Kuartlotron Error Correcting Super Buffer
- Thread starter jls001
- Start date
Thanks but I think he is using EP-40-3M and I do not see this model on the site.
I'm having problem uploading to my usual image hosting site imgur for many days now.
Can someone suggest an alternate image hosting site that allows BB Code link to be copy-paste into HFV type forum posts, so that the image gets directly displayed in the post?
Can someone suggest an alternate image hosting site that allows BB Code link to be copy-paste into HFV type forum posts, so that the image gets directly displayed in the post?
I think Sachin in the earlier posts posted on the photobucket.com site. You can use it as well, I am just waiting for your build pictures with exact components where to be placed and the trimmer adjustments, right free time on the weekend night
sachu888
Well-Known Member
Posting few pics of Joshua's build.
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Regards
Sachin
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Regards
Sachin
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Some pointers to be followed while building your Kuartlotron buffer:
1) General layout: choose a decent-sized cabinet. If you're planning to house both power supply unit and the buffer in a single cabinet, maintain the furthest separation between the PSU/transformer and the Kuart board. Physical separation helps avoid interference from PSU to the sensitive electronic parts on the Kuart board. A panel made of mild steel sheet of 0.5 to 1 mm thickness to separate the power section and the electronics section will further help in isolation.
In my case, I'm using a mild steel sheet cabinet, 12 inch wide, 8 inch deep, and 3 inch height. For separation I use two panels of 2 mm thick aluminum sheet (I already had the aluminium sheet, so didn't want to waste it). The electronics section in my case needs more space because I have put both source selection switch and potentiometer inside the cabinet, as close to the board as possible to avoid longer run of signal wires. I'm not sure how much benefit this will bring, but one thing it has surely done is to make the build that much more complicated. Recommended only for intrepid buffer builders
2) Internal cabling:
(a) for AC power cables, make sure that wires from IEC socket to the transformer or front panel power switch (if you plan to use one) must be neatly twisted together, and routed as neatly as possible. Use cable ties where appropriate. You can also use self sticking cable guide stuck to panel to route cables. Buy a good quality; you don't want the sticky side peeling off after some months.
(b) Terminate power cables with appropriate spring loaded lugs so that you can securely plug it into the IEC blade terminals. A loose connection is dangerous. Sparking power connections can cause fire.
(c) Internal signal wiring: There are two choices for signal wiring - shielded balanced cable, and twisted pair. If you plan to use shielded balanced cable, do follow a good wiring practice as follows:
Input RCA socket has two leads, namely, signal lead (center) and return lead (barrel). Strip the shielded balanced cable by about 3/4" and dress the two leads. Select a portion of the shield and twist it tightly so that the thickness of the twisted shield is about the same as the other leads (typically 23-24 AWG). Cut off the unused portion of the shield and dispose off. Use appropriate size heat shrink to insulate the shield you just twisted. Solder red wire of the balanced wire to center pin of RCA socket, and the other wire (could be black or blue or white) to barrel connector of the RCA socket. Do not solder the shield to anything yet.
Now, for a moment consider the flow of the signal from the RCA input socket to the source selector (if you plan to use one), then to the circuit board. The RCA socket in this case is the beginning of the circuit, and the circuit board is the destination. Similarly, for the output wires from circuit board to output RCA sockets, the source is the circuit board and output RCA socket is the destination. So the definition of source-destination is case based.
What we are going to do is ground the shield to the equipment chassis at the SOURCE end of the wire only, and leave it open at the destination. This is to avoid any ground loop in the signal path.
After you have made all wiring connections from input RCA sockets to board, and board to output RCA sockets, run a wire which must connect all the shield leads at the SOURCE end only. Cut a small section of this wire near the shield of the signal wires and solder it. The end of this shield wire must be connected to chassis by lug and screw. Scrape off any paint or insulation or anodising on the cabinet where the screw must be fastened. The shield has to be electrically grounded to the chassis. The lug must touch the raw part of the chassis. Use two nuts for extra security.
