Dear all,
While at work today I had what seems to me like a good idea. The transistors TR5 and TR6 could be converted from NPN to PNP so negating the DC bias issue that I was concerned about. I will get extra PNP transistors so I can see if this helps for TR2/TR3.
I will post the new schematic in the near future. I will also get some extra coupling capacitors.
I am also thinking that if I make the circuit split rail so the capacitors C6 and C12 can be omitted. (my RIAA preamp already has an over built split rail supply)
Does any one have any thoughts on these potential changes?
While at work today I had what seems to me like a good idea. The transistors TR5 and TR6 could be converted from NPN to PNP so negating the DC bias issue that I was concerned about. I will get extra PNP transistors so I can see if this helps for TR2/TR3.
I will post the new schematic in the near future. I will also get some extra coupling capacitors.
I am also thinking that if I make the circuit split rail so the capacitors C6 and C12 can be omitted. (my RIAA preamp already has an over built split rail supply)
Does any one have any thoughts on these potential changes?
Actually no scrap that, I was tired.
You still need the caps as the output from the transistors will be at around -0.65V, unless you get clever with the biasing, which may be difficult to work out due to interaction with the filter resistors.
In a discrete circuit stick with single-ended supply, in an op-amp circuit where there are no inherent offsets use a split supply and DC coupling.
You still need the caps as the output from the transistors will be at around -0.65V, unless you get clever with the biasing, which may be difficult to work out due to interaction with the filter resistors.
In a discrete circuit stick with single-ended supply, in an op-amp circuit where there are no inherent offsets use a split supply and DC coupling.
Do I have decided on transistors. Mostly based upon what was available in my local store with high HFE. Maybe later I will pick different transistors.
For NPN I will use, BC547C. For PNP I will use BC557C
For the standing current in both transistors I will use, about 4 mA as this is still within the maximum gain of the transistors.
Across the outputs I will use +15V 0V and -15V as that's what I have.
Having thought about what richie00boy was saying C6 and C12 can't be removed and the variable resistor be sent directly to earth unless some thing is done cleverly with bias voltages of the transistors, making the design to dependent on transistors, so I will leave it with a relatively high capacitor values for C6 and C12.
Here is the amended circuit diagram.
For NPN I will use, BC547C. For PNP I will use BC557C
For the standing current in both transistors I will use, about 4 mA as this is still within the maximum gain of the transistors.
Across the outputs I will use +15V 0V and -15V as that's what I have.
Having thought about what richie00boy was saying C6 and C12 can't be removed and the variable resistor be sent directly to earth unless some thing is done cleverly with bias voltages of the transistors, making the design to dependent on transistors, so I will leave it with a relatively high capacitor values for C6 and C12.
Here is the amended circuit diagram.
Attachments
I have not read all the previous posts but one solution might be to try the Liniac. This was a nice little unit designed by John Linsley Hood about 40 yrs ago now. It comprises a small signal Fet, bi-polar transistor, a Darlington and a small number of resistors.
It is single rail and "inverting" which I've always thought would make a good basis for a Xover as you can easily create those multiple feedback designs that allow for simple implementation of 3rd order Butterworth filters.
As a rule his circuits were usually stable and had good PSRR.
Googling "Liniac" will probably get the schematic........I know I've seen it somewhere on the Web.
EDIT. OOOOOOOOOOKAY Google not so wonderful on this occasion.
Try "Paul Kemble web page John Linsley Hood pre amp designs" That should bring more joy.......JB
It is single rail and "inverting" which I've always thought would make a good basis for a Xover as you can easily create those multiple feedback designs that allow for simple implementation of 3rd order Butterworth filters.
As a rule his circuits were usually stable and had good PSRR.
Googling "Liniac" will probably get the schematic........I know I've seen it somewhere on the Web.
EDIT. OOOOOOOOOOKAY Google not so wonderful on this occasion.
Try "Paul Kemble web page John Linsley Hood pre amp designs" That should bring more joy.......JB
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Experiences with bought designs to improve upon.
