abostick@gethen.UUCP (Alan Bostick) (07/18/88)
Because I fundamentally distrust snake-oil sellers in both the dealerships and the magazines, I am interested in building my own audio equipment. In particular, I am thinking of starting out with a stereo amplifier, capable of feeding at least 25 W per channel into 8 ohm speakers. I am interested in making a QUALITY piece of equipment, not something that will just do the job (Given what electronics parts cost, and given the value I place on my own time, It is simply cheaper to buy low-end equipment than to build it.) I have a fair amount of analog design and construction experience, including some low-noise techniques. I don't have experience with electron tubes, don't intend to use them, and don't want to get into a "silicon vs. vacuum tube" debate. Can anyone on the net give me some clue as to how hard or easy this might be? Are there good references (either how-to books or solid engineering texts) available for audio amplifier design? What sort of test equipment would be useful for such a project (beyond the obvious VOM, signal generator, and oscilloscope? "DIY!" Alan Bostick --Peter Gabriel ucbvax!unisoft!gethen!abostick
chris@a.cs.okstate.edu (Chris Schuermann) (07/19/88)
From article <1075@gethen.UUCP>, by abostick@gethen.UUCP (Alan Bostick): > Because I fundamentally distrust snake-oil sellers in both the > dealerships and the magazines, I am interested in building my own audio > equipment. In particular, I am thinking of starting out with a stereo > amplifier, capable of feeding at least 25 W per channel into 8 ohm > speakers. I am interested in making a QUALITY piece of equipment, not > > What sort of test equipment would be useful for such a project (beyond > the obvious VOM, signal generator, and oscilloscope? > > "DIY!" Alan Bostick > --Peter Gabriel ucbvax!unisoft!gethen!abostick There are some VERY good amps available out there, but I gather that you are more interested in building this "for the sake of doing it yourself" First, start out by finding yourself two GOOD transformers. Center tap with +- 50Volt or so. Add filtering caps and some BIG electrolytics to give you a really solid power supply. I would recomend going with a class B type amp for simplicity and greater power! I have built one using 8 stages of push-pull mosfets (They were some TO3 *case Hitachi units). I think my amp is capable of putting out over 1Kw per channel, but I couldn't find large enough transformers to do the main amp section justice :-). Ther are some audio magazines that have had artices discussing how to build clean lo-noise front ends for audio amps. I would look in your local library to find out more. I WOULD recomend building a higher power than 25W amp . If you listen to CDs at all, that 25W will run out all too quickly. The power supply seems to be the hardest part. Getting good high curre&nt transformers is expensive. My amp needed +- 140 Volt to put out full power, but I had to settle for 70V. As for test equipment, I fou nd that a 'pink" noise' generator and spectrum analyzer came in handy also. Good luck! Building your own audio stuff is really fun and rewarding! ( and also a headache sometimes :-) -- Chris Schuermann Unemployed... chris@a.cs.okstate.edu
ornitz@kodak.UUCP (barry ornitz) (07/20/88)
In article <1075@gethen.UUCP> abostick@gethen.UUCP (Alan Bostick) writes: >Because I fundamentally distrust snake-oil sellers in both the >dealerships and the magazines, I am interested in building my own audio >equipment. ... > >Can anyone on the net give me some clue as to how hard or easy this >might be? Are there good references (either how-to books or solid >engineering texts) available for audio amplifier design? Good for you Alan. You will learn a lot, have fun, and end up with an amp you can be proud of! My suggestion is that you start out with a conventional bipolar junction transistor design. Parts are cheap, the important concepts are there (and you are less likely to fry yourself with high voltages!). If you can find it (look in a large public library or an engineering college library) a good book is: RCA Designer's Handbook: "Solid-State Power Circuits" Technical Series SP-52, RCA Solid State Division, Somerville, NJ 08876 (1971). This book has an excellent chapter on audio power amplifiers. The chapter begins with the basics and ends with a "Universal-Amplifier Design Approach." After you have mastered the techniques discussed in this book, you can move up to power MOSFETS. You need to master such things as heat sinking and good power supply design (which is more than just getting a big transformer and the biggest capacitors you can find). I wish you lots of luck with your project. If I can be of help, please ask. BTW, find some local amateur radio operators and ask them about local hamfests and electronic flea markets. With some luck you can likely find most of what you need surplus for less than $50. Happy Homebrewing, Barry
