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My Borbely All-Fet Preamp with Subbu
My Borbely All-Fet Preamp with Subbu
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Old 27th February 2016, 11:08 PM   #1
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
Default My Borbely All-Fet Preamp with Subbu

Hi. In the next post I'll present my newly completed Borbely All-Fet Preamp with Subbu built-in DAC. I'll try to explain the complete built process to give you an idea of the complexity of a line preamp.

At first I was lucky enough to buy from the Swap Meet a Borbely All-Fet preamp stereo PCB with all the options, Teflon PCB, Caddock & Dale resistors, Black Gate & Wima capacitors. The treat

I already had the Subbu and its pcb in stock that was waiting to be put to good use. I decided to install it inside the preamp, hence it will have a digital input option built-in. The Subbu DAC itself will be mounted inside a nice little mu-metal shielded enclosure to prevent noise contamination inside the preamp.

For the volume I was lucky enough to get a nice Muse stereo controller that supports IR remote control. It has a Mute function, IR code learning mode and we can set the starting volume.

Finally I had a nice enclosure that I bought years ago from an other member. I was planning to build a PassLabs preamp inside it, but since I built my XP-20 clone, it was not needed. I decided to use it for the Borbely.

So this is what I had at the beginning, but I was far from a complete preamp
Attached Images
File Type: jpg Img_1181.jpg (197.1 KB, 924 views)
File Type: jpg Img_7801.jpg (82.3 KB, 900 views)

Last edited by Algar_emi; 27th February 2016 at 11:11 PM.
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Old 27th February 2016, 11:23 PM   #2
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
Then I had to figure out what was missing, and to build the needed PCB assy.
First the preamp supply. I didn't bought the original Borbely high current rectifier and mute pcb and the custom power transformer.

For the transformer I went the dual mono route, using nice Amveco 12.5VA per channel. But I needed a pcb to mount them...

Then I needed an hardware mute delay to let the Borbely preamp servo settle at start-up. The original Borbely rectifier pcb was providing that. I also need an auxiliary supply isolated from the Preamp & Muse for the controller display. I also decided to use as much of my pcb leftover pcb material as possible. Here came the small auxiliary 12V supply and Mute timer.

Then to supply the preamp, my own replica of the Borbely high current rectifier PCB with Hexfred rectifiers and Nichicon Muse Gold KG filtering caps.
An other PCB was needed.

The rear connectors Input/Output connectors selection and routing was needed. Instead of having the input signal going around inside the preamp, and without a controller for the input selection, I decided to use a nice Elma input selectot switch I had in stock for the inputs selection. And a custom pcb installed on the back with take care of the In/out duty and the output Mute relay.

Finally the enclosure I use had a separate Tape output selector, dawn i needed to cover for that as well Then I decided to use a front rotary switch, coupled by flat cable to the back, where the inputs will be selected for the Tape output. An other PCB

You can see here all the PCB I made
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File Type: jpg Borbely_Preamp_PCB.jpg (213.7 KB, 847 views)
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Old 27th February 2016, 11:25 PM   #3
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
With all these PCB to install into the preamp, I decided to install a sub mounting plate inside. All the PCB will be fix to this plate and only a few standoff will hold the plate inside the preamp. I can also use this plate as insulation for the signal cables that will be routed underneath. This plate was treated with vibration absorption pads to prevent vibration.
Attached Images
File Type: jpg Img_1184.jpg (83.2 KB, 805 views)
File Type: jpg Img_1185.jpg (88.7 KB, 748 views)
File Type: jpg Img_1188.jpg (90.3 KB, 116 views)
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Old 27th February 2016, 11:27 PM   #4
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
Here the supply PCB completed, preamp dual mono transformers, high current HEXFRED rectifiers and auxiliary 12V supply and Mute timer. This last timer is also use to supply the front blue power-on led.
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File Type: jpg Img_7796.jpg (166.9 KB, 267 views)
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Old 27th February 2016, 11:32 PM   #5
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
The Muse controller used for Volume is has good as its supplies. The Muse controller doesn't have built-in pre-regs and it needs +/-15V. I used the already available +/-24V full discrete low noise supplies from one channel of the Borbely preamp to supply +/-15V pre-regs mounted on a separate PCB on the Muse controller. The pre-regs have CRC pre-filter for the lowest noise supply possible

The controller can control a I2S display, but the display is noisy and will pollute the preamp and Muse supplies. To prevent that I use a I2S magnetic insulator and a separate 5V supply that I produce from the auxiliary 12V Mute supply.
I mounted this small pcb on the Muse Controller.
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File Type: jpg Img_1186.jpg (125.1 KB, 312 views)
File Type: jpg Img_1187.jpg (135.6 KB, 225 views)
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Old 27th February 2016, 11:40 PM   #6
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
This is the Subbu DAC and its supply installed inside the preamp. I use a DPDT switch on the preamp back to select the Input 1 source, normal analog Single-ended input or the Supply output. The DAC has an insulated SPIDF BNC connector on the back as well.

