Transformer on feedback path

NIC1138 · 2nd May 2007, 04:16 PM

Hello folks. This is my first post... And I hope an interesting one!

I'm doing this project, a scientific experiment if you will, and I need fo feed a low-impedance load (1.5 ohms) with about 2 amps. It's a very experimental stuff, nothing very certain yet.

I was building a simple AB push-pull with a pair of TIP41/42 and a TL071 to feedback and eliminate the crossover distortion, but then I started to feel like using a transformer before the load (I'm also starting to believe the current might be too high for the transistors)

Well, I also want to measure the current somehow... I want to sample the voltage and current going through the load. So I was thinking about putting a resistor in series with the load, on the other side of the transformer, and feeding back the voltage drop on it using a INA114. So the input is the current we want through the load, and the output is the voltage on it.

So, I was looking for suggestions, criticisms... Has anybody ever seen a feedback with a transformer on the way for current gain? No big deal?...

PS: If you are curious, the experiment is to pass a current through a GUITAR STRING with a large magnet nearby, to move it!... =) Yes, it works, I already attached it to the power outlet using transformer to take the voltage down to 6v, and controlling the power with a dimmer. I tuned down the E string, and it vibrated!... Now I'm going to control the frequency from the computer... Yes, this might become an electric hammerless piano in the future!

jcx · 2nd May 2007, 04:50 PM

the tip41/42 won't have a problem with 2 A, Xfmrs in a feedback path suck - they are bandpass filters and severely limit the feedback that can be applied before phase shift turns the amp into a oscillator

the likely problem is that the op amp won't have enough drive current to drive the tip base currents, you should add a buffer stage, look for "diamond buffer" schematics

NIC1138 · 3rd May 2007, 03:40 AM

Hmmmm... Right, I totally disconsidered thecurrent at the ampop.

Perhaps MOSFET could be a better choice??... It's just that I'm not too used to it.

I don't need a great bandwidth... Just 1kHz should be just fine... And 10W maximum...

Guess I better at least run a simuation before asking for more help!

I'll be back when I have something more substantial...

NIC1138 · 9th May 2007, 06:41 AM

Just for the record, I gave up on the idea, for now, and I'm trying a TDA2050 amp, which might be just the power I needed... Thanks for the (wideband) feedback!

2nd May 2007, 04:16 PM	#1
NIC1138 diyAudio Member Join Date: Apr 2007	Transformer on feedback path Hello folks. This is my first post... And I hope an interesting one! I'm doing this project, a scientific experiment if you will, and I need fo feed a low-impedance load (1.5 ohms) with about 2 amps. It's a very experimental stuff, nothing very certain yet. I was building a simple AB push-pull with a pair of TIP41/42 and a TL071 to feedback and eliminate the crossover distortion, but then I started to feel like using a transformer before the load (I'm also starting to believe the current might be too high for the transistors) Well, I also want to measure the current somehow... I want to sample the voltage and current going through the load. So I was thinking about putting a resistor in series with the load, on the other side of the transformer, and feeding back the voltage drop on it using a INA114. So the input is the current we want through the load, and the output is the voltage on it. So, I was looking for suggestions, criticisms... Has anybody ever seen a feedback with a transformer on the way for current gain? No big deal?... PS: If you are curious, the experiment is to pass a current through a GUITAR STRING with a large magnet nearby, to move it!... =) Yes, it works, I already attached it to the power outlet using transformer to take the voltage down to 6v, and controlling the power with a dimmer. I tuned down the E string, and it vibrated!... Now I'm going to control the frequency from the computer... Yes, this might become an electric hammerless piano in the future!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Audio Transformer/Cathode Feedback Info	LinuksGuru	Tubes / Valves	4	26th April 2009 09:13 PM
DC blocking cap in feedback path or DC servo?	roender	Solid State	27	19th September 2007 09:40 AM
Transformer Feedback	SillyCone	Solid State	3	12th September 2006 01:20 AM
Transformer based feedback?	bigwill	Solid State	25	6th January 2006 08:02 AM
Speaker cable in amp feedback path	MRehorst	Solid State	16	23rd November 2002 08:47 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

2nd May 2007, 04:50 PM	#2
jcx diyAudio Member Join Date: Feb 2003 Location: ..	the tip41/42 won't have a problem with 2 A, Xfmrs in a feedback path suck - they are bandpass filters and severely limit the feedback that can be applied before phase shift turns the amp into a oscillator the likely problem is that the op amp won't have enough drive current to drive the tip base currents, you should add a buffer stage, look for "diamond buffer" schematics

3rd May 2007, 03:40 AM	#3
NIC1138 diyAudio Member Join Date: Apr 2007	Hmmmm... Right, I totally disconsidered thecurrent at the ampop. Perhaps MOSFET could be a better choice??... It's just that I'm not too used to it. I don't need a great bandwidth... Just 1kHz should be just fine... And 10W maximum... Guess I better at least run a simuation before asking for more help! I'll be back when I have something more substantial...

9th May 2007, 06:41 AM	#4
NIC1138 diyAudio Member Join Date: Apr 2007	Just for the record, I gave up on the idea, for now, and I'm trying a TDA2050 amp, which might be just the power I needed... Thanks for the (wideband) feedback!