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Chip Amps Amplifiers based on integrated circuits

My_Ref Fremen Edition - Build thread and tutorial
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Old 8th February 2018, 09:05 PM   #3631
Joseph K is offline Joseph K  Hungary
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Jac, again ��

And yes, I was talkibg about HSgnd.

And I think your problem merits a bit of discussion:
A good balanced/ SE converter in front of the amp, and how to integrate it into the system..

Ciao, George
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Old 9th February 2018, 02:10 AM   #3632
madisonears is offline madisonears  United States
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Jac and others:

I just finished rebuilding my friend's amps (installing Evo compensation and putting them in proper enclosures) using your wonderful little converters, running off the regulated LM318 supply with no difficulties. These provide superb fidelity and an excellent opportunity to implement balanced cable input to the MyRef. If you ever consider getting boards made, I'd gladly buy a couple more just to have them around. I don't foresee changing out the LM318, and they could be handy in other applications.

Too bad they don't play nice with other opamps' power supply, so you need to build another complete supply to adequately isolate them from the new opamps? What a weird interaction. Hope it's worth it.

In my friend's amps, I have installed a DPDT switch (signal and return) to allow selection between single-ended and balanced inputs. The switch is high quality, but in either position puts a slight veil over the sound. I compared by bypassing the switch. I'm sure in many systems and with many speakers and to some listeners it would be inaudible. I actually prefer the single-ended connection but he hasn't decided. He spent a LOT of money on the balanced IC's and hates to not use them.

Peace,
Tom E
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Old 9th February 2018, 07:57 AM   #3633
koldby is offline koldby  Denmark
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Quote:
Originally Posted by Kim Schultz View Post
Thx Dario

I made some progress today and now I just have to wait for the last parts to arrive from Mouser.

The BOM and clear instructions really make this build as easy as a kit build.

Now I need to decide what to use for cabinets for these amps.
Hi Kim
You have 4 ampboards, are you planning to make a balanced version ?
I am asking as I have 4 boards unassembled with that (balanced and more power) strategy in mind.
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Old 9th February 2018, 01:27 PM   #3634
lehmanhill is offline lehmanhill  United States
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Quote:
Originally Posted by madisonears View Post
Jac and others:

I just finished rebuilding my friend's amps (installing Evo compensation and putting them in proper enclosures) using your wonderful little converters, running off the regulated LM318 supply with no difficulties.
That's great news! It's not clear why the change from the LM318 to the ADA4627 caused the oscillation. The LM318 actually takes a little more power, but the ADA4627 is a little faster.

I was getting about 90 mV of DC offset in one channel only when the balanced line receiver was powered and no input. Per George, that indicates that the balanced line receiver was oscillating even with no input. Both channels distorted badly with music using the ADA4627 and the balanced line receiver, so the power supply issue seems to be a bit worse with music. One possibility suggested by George is that an oscillation on the power supply lines may be powered by the inductance of the wires running between boards and the capacitors on the balanced line receiver.

George,

Anything to add?

[/QUOTE=madisonears;5335224]Too bad they don't play nice with other opamps' power supply, so you need to build another complete supply to adequately isolate them from the new opamps? What a weird interaction. [/QUOTE]

Actually, I'm happy to know what the problem is and how to fix it. It also gives me a chance to build a Jos regulator, my name for it, from the Reliaxed 2 pre-amp. It's perfect for a low current supply like this and gives a measured -120 dB noise.

[/QUOTE=madisonears;5335224]In my friend's amps, I have installed a DPDT switch (signal and return) to allow selection between single-ended and balanced inputs. I compared by bypassing the switch. I'm sure in many systems and with many speakers and to some listeners it would be inaudible. [/QUOTE]

I agree that going balanced isn't really needed in most home audio systems. I went that way because I was originally planning on having each amp channel and crossover sitting behind each speaker. That would make a long, line level IC run which would potentially benefit from the lower common mode noise of the balanced line. Looking back, single ended would probably have been fine. Besides, I have never gotten around to moving the amps out to the speakers.

It looks like my attempt at multi-quote didn't work well. Sorry. Still learning.

Jac

Last edited by lehmanhill; 9th February 2018 at 01:38 PM.
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Old 9th February 2018, 02:14 PM   #3635
lehmanhill is offline lehmanhill  United States
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Default Overview of My Ref and Balanced input

It might be a good time to discuss balanced input and the My Ref amp. Although there are amps that are designed to be balanced input, the My Ref is designed for single ended input (you know, that RCA IC input). There a lots of ways to handle the balanced input with My Ref.

