Vintage Silicon

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Ray P
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#16 Re: Vintage Silicon

Post by Ray P »

Most of the DACs I have built have. or are able to have, differential/balanced (ought to find out the difference) outputs, typically with transformers or because they're balanced voltage out devices. It makes sense to have the option to use that balanced capability so I thought I would make a new buffered passive 'pre-amp' using my remaining four BUF-03 devices (and, obviously, a suitable attenuator).

Here's a schematic of the single-ended BUF-03 buffer;
Capture.JPG
I'm thinking I'll just double up on the buffers so that there's one on each hot/cold signal line or is that simplicity exposing my lack of knowledge about these things? I'm assuming DC offset would still need to be nulled on each line realtive to ground.

Any advice/observations will be greatfully received.
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Nick
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#17 Re: Vintage Silicon

Post by Nick »

I'm assuming DC offset would still need to be nulled on each line realtive to ground.
That's sort of the point with balanced, there is no ground just the difference between the two lines.
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#18 Re: Vintage Silicon

Post by Ray P »

Thanks Nick.

Methinks I should've had more coffee before posting the question; I do understand the basic principle of having the two lines so that the differntial signals cancel common mode noise, although, to be honest I had always assumed pin1 of an XLR to be ground.

I'll have a think and try again.
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#19 Re: Vintage Silicon

Post by Nick »

although, to be honest I had always assumed pin1 of an XLR to be ground
Pin 1 is connected to the shield of the cable, but the pin inside the equipment is connected to ground, chassis, signal ground or nothing varies. Also don't assume that ground is voltage wise between the hot and cold pin, consider phantom power.
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#20 Re: Vintage Silicon

Post by Ray P »

I've been having a think about this and have concluded that I was asking the wrong questions.

It is true that most of my source components are equipped with balanced outputs (or could be very easily) but I allowed my thinking to be muddied by a discussion about the input stage of the Mellow OTL amp (on the 'Beginners' topic), which is able to take a balannced input that is likely to yeald better results than the single-ended option. The reality is that I haven't build a Mellow OTL amp so it's all hypothetical whereas the amps I have working (or in progress) all have single ended inputs. So the question is actually about using balanced sources with single-ended amplifiers.

I want the ability to use an analogue attenuator (rather than relying on digital volume control) and I have a balanced passive attenuator so what I believe I actually need is a buffer stage that'll take the outputs from the balanced attenuator and convert them to single-ended to drive my single-ended amplifiers.

If the Mellow OTL ever becomes a reality I could just put a suitable balanced attentuator on its inputs.

I'll start to look out for a balanced to single-ended unity-gain buffer and start a new thread in due course.
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#21 Re: Vintage Silicon

Post by Ray P »

I finally got around to reworking my buffered passive to make use of the Academy Audio Muses volume control module I have available. Still some stuff to do to reinstall the power supply but tested it on the bench today with a temporary hook-up and it's coming together well. The Muses unit has an LED display and remote control sensor and I've experimented with having a front panel 3D printed to accomodate them - quite pleased and the textured finish you get with 3D printing looks quite nice - I'll use 3D printing again!

Image

Image
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pre65
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#22 Re: Vintage Silicon

Post by pre65 »

The front panel screw looks wrong, should it be a countersunk type ?
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#23 Re: Vintage Silicon

Post by Ray P »

pre65 wrote: Sat Mar 20, 2021 9:07 pm The front panel screw looks wrong, should it be a countersunk type ?
Yep, the countersinks are actually for allen bolts - didn't have them to hand when I was putting it together to test.
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#24 Re: Vintage Silicon

Post by Nick »

To be more helpful
I'm thinking I'll just double up on the buffers so that there's one on each hot/cold signal line or is that simplicity exposing my lack of knowledge about these things? I'm assuming DC offset would still need to be nulled on each line relative to ground.
Yes, you could but by doing that you are not taking advantage of the balanced nature of the signal. If you used something like a THAT 1200 or a transformer you would get the advantage of the cancellation of errors and ignoring any DC offset (up to 12v with the THAT part).

https://www.mouser.co.uk/datasheet/2/40 ... 532288.pdf
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#25 Re: Vintage Silicon

Post by Ray P »

Thanks Nick, that looks interesting and helpful - I'll have a proper read later as (proper) balanced operation is still something that is of interest.

It'll not be with the BUF-03s though as, apart from this buffered passive preamp project, I've reserved the remainder of them (including a couple of spares) for use in the preamp I'm working on for the MoFo/OB project. That preamp will use, after the volume control, 2P29L valves to give around 20dB gain for the MoFo but I'm also including a second set of outputs after the volume control, buffered with the BUF-03s, to feed the LP filter/bass amplifier. In essence I'm putting active and buffered passive 'preamps' together in one chassis so it will be quite versatile for other use cases.

Although I'm not currently using the balanced operation possibility, the fact that my DSD DACs have transformer coupled outputs is useful as it means the Muses volume control module shouldn't see any DC offset on its input, eliminating the need for (electrolytic) caps there.
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#26 Re: Vintage Silicon

Post by Ray P »

Finished of my BUF-03 equipped buffered passive 'preamp' this morning - nulled the DC offset of the buffer stage and had a listen with headphones - sounds good and no pops or other nasties (I omitted the DC blocking caps from the volume control) - just letting it cook before final adjustment of the DC offset and fitting the top of the enclosure.

Image

Image

For info, it's equipped with an Academy Audio Muses volume control with remote control (volume, balance, mute) and the power supply is a Jan Didden 'Silent Switcher' (+/-15VDC from a 5V wallwart).

I'm now using countersunk allen bolts to fit the front panel to keep Phil happy.
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#27 Re: Vintage Silicon

Post by pre65 »

Ray P wrote: Sun May 02, 2021 10:58 am
I'm now using countersunk allen bolts to fit the front panel to keep Phil happy
Allen set screws ? :lol:
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#28 Re: Vintage Silicon

Post by steve s »

pre65 wrote: Sun May 02, 2021 11:12 am
Ray P wrote: Sun May 02, 2021 10:58 am
I'm now using countersunk allen bolts to fit the front panel to keep Phil happy

Allen set screws ? :lol:
??? Aren't set screws headless
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#29 Re: Vintage Silicon

Post by Ray P »

The packaging says 'Countersunk Allen Bolts' so that'll do me.

I know set screws as grub screws so I'm with Steve.
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#30 Re: Vintage Silicon

Post by pre65 »

steve s wrote: Sun May 02, 2021 12:13 pm
pre65 wrote: Sun May 02, 2021 11:12 am
Ray P wrote: Sun May 02, 2021 10:58 am
I'm now using countersunk allen bolts to fit the front panel to keep Phil happy

Allen set screws ? :lol:
??? Aren't set screws headless
No, a bolt is only partially threaded but a set screw is threaded it's entire length.

Headless threaded thingies could be grub screws.
The only thing necessary for the triumph of evil is for good men to do nothing.

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