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.
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.
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
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
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
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
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.
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.
Hi,
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
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
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.
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.
You can use line input and line output audio transformers for this purpose. You only need 2 of each for stereo.
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.
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).
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.
I don't really see the need of the output transformer, if the source has already low output impedance.
D.
Hi,
You can use them as "input" Transformers. This means place them near the input of a unbalanced Amplifier or Preamplifier to give it a balanced input, or reverse, you can keep them in line just SE->SE or BAL->BAL. make sure the load on the secondary side is > 15KOhm and do not have long or high capacitance cables after the transformer.
The official line out from Jensen is this:
http://www.jensen-transformers.com/datashts/11bmcf.pdf
A friend of mine cloned this one (only a few for testing) and gave me a pair, they are excellent line outs and as long as you drive from a very low impedance they are capable to drive any length cable.
IF (a big if) I was to make a Line Pre using transformers and solid state it would probably look like this:
Input switching (balanced) with XLR inputs and RCA's connected between Pin 2 & 3 of XLR, switch to connect pin 3 to chassis (earth) via 100R/100n if needed (hum on input as source is floating)
Jensen JT-10KB-D Input transformer
2.5K Stepped Attenuator, 4-deck true ladder preferred
AD815 as Linestage with 18dB or 24dB (selectable) gain for 6 or 12 dB Linestage Gain (basically Carlos FM linestage)
JT-OLI-2 Load Isolator
Jensen JT-11-BMCF Output Transformer
XLR outputs and RCA's connected between Pin 2 & 3 of XLR, switch to connect pin 3 to chassis (earth) via 100R/100n if needed (hum on output as Amp is floating)
The result will be a very nice pre with the ability to handle any kind of source.
Other line stage amplification options may of course be applied, instead of AD815, but it is known to work well together with the Jensen Output transformer, it was used in one of the Jeff Rowland Line Preamp's like that.
Ciao T
You can use them as "input" Transformers. This means place them near the input of a unbalanced Amplifier or Preamplifier to give it a balanced input, or reverse, you can keep them in line just SE->SE or BAL->BAL. make sure the load on the secondary side is > 15KOhm and do not have long or high capacitance cables after the transformer.
The official line out from Jensen is this:
http://www.jensen-transformers.com/datashts/11bmcf.pdf
A friend of mine cloned this one (only a few for testing) and gave me a pair, they are excellent line outs and as long as you drive from a very low impedance they are capable to drive any length cable.
IF (a big if) I was to make a Line Pre using transformers and solid state it would probably look like this:
Input switching (balanced) with XLR inputs and RCA's connected between Pin 2 & 3 of XLR, switch to connect pin 3 to chassis (earth) via 100R/100n if needed (hum on input as source is floating)
Jensen JT-10KB-D Input transformer
2.5K Stepped Attenuator, 4-deck true ladder preferred
AD815 as Linestage with 18dB or 24dB (selectable) gain for 6 or 12 dB Linestage Gain (basically Carlos FM linestage)
JT-OLI-2 Load Isolator
Jensen JT-11-BMCF Output Transformer
XLR outputs and RCA's connected between Pin 2 & 3 of XLR, switch to connect pin 3 to chassis (earth) via 100R/100n if needed (hum on output as Amp is floating)
The result will be a very nice pre with the ability to handle any kind of source.
Other line stage amplification options may of course be applied, instead of AD815, but it is known to work well together with the Jensen Output transformer, it was used in one of the Jeff Rowland Line Preamp's like that.
Ciao T
Hi,
Yes, this will work splendidly. Add a JT-11-BMCF which you can directly couple the the DCB1 and you will have your own "Virtual Reality Engine" that can drive SE or Balanced Amplifiers.
Ciao T
Yes, this will work splendidly. Add a JT-11-BMCF which you can directly couple the the DCB1 and you will have your own "Virtual Reality Engine" that can drive SE or Balanced Amplifiers.
Ciao T
Output transformers with an upper limit of 15MHz! wow! The bandwidth of these Jensen transformers is incredible. Does anyone have an inexpensive source for these? I see they cost anywhere from about $60 and up at all the sites I've looked at. Even used ones are expensive.
Hi,
Not incredible, almost any bifilar would audio transformer gets into the MHz region.
There is a very large chunk of 80% nickel alloy in there. They cannot be "cheap", sorry.
Also, it is my experience is that cheap transformers are usually too bad to be worth having. Diyhifisupply have a box of 1:1 line transformers which even at their best options and even driven from 50 Ohm are so bad, I'd not touch them with a bargepole.
Ciao T
Not incredible, almost any bifilar would audio transformer gets into the MHz region.
There is a very large chunk of 80% nickel alloy in there. They cannot be "cheap", sorry.
Also, it is my experience is that cheap transformers are usually too bad to be worth having. Diyhifisupply have a box of 1:1 line transformers which even at their best options and even driven from 50 Ohm are so bad, I'd not touch them with a bargepole.
Ciao T
I get them from Markertek.com. I guess I'll just have to pay the price for high quality. Thanks.
I am sure that there is a smarter way to do what I want, but up to now the solution that satisfy all my nees is the following, with two interconnected pre, one for SE input and one for Bal input:
1) The se amp will have an additional balanced output placed just after the source selection, before the volume control
2) The se amp will have a balanced input.
3) The balanced pre will have an additional balanced output just after the source selection.
Like this I can have all the balanced sources and balanced amps connected to the balanced pre and all the SE sourcesand amps connected to the SE pre.
When I mix them the signal will go alway through a single conversion, buffering and volume control.
Additionally I have the SE pre, with enough space to fit the extra in and out.
Any thoughts ?
D.
1) The se amp will have an additional balanced output placed just after the source selection, before the volume control
2) The se amp will have a balanced input.
3) The balanced pre will have an additional balanced output just after the source selection.
Like this I can have all the balanced sources and balanced amps connected to the balanced pre and all the SE sourcesand amps connected to the SE pre.
When I mix them the signal will go alway through a single conversion, buffering and volume control.
Additionally I have the SE pre, with enough space to fit the extra in and out.
Any thoughts ?
D.
Nikon1975,
I'm very interested in these plans for a "universal" pre-amp, but I'm not sure I can follow your scheme. Could you draw a block diagram?
Are two volume controls required (one for Bal and one for SE)?
How many buffers and Bal:SE converters are needed?
Cheers,
Nic
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