laitue5

Line output transformers
« on: October 26, 2020, 06:59:31 AM »
I’m trying to list hi-quality line output transformers options I have to add in a simple design I have in mind (nothing fancy, RIAA op amp preamp + output transformer to balance and load six or seven meters cables).

I found: Lundahl LL5402, Sowter 4652
I would like to buy Jensen JT-11-BMCF, find Triad HS56/66 or Freed 32035 but even at nice prices, overseas shipping cost is too much.

So, do you know european transformers that will do the job, contemporary or vintage (Haufe? Pikatron? Neutrik ? Studer?)
I’ll use it at the end of something like this: https://sound-au.com/project06.htm
metal film 1/4W is ok


RuudNL

Re: Line output transformers
« Reply #1 on: October 26, 2020, 02:43:56 PM »
I just looked at the schematic.
It seems there is some filtering at the output: 750 (820, 910) ohms, 100 nF, and a 1 uF output capacitor.
Most transformers like to be driven from a low impedance.
Also there is a risk that the 100nF + 1 uF will produce a resonance with the inductance of the transformer winding.
Personally I would prefer an extra buffer stage that drives the transformer from a low impedance.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Moby

Re: Line output transformers
« Reply #2 on: October 26, 2020, 06:52:25 PM »
I’m trying to list hi-quality line output transformers options I have to add in a simple design I have in mind (nothing fancy, RIAA op amp preamp + output transformer to balance and load six or seven meters cables).

I found: Lundahl LL5402, Sowter 4652
I would like to buy Jensen JT-11-BMCF, find Triad HS56/66 or Freed 32035 but even at nice prices, overseas shipping cost is too much.

So, do you know european transformers that will do the job, contemporary or vintage (Haufe? Pikatron? Neutrik ? Studer?)
I’ll use it at the end of something like this: https://sound-au.com/project06.htm
If you decided to use 2 opamp RIAA (nothing fancy) why not opamp balanced driver?
https://sound-au.com/project51.htm
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

john12ax7

Re: Line output transformers
« Reply #3 on: October 26, 2020, 07:48:49 PM »
Lundahl,  Sowter,  and Carnhill would be the 3  I can think of for Europe.  OEP as well for a cheaper option.

laitue5

Re: Line output transformers
« Reply #4 on: October 27, 2020, 05:19:33 AM »
I just looked at the schematic.
It seems there is some filtering at the output: 750 (820, 910) ohms, 100 nF, and a 1 uF output capacitor.
Most transformers like to be driven from a low impedance.
Also there is a risk that the 100nF + 1 uF will produce a resonance with the inductance of the transformer winding.
Personally I would prefer an extra buffer stage that drives the transformer from a low impedance.
And move the DC blocking cap after the buffer stage, right?
My better option is maybe to go to op amp balancing stage and drop transformer.


Lundahl,  Sowter,  and Carnhill would be the 3  I can think of for Europe.  OEP as well for a cheaper option.
Yes, I forgot Carnhill, thank you.

If you decided to use 2 opamp RIAA (nothing fancy) why not opamp balanced driver?
https://sound-au.com/project51.htm
Yes, you're right. It's a cheaper way and probably easier. I guess I’ll try this.
The reason I thought of transformer option is:
  • magic dust it could add to the sound
  • I have four LME49710 laying around in TO-99 box, not eight
But I could use another op amp for balancing. I'll look for a TO-99 one: I already have LM317/LM337 regulators in TO-99, I'd like to keep the visual coolness because the box will be transparent PMMA ;D
« Last Edit: October 27, 2020, 05:19:27 PM by laitue5 »
metal film 1/4W is ok

Moby

Re: Line output transformers
« Reply #5 on: October 27, 2020, 05:27:32 AM »
And move the blocking cap after the buffer stage, right?
My better option is maybe to go to op amp balancing stage and drop transformer.

Yes, I forgot Carnhill, thank you.
Yes, you're right. It's a cheaper way and probably easier. I guess I’ll try this.
The fact I thought of transformer option is:
  • magic dust it could add to the sound
  • I have four LME49710 laying around in TO-99 box, not six
But I could use another op amp for balancing.
with 1:1 ratio transformer the "mojo" or "magic dust" is really negligible. Unless you proceed with poor designed one or if you "push" it with the huge signal. If you want to make some soundstamp you can proceed with tube buffer to step down transformer, but that will be far away from simple few op-amp design. ;)
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

laitue5

Re: Line output transformers
« Reply #6 on: October 28, 2020, 04:19:29 AM »
I just looked at the schematic.
It seems there is some filtering at the output: 750 (820, 910) ohms, 100 nF, and a 1 uF output capacitor.
Most transformers like to be driven from a low impedance.
Also there is a risk that the 100nF + 1 uF will produce a resonance with the inductance of the transformer winding.
Personally I would prefer an extra buffer stage that drives the transformer from a low impedance.
I’m a bit confused with this DC blocking capacitor + transformer problem.
How should I use the two?
Here we have DC blocking capacitors right? https://www.jensen-transformers.com/wp-content/uploads/2014/08/as022.pdf
How do you set the value of this capacitor to keep it as silent as possible and not interact badly with an output transformer?

In the LME49710 datasheet they show an RIAA two stages preamp schematic without blocking capacitor.


Could I omit DC blocking serie capacitor thanks to LME49710 ultra low offset — and avoid DC-servo — and use gapped output transformer to be sure there will be no long term damage to the transformer?
« Last Edit: October 28, 2020, 04:32:15 AM by laitue5 »
metal film 1/4W is ok

abbey road d enfer

Re: Line output transformers
« Reply #7 on: October 28, 2020, 08:17:16 AM »
I’m trying to list hi-quality line output transformers options I have to add in a simple design I have in mind (nothing fancy, RIAA op amp preamp + output transformer to balance and load six or seven meters cables).

I found: Lundahl LL5402, Sowter 4652
I would like to buy Jensen JT-11-BMCF, find Triad HS56/66 or Freed 32035 but even at nice prices, overseas shipping cost is too much.

So, do you know european transformers that will do the job, contemporary or vintage (Haufe? Pikatron? Neutrik ? Studer?)
I’ll use it at the end of something like this: https://sound-au.com/project06.htm
Since you already need a bipolar power supply, why wouldn't you use one of the balanced driver IC's, such as THAT1646, SSM2135 or DRV134? Much cheaper than a good xfmr and much better performance.
An even cheaper alternative is using impedance balanced outputs; cost a penny.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

laitue5

Re: Line output transformers New
« Reply #8 on: October 28, 2020, 09:54:12 AM »
Since you already need a bipolar power supply, why wouldn't you use one of the balanced driver IC's, such as THAT1646, SSM2135 or DRV134? Much cheaper than a good xfmr and much better performance.
Yes, it would be a better way in many aspects. But I would like to etch my PCB with rounded traces, solder pretty TO-99 IC, axial capacitors… A bit strange I guess. It’s a difficulty I add to this project because I have four LME49710HA and a few TO-99 LM317/337 regulators in my drawer. This strange “artistic” exercise is an opportunity to learn more about op amps, line level, RIAA, balancing line level…

An even cheaper alternative is using impedance balanced outputs; cost a penny.
Hey, i've never thought about that. I have to read more.
« Last Edit: October 28, 2020, 09:58:31 AM by laitue5 »
metal film 1/4W is ok

 

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