| silverD |
| After looking into building a small amp for a friend, I ran into all this info about gainclones......I had to build one. I reused and found leftovers for this amp. It sounds good, but some better parts will help. How nice are the United Chemi-con 500uF 50v caps I'm using? I used Thorsten's schematic, but with an old alps 250k dual pot, it doesn't get loud until the last 1/4 turn. I hear the 50k log is what to go with. I left out the .22ohm, 1uF, .1uf, and 2.2uF dc offset. I have a dc voltage that ranges from 50mV to 200mV, what will cure this? Thanks for the info...here's a pic |
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| uvodee |
of color ink inside my monitor, no pic here!
J-P |
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| silverD |
| I think they had to check my post for content......I'm new. The pic is there now, maybe you viewed the post before they had it up. |
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| Nappylady |
The pic is just fine AFAICT, and it looks quite... cute...
Is that much cooling really enough? Does it get warm? Do you cook on it? |
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| Peter Daniel |
| quote: | Originally posted by silverD
I have a dc voltage that ranges from 50mV to 200mV, what will cure this? Thanks for the info...here's a pic |
Are you sure that DC is not coming from your source? IGC by itself, shouldn't provide that much offset, even without a coupling cap. |
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| Nuuk |
| quote: | | I have a dc voltage that ranges from 50mV to 200mV |
Do you mean that it actually varies while you are measuring it?
How do you measure it? |
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| silverD |
| It varies with the pot. High dc at low "volume" and low dc at middle "volume" and high again at high volume. Thanks for the help. This was just a fast mock-up, I have an old car amp heatsink (3 sided) that I will convert to an enclosure. |
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| ronc |
I have to question how the offset can vary?
ron |
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| ronc |
Sorry Nuuk bro. I should read the responses before i post.
ron |
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| Peter Daniel |
| quote: | Originally posted by ron clarke
Sorry Nuuk bro. I should read the responses before i post.
ron |
Read it again, as I just unmoderated his previous reply;) |
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| Nuuk |
SilverD - Do you have a source connected when you measure the offset? Also, do you use a resistor on the output and measure the voltage across that?
Ron - you just dag nam hol' your hosses pardner! :sarge: |
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| silverD |
| I have a cd player hooked to it when I measure the dc voltage without a load. I checked the dc voltage of the cd player and it is zero. Since I have two seperate grounds on the case there could be a loop or the pot sucks. |
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| ronc |
Ahhhhhhhh!!!! the old sucking pot glich?
ron |
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| Nuuk |
| quote: | | Since I have two seperate grounds on the case there could be a loop or the pot sucks. |
Ahhhhhhhh!!!! the old sucking pot glich? ;)
Could you show us the complete wiring diagram? |
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| silverD |
| It's your standard thorsten IGC without the 1uF across the rails, 220K's on the feedback and non-inverting, no output resistor, no .1uF on non-invert, and an old alps dual 250K pot. |
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| Nuuk |
| quote: | | It's your standard thorsten IGC without the 1uF across the rails, 220K's on the feedback and non-inverting, |
If the feedback resistor is connected to non-inverting input (pin 8), it is not an I(nverted)GC! |
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| silverD |
| quote: | Originally posted by silverD
It's your standard thorsten IGC without the 1uF across the rails, 220K's on the feedback and non-inverting, no output resistor, no .1uF on non-invert, and an old alps dual 250K pot. |
The 220K resistor on the non-inverting input is to ground, I stated it on the non-inverting because others have used other resistances on this input. Are the UCC caps I'm using any good? I'm thinking of using Allen-Bradley resistors instead of your standard 5% carbon film. I have some mur860's on the way and was wondering what VA trans, and sec. voltage (24v and not 30v lets say) I'd need for a 2 channel setup. I don't want to spend too much on parts and was wondering what are some good budget parts that i have over looked.
Thanks for the help, Nate |
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| Nuuk |
I would go with a straight wire to ground, rather than the 220K resistor! In my experience (not opinion) it sounds better.
