Designing a versatile pre with balanced and unbalanced in/out - Page 3

SGregory · 21st December 2011, 07:36 PM

Nikon,
You could use a regulator on it.
Typically when using in SE, the (-) input is tied to ground. I have a jumper pin that I slip into the XLR to do that. You can also make a XLR to RCA conversion cord that does it for you. IIRC you tie 1&3 to ground.

As far as reduced voltage maybe Mr. Pass himself would answer that for you in the Pass forum. It has been many years since I built that circuit, but I do recal that he had a reason for the voltage that he ran at.

NicMac · 21st December 2011, 07:55 PM

Ciao Nikon,
did you have a look at the RelaiXed?
I'm using this pre most of the time and it has most of the features you are looking for. There is no SE output.
Cheers,
Nic

Nikon1975 · 3rd January 2012, 02:13 PM

Funny thing, holidays is always a busy time. Should be the opposite...anyway.

I have two second end Jensen transformers on their way, just to try.

I also simulate the suggested Pass circuit with LTSpice. It looks like I could have decent results with 30 V supply, using IRF510.

Any suggestion for alternative mosfet to try in the simulation ?

One thing is still not clear: If used like SE to balanced converter, the circuit produces two outputs that are not 100% symmetrical. The negative has higher amplitude than the positive. This is kind of expected, as the circuit inverts. Does this matter in real life ?

Thanks,

Davide

Nikon1975 · 3rd January 2012, 02:20 PM

Nic,

I checked the design you suggested, but I cannot see anything really attractive, at first look, is a opamp pre. But I am not an expert: what am I missing ?

D.

ThorstenL · 3rd January 2012, 02:34 PM

Hi,

Quote:

Originally Posted by Nikon1975

One thing is still not clear: If used like SE to balanced converter, the circuit produces two outputs that are not 100% symmetrical. The negative has higher amplitude than the positive. This is kind of expected, as the circuit inverts. Does this matter in real life ?

First, the asymmetry is a result of the use of resistors instead of current sources and the limited transconductance of the mosfets.

Does it matter? If it does not matter to your actual pre-amplifier circuit, then you did not need a SE -> Balanced converter to start with.

Ciao T

Nikon1975 · 4th January 2012, 03:42 AM

Thorsten,

Thanks for the tip. I tried to replace the lower resistor with a current sink, the asymmetry goes away, but the distortion increase, not sure why.

D.

dirkwright · 5th January 2012, 07:49 PM

Quote:

Originally Posted by Nikon1975

Dear All,

My electronic knowledge does not allow me to design cutting edge circuits, but I understand enough to combine and adapt other people designs to my needs.

So, the situation is the following:
1) I have some SE and some Balanced sources.
2) I have some SE and some Balanced amps.

I'd like to have the possibility to connect them all, switch between them without sacrifice in term of quality. I have various options:

a) install both SE and balanced output to all the sources, use two different pre amps, one for the balanced amps and one for the SE amps.

b) assemble a preamp that can combine both, but here I am not sure it is possible without double conversions, that I want to avoid.

Of course I can take shortcuts, and use only one phase of the balanced, but I feel like it is a waste.

I am sure I am not the first one to have this problem, and I see the high-end commercial amps (even HT) have these features, but this does not mean it is implemented in an optimum way.

Any hint ?

Thanks,

Davide

You can use line input and line output audio transformers for this purpose. You only need 2 of each for stereo.

Nikon1975 · 6th January 2012, 12:58 AM

So, I have two of these:

http://www.jensen-transformers.com/datashts/11p1bn.pdf

As I understand, I can use them to convert a balanced signal to feed an SE amp, but I am not sure it will have good performances the other way around, as there is an RC network built in.

Am I correct ?

D.

dirkwright · 6th January 2012, 01:18 AM

Quote:

Originally Posted by Nikon1975

So, I have two of these:

http://www.jensen-transformers.com/datashts/11p1bn.pdf

As I understand, I can use them to convert a balanced signal to feed an SE amp, but I am not sure it will have good performances the other way around, as there is an RC network built in.

