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Author Topic: Appropriate Chip Selection  (Read 7133 times)

paku5535

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Appropriate Chip Selection
« on: February 21, 2012, 01:46:50 PM »
Hi everyone

actually i want to build a versatile guitar amplifier using eminence guvnor 75w speaker.
i want to build around max 30-35 w.
for the power section what chip you suggest?(like 3886 3875 etc ).
can u please refer any good schematic of the power supply?

i have found lots of crying for both 3886 and 3875 in different perspectives.
but you guys please suggest me in terms of guitar amplifier?

do you think 3886 /3875 are more than enough for 30/35w or the TDA chips will do?
what is the difference in producing quality sound for LM3886 types vs TDA 2030 types chips?(in terms of guitar power amp).

or instead i should go with discrete solid state(mk ii)??

please suggest your valuable experience from your DIY journey.
thanks

J M Fahey

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Re: Appropriate Chip Selection
« Reply #1 on: February 21, 2012, 03:33:55 PM »
Basically answered in your other post.
A TDA2050 is just on the edge producing 30W, while an LM3886 will work for ages, because it will be overspecified. (good).
Google chipamps and see what they offer.

paku5535

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Re: Appropriate Chip Selection
« Reply #2 on: February 21, 2012, 03:56:15 PM »
fahey thanks for  the reply...
plz suggest transformer rating for max 30w +-18v

is dual rail transformer 18v+18v means center tap +18 0 -18?

i am going to add sansamp gt2 clone in the preamp. does it requires to go through any intermediate
circuitry or directly feed into power amp?

another question....
3886 has a 10k pot prior to the onon inv. input. in ggg.com it is mentioned as a 10k trimmer.
should i use it as a pot or trimmer with a fixed value or can eliminate since sansamp circuit has its own
output level control.....

little worried since its my first power amp project.....need you...........

joecool85

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Re: Appropriate Chip Selection
« Reply #3 on: February 22, 2012, 02:41:59 PM »
fahey thanks for  the reply...
plz suggest transformer rating for max 30w +-18v

is dual rail transformer 18v+18v means center tap +18 0 -18?

No, a 18v+18v transformer would be center tapped 18v AC - 0 - 18v AC.  There is no +/- yet.  You will need to build a power supply that hooks up to the transformer and takes the AC from the transformer and makes + and - DC for your amp.  If you need +/-18v for your chip you would need a transformer that puts out 12.6v-0-12.6v (AC x 1.4 = DC voltage after rectification).
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paku5535

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Re: Appropriate Chip Selection
« Reply #4 on: February 22, 2012, 03:54:45 PM »
joecool please elaborate the transformer rating plz

joecool85

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Re: Appropriate Chip Selection
« Reply #5 on: February 22, 2012, 04:15:19 PM »
joecool please elaborate the transformer rating plz

I'm not sure how I can spell it out any better than that really.  Transformers only output AC, alternating current.  You need DC, direct current.  So you run the transformer into a PSU (power supply unit) board and that will output your DC "rails" (positive and negative voltages) to run your amp.

Read this thread and see if it helps you: http://www.ssguitar.com/index.php?topic=16.0
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J M Fahey

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Re: Appropriate Chip Selection
« Reply #6 on: February 23, 2012, 08:43:04 AM »
Start by reading this to see what you are getting into.
Your amp will be simpler because it will be mono (1/2 of what is shown here) and will have a somewhat simpler Power Supply and transformer than the one shown.
http://diyaudioprojects.com/Chip/LM3886_CA/LM3886_CA.htm
A 18+18V AC transformer will give you about +/- 25V DC, perfect for this amp.

paku5535

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Re: Appropriate Chip Selection
« Reply #7 on: February 23, 2012, 03:17:28 PM »
hello fahey and joecool
thanks to both of you for your prompt reply. acually 18v+18v transformer is not available in india....
instead can i use center tap transformer with 18 0 -18 rating..........so through bridge rectifier i can get +-25v (around)...shown in the picture....
what are its drawback.........compared to 18v+18v
kindly reply

joecool85

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Re: Appropriate Chip Selection
« Reply #8 on: February 23, 2012, 04:27:38 PM »
hello fahey and joecool
thanks to both of you for your prompt reply. acually 18v+18v transformer is not available in india....
instead can i use center tap transformer with 18 0 -18 rating..........so through bridge rectifier i can get +-25v (around)...shown in the picture....
what are its drawback.........compared to 18v+18v
kindly reply

No drawbacks.  I have built amps with toroidal dual output transformers as well as CT transformers and they both work just fine.  Most commercial amps use CT actually.
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paku5535

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Re: Appropriate Chip Selection
« Reply #9 on: February 24, 2012, 03:14:04 AM »
thanks for the reply.

please reply me for the following question......



i am going to add sansamp gt2 clone in the preamp. does it requires to go through any intermediate
circuitry or directly feed into power amp?

