assembly as big as a coffin and power transformer should weight 150 pounds.
It must be class AB but a very powerfull amp 300 watts RMS per chanel in 8 ohms !
earlier in the thread I explained that there were two pionts to take bias measurements. The first was 24 1 ohm resistors for each channel one each for each output transister. The second was 2 , one for each channel, 10 ohm resistors for each board. measuring at the 10 ohm resistor a .7 or 700ma reading results in a measurement at the individual 1 ohm bias resisotr of 70ma or .070
I included the readings at the 10 ohm resistor becuase I found in the threashold world, references to very high readings which did not make sense until I understood the function of the 10 ohm resistor, then it made sense.
so if you are a threshold person and tell me to bias at .700 ma then I know that means .070 ma on each transistor bias resister.
Sorry to persist, but is that division by ten because of twenty output transistors in the Threshold design, whereas this has 24? I distinctly remember there was a *large* thread on the R1.5 here with pictures and possibly a schematic, but I can't seem to find it now.
And the amp is not described as a Class A amp anymore on the Usher website either, so the plan to bias in Class AB seems about right.
I would think the right way would be to bias it such that crossover distortion disappears at your lowest listening level (needs a scope). Many commercial amps are biased between 50 and 70mA per pair for best results, some even lower.
And the amp is not described as a Class A amp anymore on the Usher website either, so the plan to bias in Class AB seems about right.
I would think the right way would be to bias it such that crossover distortion disappears at your lowest listening level (needs a scope). Many commercial amps are biased between 50 and 70mA per pair for best results, some even lower.
I wondered about that. I am indicating direct observations. How does this work .....no idea. Intuitively you would expect that .7/24 would give you 1/24th of the N number. But in actual measurements, the 24 transister co located 1 ohm resister come back at approx 1/10 of the value of the 1 10 ohm resister. My guess is that the 10 ohm resister is across each of the PP sides on each channel. SO 24 transisters per channel, 12 push, 12 pull, this 10 ohm resister is going across the 12 and 12.
I only brought it up incase thresold familuar folks came back with numbers that were based on the 10 ohm resister vs the 1 ohm resisters. the bias pot effects both the 10 and the 1 ohm resisters at exactly 10:1 ratio.
don't have a scope, so can't use the scope method.
thanks for all the questions...it's been helpful in my thinking.
ok, done deal. leaving it at .7 via the board 10 ohm resister or if measuring at the 1 ohm resisters, 70ma's.
amp sound fine, and the heatsink heat being generated is slightly above warm.
speakers in my office/workbench area are full sized klipsch kpt-535's over mini KPT-904's. basically a 3 way using a 1 inch tweet driver/horn, 2 inch mid driver/horn, and 15 inch woofer in a vented box. my work bench speakers are a pair of bookshelf sized klh speakers.
amp sound fine, and the heatsink heat being generated is slightly above warm.
speakers in my office/workbench area are full sized klipsch kpt-535's over mini KPT-904's. basically a 3 way using a 1 inch tweet driver/horn, 2 inch mid driver/horn, and 15 inch woofer in a vented box. my work bench speakers are a pair of bookshelf sized klh speakers.
compared to the tube amps I own now, SS amps I own now, tube amps and ss amps I owned in the pass, once I did the power supply cap by pass upgrade, the amp has a very detailed, warm, dynamic sound. better than consumer grade gear, but about the same as reference grade gear
own now, Tube gear - dynaco, shanlin, manley , antique sound labs, peavey, marshall, carvin. SS Gear - pioneer m-25, marshall, onkyo
If I had a second, would love to hear them in bridge mode in a large venue.
I just read a post from Nelson Pass from a Pass Labs forum thread called, Are Usher Amps just lookalikes or built on license. He states he would set the bias so heat sink temp would be 50 degrees c, and says that would be 10 second hand on time. I just thought I should pass this on as an earlier post said it was five seconds.
I know it's a very old post but if anybody can benefit from my post then it's great. The Usher R1.5 is a stunning sounding amp and it benefits from a great pre amp that might cost twice the Ushers price the Usher is a steal at the price it comes ,manufacturers or Hiend has lot of overcharging factor,really a lot. Now coming to the point the Usher's default BIAS is 500mA and it generate 38/42 watts of class A . Can be safely Bias ed till 750mA. Give it a good pre and speakers it will kill Amps costing thrice as much.
Umm. 42 watts class A dissipates more than 84 watts at idle. If the bias is 500mA then the power supply has to be at least 168 volts DC (or +/- 84 VDC), and the output would have to be via a stepdown transformer to get to 8 ohms. If that's not the case, you're being mislead about this amp being a real 42W of class A. If no transformer, I'd bet on more like around 4W, transitioning to class AB for more.
Just sayin'
Just sayin'
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.