| Kofi Annan |
With some initial guidance concerning basic electricity from a few forum members, extensive studying and research on Decibel Dungeon and forum posts (I used Llammas' post here ), I have made a semi-crappy attempt at my first amplifier-- a Gainclone.
Thanks to all who participate in this forum. The guidance I received here has been indispensable. While I realize that my amps (still need to make a box for the other one) will not be a showcase piece at an audiophile convention it means a lot to me that they are completed. I had absolutely no experience in electronics until I began to study basic electricity three months ago. I built a few low-power amps along the way to get used to soldering and to gain an understanding of the basic concepts (Example: your thumb and forefinger make a really bad signal ground), but I have completed this due in large part to the posts and the responses to my questions that I received in this forum.
Of course, I have a few more questions:
1. There is a rather annoying "power-down thump" in the amp. From what I have read on the forums this will not damage the speaker, but I'd like to get rid of it if I can. Any suggestions?
2. I don't have a "star ground" per se and I don't notice any ill effects. Is there a side effect that I will not notice that will eventually kill me and my family or damage my speakers / amp?
3. I get a little (VERY little) RF interference in the amp. Since I don't really want to rewire the whole thing, can I line the case with foil and get away with a moderate amount of shielding?
4. I have kinda crappy Technics speakers (I'm slowly upgrading all of my audio equipment from the Sears specials I own to something a little more reasonable) and I notice that the highs sound like they're (novice talk here) "tearing" the tweeter. Does this sound like just a crappy speaker or could it be the source, speaker cables, RCA cables, etc.? Maybe I need a line level preamp? I'd also like to build a set of speakers next-- can anyone recommend a cheap / inexpensive DIY speaker kit or design?
By the way, I know that the electrical tape holding the panel mount fuse is unacceptable. I plan to change this soon, but I wanted to make sure it worked in the box.
Thanks again for all the guidance and thanks in advance for any additional remarks or "constructive criticism" you can offer. |
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| Kofi Annan |
Another photo of my ghetto GC and one more comment. My favorite part of this construction came three days ago when I went to my local electronics shop. I needed something to act as legs / feet for the amplifier box so I talked to the crusty old barnacle behind the counter and the conversation went like this:
Me: Excuse me, but do you have rubber feet?
Barnacle: Yes, I do.
I really enjoyed that. |
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| sss |
| quote: | Originally posted by Kofi Annan
Another photo of my ghetto GC
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nice one :) :) :) |
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| analog_sa |
| Stunning workmanship indeed. Bet it sounds as good as it looks. |
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| hacknet |
| try shortening the wires between the cap and the chip, i`ve got better sound with shorter leads. |
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| B.I.G |
A prototype board could have been more confortable .
With your conections you can get your amp dead :dead: if you use p2p you should make sure that all the components are rigid . |
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| Kofi Annan |
I know I'm in for some rewiring. This was my first real attempt at a project so while i planned to make it neat, I wound up settling for this.
I'm waiting for some enclosures to show up. When I transfer this from the prototype box to the real enclosures, I'll plan the rewiring effort and make sure all the components are secured and the wiring is rigid.
I fixed the "power-down thump" and I found the cause of the tweeter "tearing", but I'd still like some answers to my other questions, if anyone would be so kind.
Learning. Always learning. |
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| fedde |
It would surprise me if your amp is not oscillating like hell...
Really, try to build it 10x more compact! Solder all wires, avoid connectors. Some more information about layout can be found on my website (see below). If you don't want to make it more compact with PP try PCB's...
BTW: my experience is that oscillation often causes power down thumps.
Ciao,
Fedde |
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| Kofi Annan |
Thanks for the advice. I was concerned about buiding the power supply too close to the chip, but if you think I can compact it, I'll make sure that I get it closer.
I'll rewire once I get the new enclosures. Also, thanks for the link to your site-- I've been there before and its very helpful.
I thought about PCBs, but I thought they might have been more trouble than they were worth. Now that I see the outcome from my point-to-point debacle, I'll PCB in the future.
Any advice on a DIY home speaker kit (cheap / inexpensive one. preferrably)? |
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| fedde |
The location of the transformer and bridges is ok, I wouldn't put them too close to the opamp. I would connect the supply wires on the same side of the connect block as the wires from the bridges. Then the wires will make direct contact. Put the large caps as close as possible to the opamp, and the feedback resistor even closer...
In the beginning I didn't like the idea of PCB's too, but now I wouldn't make an amp without. Especially when you regarly modify your amp, the solder connections of a PP amp can get bad... (it's really hard to make good star grounds with five wires in the air you know...)
Fedde |
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| Kofi Annan |
Aha! That makes sense. OK-- I'll rewire the supply leads and the filter caps per your advice.