If you use simple unshielded twisted pair, you can't do the above grounding. So consider using shielded twisted balanced pair as the better option. If you take good care in routing wires, even unshielded twisted pair will also produce very good noise immunity. Your choice
Another good practice is to bundle the return wires of all input left channels into one, and run this single wire to the circuit board. Remember the circuit board has only one left input and only one right input. If you must use multiple sources, you can use a simple 2-way, 4 to 6 throw rotary source selector like I did (can explain in more details if anyone is interested in using this type of source selector - FWIW, it works beautifully for me) Or you can use active relay based source selector.
Similarly, bundle all return wires of right input channels and solder this single wire to right ground input point on the circuit board. In my experience, this practice seems to improve crosstalk separation, leading to better image separation.
Mains safety:
The earth pin of the IEC socket MUST be grounded to the chassis. This is a good safety practice. In case of inadvertent shorting, current will be drained to the earth.
Regarding populating components on the board, the board is very well marked by part numbers and values. And Sachin has sent parts properly labeled. So it is just a case of putting the correct part into the board and soldering it. I don't think anyone will have a confusion, but if there are specific doubts, please post. One point to note - since this circuit board contains both left and right channels, the component numbers are not repeated. For example, R2 of left side is not labeled R2 on right side. But there should be no confusion as the layout of the right is just a copy-paste of the left, so you can visually confirm.
Hope this helps. In case anyone has doubts, please feel free to ask.
1) General layout: choose a decent-sized cabinet. If you're planning to house both power supply unit and the buffer in a single cabinet, maintain the furthest separation between the PSU/transformer and the Kuart board. Physical separation helps avoid interference from PSU to the sensitive electronic parts on the Kuart board. A panel made of mild steel sheet of 0.5 to 1 mm thickness to separate the power section and the electronics section will further help in isolation.
In my case, I'm using a mild steel sheet cabinet, 12 inch wide, 8 inch deep, and 3 inch height. For separation I use two panels of 2 mm thick aluminum sheet (I already had the aluminium sheet, so didn't want to waste it). The electronics section in my case needs more space because I have put both source selection switch and potentiometer inside the cabinet, as close to the board as possible to avoid longer run of signal wires. I'm not sure how much benefit this will bring, but one thing it has surely done is to make the build that much more complicated. Recommended only for intrepid buffer builders
2) Internal cabling:
(a) for AC power cables, make sure that wires from IEC socket to the transformer or front panel power switch (if you plan to use one) must be neatly twisted together, and routed as neatly as possible. Use cable ties where appropriate. You can also use self sticking cable guide stuck to panel to route cables. Buy a good quality; you don't want the sticky side peeling off after some months.
(b) Terminate power cables with appropriate spring loaded lugs so that you can securely plug it into the IEC blade terminals. A loose connection is dangerous. Sparking power connections can cause fire.
(c) Internal signal wiring: There are two choices for signal wiring - shielded balanced cable, and twisted pair. If you plan to use shielded balanced cable, do follow a good wiring practice as follows:
Input RCA socket has two leads, namely, signal lead (center) and return lead (barrel). Strip the shielded balanced cable by about 3/4" and dress the two leads. Select a portion of the shield and twist it tightly so that the thickness of the twisted shield is about the same as the other leads (typically 23-24 AWG). Cut off the unused portion of the shield and dispose off. Use appropriate size heat shrink to insulate the shield you just twisted. Solder red wire of the balanced wire to center pin of RCA socket, and the other wire (could be black or blue or white) to barrel connector of the RCA socket. Do not solder the shield to anything yet.
Now, for a moment consider the flow of the signal from the RCA input socket to the source selector (if you plan to use one), then to the circuit board. The RCA socket in this case is the beginning of the circuit, and the circuit board is the destination. Similarly, for the output wires from circuit board to output RCA sockets, the source is the circuit board and output RCA socket is the destination. So the definition of source-destination is case based.
What we are going to do is ground the shield to the equipment chassis at the SOURCE end of the wire only, and leave it open at the destination. This is to avoid any ground loop in the signal path.