wolfgang@mgm.mit.edu (Wolfgang Rupprecht) (07/20/88)
In article <1075@gethen.UUCP> abostick@gethen.UUCP (Alan Bostick) writes: >I am interested in building my own audio equipment. In particular, I >am thinking of starting out with a stereo amplifier, capable of >feeding at least 25 W per channel into 8 ohm speakers. One good reference of for a excellent "generic" power amp, is: "Build a low TIM Amplifier" W. Marshall Leach, Feb 1976, Audio Magazine *and* "Low TIM Amplifier, Part II" W. Marshall Leach, Feb 1977, Audio Magazine. This amplifier is the basic mirrored 2-transistor differential, driving a pair of common-emmitter transistors on both the + and - rails, followed by a triple darlington output stage. The really novel thing about this amplifier is that it is designed to work well with low amounts of (feedback) loop gain. All internal stages have lots of local feedback. The whole amplifier is compensated with a single-pole feed-forward circuit, which allows a relatively large high frequency cut-off. The intention is that even modest amounts of high frequency energy at the input won't cause the front-end differential pairs of this amp to be overloaded. I built up a pair of these amps using 100v transistors and +/- 50v supplies. This is good for > 200 watts into 4 ohms, and probably ~800 watts when bridged. No, I never bought enough output transistors to build the bridged version. (I do have the full power-supply, with 2Kw of 100vdc ;-) --- Wolfgang Rupprecht ARPA: wolfgang@mgm.mit.edu (IP 18.82.0.114) TEL: (617) 267-4365 UUCP: mit-eddie!mgm.mit.edu!wolfgang
mkp@luna.UUCP (Michael Peterson) (07/22/88)
I'll second the recommendation of the "Low TIM Amp" articles by Leach.
I used them as background material when I was building amps as an EE
undergrad.
People have been alluding to adequate "safe operating area" for
the output stage ("use 100V power transistors," etc.) without stating
it explicitly. The high slew rate, low distortion, 100W per side
(into a resistive load on the test bench!) amp that I built my
senior year was blown up when I pushed it hard while connected to the
transmission line speakers I built the next year in grad school ...
beware the inadequate SOA,
--
Michael K. Peterson mkp@scgvaxd.hac.com
Space & Communications Group mkp%scgvaxd.hac.com@oberon.usc.edu
Hughes Aircraft Company
213 416-0323hjortsho@cg-atla.UUCP (07/23/88)
I am interested in this discussion, but I have what I want for a home amplifier already. I am, however, interested in building CAR amplifiers. I sounds like fun and if it can be done for a reasonable price I will do it. I am looking into it regardless. I don't have any experience with this however. The references given in this group are helpfull but I whant to know how much harder it is to make car amps. Are they safe enough to stick in the car? Is the 12V (14V) power source a problem. What about heat sinks? Thanks much. Erik Hjortshoj
darrellm@pogo.GPID.TEK.COM (Darrell McGinnis) (07/27/88)
I've got one comment on power-amps when rolling-your-own. In the power supply, the bigger the caps you use the better the ripple filtering (60Hz stuff) BUT ALSO the bigger the current surge through your rectifying diodes. As the ripple gets smaller the 'conducting-time' (forward bias) of the rectifying diodes gets smaller. If the power to the load stays the same then the current during foward bias gets bigger. (lots bigger, the average current [over time] must be constant for a given load.) So, for mongo(big) use mongo rectifiers. just a thought. :) dsm
larry@kitty.UUCP (Larry Lippman) (07/27/88)
In article <5741@pogo.GPID.TEK.COM>, darrellm@pogo.GPID.TEK.COM (Darrell McGinnis) writes: > > I've got one comment on power-amps when rolling-your-own. > In the power supply, the bigger the caps you use the better > the ripple filtering (60Hz stuff) BUT ALSO the bigger the > current surge through your rectifying diodes. While I have not as yet tried this myself, I have a suggestion as to a power supply method which will totally eliminate any possibility of AC power line hum - use batteries! The problem of having large filter capacitors, inductors, etc. is also eliminated. Now, before you laugh, consider a reasonable method to implement the use of batteries: use two banks of gel cells, with one bank being charged while the other bank is in use. Consider, for example, an amplifier rated at 100 watts RMS requiring + and - 24 volt supplies. Conservatively speaking, 8 amperes per supply should be more than sufficient to assure full output power. Gel cells are readily available in 30 ampere-hour size, which should provide at least 4 hours of operation at full output power. More realistically, a 30 ampere-hour gel cell for such a 100 watt amplifier should last much closer to 8 hours of normal listening since one is hardly going to deliver a continuous 100 watts RMS. I would use a manual switch to change each bank of batteries from charger to amplifier. In fact, the charger should be capable of charging both banks of batteries simultaneously, say during the night, in order to increase listening time. I would also use a voltage comparator/alarm circuit to warn of low battery condition, so as not to run the risk of inadvertently listening to distorted sound resulting from abnormal supply voltage. The above methodology, can, of course, be applied to preamplifiers and other audio components. <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {att|hplabs|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
