Terry,
You still need to verify that both rails are discharging at equal rates, and it is also possible that you are oscillating on shutdown so a working scope may be in order about now in order to see if thats happenning. All your grounds snould ONLY connect at one point and thats the power supply common point between the rails.
Mark
You still need to verify that both rails are discharging at equal rates, and it is also possible that you are oscillating on shutdown so a working scope may be in order about now in order to see if thats happenning. All your grounds snould ONLY connect at one point and thats the power supply common point between the rails.
Mark
Hi Mark,
I disagree.
The signal ground should be separate.
The power ground should be separate.
The mains safety earth and metallic chassis should be separate.
The PSU common should be separate.
Then start by interconnecting them all together with a single wire between each.
The exception could be using a resistor instead of a wire to interconnect the signal ground to the power ground. This is the Leach scheme.
Some recommend a switchable cap and/or diode and/or resistor to interconnect the mains safety earth & chassis to the power ground. NEVER disconnect the mains safety earth from the chassis.
This scheme helps prevent noise appearing on the signal ground and then getting amplified and fed out of the output as buzzing/hum/high frequency hash/noise/etc.
I disagree.
The signal ground should be separate.
The power ground should be separate.
The mains safety earth and metallic chassis should be separate.
The PSU common should be separate.
Then start by interconnecting them all together with a single wire between each.
The exception could be using a resistor instead of a wire to interconnect the signal ground to the power ground. This is the Leach scheme.
Some recommend a switchable cap and/or diode and/or resistor to interconnect the mains safety earth & chassis to the power ground. NEVER disconnect the mains safety earth from the chassis.
This scheme helps prevent noise appearing on the signal ground and then getting amplified and fed out of the output as buzzing/hum/high frequency hash/noise/etc.
AndrewT said:
Ok, I thought about this and feel that not having the PCB connected to the CT is somehow just wrong. So I've reconnected the wire from the PCB to the star and with nothing plugged into the input it is dead quiet and the DC offset is 0.00. Switching on and off only causes the DC offset to jump maybe 20mV at most. This has got to be right. Still, when I plug in the preamp I get a slight buzz/hum. It's not real loud but enough to bug me. Is there something I should look for to correct this? Presently the ground wire from the RCA is connected to the terminal on the PCB.
Thanks, Terry
Of course they are all seperate! But I've always used the common on the caps as my common point and everyt time with sucess, my input ground gets ties at the input on the board. I wasn't talking SC grounds in TErrys case because he already has that properly hooked up. One thing thats novel that one can do(and I always do) is the way Pass does his AC ground and that is through a CL-60. This keeps the safe ground but at the same time eliminates the possibility of ground loops that way round.
Mark
Mark A. Gulbrandsen said:
OK. I guess I'll just live with the small hum from the preamp for now. You can't hear it except during silent passages. I may try the CL-60 for the AC ground, but I doubt that will solve it. I disconnected the earth ground and there was no change. The only thing I've found that will get rid of it is to unplug the input cables or disconnect the ground wires from the CT and I'm not going there again.
I must say that this amp is very nice sounding. I wish I could tell you that is sounds better than the P101 but after two days of pretty intense listening I can't. Maybe through some more sensitive or less efficient speakers I could but through my JBL 4412's or 4425's there is no clear winner. Those who doubt this should maybe build a P101 and see for yourself.
Blessings, Terry
still4given said:
That's good to hear Terry!
I'm in two minds as to whether implementing 6 Krell Clones for Tri-amping is going to be sensible given the amount of heat and noise all these would produce. The JBL you have are by all accounts good speakers, so they would reveal any significant differences in quality.
I'll probably just flog on my boards and go for the AKSA afterall.
Terry wrote: hum from the preamp
Hi Terry, try to disconnect the ground-wire from one preamp channel, so only ground pre and poweramp on one channel , maybe this will solve the hum problem.You can try to insert an extra 10 ohm resistor on one channel ground to prevent a loop.
Good luck, Loek
Hi Terry, try to disconnect the ground-wire from one preamp channel, so only ground pre and poweramp on one channel , maybe this will solve the hum problem.You can try to insert an extra 10 ohm resistor on one channel ground to prevent a loop.
Good luck, Loek
krell clone
Got the clone basically done- thread is here. if you care to comment.
Interesting observations- This thing gets frickin hot! But you already knew that. I'm running it with Vandy 2Ce's now and an iPod, sounds great. Going to use a preamp and a real source soon hopefully if I have time.
Hey, the driver heat sinks i'm using are very big, but measure at about 43 degrees C, much hotter than I would have guessed. So use big sinks or do what Terry did and let the air from the fans hit these too.