After you have made all wiring connections from input RCA sockets to board, and board to output RCA sockets, run a wire which must connect all the shield leads at the SOURCE end only. Cut a small section of this wire near the shield of the signal wires and solder it. The end of this shield wire must be connected to chassis by lug and screw. Scrape off any paint or insulation or anodising on the cabinet where the screw must be fastened. The shield has to be electrically grounded to the chassis. The lug must touch the raw part of the chassis. Use two nuts for extra security.
If you use simple unshielded twisted pair, you can't do the above grounding. So consider using shielded twisted balanced pair as the better option. If you take good care in routing wires, even unshielded twisted pair will also produce very good noise immunity. Your choice
Another good practice is to bundle the return wires of all input left channels into one, and run this single wire to the circuit board. Remember the circuit board has only one left input and only one right input. If you must use multiple sources, you can use a simple 2-way, 4 to 6 throw rotary source selector like I did (can explain in more details if anyone is interested in using this type of source selector - FWIW, it works beautifully for me) Or you can use active relay based source selector.
Similarly, bundle all return wires of right input channels and solder this single wire to right ground input point on the circuit board. In my experience, this practice seems to improve crosstalk separation, leading to better image separation.
Mains safety:
The earth pin of the IEC socket MUST be grounded to the chassis. This is a good safety practice. In case of inadvertent shorting, current will be drained to the earth.
Regarding populating components on the board, the board is very well marked by part numbers and values. And Sachin has sent parts properly labeled. So it is just a case of putting the correct part into the board and soldering it. I don't think anyone will have a confusion, but if there are specific doubts, please post. One point to note - since this circuit board contains both left and right channels, the component numbers are not repeated. For example, R2 of left side is not labeled R2 on right side. But there should be no confusion as the layout of the right is just a copy-paste of the left, so you can visually confirm.
Hope this helps. In case anyone has doubts, please feel free to ask.
Thanks a lot Sachin. If you can still edit your above post, can you kindly name the pictures as 1, 2, 3 etc from top to bottom, so that it will be easier to identify them for any further explanation. Thanks again:thumbsup:
sachu888
Well-Known Member
Joshua, excellent build and nice write up. Congratulations.
Only one thing I felt odd - why those PCB snap on spades soldered? It is unwarranted. You can directly solder wires to PCB anyway.
Try rotating buffer PCB 90 or 180 degrees Clockwise. Either make make PS pads towards PS or front. This will either make volume control pads towards Volume Potentiometer.
For everybody - try keeping wires near bottom of chassis. Rotate potentiometer such that pins pointing downwards. No flying in air of twisted wires. Anyway you are following most of it.
Only one thing I felt odd - why those PCB snap on spades soldered? It is unwarranted. You can directly solder wires to PCB anyway.
Try rotating buffer PCB 90 or 180 degrees Clockwise. Either make make PS pads towards PS or front. This will either make volume control pads towards Volume Potentiometer.
For everybody - try keeping wires near bottom of chassis. Rotate potentiometer such that pins pointing downwards. No flying in air of twisted wires. Anyway you are following most of it.
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I did this mainly for my own convenience. In the past, I've had problems when desoldering such connections, so I used snap on spades. My internal wiring is not final. I will change it if I don't like the sound after some burn in. It is definitely easier to solder or desolder with this arrangement
spirovious
Well-Known Member
Congrats Joshua, that's nice build.Thanks.
After typing such a long post, I forgot all about adjustments:lol:
Before making adjustments to the Kuart board, first adjust the DC output voltages of your power supply. Trim them as close as you can to +10V and -10V, measured at the output terminals of the power supply board, or at the DC input terminals of the Kuart board.
Here are the steps recommended by Keantoken:
The Kuartlotron
1) determining the correct value of R1 (=R2) based on the Vbe of Q4 and Veb of Q3 - measure the voltage drop across the base and emitter pins of transistor Q4. Note down this value. Positive probe of multimeter must be connected to base, and negative probe to emitter. Similarly, measure voltage drop across emitter and base of Q3 (positive probe on emitter). Note down value. Repeat for the other channel.
R1 = R2 value must be [60 + (Vbe of Q4 - Veb of Q3)]/1mV.