BTW, how can I test for oscillation? I'm imagining that its not something I can hear, but will eventually destroy my speakers. |
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| Ropie |
>> BTW, how can I test for oscillation? I'm imagining that its not something I can hear, but will eventually destroy my speakers.
You can test for oscillation with an oscilloscope - if you had one you would probably know that so I'm asuming that you don't (have one). To try and cure it put a Zobel network in, consisting of just a capacitor and resistor in series. One end (the resistor) goes on the output of the 3875 and the other end (the cap) goes to the power star ground point.
Usual values for R, 2.2 - 10 ohm
Usual values for C, 100nF - 470nF
A good choice might be 220nF and 4.7ohm but will depend on your set-up and will require some experimentation. Oscillation is unlkely to destroy your speakers but can do damage if severe enough. The 'tearing' sound you refer to could be a damaged speaker but without hearing it I couldn't be sure.
For RFI rejection, line your wooden case with a thicker brand of kitchen foil. Then the earth connection from the mains is connected directly to the foil and a connection is made from this to the power ground star via a 100R resistor with a 0.27uF cap. conected across it (in parallel).
A 'star ground' will not kill you if it doesn't look like a star, it can be a bar of metal (as you have) to which everything is connected, or it can just be a big blob of solder ;) However, i would think that keeping it as small as possible is a good idea.
As for case size/wire distances, I wouldn't worry too much about this - it's better to have a case that is too big than too small to work with. If you are worried about your transformer being close to the chip then you could try putting a piece of metal (atleast a few mil thick) across the case between the transformer and the chip(s). However, as fedde says, do make sure that the big caps and fb resistor are as close to the chip as possible, to keep lead-out lengths very short. |
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| Kofi Annan |
Thank you! Thank you! Thank you!
The schematic I'm using has an 18K resistor to ground in lieu of a Zobel network, so I'm guessing I can replace the resistor with the resistor / cap combo and be OK.
Has anyone used the PC oscilloscope program before? I think it works off your sound card. I'd just like to know if its worth the time and effort to set it up or if it sucks eggs.
It sounds like the aluminum bar is at least an OK idea, so I'm batting about .079, by my calculations (that's a baseball joke; for international crowd-- this may be translated to "LBW" for cricket, I think). I may try to PCB this so I can make the layout neater (or at least, not such a disaster).
I'm also waiting for my Bugle phono preampifier PCB (it may come today). This is from Hageman and I've heard it is a great value for the money ($30 for PCB, $30 for parts-- CHEAP, CHEAP, CHEAP!!).
Any other suggestions? Any cheap DIY speaker projects you (plural) can recommend?
Thanks again for all the advice and for being nice about my GhettoClone. I need some positive reinforcement-- my wife is getting low on positive reinforcement these days. |
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| Ropie |
Hi Kofi (obviously your real name :D) Don't worry about the look of the wiring - take a look at the Decibel Dungeon Gainclone Gallery ( http://www.decdun.fsnet.co.uk/gcgallery.html ) and you can see my first wiring effort ;) . These days I'm not much better but all my gainclones have sounded absolutely great to my ears. Don't think you'll get better sounding amps with a pcb - you'll just get a more compact layout.
For a small diy speaker, have alook at thi sthread that I started a few weeks ago ( http://www.diyaudio.com/forums/show...&threadid=28403 ). |
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| JazzzSpazzz |
| quote: | Originally posted by Kofi Annan
Any other suggestions? Any cheap DIY speaker projects you (plural) can recommend?
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For some well designed, relatively cheap speakers, try
www.speakerbuilder.net
& take a look at the "Dayton Budget 2 way". Its gotten rave reviews and will run about $100 for a pair (plus box). For the ultimate in cheap, try this link & look for "Dan Carroll's UBHT":
http://members.tripod.com/dcarroll95624/id27.htm
I apologize for the pop-ups (even though its not my site!), but the design is very nice, esp. for the cost. I built a pair with my daughter and the drivers/XO bits cost me ~$17 each speaker. It is a MTM using "buyout" 4" woofers from PartsExpress.com and tweeters now available at ApexJr.com. The impedance is 4 Ohm--take warning--not all amps will like this. If I could figure out how to put that smile face with the hammer in a post--here is where it would go! I ran it on a late 1970's Scott without any problems. also see the following link for more speaker designs using the cheap woofer:
http://www.ipee.com/NSB/NSB.html
Have fun!
Cheers,
Bret Morrow |
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| Kofi Annan |
Alright! Thanks for the vote of confidence. I was beginning to think I had tarnished the principles of DIY audio forever.
I will move the caps closer, but I'll probably leave it at that (actually, I'll likely shorten a few wires... one of the resistors has about a 9 mile length of wire [14.48 kilometers, metric])
I'm not sure why its so hard to believe that the Secretary General of the United Nations can leverage his skill in international conflict resolution in the DIY home audio realm.
