layout
metalman
have you tried different pcb layouts
i was just wondering if the circuit is suseptable to layout or
better to have the fet's thermally bonded.
At present still using SE in/out
very sounding preamp😀
metalman
have you tried different pcb layouts
i was just wondering if the circuit is suseptable to layout or
better to have the fet's thermally bonded.
At present still using SE in/out
very sounding preamp😀
No, I've only used the perboard layout that I used originally. It has worked wonderfully well, so I did as the old saying goes "if it ain't broke don't fix it." To my knowledge, there isn't any real susceptability to layout with this circuit. Thermally bonding the FET's isn't a bad idea, but isn't really necessary either, as the outputs are DC blocked by the capacitors, so relative offset that might be caused by the FET mismatch doesn't become much of an issue. In my preamp, all fets are mounted to the same section of aluminum sheet of the chassis, so they are somewhat thermally coupled in mine, but not to a significant degree.
Right now I am troubleshooting my Aleph-X monoblocks, where I have made the exact same error on both channels but haven't figured it out yet. Also, I mistakenly shorted the V+ rail to ground on one amp, and let the magic smoke out of my rectifier diodes (at least I hope it was the diodes).
Cheers, Terry
Right now I am troubleshooting my Aleph-X monoblocks, where I have made the exact same error on both channels but haven't figured it out yet. Also, I mistakenly shorted the V+ rail to ground on one amp, and let the magic smoke out of my rectifier diodes (at least I hope it was the diodes).
Cheers, Terry
layout
isn't it amazing, electronics is all done with smoke and mirrors?😉
I made my pcb's too large 120% instead of 100%
didn't worry about it at the time🙄
easier too see but inconvieniant for mounting.
i redesigned layout so all fets mounted on one side.
measures approx 4" * 2.5"
very close to symmetical
ps
I perfer to put the electrolytics around wrong way, Big pop😀
isn't it amazing, electronics is all done with smoke and mirrors?😉
I made my pcb's too large 120% instead of 100%
didn't worry about it at the time🙄
easier too see but inconvieniant for mounting.
i redesigned layout so all fets mounted on one side.
measures approx 4" * 2.5"
very close to symmetical
ps
I perfer to put the electrolytics around wrong way, Big pop😀
Nice design Metalman,
I am considering updating my X CCs Bosoz with the cascode.
How did you arrive at using the 70 volt positive rails?
Macka
I am considering updating my X CCs Bosoz with the cascode.
How did you arrive at using the 70 volt positive rails?
Macka
Simple, the original BZLS used a +60V rail, and the cascode as I am using eats about 10V, so I added an extra 10 to the positive rail to maintain the peak-to-peak voltage output swing the same as the original.
Cheers, Terry
Cheers, Terry
Well, I wanted to keep at least 5.5-6V across the gain transistors to keep them in a fairly linear region, and since I used another set of IRF610's to do the cascode there is a ~4V loss due to the Vgs drop, so 6 + 4 = 10.
Now, as I have since learned, there is no reason that bipolars could'nt be used for the cascode devices, which would save about 3.5 volts. A little less hungry?!?
Terry
Now, as I have since learned, there is no reason that bipolars could'nt be used for the cascode devices, which would save about 3.5 volts. A little less hungry?!?
Terry
Hi Terry,
I got my CC-CCS-X-BZLS going tonight.
Its sounds really great.
A slightly different blend from the previous X BZLS variation with out the CC-CCS.
I think there is more balance tonally and the highs are now spot on. There also appear to be more energy and texture in the presentation. I think using an active current source without the Cascoding tended to show up the limitations in the top end to a degree.
I highly recommend this design.
Macka
I got my CC-CCS-X-BZLS going tonight.
Its sounds really great.
A slightly different blend from the previous X BZLS variation with out the CC-CCS.
I think there is more balance tonally and the highs are now spot on. There also appear to be more energy and texture in the presentation. I think using an active current source without the Cascoding tended to show up the limitations in the top end to a degree.
I highly recommend this design.
