Hi Harold, could you explain a little bit more? I don't quite follow. Two things occur to me:
a) for AC the capacitors and resistors both present an impedance, and
b) you also have jfets that (I think) will isolate the different sections of the circuit?
Sounds more mondaine than the mundane version, getting a hard-on by balanced in/out XO's.
I use buffers at the most important positions to ensure that the frequency settings are not influenced by volume control settings and baffle step filter settings.
My baflle step circuit is derived from:
Baffle Step Compensation
It needs buffers at the input and output.
i hope this explains.
regards,
Being balanced is nice, but you need everything in twofold and you have to make sure that the principle of balanced circuits is still valid.
In my setup i would have:\
Kenwood L-1000D (balanced out)
HTPC with magicdac (also balanced)
Pre-amp with only balanced in and out (dispre2 balanced)
the crossover
2 gainclone amps (balanced and bridged) or 2xL-1000M (balanced)
regards,
Hi Harold
thanks for the nice link. I think all this is clear to me, as is how you have used buffers to separate the functional blocks in your circuit. It was your comment about varying capacitances but not resistances in the filter section that I don't get.
in this kind of circuit you can either change the capacitance or resistance for altering the dividing frequency. I do not want to change the load for the buffers, so i have choosen to switch capacitance and not the resistors. This was recommended by more people here on the forum but also on:
TLS.org | Passive Line-Level Crossover
This also explains why i use buffers. If you would not use buffers, you could et into problems when switching resistance
regards,
I have just made (point to point) a copy of the Nain Naxo crossover from spare parts that I had lying around. What a difference an active crossover makes.
So I'd like to experiment some more and consider a balanced version. I have a stack of the 170BLs so I could cheaply make the circuit from post 94.
Harolda: I can't quite make out some of the values of the resistors and caps from your diagram. Two quick questions if I may.
1 I want a crossover at 3kz. How did you work out the values of C5/6 R12/13?
2 What is the value of the cap used in the baffle step?
There are other values I can't read. Your help is greatly appreciated.
regards
Chalk
So I'd like to experiment some more and consider a balanced version. I have a stack of the 170BLs so I could cheaply make the circuit from post 94.
Harolda: I can't quite make out some of the values of the resistors and caps from your diagram. Two quick questions if I may.
1 I want a crossover at 3kz. How did you work out the values of C5/6 R12/13?
2 What is the value of the cap used in the baffle step?
There are other values I can't read. Your help is greatly appreciated.
regards
Chalk
I have just made (point to point) a copy of the Nain Naxo crossover from spare parts that I had lying around. What a difference an active crossover makes.
So I'd like to experiment some more and consider a balanced version. I have a stack of the 170BLs so I could cheaply make the circuit from post 94.
Harolda: I can't quite make out some of the values of the resistors and caps from your diagram. Two quick questions if I may.
1 I want a crossover at 3kz. How did you work out the values of C5/6 R12/13?
2 What is the value of the cap used in the baffle step?
There are other values I can't read. Your help is greatly appreciated.
regards
Chalk
Please look at the link in my previous posts for Capacitor and resistor calculations.
In my crossover:
- Frequency filters: Only Cap values are changed by jumpers
- Baffle Step Correction: Resistor and Cap values are changed. I set both the baffle step frequency and the level. To do this right, both vlaues have to be changed. I solved this by having cummulative values (adding resistors in series or capacitors in parallel) and using jumpers.
regards,
Harold
Finally completed my active crossover. It works very well. Thanks to all that have supplied schematics. At the moment its feeding balanced chip amps only but it sounds great.
I'm amazed at the difference between an active two way system and one with a passive crossover. Sound is much more dynamic and detailed. This sound is also preferable to that of a pair of full rangers. I've missed what a ribbon tweeter can do.
It's fun trying different combinations of tweeters and woofers from different boxes.
Balanced is great too! - no hum at all.
Anyone extended this to a 3-way design?
I'm amazed at the difference between an active two way system and one with a passive crossover. Sound is much more dynamic and detailed. This sound is also preferable to that of a pair of full rangers. I've missed what a ribbon tweeter can do.
It's fun trying different combinations of tweeters and woofers from different boxes.
Balanced is great too! - no hum at all.
Anyone extended this to a 3-way design?
should be: Is it necessary to use matched jFETs?
Just select jFETS with a similar Idss.
The jFET followers do NOT run at Idss. The CCS jFET has a source resistor that reduces the current draw to <<Idss. Accurate selection is NOT a requirement.
If you read Dennis Feucht you will see the Rs attached to BOTH jFETs. this cancels the output offset when run as a dual polarity Follower.
In the single polarity Follower, a lack of output offset helps keep the voltage before and after the Follower very near the ½supply level.
Cascading many stages with a similar offset will accumulate sufficient offset to use up a significant proportion of the output swing from the nominal ½supply.
adding the Feucht resistor to the upper device will remove this risk of accumulated offset.
I built up an LR4 bandpass (for a 3way) that used the output of the high pass as it's feed. With the input Buffer, two stages of High Pass, two more stages of High Pass and two stages of Low Pass, this meant I had 7 jFET Followers and the accumulated offsets had very little effect on output swing capability.
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Like the attached schematic?
Do you know if this ebay seller is realiable and not sale fakes? Qty 10 : Junction Field Effect Transistor, JFET Audio & RF, N and P Channel ff | eBay
Do you know if this ebay seller is realiable and not sale fakes? Qty 10 : Junction Field Effect Transistor, JFET Audio & RF, N and P Channel ff | eBay
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The unity gain followers must be set to 2pole Butterworth to obtain 4pole LR.
The doubled capacitor is required to get Butterworth.
Wrench is refewrring to the other Cy.,
the feedback from the output must connect to the midpoint of the two resistors.
The Cy to the gate cannot pass half supply bias and so there is no need to take them to the bias supply.
The gate connected Cy can go to supply -ve/ground.
But when you do the HP, the gate connected resistor MUST go to the bias supply.
I have a pencil and pen sch.
Do you still want a copy posted?
The unity gain followers must be set to 2pole Butterworth to obtain 4pole LR.
The doubled capacitor is required to get Butterworth.
Wrench is refewrring to the other Cy.,
the feedback from the output must connect to the midpoint of the two resistors.
The Cy to the gate cannot pass half supply bias and so there is no need to take them to the bias supply.
The gate connected Cy can go to supply -ve/ground.
But when you do the HP, the gate connected resistor MUST go to the bias supply.
I have a pencil and pen sch.
Do you still want a copy posted?
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