Am I correct ?

D.

Ah, you didn't have to buy those! But yeah, there is an RC network built in but you don't ever have to reverse this transformer since it's 1:1 ratio. You just have to make sure there is a 15kohm load or greater on the secondary side, which is the one with the zobel.

You can use this transformer to feed either a single ended OR a balanced signal to a single ended OR a balanced amplifier. It is a high impedance input transformer. You need a different kind of transformer for the output side. You need a low impedance 1:1 transformer for the output (usually 600 ohms).

Nikon1975 · 6th January 2012, 01:30 AM

I found them second hand, so they were cheaper.

I don't really see the need of the output transformer, if the source has already low output impedance.

D.

21st December 2011, 07:36 PM	#21
SGregory diyAudio Member Join Date: Apr 2003 Location: Southern Tier NY	Nikon, You could use a regulator on it. Typically when using in SE, the (-) input is tied to ground. I have a jumper pin that I slip into the XLR to do that. You can also make a XLR to RCA conversion cord that does it for you. IIRC you tie 1&3 to ground. As far as reduced voltage maybe Mr. Pass himself would answer that for you in the Pass forum. It has been many years since I built that circuit, but I do recal that he had a reason for the voltage that he ran at. __________________ Living Life Doing the Waltz in 4/4 meter.

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
Aleph P, Balanced Out if unbalanced in?	Konsti	Pass Labs	5	26th March 2008 08:36 PM
Unbalanced to Balanced	mcash257	Parts	3	14th October 2004 12:03 AM
unbalanced/balanced/unbalanced conversion using transformers	vladimir	Solid State	10	27th February 2003 06:54 PM
unbalanced or balanced	theturtle	Everything Else	4	5th January 2003 04:52 PM
Zen Balanced Line Stage Balanced vs Unbalanced	macka	Pass Labs	28	11th December 2002 06:18 AM

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

21st December 2011, 07:55 PM	#22
NicMac diyAudio Member Join Date: Feb 2009	Ciao Nikon, did you have a look at the RelaiXed? I'm using this pre most of the time and it has most of the features you are looking for. There is no SE output. Cheers, Nic

3rd January 2012, 02:13 PM	#23
Nikon1975 diyAudio Member Join Date: Nov 2009 Location: Vienna	Funny thing, holidays is always a busy time. Should be the opposite...anyway. I have two second end Jensen transformers on their way, just to try. I also simulate the suggested Pass circuit with LTSpice. It looks like I could have decent results with 30 V supply, using IRF510. Any suggestion for alternative mosfet to try in the simulation ? One thing is still not clear: If used like SE to balanced converter, the circuit produces two outputs that are not 100% symmetrical. The negative has higher amplitude than the positive. This is kind of expected, as the circuit inverts. Does this matter in real life ? Thanks, Davide

3rd January 2012, 02:20 PM	#24
Nikon1975 diyAudio Member Join Date: Nov 2009 Location: Vienna	Nic, I checked the design you suggested, but I cannot see anything really attractive, at first look, is a opamp pre. But I am not an expert: what am I missing ? D.

4th January 2012, 03:42 AM	#26
Nikon1975 diyAudio Member Join Date: Nov 2009 Location: Vienna	Thorsten, Thanks for the tip. I tried to replace the lower resistor with a current sink, the asymmetry goes away, but the distortion increase, not sure why. D.

6th January 2012, 12:58 AM	#28
Nikon1975 diyAudio Member Join Date: Nov 2009 Location: Vienna	So, I have two of these: http://www.jensen-transformers.com/datashts/11p1bn.pdf As I understand, I can use them to convert a balanced signal to feed an SE amp, but I am not sure it will have good performances the other way around, as there is an RC network built in. Am I correct ? D.

6th January 2012, 01:30 AM	#30
Nikon1975 diyAudio Member Join Date: Nov 2009 Location: Vienna	I found them second hand, so they were cheaper. I don't really see the need of the output transformer, if the source has already low output impedance. D.