Macka
Terry,
Have you tried the X as a DC and not as an AC feedback? If yes what were the subjective differences.
allan
Have you tried the X as a DC and not as an AC feedback? If yes what were the subjective differences.
allan
Hey Allan,
No, I've only built my version with the AC feedback. As to a DC feedback (I think you are referring to the feedback configuration used in the First Watt F1/F2 amps), the closest equivalent I think would be the original BZLS. Because they use split rails, the DC feedback isn't required to set the operating point, so a AC-feedbackless version would use source degeneration to set gain rather than feedback. On that topic I think Macka is probably the best versed in the subjective listening differences.
Macka,
I am glad to hear you are pleased with my variation. Thanks for the recommendation. Can we ask you to elaborate on the sonic differences between the variations?!?
Cheers, Terry
No, I've only built my version with the AC feedback. As to a DC feedback (I think you are referring to the feedback configuration used in the First Watt F1/F2 amps), the closest equivalent I think would be the original BZLS. Because they use split rails, the DC feedback isn't required to set the operating point, so a AC-feedbackless version would use source degeneration to set gain rather than feedback. On that topic I think Macka is probably the best versed in the subjective listening differences.
Macka,
I am glad to hear you are pleased with my variation. Thanks for the recommendation. Can we ask you to elaborate on the sonic differences between the variations?!?
Cheers, Terry
Terry,
Its is difficult to quantify in words.
My impressions are that nothing stands out and it is perhaps more neutral, but when call upon it delivers.
From a technical perspective on reading Neslon's Cascode article the gain Fet is operating in a more linear fashion for both voltage and current. Assuming the cascode takes nothing away and produces low non linear distortions the result sonically should be better on technical grounds.
I not you have chosen different values for the feedback resisters..being now 50 K, this perhaps also accounts for some sonic differences.
Can you please explain how you arrived at this value?
I would also like to try a BJT cascode, can you make a recommendation?
I continue to like this variety.
Macka
Its is difficult to quantify in words.
My impressions are that nothing stands out and it is perhaps more neutral, but when call upon it delivers.
From a technical perspective on reading Neslon's Cascode article the gain Fet is operating in a more linear fashion for both voltage and current. Assuming the cascode takes nothing away and produces low non linear distortions the result sonically should be better on technical grounds.
I not you have chosen different values for the feedback resisters..being now 50 K, this perhaps also accounts for some sonic differences.
Can you please explain how you arrived at this value?
I would also like to try a BJT cascode, can you make a recommendation?
I continue to like this variety.
Macka
Terry,
Yes...and the Aleph P too.
Macka, what are your subjective findings on this?
Thanks guys.
Yes...and the Aleph P too.
Macka, what are your subjective findings on this?
Thanks guys.
The Prior Art BZLS feedbackless was a different beast..its been a while since I have auditioned that version.
I recall it was more musically forgiving and engaging.
The X BSZLS more accurate, the CCS X BSZLS a bit ripe for my taste and the CC CCS X BSZLS musically compelling.
Playing Moulin Rouge.....the purity, the romance, the pleasure...and Nicole Kidman.....the love.
I recall it was more musically forgiving and engaging.
The X BSZLS more accurate, the CCS X BSZLS a bit ripe for my taste and the CC CCS X BSZLS musically compelling.
Playing Moulin Rouge.....the purity, the romance, the pleasure...and Nicole Kidman.....the love.
I would love to build it, helas my PCBs from kari were lost in space...
so for now I have to keep it as my p2p bzls
so for now I have to keep it as my p2p bzls
One observation is that in comparison to previous versions the resolution has moved on from being exacting and accurate to an almost powder like smoothness in transient behaviour .Yet details just seem to materialize out of the velvet presentation.
There are absolutely no edges in the beautiful shades of dynamic contrast.
I must set up my X Aleph power amps (currently using the turbo A 60) ..I think that will be very interesting.
Below the reference speaker, a very high resolution monitor biamped with my Hi Low Pass.
Macka
There are absolutely no edges in the beautiful shades of dynamic contrast.
I must set up my X Aleph power amps (currently using the turbo A 60) ..I think that will be very interesting.
Below the reference speaker, a very high resolution monitor biamped with my Hi Low Pass.