rbl@nitrex.UUCP ( Dr. Robin Lake ) (07/28/88)
In article <3727@okstate.UUCP> chris@a.cs.okstate.edu (Chris Schuermann) writes: >From article <1075@gethen.UUCP>, by abostick@gethen.UUCP (Alan Bostick): >> Because I fundamentally distrust snake-oil sellers in both the >> dealerships and the magazines, I am interested in building my own audio >> equipment. In particular, I am thinking of starting out with a stereo >> amplifier, capable of feeding at least 25 W per channel into 8 ohm >> speakers. I am interested in making a QUALITY piece of equipment, not >> > >There are some VERY good amps available out there, but I gather that >you are more interested in building this "for the sake of doing it >yourself" >First, start out by finding yourself two GOOD transformers. Center tap >with +- 50Volt or so. Add filtering caps and some BIG electrolytics >to give you a really solid power supply. ..... Building a power supply is too much of a chore! I've found some very hefty Lambda rack-mountable power supplies on the surplus equipment market that give just the right voltages and PLENTY of current. Relative low noise, too. "Impressive" metering. One or two needed the panel repainted or chromed (for effect). -- Rob Lake BP Research International - Research Center Warrensville uunet!nitrex!rbl mandrill.CWRU.EDU!nitrex!rbl
rpw3@amdcad.AMD.COM (Rob Warnock) (07/28/88)
Previous poster observed that big power-supply caps mean less ripple, but
also mean higher peak currents needed through diodes (and transformer, don't
forget). There are two solutions to this, one old, one new:
1. Old -- use an inductor (a.k.a. "choke") between the diodes and the caps.
This smooths out the current peaks, causing current to continue to flow
even though the voltage across the inductor is sometimes negative. This
technique is best when you have a large more-or-less-constant load, but
can be useful even with light/variable loads, particularly when combined
with "parallel" regulation (a transistor which turns on under very light
load to keep the voltage from skyrocketing). Computing the right series
inductor value can be tricky, though.
2. New -- use a much higher voltage rectifier system, with poor regulation
(smaller caps, cheaper diodes), then run a switching voltage converter
(which also uses a series inductor, see "Old" above) to step the voltage
down to your target. Also known simply as a "switching power supply".
Used to be thought bad for audio, but coming back since switching
frequencies have climbed *way* above the audio range (would you believe
up to megahertz???). (Most modern "switchers" actually rectify the 110v
input line, and step the voltage down with the switching inductor, which
becomes the isolation transformer.)
Hmmm... just thought of another, more suited to home construction:
3. "Regulate under ripple" -- Use a slightly higher transformer voltage,
slightly smaller capacitors, get more ripple, less peak diode current.
Then add series regulation (using a cheap regulator chip with a "booster"
transistor) just to regulate out the ripple. The series pass transistor
doesn't have to dissipate the whole power supply capacity, as it's
only dropping the ripple (and anyway, the input voltage drops as the
current rises).
Of the three, I think the best for home construction might be #1, the series
inductor, but you'd need to provide some kind of over-voltage limit, since
under very light load (quiet passages) the output voltage can climb to
near infinity (or high enough to kill your system).
Rob Warnock
Systems Architecture Consultant
UUCP: {amdcad,fortune,sun}!redwood!rpw3
ATTmail: !rpw3
DDD: (415)572-2607
USPS: 627 26th Ave, San Mateo, CA 94403ornitz@kodak.UUCP (barry ornitz) (07/28/88)
Larry Lippman recently proposed the use of batteries for the power supply for
audio ethusiasts. Before this is tossed off as another absurd wreck.audio
idea, consider the fact that many pieces of compact test equipment use
rechargeable batteries rather than large filter capacitors in their power
supplies. The portability feacture is "icing on the cake." NiCads have such
low internal impedances that they can effectively appear as several Farad
capacitors in power supply applications.
