Unfortunately none of his software is compatible with Mac OSX, so I am stuck without it. I have used Spice before, but again, not for Mac OSX.
I am going to take you advice and go easy for the first build. Thanks!
I am going to take you advice and go easy for the first build. Thanks!
thereverend said:
But take heart... Mac sales are growing at 3 times the rate of other manufacturers, now has 5% of the US market (15% from online/retail sales) so at some point there will be enuff of us that programs like these start coming over... and until then an Intel Mac & Parallels (or VMWare or Open OS X or Crossover Mac) make a Macintosh the best quality Windows machine you can buy (unless you are gaming)
I have a copy of BrownBags Spice but it is Classic only -- it is a pretty crude & clumsy port anyway). I have only fired it up, but University of Exeter http://www.macspice.com/ has an up-to-date OS X version -- it isn't fancy thou with just a text based UI At least that this leadin University (and a growing number of others) prefer students to use Macs is a good sign for the future (as is any picture of an AES conference session, with Apple laptops hitting 50% of what is seen in front of presenters)
http://www.macspice.com/
dave
That looks very manageable, I think I have come across that before while I was actively studying circuit analysis, but I never bothered to learn it with PSpice's wonderful GUI at my disposal. Now that I am moved out of my house I have my mac, but it isn't beyond me to do a little more computer programming (something I sit around doing every day!).
thereverend said:
If you are looking for things need writing for X i might be able to fire you some useful ideas.
dave
thereverend said:
For your PSU caps, get motor run caps off of ebay...NOT motor *start*...they'll provide the best bang for the buck. Also, don't get caught up in boutique component brands for a first project - if you catch the bug, half of your resistors and caps will be swapped out within a month or two anyway. By using inexpensive components, you may just be able to afford some chinese plate chokes somewhere down the line to make a meaningful improvement to your preamp.
Ok I have a new question: On Brett's schematic, are the caps notated Auricaps the coupling caps? This is a total newbie question. Thanks!
Motor run caps are geat, if physically very large. GE and ASC are the one's I use most.pedroskova said:
As for avoiding the 'phile components, yes. The one place I would spend a few dollars is on 2 x 4kR Mills 12W wirewound resisrtors for each anode load. There's about 5W of heat/ch there and my rule of thuumb is to rate for 4x dissipation.
Arnold added that. I've used all sorts of things. Depending on the impedance of the poweramp, you may not need that value and may be able to get away with Orange drops (Sprague 716P series).thereverend said:
Cathode bypass cap should be a Panasonic FC, or you can use 5 cheap red LEDs in series with no cap to bias. When I tried this I changed the anode to 6k and the Vg up a bit by using 11 LEDs.
Colin, I made that annotation, and yes, I wrote Auricap for the coupling caps.
On PSU capacitors, you can consider Panasonic TSHA series (400, 450V). They're damn good and reliable.
On PSU capacitors, you can consider Panasonic TSHA series (400, 450V). They're damn good and reliable.
Excellent, it is great to be getting recommendations for all of these things.
Brett, you mention that I could get away with other values? Honestly, I am not really sure what the coupling capacitors do, so maybe that is why I don't understand how the value is chosen.
Speaking of which, how exactly do you decide what value you are going to be using for each component? I understand ohm's law and all sorts of circuit analysis, but we never touched design in my limited experience. Is it just based upon the amount of current needed by the tube?
Arnold, I was just starting to wonder about what PSU caps to use, so it is good to have a recommendation! I am going to be able to put together a reasonably complete BOM soon.
Last question:
What should I use for a selector switch, and where can I look at what is available? I don't mind using something heavier duty for these mechanical parts. On my SOHA I used an Alps pot (the big blue one) for the volume and I was very impressed with the sturdiness of it as well as the nice fluid motion.
Hopefully by this weekend I will have a working BOM that I can post up for review and critique from everyone. If the Auricaps are the only expensive capacitors I use and it is appropriate to splurge for coupling caps, I think I may just do so. I don't really want to go totally all out yet, but I also am not interested in going half-assed either.
Best,
Colin
Brett, you mention that I could get away with other values? Honestly, I am not really sure what the coupling capacitors do, so maybe that is why I don't understand how the value is chosen.
Speaking of which, how exactly do you decide what value you are going to be using for each component? I understand ohm's law and all sorts of circuit analysis, but we never touched design in my limited experience. Is it just based upon the amount of current needed by the tube?
Arnold, I was just starting to wonder about what PSU caps to use, so it is good to have a recommendation! I am going to be able to put together a reasonably complete BOM soon.
Last question:
What should I use for a selector switch, and where can I look at what is available? I don't mind using something heavier duty for these mechanical parts. On my SOHA I used an Alps pot (the big blue one) for the volume and I was very impressed with the sturdiness of it as well as the nice fluid motion.