another question....
3886 has a 10k pot prior to the on inv. input. in ggg.com it is mentioned as a 10k trimmer.
should i use it as a pot or trimmer with a fixed value or can eliminate since sansamp circuit has its own
output level control.....

i will place bit by bit information here as soon as i start the work...

thanks

joecool85

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Re: Appropriate Chip Selection
« Reply #10 on: February 24, 2012, 09:29:27 AM »
thanks for the reply.

please reply me for the following question......



i am going to add sansamp gt2 clone in the preamp. does it requires to go through any intermediate
circuitry or directly feed into power amp?

another question....
3886 has a 10k pot prior to the on inv. input. in ggg.com it is mentioned as a 10k trimmer.
should i use it as a pot or trimmer with a fixed value or can eliminate since sansamp circuit has its own
output level control.....

i will place bit by bit information here as soon as i start the work...

thanks

Your preamp can go straight into the LM3886 circuit.  It's up to you if you want to use a potentiometer in between the preamp and the power amp.  You could leave it out, or you could keep it and use it as a "Master" control.  I vote to keep it, because it's cool and adds another knob to your amp  :tu:  It'll work fine either way.  Also, you can use a potentiometer or a trimmer.  A trimmer is just a small board mounted potentiometer that can't take a knob.
Life is what you make it.
Still rockin' the Dean Markley K-20X
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paku5535

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Re: Appropriate Chip Selection
« Reply #11 on: February 25, 2012, 01:49:35 PM »
thank you joecool...

how do  u print pcb...

i am trying with the copper clad board but the ironing the pcb image on the copper clad is not transferring(keeping the iron at full temparature)........

thank u again for your reply

J M Fahey

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Re: Appropriate Chip Selection
« Reply #12 on: February 25, 2012, 10:45:38 PM »
Watch a few of these.
http://www.youtube.com/results?hl=en&q=iron%20on%20pcb%20transfer&psj=1&gs_sm=1&gs_upl=4493l14685l0l17089l20l20l0l7l7l0l394l3742l2-11.2l13l0&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1024&bih=625&um=1&ie=UTF-8&sa=N&tab=w1
Then practice, thereĀ“s no other way.
You will have to clean your board *very* well, degrease it with a good detergent and warm water or *clean* cotton and medicinal alcohol, *never ever* touch it again with your bare hands, etc.
Try different kinds of magazine paper, different settings in your Laser Printer, different pressing iron temperatures, etc.
Once you get the hang of it, they come out well consistently.

paku5535

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Re: Appropriate Chip Selection
« Reply #13 on: March 12, 2012, 03:07:49 PM »
hey all

finally i have decided that i will go with lm1875. because i have realized that 20-25 watt is enough for me for my efficient guitar speaker (eminence governor) having spl of102.

now i am bit confused with which schematic to adopt for my guitar amp.(+vcc -vee) type
1. do i require any buffer between the preamp and power amp.

2. for guitar amp what should be the uF value for the filter capacitor.

3. i have decided to run it through 18 0 -18 ct transformer. for moderate efficiency what should be the ampere rating of the transformer.

4. many one are suggesting to use good grounding techniques for minimal noise and hum.. any advise ????

5. what is zobel network? do i have to adopt this for good. where i have to add this in the ckt?

6. what type of delay ckt i can add to minimize on pop sound
(plz see the attachment. this is what i have found by googling) .

7. do i have to attach the earth wire (green ) with the zero voltage pin for safety?

additionally if some one to share his opinion on lm1875 or any thing related to amp building then plz write here..

let me have those answers plz and i will start working on the project. during the time if i have any problem i will post here to get feedback from gurus..

thanks

paku5535

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Re: Appropriate Chip Selection
« Reply #14 on: March 12, 2012, 03:09:40 PM »
hey all

finally i have decided that i will go with lm1875. because i have realized that 20-25 watt is enough for me for my efficient guitar speaker (eminence governor) having spl of102.

now i am bit confused with which schematic to adopt for my guitar amp.(+vcc -vee) type
1. do i require any buffer between the preamp and power amp.

2. for guitar amp what should be the uF value for the filter capacitor.

3. i have decided to run it through 18 0 -18 ct transformer. for moderate efficiency what should be the ampere rating of the transformer.

4. many one are suggesting to use good grounding techniques for minimal noise and hum.. any advise ????

5. what is zobel network? do i have to adopt this for good. where i have to add this in the ckt?

6. what type of delay ckt i can add to minimize on pop sound
(plz see the attachment. this is what i have found by googling) .

7. do i have to attach the earth wire (green ) with the zero voltage pin for safety?

additionally if some one to share his opinion on lm1875 or any thing related to amp building then plz write here..

let me have those answers plz and i will start working on the project. during the time if i have any problem i will post here to get feedback from gurus..

thanks  to all