Commercial complete Gainclone kit for a beginner?

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#101
Peter Daniel said:
If we consider minimized circuit as in attachment, the DC offset will depend on input impedance and a chip itself. With 22k shunt resistor, the offset is usually below 80mV.

I measured at least 800 chips and offset variation (in that particular circuit) can be from 0mV to 120mV; the latter occuring for less than 2% of the chips.

If you have a potentiometer at the amp or use a preamp, the combined shunt resistance will be less than 22k and the offset goes further down, usually to less than 20mV.

So if you are certain that the source does not produce any DC offset (as it will be amplified by a factor of 30), you don't really need Ci.
Click to expand...


Thanks for the info!

What do you think of the following:

Input star ground fed by 4R

NFB 27k, and then 820 ohms

Input 22k, and then input filter cap
passive pre of, 470R, and then 1M+Alpa A20K

This is a wild guess on my part, but the intention is the following advantages:
The very good volume pot is just $1
The 470r is a compensation for that input filter cap, then. . .
The input filter cap can can be practically anything seemly from the rummage box or hobby shoppe.
The gain of 34 will work for weaker modern sources.
The resistor values come in most economy variety packs like Radio Shack's #271-312A
The 1m load at the amp board acts as a slight divider upon the input cable that leads to the pot.

This may be "too much thinking" on my part, but, if it works right, then it could skip the majority of the usual costs and troubles.
What do you think? Is it "hit" or "miss"?
 
#102
Bluto said:

From there he can make the thing simple enough for us newbees to build with limited instruction. I've agreed to write up and photograph whatever he comes up as I build it if Gychang likes the idea.

I appreciate the input of true Pro's on this as it will only help Dan design an excellent beginner Amp.

Thanks - Bluto
Click to expand...


This is great, Bluto and Dan, please lead us into the world of Gainclone for the dummies, or dummy me.

gychang
 
#104
Nuuk said:
I really am keen to help so could you point to something (anything?) that I have said that has 'lost' you?
Click to expand...

Well, my mistake, not yet corrected, is that I didn't create an itinerary. You know, like a road map. The great example that you and others have given me (post#77) leads to the idea. . . that its like some friends left for a journey, two days ago, and an itinerary is needed to catch up.

I was thinking of a web-based assembly manual, mostly photos, with very little chatter. On the web, the photos could be made click-able, which would lead to a more complete text reference with details only for the item pictured.

There's also the operation of tools. There are some tools that don't visually appear to be tools, like a jar of flux, the capacitor values chart, the light bulb test device, a ball of #0000 steel wool (cleans flux off iron), the cap drainer, the desoldering bulb, and a really bright light for the workspace. And, who would expect that tools from non-electronics fields, like hemostats, would be so useful?

I think its that, even though the materials are simple, they do visually appear to be complex.

EDIT: Here's a frequent example of a visual complexity: The chipamp.com power supply has a simple and elegant schematic. . . however, the beginner is often thoroughly confused during its assembly and hookup.
 
#106
I think that the beginner would enjoy soldering if flux gel were painted onto the surfaces to be soldered--before picking up the soldering iron.

That makes soldering easy and fast. And, its so much better than repeated tries or roasting components.

After finishing (in record time) the mess of flux can be removed in a few seconds with alcohol and an old toothbrush.

Here is the tool:
(electronics grade gel/paste flux)
 

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#107
Zero offset

Referring to post 97 and post 101

After adding the input filter cap (so there's no worries about dc from the source), I measured the DC offset, which had gone up to 127mv. That's no good.

Then I realized. . .
The 50k pot and the 22k resistor (in Peter Daniel's schematic of post 97) makes a load less than 22k. Forehead slap.
So, the load on the input would actually correspond to common resistor values of either 15k or 18k, and 15k is zero dc offset (this time).

Great!

Now, I've got a power thump.
Watching the analog multimeter (on DC scale), after pulling the power plug, the needle slowly pulls down lower than zero, the woofer slowly pulls inwards, and then releases with a "thunk" noise. Ah darn.
 
#110
Now transformers

Good tips and links!

The thread is moving forward in the right way.

I ordered the parts in Farnell.com and in the meantime I got on ebay a couple of toroidal transformers as part of unfinished active speaker amps. They were advertised as 120V 18-0-18. However, the label says:

Pri: 230V 50Hz
Sec 18-0-18 White - Black- White
0V-11.5v RED-RED
33-0-33 Green- Blue- Green
3.5-0-3.5 Blue-Black- Blue
2-0-2 Yellow-Black-Yellow

I have not found answers for these questions:

Why was it advertised as 120V? Why it does not say VAC anywere. Are they in fact 230 VAC?

As you can see there are many cables coming out from this things. Will I use only the 18-0-18 ones? Can I use the low V ones to feed a switch with an on-off led.

More questions will follow after I start making the connections to the diodes, but in the meantime I will be grateful if someone can clarify the above.