Double the Amps

It sound like Kolby and perhaps Kim are planning on turning the My Ref into a true balanced amp. In this case, they will use one My Ref for the '+' input and another My Ref for the '-' input. The result will be twice the power, balanced design all the way to the speaker terminals, and no need to convert the input to single ended. Very Sweet.

If you don't go that way, you need to convert the input signal from balanced to single ended and you have to make sure that converter is of high quality or you will lose any noise/sound quality improvement that you paid for with the balanced lines.

There are a couple of ways to convert balanced to single ended.

Transformer

The first is an input transformer. These are very nice and can maintain a high level of CMRR across a wide range of frequencies. They do have a few drawbacks. First, they are expensive. Typically $75 or more per channel. Also, they do limit bandwidth, some would say a little more than desirable. And they are a touch finicky. You have to be careful to balance input impedance with ringing of the transformer. And input impedance affects bandwidth. No free lunch here.

Active Converter

The second approach is an active approach, essentially an op-amp that measures the difference between the input '+' and '-' and outputs a single voltage to the single ended input. As I discovered, this needs a high quality power supply that should be isolated from other supplies. You also need to be careful to have matched impedance all the way through. The homemade boards that Tom and I used are the simplest type of balanced line receiver with just a single high quality op-amp and relatively low impedance resistors (1k).

There are other, more complicated designs and IC designed for this purpose. I felt like I could get better specs with discrete precision resistors and a simple design, but some of the more complicated versions (THAT 1200 series, for example) provide bootstrapped CMRR and RF filtering.

After playing with this stuff for a few years, my opinion is that balanced lines are great for pro's using very long IC runs, but not really worth the trip for home audio. But if you find yourself with a nice piece of balanced equipment and want to integrate it with your single ended amps, take the time to learn about converting to single ended and make sure you put together something that is high quality.

Jac
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Old 9th February 2018, 03:53 PM   #3636
koldby is offline koldby  Denmark
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Quote:
Originally Posted by lehmanhill View Post

It sound like Kolby and perhaps Kim are planning on turning the My Ref into a true balanced amp. In this case, they will use one My Ref for the '+' input and another My Ref for the '-' input. The result will be twice the power, balanced design all the way to the speaker terminals, and no need to convert the input to single ended. Very Sweet.


Jac
Actually more like 4 times the power, if the load is not too low. Double the voltage out results in four times the power.
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Old 9th February 2018, 04:30 PM   #3637
lehmanhill is offline lehmanhill  United States
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My mistake, you power hungry dude. :-)
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Old 9th February 2018, 10:19 PM   #3638
koldby is offline koldby  Denmark
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;-)
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Old 11th February 2018, 05:00 PM   #3639
Panelhead is offline Panelhead
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Default Balanced My_Ref

I have considered making a balanced version. Do not have any two amplifiers the are identical.
My main reasoning is my dac/preamps are balanced output only. Been shorting ground to - to go single ended. Not exactly SOTA.
I have a box of Cinimag input transformers left from a bunch of preamp projects. Considered shoe horning a pair into a Full Evo. But have not found the time. Also concerned about EMI and RFI levels at the rear of the chassis. But to downgrade the Sonics.
Would also consider bypassing the input cap to see if a transformer would keep the unit stable. Never liked using an input transformer directly into an AC coupled input.
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Old 11th February 2018, 05:24 PM   #3640
lehmanhill is offline lehmanhill  United States
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Quote:
Originally Posted by Panelhead View Post
My main reasoning is my dac/preamps are balanced output only. Been shorting ground to - to go single ended. Not exactly SOTA.
I have a box of Cinimag input transformers left from a bunch of preamp projects. Considered shoe horning a pair into a Full Evo. But have not found the time. Also concerned about EMI and RFI levels at the rear of the chassis. But to downgrade the Sonics.
Would also consider bypassing the input cap to see if a transformer would keep the unit stable. Never liked using an input transformer directly into an AC coupled input.
If you want to convert balanced to single ended, download the AD797 datasheet. Near the end, they have an app note for a "differential line receiver". That's what I have used with success. Of course, powering it separately, even if it's only it's own regulator, should be considered.

I was going to comment on another project I did with DC coupled input transformers, but on second thought, it was tubes and that's a very different animal.

Jac
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