Now for the inane comments! Think of the prestige of having the only 250 watt
per channel boombox in the neighborhood capable of pumping out the noise for
hours and hours after a power failure. :-)
Barry
-----------------
| ___ ________ |
| | / / | | Dr. Barry L. Ornitz UUCP:...!rochester!kodak!ornitz
| | / / | | Eastman Kodak Company
| |< < K O D A K| | Eastman Chemicals Division Research Laboratories
| | \ \ | | P. O. Box 1972
| |__\ \________| | Kingsport, TN 37662 615/229-4904
| |
-----------------jasonv@xroads.UUCP (Jason Vagner) (07/28/88)
I've owned a Sony D-T3 CD player for several months now, and I am fairly happy with its performance except for one major annoyance. If I set the player out uncovered (read on) the spinning of the disk is so load that I have to grab a pillow or jacket and cover it. I'm not very knowledgable in CD technology, but the only thing I can think of is an overly loud motor - if nothing is wrong with it. Is this just an "annoying feature"? or should I send it in (I've had it since January)? Jason Vagner jasonv@xroads.UUCP ...!hplabs!hp-sdd!crash!xroads!jasonv -- \ / C r o s s r o a d s C o m m u n i c a t i o n s \/ (602) 971-2240 /\ (602) 992-5007 300|1200 Baud 24 hrs/day / \ hplabs!hp-sdd!crash!xroads!*
klein%gravity@Sun.COM (Mike Klein) (07/28/88)
| Now, before you laugh, consider a reasonable method to implement |the use of batteries: use two banks of gel cells, with one bank being |charged while the other bank is in use. Consider, for example, an |amplifier rated at 100 watts RMS requiring + and - 24 volt supplies. |Conservatively speaking, 8 amperes per supply should be more than |sufficient to assure full output power. Gel cells are readily available |in 30 ampere-hour size... More important than the ampere-hour rating will be, as for any power source you are using, the output impedance. Figure what your maximum current drain will be at what frequencies, and see if the voltage drop on the power rails will be acceptable to you. If not, you are back to the original problem with AC power supplies, which is how to reduce the output impedance (although you do not have to worry about 120 Hz ripple). The obvious solution is to use capacitors as in the AC supply -- big ones to provide lots of low-frequency current, in parallel with smaller (a few uF) high-quality film capacitors to provide high-frequency current. This is an interesting thought for a "transportable" power amplifier but with simple design techniques and good grounding you can build, for about $20-$40 if you buy at surplus stores, a very sturdy power supply for audio purposes that will have plenty of reserve, a very small output impedance at audio frequencies, and as good a 60 Hz isolation as you will need (the ripple is actually 120 Hz since the negative half of the waveform is reflected up by the bridge rectifier). I have built a number of these, one for a 100W single-channel subwoofer amplifier, another for a moving coil preamp, all of my own design, and have had no trouble with any of the above. None of the parts required are high-tech and the cost is really quite low. -- Mike Klein klein@Sun.COM Sun Microsystems, Inc. {ucbvax,hplabs,ihnp4,seismo}!sun!klein Mountain View, CA
awpaeth@watcgl.waterloo.edu (Alan Wm Paeth) (07/29/88)
In article <2627@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: > While I have not as yet tried this myself, I have a suggestion as >to a power supply method which will totally eliminate any possibility >of AC power line hum - use batteries! The problem of having large >filter capacitors, inductors, etc. is also eliminated... >... More realistically, a 30 ampere-hour >gel cell for such a 100 watt amplifier should last much closer to >8 hours of normal listening since one is hardly going to deliver a >continuous 100 watts RMS. Larry's intriguing idea has another bonus: you can continue to serenade your neighbors for many hours even after they rip out your power lines. Or for the neo-Neros: you can listen to the 1812 Overture when WWIII begins. Briefly. /Alan Paeth Computer Graphics Laboratory University of Waterloo
tomb@hplsla.HP.COM ( Tom Bruhns) (07/29/88)
I didn't notice any replies here mentioning "The Audio Amateur" as a good source of DIY audio articles. I don't even know if they are still in business, but they sure used to have a lot of really nice articles. I dropped my subscription for lack of time to do anything, not because they didn't have lots of neat stuff. Everything from the signal source to the speaker, with test equipment on the side. I did build a few channels of a friend's design -- precursor of the stuff put out by DB Systems. It helps a lot to have a PC board design, but of course you can do it point-to-point, too. We used regulated power supplies, because hum on power busses can cause very significant intermodulation when the amp is driven to clipping. Probably a better way is a clipper at the input so the amp stays linear all the time. We had a switch to go between class AB and class A; my tin ears could never tell the difference. I believe we got typical distortion in the .005% range at all powers/freq's; DB guarantees a little better than that as I recall. These are relatively low-power amps -- 30-40 watts into 8 ohms. But they can drive down below 2 ohms with no significant distortion increase, yielding more like 120 watts. That, of course, makes them good for bridging. Anyway, the point is -- yes, you can build some really good stuff yourself. If you keep your mind open as you do it, you will learn a whole lot! Tom Bruhns uucp: ...!hplabs!hplsla!tomb