For example, I got 60.XXX ohms for both channels with measurement. The circuit specifies R2 as 56 ohms, so there is a slight variation but nothing to worry about. If one has a resistor closer in value to the calculated value, out can be used in place of R2. But the variation here is less, so no need to bother.
I use transistors I purchased earlier, and not the ones sent by Sachin. The hFE values of my transistors and those received from Sachin are quite different, so your measured values may differ from mine. The above numbers are for guidance purpose.
Note: to measure the above voltage you may have to extend the tip of your probe by a thin solid core wire to be able to accurately touch the transistor pins.
2) next, short the left and right inputs and adjust value of trimmer R5 so that the reading at test point TP is exactly half of input DC voltage.
3) with inputs still shorted, measure value of DC offset at the output RCA sockets. Aim for zero mV but any value below 10 mV is OK. Adjust the offset with trimmer R1. I got offset of 0.012 to 0.015 mV after trimming. What we are doing here is to ensure that the buffer does not produce unwanted DC voltage on its own (which is why we measure with no input and input terminals shorted), which can damage the speakers after it is amplified by the power amplifier section. Of course this will not protect against DC voltage produced by the source itself!
Remove input shorting wires, and your ready to rock!
A quick note on mounting the four transistors on the board: Q4 and Q2 must be thermally coupled so the flat surfaces must touch each other. When you solder the transistors, bend the pins such that they fit snuggly in the holes, don't push them too deep. Let the legs be visible so that your multimeter probe can touch it for Vbe and Veb measurements. Place both transistors on the holes, and solder only one leg each, then when they're no longer movable, press the two transistors together so that the flat faces touch each other, then solder the remaining pins of the transistors. This will equalize the heat of the two transistors.
Ditto for Q3 and Q1.
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Pic.6
Note on wiring return leads - note the green wires which are the return lead from input RCA socket directly shorted to the return wire from source selector to input of board. The return lead is intentionally not passed through the source selector for safety reason - in case the source selector fails for whatever reason, the return leads which are NOT passed via the switch will continue to ground any high voltage that may come from source. The chances of the source selector switch suffering a catastrophic failure may be remote, but it is better to be prepared for this eventuality.
I have four inputs, three yet to be wired. So when I eventually wire them up, the return leads of all left channel of all four inputs wires from input RCA sockets will be shorted near the source selector switch (as you can see in the photo above), then these four will eventually be connected to return lead from source selector to board.
Ditto for right channel return leads.
One may ask why go through all this trouble, and why not just short all left return leads and run a single wire from the nearest RCA socket direct to board? Well, it can be done but since we are using twisted pair wiring, separating the signal and return leads will lose the noise rejecting benefits of the twist. Hence we maintain the twist as much as we possibly can.
Enough of all this nonsense. Now please go build your Kuartlotrons
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Pic.9
And that is how NOT to wire up your power supply section. I re-used the red-white wire pair from my previous Kuart build where the front panel switch was much further. I wanted to shorten the wire to smarten up the wiring mess but don't have lugs at the moment. Hence the extra, coiled length.
@jls001, I think we can just replace the DCB1 with this buffer, can you also point out the C,CW etc (-/+) connections from the pot that needs to be connected to one of the inputs (R23, 25K).
@Sachin, in your kit I see that you have provided 4.7M for R20/R9 but the board specifies 2.7M. Can I use the 4.7M for R20 and R9?
@Sachin, in your kit I see that you have provided 4.7M for R20/R9 but the board specifies 2.7M. Can I use the 4.7M for R20 and R9?
Om had confirmed that the hole closest to the letter "quad" is CCW.
Parallel two 4M7 to get about 2M35. Or if you have a 1% or 5% resistor of 4M7, just use single value (I did).
Hmm from the build of Raghu that Sachin posted from the pictures I see that he has used a single M value for R9 & R20 and I believe he also build it from the kit supplied by Sachin. So I am not sure whether Sachin marked it correctly. Will check it out.
Thanks for the CCW part but the closest to "quad" there are 2 holes, one from R23 and the other from 25k. So which is the one goes to what and also what about the other 2 holes for each of the R23 and 25K. I believe one of these holes is a -ve value but not sure its either the centre one or the last one as their is a "-" marked in between.
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