The low bass on the quads is lovely for night time low level listening as the dipole bass does not disturb the neighbors I guess because of the directive nature of the Bass, but it is a little low on output and does not sound right for my electronic or dub music when I want daytime listening levels. The bass is very directional from the Quad's which as I said above is a strength late at night, with guests round for a beer or three its not ideal.
For this reason I am definitely going to have a switch in the cross over to bypass the Woofer stage and run the Quads full range for late night. Maybe in the long run a voltage overload detector to switch the cross over frequency depending on peak voltage level delivered to the Quad ESL 63's.
I revived a very nice circuit from a friend on the mailing list and it will definitely inspire the further design process, in summary they increase the gain by using Darlington NPN/PNP pairs which seems sensible following the advice of me Chip designer friend. I also bought some cheap LM833 op amps to experiment with while I get the design finalized.
Being keen on prototyping and seeing what I am going to get, I thought I would tell you the last experiments before the build is starting (components have been ordered).
My Behringer CX3400 from ebay was nice for making my Linn Helix two ways active but is not tuned for Quad / Woofer integration but this experience showed the reason for getting a variable cross over before building a custom cross over. Then I found Mc Crypt Active switch X-Over 80 MK III which is tuned for the right cross over frequencies.
Unfortunately the X-Over 80 has a worse sound signature than the Behringer CX3400 but maybe because I could not test due to cross over frequencies its just the Quad ESL 63 is too good!
Anyway this playing has shown me that even just a pair of Linn Helix speakers can provide some protection extension and improvement to the Quads as a bass hybrid. Also the direction the Linn Helix face has little to do with the performance if anything pointing them away from the listener makes them interfere with the Quads less. This makes me inclined toward having the bass drivers down, up, or side facing.
The quads can be crossed over at 70-90Hz without an obvious audible change to their response. Best effect seems to be crossing over a little higher at closer to 100-110Hz as the Quads benefit from not doing the little extra bass.
I am thinking fine of the tuning the subwoofer is going to require time and a lot of test signals and maybe a measurement microphone and mostly involve this cross over.
I am currently thinking I may get slightly better bass from a infinite baffle (closed baffle) 10" drivers and am wondering if the following drivers would make a nice sealed enclosure, that might better the slot loaded Helix 7-8' drivers.
The Dayton RS225S-8 8" drivers should be good enough with just one, judging from my Linn speakers, That said I would want an improvement and so I am considering at least two of them, or even two of the alternative 10" speakers.
Currently I am bias toward the Dayton RS270S-8 10" as it has the same extension as the Peerless 10" according to winISD (running under wine on linux) although its Xmax is lower so RS270S-8 will play less loud, but I suspect the ESL 63's will still be the limiting factor, and if this matters I would just get another pair.
I notice Martin Logan have both sealed and ported woofers on their hybrids so if the bass extension is unsatisfying (I doubt it will be) I may try them in a ported enclosure.
The low bass on the quads is lovely for night time low level listening as the dipole bass does not disturb the neighbors I guess because of the directive nature of the Bass, but it is a little low on output and does not sound right for my electronic or dub music when I want daytime listening levels. The bass is very directional from the Quad's which as I said above is a strength late at night, with guests round for a beer or three its not ideal.
For this reason I am definitely going to have a switch in the cross over to bypass the Woofer stage and run the Quads full range for late night. Maybe in the long run a voltage overload detector to switch the cross over frequency depending on peak voltage level delivered to the Quad ESL 63's.
I revived a very nice circuit from a friend on the mailing list and it will definitely inspire the further design process, in summary they increase the gain by using Darlington NPN/PNP pairs which seems sensible following the advice of me Chip designer friend. I also bought some cheap LM833 op amps to experiment with while I get the design finalized.
Being keen on prototyping and seeing what I am going to get, I thought I would tell you the last experiments before the build is starting (components have been ordered).
My Behringer CX3400 from ebay was nice for making my Linn Helix two ways active but is not tuned for Quad / Woofer integration but this experience showed the reason for getting a variable cross over before building a custom cross over. Then I found Mc Crypt Active switch X-Over 80 MK III which is tuned for the right cross over frequencies.
