AndrewT said:
Hi guys,
Allow me not to agree on this. The multiple star-ground points method is not an optimal solution where big caps are placed on the amplifier board, even less so when two amplifier boards are supplied from one power supply. This is a longish issue but I'm afraid I do not have the necessary teaching inclinations to elaborate.
In any case, you may do whatever you please. I was trying to help and have no intention of butting in any further.
Regards,
Milan
JensRasmussen said:
Crown amplifiers take the feedback both before and after the output inductor.
Feedback before inductor is refered to Gain Control Feedback
whereas feedback after inductor is being refered to Damping Control Feedback.
moamps said:
Please keep posting...
I intended the caps on board as buffers. I will use a central capacitor bank for each channel and seperate transformers or windings.
\Jens
Workhorse said:
The inner feedback control loop sets the gain (and z out) and therefor the damping factor. Unless you use an output inductor with a high ohmic value above 100mohm.
\Jens
Hi Jondoe,
You are almost there.
The usual method for the input signal ground is:-
A ground wire from input RCA to input ground and from input ground to central ground. In Leach a resistor from input ground to power ground ( ground plane in Leach Clone) for each channel. The RCA ground is easier if the RCA is insulated from the chassis.
Hi Moamps,
I wish you could take the time to expand your thoughts (even another thread - amp grounding strategies). The more knowledge you & everyone posts the more we can all agree especially when there are exceptions to the general rule. Here you seem to be alluding to just such an exception. Please contribute.
Following on from Jondoe's stereo case :-
what chance a hum loop from 2 inputs from a common source & common ground to the 2 RCA inputs which in turn both connect to central ground. The DC paths will have identical volts but could the different paths have differently induced voltage on the ground wires and set up a loop feeding hum & other trash into the input ground? If so what is the solution?
You are almost there.
The usual method for the input signal ground is:-
A ground wire from input RCA to input ground and from input ground to central ground. In Leach a resistor from input ground to power ground ( ground plane in Leach Clone) for each channel. The RCA ground is easier if the RCA is insulated from the chassis.
Hi Moamps,
I wish you could take the time to expand your thoughts (even another thread - amp grounding strategies). The more knowledge you & everyone posts the more we can all agree especially when there are exceptions to the general rule. Here you seem to be alluding to just such an exception. Please contribute.
Following on from Jondoe's stereo case :-
what chance a hum loop from 2 inputs from a common source & common ground to the 2 RCA inputs which in turn both connect to central ground. The DC paths will have identical volts but could the different paths have differently induced voltage on the ground wires and set up a loop feeding hum & other trash into the input ground? If so what is the solution?
JensRasmussen said:
I agree with you , but in Crown amplifiers the Inductor is 2uH formed by just 10 turns of 14SWG , and i dont think its a highly ohmic type.
Just wondering but have anyone made any scientific evaluation (and compared to real life experience) about how many transistor which are really needed as a minimum? Sometimes "more is better" so it seems but is it really?Mikett said:
Self did some stuff on this, it's in the second edition of his book. I don't have it with me, but IIRC he found that adding outputs decreased distortion.
peranders said:
I tried and have covered the resistive loading, I'm now looking for a way to examine the worst case reactive loading. All is avalible in the manual for the 10 transistor leach and might be a document on its own if I feel the quality of the section is good enough.
\Jens
I think that there's something important to mention. Generally in output devices (mosfets or bipolar) the emitter power resistors can do a lot of problems like instability if they are inductive types Almost every wirewound resistors (except MILLS as far as I know) are inductive. I have seen this problem many times in the past (oscillation etc) so maybe it's preferable to add holes for other types of power resistors (non inductive) like MPC71 ( I think they have 5mm grid) or Cadock or whatever. Just add holes in case that someone want to replase them with something else
Just a thought........
Just a thought........
A very nice thought.
Adding holes would be great, especially for MPC71's.
The MPC71 grid is strange, 9 mm, should be like 354 mills ?
(MPC71 are low inductive, for the real thing you need inductance free wirewounds, Caddocks, PBH, or the really really expensive)
Adding holes would be great, especially for MPC71's.
The MPC71 grid is strange, 9 mm, should be like 354 mills ?
(MPC71 are low inductive, for the real thing you need inductance free wirewounds, Caddocks, PBH, or the really really expensive)
Jacco are you always online
????????/
You are right, the MPC71 it's a good midprice solution(9.0 mm grid) Unfortunatelly PBH and Caddock are very expensive and MILLS (which are true non inductive wirewounds) are expensive too and difficult to find them.
????????/You are right, the MPC71 it's a good midprice solution(9.0 mm grid) Unfortunatelly PBH and Caddock are very expensive and MILLS (which are true non inductive wirewounds) are expensive too and difficult to find them.
I am lazy, i dont bother to log off.
And, whenever someone posts something on a thread i am subscribed to, i hear this very annoying buzz from my computer.
And, whenever someone posts something on a thread i am subscribed to, i hear this very annoying buzz from my computer.
Spirtos said:
I have never seen problems created by emitter resistors beeing inductive, but I will se what I can do. 5 mm spacing is not possible as the resistors have to bridge a 6 mm track.
Jacco said that they are 9 mm, is this true?
I general I never bother with non inductive types as emitter resistors, they are very expensive, and I feel the money is better spend somewhere else - IMHO
\Jens
I planned on some cheaper compromise solution.
My plan was to use 2 paralelled cement wirewound 1ohm resistors for each of the 0.47ohm ones. That would halve the inductance and anyway, these types i can get and 2x1ohm is approx 1.2 the price of 0.47 ohm (if the wattages are added, 2x1ohm/3W vs 1x0.47ohm/5W).
It does not eliminate the inductance, it just halves it, and is not a necessarily pretty picture (2 resistors on top of each other) but it's an ok solution. At least for me.
Have a nice day
My plan was to use 2 paralelled cement wirewound 1ohm resistors for each of the 0.47ohm ones. That would halve the inductance and anyway, these types i can get and 2x1ohm is approx 1.2 the price of 0.47 ohm (if the wattages are added, 2x1ohm/3W vs 1x0.47ohm/5W).
It does not eliminate the inductance, it just halves it, and is not a necessarily pretty picture (2 resistors on top of each other) but it's an ok solution. At least for me.
Have a nice day
Jacco has right, it's 9.0mm as I seen in datasheet not 5.0mm as I said yesterday. Sorry.Try it only if it's easy for you Jens as an extra option (between the holes of normal wirewounds as you have place them)😉 😉
Jondoe\s thought is an idea also
Jondoe\s thought is an idea also
At the time when i couldnt get my hands on decent emitter resistors i used 4 metalfilm types in parallel, 1 watt models.
Bought in a large number price was really good, and absolutely induction free.
(but dont buy to many, i still have a bag full, bought in 1988 or so
)
Not my invention, a number of diy-designs in the low 80s used the trick.
MPC71 bought in Germany is like 3 DKK the piece, they are very small, and fireproof.
I think emitter resistor quality has a significant influence, especially with high slewrate amplifiers.
Not sure whether it pays off to use funny stuff like Caddocks, but Spirtos statement is a quote from quite a few publications.
Bought in a large number price was really good, and absolutely induction free.
(but dont buy to many, i still have a bag full, bought in 1988 or so
)Not my invention, a number of diy-designs in the low 80s used the trick.
MPC71 bought in Germany is like 3 DKK the piece, they are very small, and fireproof.
I think emitter resistor quality has a significant influence, especially with high slewrate amplifiers.
Not sure whether it pays off to use funny stuff like Caddocks, but Spirtos statement is a quote from quite a few publications.
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