In the mean time Carl will send the boards I search for parts and found, that XLR on Mouser AC3FAH2-AU-B is not available. There is only AC3FAH-AU-PRE.
https://cz.mouser.com/ProductDetail/Amphenol-Audio/AC3FAH2-AU-B?qs=Lbk6Md3wKLvtE6MirwUChA==
https://cz.mouser.com/ProductDetail/Amphenol-Audio/AC3FAH-AU-PRE?qs=4QugYJNEYLdidlNgCmPpvA==
can I use it without problems? According the documentation there is missing extra groudning pin. Or can you recommend me another suitable one?
https://cz.mouser.com/ProductDetail/Amphenol-Audio/AC3FAH2-AU-B?qs=Lbk6Md3wKLvtE6MirwUChA==
https://cz.mouser.com/ProductDetail/Amphenol-Audio/AC3FAH-AU-PRE?qs=4QugYJNEYLdidlNgCmPpvA==
can I use it without problems? According the documentation there is missing extra groudning pin. Or can you recommend me another suitable one?
I bought these, but I haven't started assembling anything, still practicing with little projects for my kids so I don't mess up.
Note: This is my first project, so I no guarantee that the choices are consistent or valid, but here is my consolidated sheet -
| Neutrik | NC3FAAH2 | 568-NC3FAAH-2 | XLR Connectors 3P FEMALE HORIZ PIN 1 & GRD SEPARATE |
| Neutrik | NC3MAAH-0 | 568-NC3MAAH-0 | XLR Connectors 3P MALE HORIZ CHASS PANEL ISOL |
Note: This is my first project, so I no guarantee that the choices are consistent or valid, but here is my consolidated sheet -
Yes, I've been considering modern digital source levels. Years ago, analogue was 0.3V-0.5V, with 1V arriving probably during the 1980's. Today's digital sources can be at 3V. The BluRay/UHD players I own are about twice as loud as older CD players, or tape.
That begs a question:
Do we know the clipping voltage threshold for the preamp's input? I must say, I'm unsure if I could attenuate the incoming signal without upsetting the FR filter, as I don't design electronics by profession.Had a look at TKD's 601 and 2511 attenuation last evening. Nice, but weighted towards higher level playback. The level ramps up pretty fast in the first bit of rotation. It's a normal curve, but is shifted counter-clockwise. Based on Mr. Self's graph, it looks like the active volume accomplishes a similar curve.
Today, I measured some of Alpha's 80-cent pots. I found one gem in the 10k Ohm log version so far. The image below shows the attenuation for the complete 300-degrees of rotation, but this isn't typical of the others. The log curve is very gradual in this case and should be easy to adjust low volumes - ie the curve is widened for the first 60 degrees, shifted clockwise. In fact, I'd say this is close to perfect for me. The pot's tracks were 9080 and 10520 Ohms, and yet, the wiper positions were perfect to pass the same voltage. 1dB max L-R tracking error from -76 to 0dB, as if they were matched.
I don't want to alter the careful design of the preamp. I respect Doug Self's intuition and Carl's hard work. Humbly, I keep thinking of this reversible change, should I need more control at low levels. Hopefully another option will come with time. What I've postulated is that the low side of the pot can be instead wired to the common ground point via, next to the frequency adjust pot. That should provide a normal pot function. Is this how you completed your board with the TKD pot, Cyberpup?
When I became interrested in this preamp, there were no PCBs available. Rather than wait, I downloaded Kicad and designed my own board. The lowest value for the TDK motorized pot was 10K, so there was no need for the two LM4562s in parallel to drive it. I simply fed the output C40 to the input of A6a, eliminating C41. It looked like this:
Just a simple inverting buffer where the gain could be set with Rin/Rfeedback. The more important detail is that I placed the TDK pot after this circuit, not before, as you have suggested. Your placement would add to the loading of A3a. I am not able to answer if this additional loading would be detrimental. As noted, Mr Self's design is a carefully thought out work of art. Note also that with my placement of the volume pot after the buffer amp, the output impedance of the circuit now is the pot itself, not the low impedance of the buffer stage. It now becomes important what the circuit is driving. It may be necessary to add back the final buffer stage. I did this on the PCB that mounted the TDK pot and its drivers.
Just a simple inverting buffer where the gain could be set with Rin/Rfeedback. The more important detail is that I placed the TDK pot after this circuit, not before, as you have suggested. Your placement would add to the loading of A3a. I am not able to answer if this additional loading would be detrimental. As noted, Mr Self's design is a carefully thought out work of art. Note also that with my placement of the volume pot after the buffer amp, the output impedance of the circuit now is the pot itself, not the low impedance of the buffer stage. It now becomes important what the circuit is driving. It may be necessary to add back the final buffer stage. I did this on the PCB that mounted the TDK pot and its drivers.