Unfortunately the X-Over 80 has a worse sound signature than the Behringer CX3400 but maybe because I could not test due to cross over frequencies its just the Quad ESL 63 is too good!
Anyway this playing has shown me that even just a pair of Linn Helix speakers can provide some protection extension and improvement to the Quads as a bass hybrid. Also the direction the Linn Helix face has little to do with the performance if anything pointing them away from the listener makes them interfere with the Quads less. This makes me inclined toward having the bass drivers down, up, or side facing.
The quads can be crossed over at 70-90Hz without an obvious audible change to their response. Best effect seems to be crossing over a little higher at closer to 100-110Hz as the Quads benefit from not doing the little extra bass.
I am thinking fine of the tuning the subwoofer is going to require time and a lot of test signals and maybe a measurement microphone and mostly involve this cross over.
I am currently thinking I may get slightly better bass from a infinite baffle (closed baffle) 10" drivers and am wondering if the following drivers would make a nice sealed enclosure, that might better the slot loaded Helix 7-8' drivers.
- Dayton RS225S-8 8" Reference Shielded Woofer 8 Ohm
- Dayton RS270S-8 10" Reference Shielded Woofer 8 Ohm
- Peerless 830668 SLS 10" Subwoofer
The Dayton RS225S-8 8" drivers should be good enough with just one, judging from my Linn speakers, That said I would want an improvement and so I am considering at least two of them, or even two of the alternative 10" speakers.
Currently I am bias toward the Dayton RS270S-8 10" as it has the same extension as the Peerless 10" according to winISD (running under wine on linux) although its Xmax is lower so RS270S-8 will play less loud, but I suspect the ESL 63's will still be the limiting factor, and if this matters I would just get another pair.
I notice Martin Logan have both sealed and ported woofers on their hybrids so if the bass extension is unsatisfying (I doubt it will be) I may try them in a ported enclosure.
Hi Owen,
first let me congratulate You to the decision of using discrete components instead of OP-Amps. It´s the right decision on the way to good sound ;-)
I personally prefer JFETs where voltages are involved and bipolar transistors rather for current tasks (similar to triodes vers. pentodes in the tube world).
You might consider for example using the common and easy to source BF246A N-Channel JFETs as buffers. A pair of BFs, one connected as a sourcefollower and the second as a current source to the first, works excellent, either with single supplies or dual supplies. The latter would even allow for the ommittance of several coupling caps.
Besides the buffer-supported passive filtering You show in Your schematics the classical unity-gain Sallen-Key structure (using the above described JFET-Buffer stages) allows for very well sounding circuits. Looking off of the common filter menue plate You can find very interesting filter topologies which allow for a lower stage number count or lower parts count in the signal path. LT-Spice is a powerful tool in evaluating those off-the-normal type filters.
jauu
Calvin
ps: I´d prefer the Dayton driver over the Peerless. They are excellently equipped and beautifully built drivers and to my taste they sound better than the Peerless.
first let me congratulate You to the decision of using discrete components instead of OP-Amps. It´s the right decision on the way to good sound ;-)
I personally prefer JFETs where voltages are involved and bipolar transistors rather for current tasks (similar to triodes vers. pentodes in the tube world).
You might consider for example using the common and easy to source BF246A N-Channel JFETs as buffers. A pair of BFs, one connected as a sourcefollower and the second as a current source to the first, works excellent, either with single supplies or dual supplies. The latter would even allow for the ommittance of several coupling caps.
Besides the buffer-supported passive filtering You show in Your schematics the classical unity-gain Sallen-Key structure (using the above described JFET-Buffer stages) allows for very well sounding circuits. Looking off of the common filter menue plate You can find very interesting filter topologies which allow for a lower stage number count or lower parts count in the signal path. LT-Spice is a powerful tool in evaluating those off-the-normal type filters.
jauu
Calvin
ps: I´d prefer the Dayton driver over the Peerless. They are excellently equipped and beautifully built drivers and to my taste they sound better than the Peerless.
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