Hello Aleph X experts.
I finished another pair of Aleph X Monos. When I first hokked them up to the speakers I was surprised how quiet they are. Almost no noise from my very efficient speakers (97dB).
Next I connected my preamp via RCA. One of the X Amps started a 100Hz Hum. Only one! It's not a huge hum but its disturbing and it comes from only one amp.
I changed the RCA's left/right same power amp humming.
I disconnected everything from the preamp to avoid ground loops. Same.
I connected another preamp. Same.
I connected the third preamp I own via XLR balanced. Same.
When I disconnect either of the preamps it's quiet.
Has anyone ever had a similar problem? It seems that one of my X-Amps do not like being connected to whatever.
Do I have a problem in the input stage?
Otherwise the amps sound fine.
I finished another pair of Aleph X Monos. When I first hokked them up to the speakers I was surprised how quiet they are. Almost no noise from my very efficient speakers (97dB).
Next I connected my preamp via RCA. One of the X Amps started a 100Hz Hum. Only one! It's not a huge hum but its disturbing and it comes from only one amp.
I changed the RCA's left/right same power amp humming.
I disconnected everything from the preamp to avoid ground loops. Same.
I connected another preamp. Same.
I connected the third preamp I own via XLR balanced. Same.
When I disconnect either of the preamps it's quiet.
Has anyone ever had a similar problem? It seems that one of my X-Amps do not like being connected to whatever.
Do I have a problem in the input stage?
Otherwise the amps sound fine.
JBL4435 said:
Well this is not right if I read you correctly it is very dangerous.
The amp chassis must been grounded to earth.
If you have access to a Pass Aleph schematic you will be able to follow the standing earthing practise. If not I can send you one.
It involves a thermister CL60 from the ampliifier circuit earth to chassis ground and has about 5 ohms nominal DC resistance. If a problem occurrs or significant current flows the thermister DC resistance drops.
"TH1 is a power thermistor used to connect the circuit and chassis ground to the AC outlet
ground. It will normally operate at 5 ohms, suppressing ground loops in the system, but will
drop to a low impedance if significant current is passed through it."
JBL4435 said:
One thing to remember is that the amps have low gain without
a source impedance, in other words, when there is no source
connection.
If you want to evaluate the amplifier's own noise without a
connection to a preamp, I suggest that you use shorting plugs
to see to it that both inputs (+ and -) are grounded.
same thing with mines
I have the same problem, When a RCA is connected, the amp has a 60Hz hum. The chassis and everything is grounded correctly. When there is no input connected, (even just a cable with no connection at the other end) the amps are very quiet. I tried experimenting with grounding techniques between the preamp and the amps. After fiddling with it for a while, i connected a wire from the amp chassis to the preamp chassis. The hum has gone down quite alot, however, it is still not as quiet as when there is no input connected. BTW, all equipments have earth ground and are running off the same AC outlet. The hum is still annoying me, even at this low level. Any ideas? I have not tried inserting a small resistor between earth and chassis.
I have the same problem, When a RCA is connected, the amp has a 60Hz hum. The chassis and everything is grounded correctly. When there is no input connected, (even just a cable with no connection at the other end) the amps are very quiet. I tried experimenting with grounding techniques between the preamp and the amps. After fiddling with it for a while, i connected a wire from the amp chassis to the preamp chassis. The hum has gone down quite alot, however, it is still not as quiet as when there is no input connected. BTW, all equipments have earth ground and are running off the same AC outlet. The hum is still annoying me, even at this low level. Any ideas? I have not tried inserting a small resistor between earth and chassis.
I had the same problem with the right channel of my amp. I disconnected the preamp/amp interconnect and shorted the amp input...silence...so the hunt was on outside the amp. The culprit...cable TV.
I removed the co-ax from receiver to TV and the hum went away. Using RCA interconnects instead of the coax brought the hum back but now I can disconnect easily from the TV front input whenever I turn my amp on. BTW, turning the receiver off does not remove the hum.
I removed the co-ax from receiver to TV and the hum went away. Using RCA interconnects instead of the coax brought the hum back but now I can disconnect easily from the TV front input whenever I turn my amp on. BTW, turning the receiver off does not remove the hum.
Blues said:
you need this between cable and any TV and/or receiver in house
cable just rarely have it's ground on same potential as safety ground , and that's whats inducing hum , if you have these two potentials galvanic connected
(you don't know that just because you're wastin' too much time on that crazy music
)Attachments
OK, here we go.
the Master was OF COURSE right. Thanks for trying to help here Mr. Pass.