Thanks also for the link to the cheap speakers, JazzzSpazzz (your post showed up whil I was responding to Ropie's). I'm definitely going to build a set, its just convincing the wife that its its a worthwhile use of the bonus I received for my work on the Iraqi Loya Jirga.
I'm thinking I can run my Gainclone on 4 ohm speakers since my power supply is only +/- 18V. Does that sound right?
Thanks again to all! |
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| Ropie |
| quote: | Originally posted by Kofi Annan
I'm not sure why its so hard to believe that the Secretary General of the United Nations can leverage his skill in international conflict resolution in the DIY home audio realm. |
Yes, I can believe it, in fact I have my suspicions that you have been drafted in by the moderators to restore calm to the inverting vs. non-inverting camps. The words "your", "work", "cut" and "out" spring to mind :D
As to your q about 4 ohms / 18V, I think you will be OK, but I am not totally sure - someone will set us straight.... |
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| fedde |
It would be more convincing if you'd make a picture of yourself holding the gainclone... :D
Fedde |
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| Kofi Annan |
I have a meeting with Hamid Karzai this afternoon :dead: and I must wrap up some negotiations with Beijing :hot: , but I should have time to take a photo of me with my Gainclone tonight.
Also, any thoughts on the PC oscilloscope program? Anyone ever used it?
Kofi |
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| fedde |
I have not used a PC scope yet. But I'd think you need a very good sound for it (not the standard SBlive ones). Anyway, you'll need see oscillations on it because they are in the kHz or MHz range!
Fedde |
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| h_andree |
I think most sound cards do not sample fast enough to
see oscillation (Otherwise you would hear it).
Harry |
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| JonPike |
| quote: | Originally posted by Kofi Annan
Thank you! Thank you! Thank you!
The schematic I'm using has an 18K resistor to ground in lieu of a Zobel network, so I'm guessing I can replace the resistor with the resistor / cap combo and be OK. |
The Zobel will help with general stability, tho maybe not oscillation. Shortening your feedback path, as well as some of the others (audio path) and putting on some small value bypass caps (.1uF) very close across the power supply pins of the chip will.
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Has anyone used the PC oscilloscope program before? I think it works off your sound card. I'd just like to know if its worth the time and effort to set it up or if it sucks eggs.
It sounds like the aluminum bar is at least an OK idea, so I'm batting about .079, by my calculations (that's a baseball joke; for international crowd-- this may be translated to "LBW" for cricket, I think). I may try to PCB this so I can make the layout neater (or at least, not such a disaster).
I'm also waiting for my Bugle phono preampifier PCB (it may come today). This is from Hageman and I've heard it is a great value for the money ($30 for PCB, $30 for parts-- CHEAP, CHEAP, CHEAP!!).
Any other suggestions? Any cheap DIY speaker projects you (plural) can recommend?
Thanks again for all the advice and for being nice about my GhettoClone. I need some positive reinforcement-- my wife is getting low on positive reinforcement these days. |
PC O-scope programs can be easy to use and set up.. haven't been using any recently, tho. Their limitation is that since you are using your sound card, you only have the audio range available to you. So you can see if you're clipping or distorted, but if you have some several MHz RF oscillation going on, you won't have a clue. That's where the REAL 'scope comes in, or one of the PC ones that uses special hardware instead of the sound card.
I got the Bugle kit.. it's extremely good for the price range. AudioXpress magazine did a shootout with several other econo and kit preamps, costing up to $250, the Bugle was the far ahead winner of the pack. Very simple to build, well documented, and Jim is a nice and helpful guy. Couple of tips, you might want to put IC pins (get good machined pin sockets to steal from) in some of the part places, then you can easily change gain values, cartridge loading caps, till you find out what's best for your setup. As well as the IC's themselves, so you can go DIY crazy and try different op amps if you're so inclined. ;) Also, if you don't want to kludge together your own power supply, getting his matching one is probably an idea, it does go thru the batteries pretty fast.
And, though I haven't built them (yet), the already mentioned WJ's Dayton Budget's or his Dayton III's are cheap and well thought of in the speaker building community. |
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| Kofi Annan |
Thanks again for the advice!
I already have a .1uF cap across the PS pins, but I'll shorten the signal path and put the PS caps / feedback resisitor closer. I have to say, I am really impressed with the sound quality as it is, but I started this thing only partly for listening. Mainly, I built it so I can mess with it and gain an understanding of audio design, so I'm kind of glad to hear that I should rework it.
I think I'm going to try the PC oscilloscope just to see how it works (unless there's a really cheap oscilloscope out there; from what I've seen, they're all our of my price range).
That's a great idea about the putting the socketed IC pins on the board-- I never would have thought of that! Since you have the Bugle, let me ask yet another question.
