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Paul Spencer

DIY audio: what are you building?

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10 minutes ago, highcut28 said:

is that pre amp kit from www.tubes4hifi.com ?

yes indeed it is

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Thanks Owen.  Yep, I had to do a bit of googling to remind myself about which direction is which :)

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Ever tried to fix something which is not broken because you think it shouldn’t work that way it does. I have made four of these active load preamps. In the second last one I added a headphone driver. When head phones are plugged in the jack it cuts out the RCAs out which are used when Elite is just a preamp. 

To get better performance from the preamp/HP amp I moved the pot from the backend (where it is on the other three builds) to the front end. That meant the expensive Jansen CuPIO output caps could feed directly into the HP chip amp with no other input cap needed. 

The reason why this cct. is described with attenuator on the rear is because active load is very microphonic. With the attenuator on the output you hold the noise down and the music level very quickly swamps any noise from the tubes. BUT put the pot on the front you get the full microphonic noise unattenuated and the music level lower. Fortunately some old RCA 6SN7s aren’t naturally noisy and with these in the system the preamp/HP amp is very good. But put some better Psvane or Chuguang tubes in the noise swamps the music. 

I’ve spent two weeks trying to get the microphonics out. It’s a part of the build. Best I can do is move the pot to the backend and add some interstage caps into the HP chip amp section. Best way to go.

7E1E4D85-4AFE-4F5B-8218-877C69B30374.jpeg

25BF875C-0789-4A6A-B9A1-9762CF509581.jpeg

9F28A68B-EC1B-48F9-BA3A-A15360BC7F44.jpeg

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A little bit closer.  Probably another few hours of work left.
 
installed a Khozmo 64step attenuator with amrg resistors. 
 
duelund 20ga tin plated wire used for hook up.
 
will heatstrink exposed cables after run-in.
 
58F00717-FF40-4EE5-B3F4-74C6377338B4.thumb.jpeg.0c9f0a93f89e19fa9c4a0b8002048010.jpeg
Nice work mate. You always have nice taste in gear.

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5 hours ago, Sub Sonic said:

Can I ask where you got the tubing? Looks interesting 🙂

A place in melbourne called Darpac. They use similar tubing for concrete pillars, but it is often plastic lined, which i avoided as i'm relying on adhesives a lot for this build

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4 hours ago, tuyen said:

A little bit closer.  Probably another few hours of work left.

 

installed a Khozmo 64step attenuator with amrg resistors. 

 

duelund 20ga tin plated wire used for hook up.

 

will heatstrink exposed cables after run-in.

 

58F00717-FF40-4EE5-B3F4-74C6377338B4.jpeg

You have some nice capacitors there. Have you had a chance to experiment much with the Miflex caps?

 

SS

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1 hour ago, Upfront said:
4 hours ago, tuyen said:

A little bit closer.  Probably another few hours of work left.
 
installed a Khozmo 64step attenuator with amrg resistors. 
 
duelund 20ga tin plated wire used for hook up.
 
will heatstrink exposed cables after run-in.
 
 

Nice work mate. You always have nice taste in gear.

Thanks mate.  I cant help myself. Go crazy on partsconnexion after every payday.   Forever poor.    Boutique hifi though!

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Thanks mate.  I cant help myself. Go crazy on partsconnexion after every payday.   Forever poor.    Boutique hifi though!
I actually laughed out loud when I read that!

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8 minutes ago, Sub Sonic said:

You have some nice capacitors there. Have you had a chance to experiment much with the Miflex caps?

 

SS

 This will be my first taste with the Miflex copper foil caps.   They seem well built.  Price was right as well  (compared to duelund/mundorf sgo/jupiters).    

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1 hour ago, tuyen said:

Thanks mate.  I cant help myself. Go crazy on partsconnexion after every payday.   Forever poor.    Boutique hifi though!

Have you used Hificollective in the UK? Decent prices and realistic shipping cost compared to North America 🙂

 

SS

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Posted (edited)
On 23/05/2019 at 3:27 PM, A J said:

I think I want this t-shirt

I have one.

 

Although is a bed shirt these days  :)

 

EDIT:  Oh wow... That was an old post.  Have I been gone that long  (?!!)

Edited by davewantsmoore

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Made these up for a fellow SNAer and DIYer. 1/2M twisted silver plated fine copper  wire. Two earths at the originating end one at the terminating. Following Allan Wright’s guidelines for light weight RCA plugs. Silver soldered and directional. 90pf capacitance. 

BBD49031-985C-476F-92D4-A6418777333D.jpeg

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Going on with the Audio Analyser thingo...

 

Small recap: STM32H7 nucleo microcontroller board with Ethernet interface, a DAC and an ADC, and software in Python to see audio data over the Ethernet interface. All open source.

 

Work is ongoing, no easy task, however, some major successes that encourage to go on:

- Was able to find a configuration that allows me to sample at 96KHz smack on.

- Was able to send out a waveform through the DAC (PCM1793)

- Was able to get data in on the ADC (PCM1802)

- Was able to send commands (stop, start, read, etc) to the microcontroller using the Ethernet interface and Protocol Buffers (Google: "protobufs").

- Able to read in data from the ADC and send it over the network interface to the PC.

 

And this is where we're at. I still have some issues to look at, synchronisation, operation, GUI, and many more, but, the basic stepping stone is there.

 

First image is the device itself: at the far end, in white, the controller board and just in front the ADC and DAC. Both are bridged together, basically the DAC output feeds into the ADC input. A tangle of cables, but it works. That should be replaced in some future by just one board.

IMG20190818190000.thumb.jpg.09dc347b33fd8c22fc485d46291fb5f0.jpg

 

And here, the data capture displayed on the PC:

Figure_1.thumb.png.9442a5edeb582ed08a1ed0cec2d81bf6.png

I haven't scaled anything, the format is still 32 bit signed integer and you can see I have some spikes that are due to some memory overlap on the data transferring. I need to sort that out, like I said, among other things.

 

Cheers,

 

Alberto

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On 13/08/2019 at 6:54 PM, Sub Sonic said:

Have you used Hificollective in the UK? Decent prices and realistic shipping cost compared to North America 🙂

 

SS

Used them on a number of times. 

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