With shorting plugs I get the hum. So we can safely say that the hum comes from the amp and not preamp.
I used shorted RCA and shorted XLR plugs. Here are the measurements all peak to peak:
"Bad" Amp
RCA input shorted to ground
3,3 - 5 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
4,4 - 8 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
RCA input connected to Rotel RC972 Preamp
6,5 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to Harman Signature 1.0 Preamp
6,7 – 8,3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
"Good" Amp
RCA input shorted to ground
1,4 - 2,2 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
3,3 - 4,3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
RCA input connected to Rotel RC972 Preamp
3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to Harman Signature 1.0 Preamp
4,4 – 5,7 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
The audible difference between both amps is huge!
Any ideas?
the Master was OF COURSE right. Thanks for trying to help here Mr. Pass.
With shorting plugs I get the hum. So we can safely say that the hum comes from the amp and not preamp.
I used shorted RCA and shorted XLR plugs. Here are the measurements all peak to peak:
"Bad" Amp
RCA input shorted to ground
3,3 - 5 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
4,4 - 8 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
RCA input connected to Rotel RC972 Preamp
6,5 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to Harman Signature 1.0 Preamp
6,7 – 8,3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
"Good" Amp
RCA input shorted to ground
1,4 - 2,2 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
3,3 - 4,3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
RCA input connected to Rotel RC972 Preamp
3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to Harman Signature 1.0 Preamp
4,4 – 5,7 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
The audible difference between both amps is huge!
Any ideas?
Previous X-Monoblocks
As per Mackas request here are the measurements of my previous X Monoblocks.
It seems that I also have a "good" and a "bad" amp here but didn't notice as it seems that my Pass DIY Preamp seems to eliminate the output noise compared to shorted input. How is that???
"Bad" Amp
RCA input shorted to ground
2,5 - 3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
6,5 - 9 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to DIY Pass P1.7
1,1 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
"Good" Amp
RCA input shorted to ground
1,1 - 1,4 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
4,1 - 5,6 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to DIY Pass P1.7
2,2 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
As per Mackas request here are the measurements of my previous X Monoblocks.
It seems that I also have a "good" and a "bad" amp here but didn't notice as it seems that my Pass DIY Preamp seems to eliminate the output noise compared to shorted input. How is that???
"Bad" Amp
RCA input shorted to ground
2,5 - 3 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
6,5 - 9 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to DIY Pass P1.7
1,1 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
"Good" Amp
RCA input shorted to ground
1,1 - 1,4 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input + and - shorted to ground
4,1 - 5,6 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
XLR input connected to DIY Pass P1.7
2,2 mV noise at the amp output. Not a sine at the scope but one can see peaks at 100Hz (we have 50Hz mains here)
I find it strange you have a another good and bad amp, that is more than mere coincidence.
Can you post a picture of both amps and where they are located?
Here is a thread of the previous
amps.http://www.audioheritage.org/vbulletin/showthread.php?t=19161&highlight=Aleph
Its a bit of a mine field.
I take it you are hearing a hum only and not a buzz from the loudspeaker? The noise could be induced from nearly field of interference. ie the chokes, power supply wiring.
Do you have a low voltage reading lamp or other mains transformer device near one of the amps?
If you come up blank am taking a wide berth here but I suspect there is an issue with the input differential pair, either matching or power supply induced noise.
Your need to be very careful where the earth wire to the driver board is routed as you have alot of high current wiring (ripple) because you are baising for 4 ohms.
Imac
Can you post a picture of both amps and where they are located?
Here is a thread of the previous
amps.http://www.audioheritage.org/vbulletin/showthread.php?t=19161&highlight=Aleph
Its a bit of a mine field.
I take it you are hearing a hum only and not a buzz from the loudspeaker? The noise could be induced from nearly field of interference. ie the chokes, power supply wiring.
Do you have a low voltage reading lamp or other mains transformer device near one of the amps?
If you come up blank am taking a wide berth here but I suspect there is an issue with the input differential pair, either matching or power supply induced noise.
Your need to be very careful where the earth wire to the driver board is routed as you have alot of high current wiring (ripple) because you are baising for 4 ohms.
Imac
macka said:
I only hear that 100Hz Hum
macka [/i]Do you have a low voltage reading lamp or other mains transformer device near one of the amps? [/B][/QUOTE] Not near the old and not near the new amps. [QUOTE][i]Originally posted by macka said:
The input differntials are matched very careful!!
I tried to move PS wiring, input wiring, main PCB. It cartainly makes a difference where I move it but I just can't get the hum lower
Pic "Bad" Amp below
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.