I know the schematic is set for 40dB but that you can change a few values (probbaly resisitors?) and get it up to 60dB. Have you done this? Do you know what I would need to change?
I haven't received it yet and I am chomping at the but to get my hands on it. I have not been able to listen to any vinyl for a while and I'd really like to see how it sounds on my Ghettoclone.
Also, glad to hear about the Dayton Budgets being a nice choice. I am also thinking about a Voigt (sp?) pipe. Anyone had any experiences with these? Do they just look cool or do they really sound as good as they say?
Yours in questions,
Kofi |
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| Kofi Annan |
| quote: | | I am chomping at the but to get my hands on it |
Correction: I am not chomping at the but. I am chomping at the bit.
Thats "bit".
Yikes. |
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| Kofi Annan |
Thanks for the link, Dennis.
As promised, for those who doubted my true identity here's a photo of me, Chirac and a few friends posing with my new Ghettoclone at a conference in Geneva.
Chirac said I should have gone with the valve-buffered version, but as I told him, I'm working my way toward tubes, but I'm not there yet.
Kofi |
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| JonPike |
| quote: | Originally posted by Kofi Annan
Thanks again for the advice!
[snip]
That's a great idea about the putting the socketed IC pins on the board-- I never would have thought of that! Since you have the Bugle, let me ask yet another question.
I know the schematic is set for 40dB but that you can change a few values (probbaly resisitors?) and get it up to 60dB. Have you done this? Do you know what I would need to change?
I haven't received it yet and I am chomping at the but to get my hands on it. I have not been able to listen to any vinyl for a while and I'd really like to see how it sounds on my Ghettoclone.
Also, glad to hear about the Dayton Budgets being a nice choice. I am also thinking about a Voigt (sp?) pipe. Anyone had any experiences with these? Do they just look cool or do they really sound as good as they say?
Yours in questions,
Kofi |
Well.. you shouldn't need that much gain unless you have the lower output moving coil (hope I'm not mixing them up) as opposed to moving magnet type cart. Remember, 40dB gain is x10,000.. but 60dB is x1,000,000!! Most carts are the former and 40 is about right.
And yes, you just change two values, maybe four, if I remember right. Use the very convienent online calculator he has on the site.
I thought "boy, I don't know what I want" and ordered 5 extra resistor sets for different gains, and basically just ended up using the 40dB. Cart is a Shure M94E, cheap but good, fairly common at 5mv output. I was planning on outputting into a sound card, for recording to CD's and the level that worked there worked well into my amp for straight playing. If your cart has more or less output, you may need something else. Resistors are cheap, might as well get 35, 40, 45 dB or so values, and see how it goes. I went with the better OPA2134 suggested parts. I also tried AD826's, which seemed to sound somewhat better, and probably run thru the batteries even faster. The only other "tweaking" I did was to order Panasonic FC type caps for the two 220uF power filter caps, and I went to 470uF's just for the heck of it. Cost an extra buck or two..
Finally, there is a paper he wrote about getting the load capacitance right for your cart.. look in the Hagtech forums for that. Idea is, your cart's inductance, and the capacitance of the cables and whatever you add makes a filter circuit, where (usually) too much is bad, and sometimes too little as well. He's got calculators for that too, but you need to know your cart's inductance and resistance to use it. If not, work without any extra caps, usually the cableing has enough.
Digikey, where you can get all the parts, is very good on delivery.. if you want to pay for it, and call early enough in the day, they'll have it on your doorstep tomorrow.
Voight pipes.. haven't heard many direct reviews.. I think they are transmission line type speakers, (TL) and as a type, TL's have a very smooth musical bass response, and fairly low.. but not very powerful and "fast". So, very nice for jazz vocalists, acousitc instrumental stuff, but sort of disadvantaged for loud impacting stuff like rock, electronica, etc.. Depending on your tastes, maybe good, maybe not so good.
Anyway.. hope that helps.. |
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| Kofi Annan |
I have a Music Hall MMF 2.1 turntable (not the greatest, but good for a guy on a budget) and I'm sure its got a moving magnet cartridge (it says its a "Music Hall" cartridge, but I think its really a low-grade Goldring). I'll keep it at 40dB and see how it sounds.
I'll probably order various resistor values from Digikey (I agree-- they have really fantastic service. I have ordered parts from them several times and they have delivered them to my door in two days using super cheap Priority Mail) and see what I can change around.
After all this calms down, maybe I'll fashion a DAC / line-level preamp instead of speakers. My old Technics actually sound pretty good to my ears and I really prefer the electronics work over the woodworking.
Any recommendations on a good cheap DIY DAC / line-level preamplifier project? I have seen Fedde's DAC project (great websiite!) and it looks well documented and fun to build, so maybe that one unless you think a newbie can't handle it.
Again with the questions!
Kofi |
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