Thanks

Regards

Antonio
 
#111
Hi Antonio,

If the label says 230V, 50Hz for the primary then
I would take it to be a transformer suitable for
the U.K. (50Hz AC frequency, 230V)

I'm also puzzled by the 120V claim. It can simply
be an error, or someone may actually be using
it with 120V primary (say US and Canada) and
getting roughly 18VAC from the 33-0-33 secondaries.

Does the label on the transformer give any current
ratings for the various secondaries?

Cheers,
Dennis
 
#112
Re: Now transformers

A Sanchez said:
Good tips and links!
. . . I got on ebay a couple of toroidal transformers as part of unfinished active speaker amps. They were advertised as 120V 18-0-18. However, the label says:

Pri: 230V 50Hz
Sec 18-0-18 White - Black- White
0V-11.5v RED-RED
33-0-33 Green- Blue- Green
3.5-0-3.5 Blue-Black- Blue
2-0-2 Yellow-Black-Yellow

I have not found answers for these questions:

Why was it advertised as 120V? Why it does not say VAC anywere. Are they in fact 230 VAC?

As you can see there are many cables coming out from this things. Will I use only the 18-0-18 ones? Can I use the low V ones to feed a switch with an on-off led.

More questions will follow after I start making the connections to the diodes, but in the meantime I will be grateful if someone can clarify the above.

Thanks
Regards
Antonio
Click to expand...

Here's a link to the power supply forum here at diyaudio.com: http://www.diyaudio.com/forums/forumdisplay.php?s=&forumid=67

For reference, see: http://www.diyaudio.com/forums/showthread.php?postid=1496729#post1496729 that post, and its explanation of transformer selection.

Just in case, let me give my position on transformers one more time. For beginners, the Single Primary input, with Center Tap output, style of transformer is safest. That's two wires in, and 3 wires out.

Like this. . .
An externally hosted image should be here but it was not working when we last tested it.

(nice 4 amper Stancor
with 20-0-20 ac)

Not this. . .
spaghetti-without-mess.jpg
 
#113
Dennis Hui said:
Hi Antonio,

If the label says 230V, 50Hz for the primary then
I would take it to be a transformer suitable for
the U.K. (50Hz AC frequency, 230V)

I'm also puzzled by the 120V claim. It can simply
be an error, or someone may actually be using
it with 120V primary (say US and Canada) and
getting roughly 18VAC from the 33-0-33 secondaries.

Does the label on the transformer give any current
Hi ratings for the various secondaries?

Cheers,
Dennis
Click to expand...

Hi Dennis,

The seller is in the UK and in response to my question said that the 230V was peak current and that the 120VA was the maximum continous current. Does this make sense to you?.

No it does not say anything else for the secondaries apart from what I wrote: ie. 18-0-18, 30-0-30, etc


Regards

Antonio
 
#116
Two photos of the transformer (Label and Cables):

http://www.flickr.com/photos/11571687@N02/sets/72157603119448350/

I hope they work with a LM3886 and my speakers, otherwise I will sell them.

I will be running Jordan SX92s single drivers: 6 ohm and 88db sensitivity (or maybe 85db after BSC) . I went for 18-0-18 sec and LM3886 because from what I read this would be appropriate for these drivers specs. I am not interested in very high volume. I am more for relax, detailed sound at lower volumes.

Edit. I am planning to use one PSU per amp/channel

Regards

Antonio
 
#118
Bluto said:

The reason for the thread is because as with all forums it's tough to get help for newbees on subjects others mastered moons ago. Newbees get ignored - just a fact. As I read down I see an Amp that I had saved to my personal picture Gallery long ago as a 'goal amp' for me. Didn't know til 3 minutes ago it was you. So, you obviously know your stuff. I see you and Dan know each other and you obviously have a degree of respect for him until he says something you disagree with and now your taking your toys and going home.

I guess this means that if I ever get to the point in my learning I really want to build the Amp you did I'm not going to get any help from you?
Click to expand...


Thanks for the compliment. 🙂

Maybe one of the reasons newbies (I'm still one in many eyes) get ignored is because the old timers don't feel like arguing with them over text book stuff. It's very easy to learn the basics in a short while with a little research. Rod Elliot's ESP is a wealth of info. Nuuk's DD is very informative. There are many others.

I don't actually know Dan, but anyone can read his interactions with others by clicking the magnifying glass next to his name. He has had "disagreements" with a few more than me. 😉

I won't stay in this thread, and my knowledge is limited anyway. I am not an expert in this, just another grunt building stuff.
Besides, with Dan at the helm, you guys are set.
Good luck. :up:
 
#119
Nuuk,

Thanks

I already bought them. I paid 40 pounds inc shipping for the two transformers, and the amps included two heathsinks and all the connectors I need to build my gainclone - in addition to lots of unused capacitors of many sizes (inc 4 2200UF) for this and future projects.

If the trafos are ok for my project I think (hope) I made a good deal.

Regards


Antonio
 
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