For the ones not familiar with the Subbu DAC, well it is a killer little DAC, excellent sounding. It uses the self contains ESS ES9023 DAC (no output op-amp needed) and the excellent Wolfson WM8804 SPDIF digital receiver. The WM8804 uses advanced jitter attenuation PLL with low intrinsic jitter, and is compatible with 24bits/192kHz. Even if it a very small footprint DAC board, it is very well designed, with CLC filtered pre-filters and separate regulators for all supplies. Extensive listening was done for every part selection and the PCB layout is optimized for the best sound. The DAC itself is mounted into a shielded Mu-metal enclosure. An external dedicated power supply, also designed for the lowest noise possible provides the +5V DAC supply. All in all, it is a great sounding DAC.
Attached Images
File Type: jpg Img_7799.jpg (155.5 KB, 223 views)
File Type: jpg Img_7811.jpg (94.5 KB, 179 views)
File Type: jpg Digital_Input.jpg (14.0 KB, 168 views)

Last edited by Algar_emi; 28th February 2016 at 12:09 AM.
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Old 27th February 2016, 11:43 PM   #7
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
This the rear Input/Output & Mute PCB. It uses an Elma dual pole rotary switch for source selection, very short path to the input connectors using resistors legs wire connection (CFM55 Dale resistor legs were used for the connection). It also has the Tape selection flat-ribbon socket and the Output Mute relay.

I use CMC RCA connectors. The preamp is Single-Ended only but the chassis I have has provision for balanced XLR In/Out connector.
I decided to installed them for convenience only. The Balance input is 'Pseudo Balance Only' and has only pin2 (+) & gnd connected.
The Output is only Pin2 and Pin3-Gnd are shorted. They are ready to connect to a PassLabs amp for example.

When you use a input selector switch on the preamp back it is always a good thing to use a flexible shaft coupler between the switch and the front connecting rod. With DIY there is always some error between switch and front button axis, and the flex coupler take care of that. I got mine from Mouser, from Adafruit, Part 485-1176
Attached Images
File Type: jpg Img_7805.jpg (180.9 KB, 224 views)
File Type: jpg Img_7810.jpg (125.0 KB, 189 views)
File Type: jpg Img_7803.jpg (123.4 KB, 159 views)
File Type: jpg Img_7804.jpg (118.3 KB, 142 views)

Last edited by Algar_emi; 27th February 2016 at 11:57 PM.
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Old 27th February 2016, 11:51 PM   #8
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
The chassis separate Tape front selection switch forces me to have this function. I used a simple front dual pole rotary switch from Lorlin. I used a flat ribbon cable to route the selected input to the rear Tape output. It worked really well.
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File Type: jpg Img_7809.jpg (109.7 KB, 142 views)
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Old 27th February 2016, 11:56 PM   #9
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
The Muse controller supports an external I2S display. It shows the volume setting, flash on/off when in mute and it is used to display the IR code learning mode sequence. I didn't want to drill the front panel, hence I installed the display so it can be seen from a top cover small ventilation vent.

As the Muse controller told me, the display adapter can cause preamp supplies noise contamination, and that was the case here. I planned in advance and the 12V Mute auxilliary supply was used to supply a separate and floating 5V supply for the Display only. The I2S controller signal is routed using a ADUM1250A I2S magnetic insulator, that decouple completely the preamp supply from the display ones, solving the noise problem.
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File Type: jpg Img_7792.jpg (124.5 KB, 170 views)
File Type: jpg Img_7800.jpg (121.0 KB, 149 views)
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Old 27th February 2016, 11:59 PM   #10
Algar_emi is offline Algar_emi  Canada
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My Borbely All-Fet Preamp with Subbu
This the complete preamp inside view. The sound is very good and the builtin Subbu Dac is a plus for sure. There is no such thing a simple full function line preamp
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File Type: jpg IMG_7814.jpg (686.4 KB, 278 views)

Last edited by Algar_emi; 28th February 2016 at 12:01 AM.
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