Yet Another Newbie Gainclone

[h_andree]

PC Scope

I think most sound cards do not sample fast enough to
see oscillation (Otherwise you would hear it).

Harry

 

[JonPike]

Re: THANKS!!!

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.

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.

 

[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

 

[Kofi Annan]

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.

 

[Dennis Hui]

Hi Kofi,

18V secondaries should be fine for 4 ohm speakers.

As for adjusting the gain, you may want to have a
look at this page:

http://www.euronet.nl/~mgw/background/opamps/uk_opampgain_1.html

Cheers,
Dennis

 

[Kofi Annan]

Pictures!

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

 

[JonPike]

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..

 

[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