I also recommend a transformer for each channel, rated between 80VA and 160VA and with 24 volt secondaries.
Use a carbon film for the input resistor and something better than plain metal film for the feedback. If you can get Dale, use one of those. I like Welwyn RC55's which I believe are very similar.
| quote: | | I don't want to spend too much on parts |
I think that anybody who has ever tried the Gainclone amps has felt the same but take it from us - it's worth the outlay to build them properly. After all, there is not much difference in cost between a budget IGC and one using good quality parts!
How many times do we read of people wanting to save a small amount on the components when in reality, the cost of the ancilliaries like case and connectors swamp the cost of the circuit components! :cannotbe:
And the results are surely worth the compatatively small outlay! |
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| matjans |
| quote: | | I think that anybody who has ever tried the Gainclone amps has felt the same but take it from us - it's worth the outlay to build them properly. After all, there is not much difference in cost between a budget IGC and one using good quality parts! |
i dear to differ with you dear nuuk. Whereas you can make a GC from left-overs or el cheapo components, investing in parts CAN put you back quite a few bucks. Black gates, Riken ohms, Caddocks and what not are not really cheap -understatement.
But then again, for an investment of about 80 euros/bucks you'll have an amp that outperforms many other, far, FAR more expensive amps.
In other words: it's *definitively* worth your investment. |
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| Nuuk |
| quote: | | i dear to differ with you dear nuuk. |
| quote: | | In other words: it's *definitively* worth your investment. |
Well, I'd hate it if you disagreed with me then! ;)
The point to be made with the basic IGC is that you need so few components that there is little difference between doing it as cheaply as possible and including some very decent parts.
Apart from the chip, we are talking just two resistors and a DC blocker. A pair of Welwyns for the FB resistors ( about 2 euros)and a cheapo carbon film input resistor (a couple of euros if you have to buy 100) will produce a great sound! A good polypropylene 4.7uF is only five or six euros. |
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| Ropie |
Well, I wouldn't call a gc cheap, a bargain maybe, but not cheap (in my case anyway; it's those cotton-pickin' power supplies that double or triple the initially favourable price!).
And, of course, there is always so much temptation to build another that for a lot of people buying gc parts becomes a monthly outgoing :wave2: Goodbye, spare cash! |
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| ronc |
Well as far as the cost of the P/S i use batteries,BUT by the time you install relays, timers, case and along with the cost of the batteries i doubt that i am ahead of the game (cost wise).
Better components will make the sound different, but is it a better sound? I believe thats up to the individual and what sounds best to them.As i hear 47 labs uses carbon resisors , i use them.I spent some of my hard earned money (sold an oil well) and bought some higher end resisors and caps.Well it sounded brighter but with either the Fe103e horns or the Fe-168e sigmas,more brighteness is not something i am looking for.I did not notice any difference with the BG vrs nichicon caps.I even eliminated the caps on he P/S pins and just used a 1 uf(mylar) between the pins and had the same
results.
ron |
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| Nuuk |
| quote: | | Well, I wouldn't call a gc cheap |
Of course it is all relative! But for the quality of sound we should be looking for, this is 'cheap'. Any amp requires a PSU (batteries or otherwise) and if you costed up the many other designs of DIY amps you will find that the basic IGC is cheaper than most, if not all of them.
(And I don't have any oil wells to sell off!) :D |
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| silverD |
I've looked into the caddock resistors and Allied (where I will buy from) doesn't have 220k, but they do have 200K will that affect the gain much? I have chosen not to use a pot, so I should use a 56K to ground, right? What range is acceptable for this resistor? Should I use caddocks all around or what would sound best? I'll have caddocks, standard carbon and some allen bradley(I think).
Thanks, Nate |
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| Nuuk |
If you can't get 220K for the feedback, I would prefer 240K or 270K to 200K - ie a bit more gain than a bit less.
That 56K (instead of the pot) could be anything from 47K-100K and any type that you want but I would use a standard metal film in that location. |
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