jans@tekgvs.GVS.TEK.COM (Jan Steinman) (07/30/88)
<...I have a suggestion... which will totally eliminate any possibility of AC power line hum - use batteries!... use of batteries: use two banks of gel cells, with one bank being charged while the other bank is in use... use a manual switch to change each bank of batteries from charger to amplifier.> Naw, use one bank of batteries, get some Sovonics panels and run the whole thing for free! For +,- 24V, you'll need four panels, about $800 worth for a 92 watt system. Seems to me a much better way to spend money than on Hg filled wires! Perhaps you could sell these amplifiers to survivalists... :::::: Software Productivity Technologies -- Experiment Manager Project :::::: :::::: Jan Steinman N7JDB Box 500, MS 50-383 (w)503/627-5881 :::::: :::::: jans@tekcrl.TEK.COM Beaverton, OR 97077 (h)503/657-7703 ::::::
anand@vax1.acs.udel.EDU (Anand Iyengar) (07/30/88)
In article <22476@amdcad.AMD.COM> rpw3@amdcad.UUCP (Rob Warnock) writes: [topic:power supplies for audio amplifiers] >forget). There are two solutions to this, one old, one new: > >1. Old -- use an inductor (a.k.a. "choke") between the diodes and the caps. > >2. New -- use a much higher voltage rectifier system, with poor regulation > >3. "Regulate under ripple" -- Use a slightly higher transformer voltage, > slightly smaller capacitors, get more ripple, less peak diode current. Anyone in the know care to comment on how Carver handle supply?? I get the feeling that they resemble switching supplies the most, but not enough to fall into that catagory. Anand.
al@cs.strath.ac.uk (Alan Lorimer) (08/01/88)
>I've owned a Sony D-T3 CD player for several months now, and I am fairly >happy with its performance except for one major annoyance. If I set the >player out uncovered (read on) the spinning of the disk is so load that I >have to grab a pillow or jacket and cover it. I'm not very knowledgable in CD >technology, but the only thing I can think of is an overly loud motor - if >nothing is wrong with it. Is this just an "annoying feature"? or should I >send it in (I've had it since January)? Most compact disc players I've come accross tend to be quite noisy. I reckonned that part of this was due to the disk slipping on the turntable, so I experimented a bit with Electrolube SCCH3 conformal coating on the Turntable. The intention was to give better adhesion of the disk to the turntable. It did in fact work rather well in terms of noise reduction as indeed the player was *much* quieter. It did however have the unfortunate side effect of glueing the CD's in to the extent that the mechanism could no longer open the drawer. (This may be acceptable if you have only one CD :-)). I've subsequently cleaned the stuff off, as it doesn't dry sufficiently to prevent this happening, but if I find a suitable rubbery aerosol I intend to try again. Any suggestions anyone? Alan. P.S. The player in question was a Sanyo effort which has since gone down with a dead processor. Thank's Sanyo. -- ____________________________________________________________________________ Alan G. Lorimer, Strathclyde University, 26 Richmond Street, Glasgow G1 1XH. UUCP: ...!seismo!mcvax!ukc!strath-cs!al DARPA: al%cs.strath.ac.uk@ucl-cs JANET: al@uk.ac.strath.cs -- ____________________________________________________________________________ Alan G. Lorimer, Strathclyde University, 26 Richmond Street, Glasgow G1 1XH. UUCP: ...!seismo!mcvax!ukc!strath-cs!al DARPA: al%cs.strath.ac.uk@ucl-cs JANET: al@uk.ac.strath.cs
strong@tc.fluke.COM (Norm Strong) (08/01/88)
In article <61833@sun.uucp> klein@sun.UUCP (Mike Klein) writes: }| Now, before you laugh, consider a reasonable method to implement }|the use of batteries: use two banks of gel cells, with one bank being }|charged while the other bank is in use. Consider, for example, an }|amplifier rated at 100 watts RMS requiring + and - 24 volt supplies. } }More important than the ampere-hour rating will be, as for any power source }you are using, the output impedance. Figure what your maximum current }drain will be at what frequencies, and see if the voltage drop on the power }high-quality film capacitors to provide high-frequency current. ............................Deleted } }This is an interesting thought for a "transportable" power amplifier but }with simple design techniques and good grounding you can build, for about }$20-$40 if you buy at surplus stores, a very sturdy power supply for audio }purposes that will have plenty of reserve, a very small output impedance at }audio frequencies, and as good a 60 Hz isolation as you will need (the Hey, I'm surprised no one's mentioned the ultimate solution to the power supply regulation problem: 3 phase power! Call your power company now! What's a couple grand when we're talking hi-fi. Just think; no capacitors at all! Perfect regulation. -- Norm (strong@tc.fluke.com)