Lets talk grounding-- I ran all the cap grounds together and then to star. All other grounds, including both AC saftey ground and L/R output grounds connect directly to the star with nothing in the way. The only grounds not direct to the star are L/R inputs, which go to the inputs on the driver board, but then there is a jumper wire from where they connect there to the star.
Turns out I've got absolutely no detectable noise or hiss at the speakers, even with ear to the tweeters. I think they are about 88 or 89 dB/w. Is this a fluke? Seems like everyone has their own ideas about grounding so I'm glad I lucked into something that is working ok.
Here is a Question- if a LM3xx voltage regulator chip has thermal resistrance of 3 deg C/watt, and its constantly at 47 degrees C (measured at heatsink), is that bad? Say its putting out 1.5 A at 12V or say 2A to be safe. the problem with the heat is caused because its taking like 27V in and outputting 12V. Had a free xformer of too much voltage.
ohhh... and what's the deal with the krell ksa 50 reviews? thought around post 3 or 4 someone said that they wanted a wiki category for these, but there are none! Anyone heard of this being reviewed, kind of want to compare notes.
Got the clone basically done- thread is here. if you care to comment.
Interesting observations- This thing gets frickin hot! But you already knew that. I'm running it with Vandy 2Ce's now and an iPod, sounds great. Going to use a preamp and a real source soon hopefully if I have time.
Hey, the driver heat sinks i'm using are very big, but measure at about 43 degrees C, much hotter than I would have guessed. So use big sinks or do what Terry did and let the air from the fans hit these too.
Lets talk grounding-- I ran all the cap grounds together and then to star. All other grounds, including both AC saftey ground and L/R output grounds connect directly to the star with nothing in the way. The only grounds not direct to the star are L/R inputs, which go to the inputs on the driver board, but then there is a jumper wire from where they connect there to the star.
Turns out I've got absolutely no detectable noise or hiss at the speakers, even with ear to the tweeters. I think they are about 88 or 89 dB/w. Is this a fluke? Seems like everyone has their own ideas about grounding so I'm glad I lucked into something that is working ok.
Here is a Question- if a LM3xx voltage regulator chip has thermal resistrance of 3 deg C/watt, and its constantly at 47 degrees C (measured at heatsink), is that bad? Say its putting out 1.5 A at 12V or say 2A to be safe. the problem with the heat is caused because its taking like 27V in and outputting 12V. Had a free xformer of too much voltage.
ohhh... and what's the deal with the krell ksa 50 reviews? thought around post 3 or 4 someone said that they wanted a wiki category for these, but there are none! Anyone heard of this being reviewed, kind of want to compare notes.
Terry wrote: how to check the caps
Connect a cap with a resistance of about 10k to a DC-voltage a little lower than the voltage specified on the cap.
The voltage measurement on the cap should read about the same as the supply after a while . If not there is too much leaking in the cap. It also has to stay cool...
Succes, Loek
Connect a cap with a resistance of about 10k to a DC-voltage a little lower than the voltage specified on the cap.
The voltage measurement on the cap should read about the same as the supply after a while . If not there is too much leaking in the cap. It also has to stay cool...
Succes, Loek
Re: krell clone
Very unlikely.
LM3xx regulators have a built-in thermal limiter.
e.g. , LM317/LM337 limit the current when Tj = 125C.
Having it constantly thermally limited will not kill it, but healthy it is not.
The thermal limiter on LM3xx's makes them very handy to calculate thermal resistance of heatsinks accurately with ease.
If some are interested i can post the procedure.
Ask Loek !
I have a copy of a KSA review from the early 80s, Xerox'd it at the time from a magazine in the library of Loek's employer.
Some time ago i went there to find a feedback article for Mikeks to discover they had moved nearly all of the paper treasures from the library to the archive storage.
I have no access to it, Loek might.
lgreen said:
Very unlikely.
LM3xx regulators have a built-in thermal limiter.
e.g. , LM317/LM337 limit the current when Tj = 125C.
Having it constantly thermally limited will not kill it, but healthy it is not.
The thermal limiter on LM3xx's makes them very handy to calculate thermal resistance of heatsinks accurately with ease.
If some are interested i can post the procedure.
Ask Loek !
I have a copy of a KSA review from the early 80s, Xerox'd it at the time from a magazine in the library of Loek's employer.
Some time ago i went there to find a feedback article for Mikeks to discover they had moved nearly all of the paper treasures from the library to the archive storage.
I have no access to it, Loek might.
Mark A. Gulbrandsen said:
I wish it were that easy. I would like to build a preamp someday. I tried this Krell on three preamps. A Yamaha Natural Sound, a Bryston .4B and a Dynaco PAS3. All exibited the same hum. I suppose it could be the pre but I don't have this hum with my P101 or any of my Haflers or Soundcraftsmen amps. All were plugged into the same surge protector and I even tried using a two prong adapter to drop the ground. I tried using shielded cable between the RCA and the PCB as well as two stranded wires twisted. No change.