Update: I realized I had a version of the tone control circuits captured in LTspice. Easy enough to add a volume pot as a load to ground after what would be A3b and see what happens. Turns out not much: distortion virtually unchanged. So I would say go ahead and give it a try. Quite unlikely to produce smoke!
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Hi Cyberpup,
It probably looked unusual at first, but I think your simulation cleared the air around it.
I’ll try to explain. In the original layout, inverse signals on each end of the pot track were used to create a negative impedance to put a log curve in the middle of the linear pot. It’s a beautiful thing. The cost is it created a load impedance far lower than the pot’s track resistance for A3a at high volume pot positions (about 1K), and did the same to A7a+A7b at low volume positions (383 Ohms). They performed perfectly even so in the article.
So, what I’ve done in the diagram is simply not connect (NC) the output of A7a+A7b to the pot. With the output of A7a+A7b no longer superimposed back on A3a, the load seen by A3a becomes the full resistance of the pot’s track at low volume wiper positions, and at high volume wiper positions the load becomes the 47K shunt at the and non-inverting input of A6a, itself about 1Meg. A7a +A7b now only see the balanced output buffer.
The value of C40 appears a bit large now. Minor detail. The passive vol gives a slower increase in volume early in its rotation.
Check out this active volume arrangement, but change the 12K to 11.5K. -V0 isn’t connected to anything and is merely available if you needed a balanced negative source. This gives a true, tailorable log curve.
It probably looked unusual at first, but I think your simulation cleared the air around it.
I’ll try to explain. In the original layout, inverse signals on each end of the pot track were used to create a negative impedance to put a log curve in the middle of the linear pot. It’s a beautiful thing. The cost is it created a load impedance far lower than the pot’s track resistance for A3a at high volume pot positions (about 1K), and did the same to A7a+A7b at low volume positions (383 Ohms). They performed perfectly even so in the article.
So, what I’ve done in the diagram is simply not connect (NC) the output of A7a+A7b to the pot. With the output of A7a+A7b no longer superimposed back on A3a, the load seen by A3a becomes the full resistance of the pot’s track at low volume wiper positions, and at high volume wiper positions the load becomes the 47K shunt at the and non-inverting input of A6a, itself about 1Meg. A7a +A7b now only see the balanced output buffer.
The value of C40 appears a bit large now. Minor detail. The passive vol gives a slower increase in volume early in its rotation.
Check out this active volume arrangement, but change the 12K to 11.5K. -V0 isn’t connected to anything and is merely available if you needed a balanced negative source. This gives a true, tailorable log curve.
I have been searching this thread and see several topics about the front panel and chassis. However in the threads it seems people are tweaking the fitment of the front and rear panel to match up with the surface mounted PCB parts . I am not that creative when it comes to design and layout of equipment. So can some one either point me to the thread or provide me with front panel file and rear panel file, along what 1RU encloser info that works best? I am a noob please be gentle with responses
Regards
Frank
Regards
Frank
Hi Frank and welcome! I too am relatively new at this. Have a look at post 1967. If you like what you see I am happy to send you fpd (front panel designer) files for both the front and rear panels. These are based on the HiFi2000 1U Slimline enclosure with 10mm thick front panel, which presented several challenges. I will warn you that my approach was not the most straightforward - requiring minor changes to the PCB components and sending the blank panels off to Schaeffer. Would have been much easier with a 3mm front panel. You will need to do a certain amount of design work re power switch, power inlet, etc - I am not aware of any true plug and play solution.I have been searching this thread and see several topics about the front panel and chassis. However in the threads it seems people are tweaking the fitment of the front and rear panel to match up with the surface mounted PCB parts . I am not that creative when it comes to design and layout of equipment. So can some one either point me to the thread or provide me with front panel file and rear panel file, along what 1RU encloser info that works best? I am a noob please be gentle with responses
Regards
Frank
It is a great preamp and well worth the effort. I use mine daily in my main system.
Best,
Mike
PM sent.Hey Mike,
Sorry if you could send me the files would be great was reading your response and I thought I had the files ! thanks in adv!!!
Regards Again
Frank
Hi Carl
Is the kit Still available ? Or at minimum the pcbs or gerber files ?
Regards
Georges
This thread and the PCB kit that I supply is based upon circuit fragments published in Linear Audio #5 e-magazine and not the 'Preamplifier 2012' as published previously by Elektor.
In my mind Linear Audio was the perfect magazine for this hobby. I wish Jan Didden could be lured to start publishing it again. I know that you were an overworked 'one man band', but I do miss the product of your hard work.
In my mind Linear Audio was the perfect magazine for this hobby. I wish Jan Didden could be lured to start publishing it again. I know that you were an overworked 'one man band', but I do miss the product of your hard work.