Hopefully by this weekend I will have a working BOM that I can post up for review and critique from everyone. If the Auricaps are the only expensive capacitors I use and it is appropriate to splurge for coupling caps, I think I may just do so. I don't really want to go totally all out yet, but I also am not interested in going half-assed either.
Best,
Colin
The coupling cap blocks the DC that's present at the anode. The value needs to be sufficiently large to not remove any bass, The load resistance of the next stage along with the cap size determines the breakpoint F = 1/(2 x pi x R x C) where R is the next stage load and C the coupling cap. I usually aim for 1Hz.thereverend said:
Correct planetary alignments and WAGing.thereverend said:
Seriously, here's one of the best and most readable anaylses. Check out the rest of JB's site if you have a spare year.
http://www.tubecad.com/articles_2003/Grounded_Cathode_Amplifier/Grounded_Cathode_Amplifier.pdf
John also has a couple of neat software apps for doing a lot of the number crunching that are very helpful. for the most commonly used tubes.
Brett said:
How can I find the impedance of my power amp without the schematic? It isn't up at B&K's website.
Also, about the Mills, I am assuming that you are refering to the capacitor coming from the PS. Why not just use a single 8kR like notated? I found one on partsconnexion. Also, the cathode bypass cap is the one marked 50-100uF? Sorry for my confusion, these terms are pretty new to me.
Ohh, I missed this thread ...
Here's another 12B4 for your consideration 🙂
http://bb.sicomm.us/diyAudio/12B4_linestage.gif
Zout = 160 ohms.
Here's another 12B4 for your consideration 🙂
http://bb.sicomm.us/diyAudio/12B4_linestage.gif
Zout = 160 ohms.
Google.thereverend said:
http://www.stereophile.com/amplificationreviews/675/index10.html
http://www.bkcomp.com/pdf/ST140Ma.pdf
They give two different numbers so I assume there may have been a change somewhere in the product cycle. Assume the lower 24k value.
The Mills are the 8k anode resistors, and they're rated at 12W. As drawn, they'll be dissipating 5W, and I like to derate a lot, usually 4x for reliability.thereverend said:
I just checked a couple of sites and couldn't find an MRA 8kR listed. I don't have my old notebooks to hand, and I went through a number of variations of this pre, so there's every chance I used a network of resistor made up from the many I have in my parts box. Two MRA12 15k in parallel or 4 x MRA5 3kR in series will be fine. I'd do the latter as it gives the opportunity to try the 6k load I mentioned earlier. These resistor, whilst a but expensive are very high quality and tough. I reuse them in other projects if the value tested is revised.
Cathode bypasses are to 50-100u.. IIRC I used some Elna Starget electro's and later polypropylene motor run caps.
Brett said:
Thank you for answering my constant onslaught of questions! I am putting together my BOM and I really appreciate all of your advice.
The B&K ST-140 was revised in the late 80's or early 90's. The first one you gave is for the single channel version, and the circuit is probably basically the same as the amp I am running. The other was from Stereophile and written in 1984, so I am assuming that the circuit changed before it was written. How exactly does input impedance effect my design? Why didn't I have to think of this when I hooked my NAD up to it?
As for the Mills MRA, go here and look at the Mills from the bottom selector buttons, I found the MRA 12 @ 8kR for $3.50 a piece.
Best,
Colin
You didn't design the NAD did you? So if there is an output coupling cap there, the designer made a decision on what value he would use. Now you get to do the same. The output coupling cap, combined with the input impedance of the following stage forms a 6dB/octave high pass filter depending on the values. get them wrong, and you may end up with a roll off starting at 100Hz for example. Bit hyperbolic example, but none the less.thereverend said:
Forgot all about Partsconnexion. Der.thereverend said:
I'd still prefer 2x16k pralleld, 2xx 4k seriesto get the power dissipation back within my preferred derating scheme.
Brett said:
So what exactly does this red LED treatment do? Also, why would changing the anode to 6k be helpful? Sorry for my confusion here. I guess I don't understand why using an LED would give the same effect as a capacitor. I can see that a charged cap would stop current in all directions, and I know that an LED stops current in the backwards direction, thus giving a forward bias.
Next question for now as well: Lat night we talked about the input impedance from my B&K. Now just speaking in a general case, what design parameters are effected by the input impedance? In other words, what, in the case of your schematic, is a function of input impedance of the power amp?
Thanks!
Colin
LEDs have a very low AC impedance when forward-biased, on the order of 4-5 ohms. And that dynamic impedance stays low and relatively constant well into the hundreds of kilohertz.
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