Disconnecting one of the grounds will eliminate the hum, but won't the channel with the ground disconnected exibit the same problem with the DC offset? How will that channel get it's ground? I will try it but I worry about my speakers if it should fail again. I will try the resistor as well. If that works it seems like the best solution.
Blessingsw, Terry
Jacco wrote:I have a copy of a KSA review
Hi Jacco, can you give me name,date and so on of the review?
As you mentioned it is more and more a digital archive here.
Terry, if your connections are o.k the boards has there own groundwire.
I had the same problem with my 1980 Leach-amp and it seamed to be an internal groundloop with the transformer(c-core) in the centre of the box and wiring. By placing the input connectors to a different location and with a 10 ohm in series with each signalgroundwire i cannot hear it anymore with headphones connected.
In a preamp the left and rightgrounds are also somewhere connected so this is not the source.
So balancing helps and thats why it is most used in professional audio systems and long cables.(as you know as musician).
Till next time, Loek
Hi Jacco, can you give me name,date and so on of the review?
As you mentioned it is more and more a digital archive here.
Terry, if your connections are o.k the boards has there own groundwire.
I had the same problem with my 1980 Leach-amp and it seamed to be an internal groundloop with the transformer(c-core) in the centre of the box and wiring. By placing the input connectors to a different location and with a 10 ohm in series with each signalgroundwire i cannot hear it anymore with headphones connected.
In a preamp the left and rightgrounds are also somewhere connected so this is not the source.
So balancing helps and thats why it is most used in professional audio systems and long cables.(as you know as musician).
Till next time, Loek
Terry,
Your ground loop is the loop formed by the shields of the right and left channels back through the preamp and back to the power amp. It is not the fault of your preamp.
Try this tip from Leach's site:
If you are sure that the hum is due to an internal ground loop, the procedure for breaking this loop is as follows:
Turn the amplifier off and wait for the power supply to discharge. Do not perform this procedure with the amplifier on.
Cut the wire to the central ground on the input side of one circuit board.
Solder a short circuit jumper wire between the ground lugs on the two input jacks.
The circuit board with the cut ground wire is now grounded back through its input ground lead to the ground of the other circuit board. Use an ohmmeter to verify the new ground connection before turning the amp back on.
Your ground loop is the loop formed by the shields of the right and left channels back through the preamp and back to the power amp. It is not the fault of your preamp.
Try this tip from Leach's site:
If you are sure that the hum is due to an internal ground loop, the procedure for breaking this loop is as follows:
Turn the amplifier off and wait for the power supply to discharge. Do not perform this procedure with the amplifier on.
Cut the wire to the central ground on the input side of one circuit board.
Solder a short circuit jumper wire between the ground lugs on the two input jacks.
The circuit board with the cut ground wire is now grounded back through its input ground lead to the ground of the other circuit board. Use an ohmmeter to verify the new ground connection before turning the amp back on.
Re: Jacco wrote:I have a copy of a KSA review
Stereoplay, do not know the number of the issue.
Think it was an '84 test, but could be '83.
The mag tested the KSA100 in March '86, and that was a few years later.
The Xerox i made skipped the bottom section with the number and year.
If you take a look inside an '85 or '86 Stereoplay issue you can find the test date of the KSA50MKII at the 'Rang Und Namen' section.
In those days somewhere between the pages 50 and 70, pages with black stripes on the sides.
loek said:
Stereoplay, do not know the number of the issue.
Think it was an '84 test, but could be '83.
The mag tested the KSA100 in March '86, and that was a few years later.
The Xerox i made skipped the bottom section with the number and year.
If you take a look inside an '85 or '86 Stereoplay issue you can find the test date of the KSA50MKII at the 'Rang Und Namen' section.
In those days somewhere between the pages 50 and 70, pages with black stripes on the sides.
Now that we are back at parts and grounding issues again. 
For the ones not using the Giant Zener's as Mr Green(or Mr Blue,whatever name he prefers now his KSA is finished) :
Zener diodes should be placed like half an inch above the board, otherwise they do not reach their power rating.
These parts generally get hot and seem to be the first source of trouble.
Besides making way too much noise.(i thought about using 9 white Led's instead of the 27V zener)
For the ones not using the Giant Zener's as Mr Green(or Mr Blue,whatever name he prefers now his KSA is finished) :
Zener diodes should be placed like half an inch above the board, otherwise they do not reach their power rating.
These parts generally get hot and seem to be the first source of trouble.
Besides making way too much noise.(i thought about using 9 white Led's instead of the 27V zener)