Macka
Attachments
Hi,
I´m also thinking of changing my X-BOSOZ to the CS-CCS-X-BOSOZ.
Looking at the schematic I noticed the two voltage references for the cascoding (10V). I read that you used special voltage references in this position. Since these are a bit difficult to get could you tell me what the problem/difference would be with a normal zener?
Isn´t it possible to get a reference voltage without the zeners by using resistors. The connection between the sources of the diff pair are always at the same voltage aren´t they?
William
I´m also thinking of changing my X-BOSOZ to the CS-CCS-X-BOSOZ.
Looking at the schematic I noticed the two voltage references for the cascoding (10V). I read that you used special voltage references in this position. Since these are a bit difficult to get could you tell me what the problem/difference would be with a normal zener?
Isn´t it possible to get a reference voltage without the zeners by using resistors. The connection between the sources of the diff pair are always at the same voltage aren´t they?
William
I am also planning on building a CS-CCS-X-BOSOZ. I am now wondering why you could not use just one voltage reference instead of two, and possibly add some gate stopper resistors?
Looking at a number of schematics this appears to be a standard method for biasing cascode transistors.
Interestingly I have seen a variation of the voltage divider where the upper resistor was replaced by a JFET constant current source. JFET tolerances aside this might give a very good PSRR / noise filtering and might be quieter than Zeners? But then again I am not an EE so take this with a pinch of salt.
Looking at a number of schematics this appears to be a standard method for biasing cascode transistors.
Interestingly I have seen a variation of the voltage divider where the upper resistor was replaced by a JFET constant current source. JFET tolerances aside this might give a very good PSRR / noise filtering and might be quieter than Zeners? But then again I am not an EE so take this with a pinch of salt.
MRupp said:
Hi,
I´m not shure if you mean it´s possible or not? (Using a resistor instead of a zener because the supply voltage and the source voltage (input fets) is constant).
Using the gate stoppers is probably a good idea, as is leaving out one reference completely!
William
MRupp & wuffwaff,
Yes, there are many ways the cascode can be implemented. For the reference voltage a single simple resistor divider between the V+ rail and ground will do fine, and a JFET current source feeding a reference resistor will probably give improved performance. Further, there is no reason to use MOSFET's for the cascode devices, and BJT's would probably serve very will here as long as they have sufficient power dissipation capacity. I've been meaning to draw up a resistor divider + BJT version but have been too busy at work plus fighting off a cold over the past couple weeks. Bear with me and I'll get to it eventually.
Why did I use MOSFETs and dual references? I had extra MOSFETs lying around, and the layout I used for compactness needs didn't make a single voltage reference convenient (perfboard routing issues). There was no special sonic reason I did it that way, and I see no disadvantages to using other configurations. I believe the group buy that Kari put together used my desing simply because it was a proven functioning design.
Lastly, I did use 221ohm gate stoppers for the cascode mosfets, and while I corrected that omission for Kari's group buy, I seem to have forgotten to update the schematic in this thread. I'll correct that and report a new final schematic.
Cheers, Terry
Yes, there are many ways the cascode can be implemented. For the reference voltage a single simple resistor divider between the V+ rail and ground will do fine, and a JFET current source feeding a reference resistor will probably give improved performance. Further, there is no reason to use MOSFET's for the cascode devices, and BJT's would probably serve very will here as long as they have sufficient power dissipation capacity. I've been meaning to draw up a resistor divider + BJT version but have been too busy at work plus fighting off a cold over the past couple weeks. Bear with me and I'll get to it eventually.
Why did I use MOSFETs and dual references? I had extra MOSFETs lying around, and the layout I used for compactness needs didn't make a single voltage reference convenient (perfboard routing issues). There was no special sonic reason I did it that way, and I see no disadvantages to using other configurations. I believe the group buy that Kari put together used my desing simply because it was a proven functioning design.
Lastly, I did use 221ohm gate stoppers for the cascode mosfets, and while I corrected that omission for Kari's group buy, I seem to have forgotten to update the schematic in this thread. I'll correct that and report a new final schematic.
Cheers, Terry
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