Borbely EB-1198/116 Preamp

[Ray P]

I think I picked up the bargain of the year!

I saw a pre-amp listed on DIY Audio - the guy said it was an Erno Borbely design but didn't know which one. I studied the photographs and had a hunch that it was the 1198/116 All-FET design so, as it was listed for a very good price, I took the plunge. It arrived this week and my hunch was correct.

https://audioxpress.com/article/The-All-FET-Line-Amp

Although I bought the pre-amp with its chassis, unfortunately the guy had dismantled it and cut all the in/out wiring so this afternoon I've hooked up some input/output connections and checked it out - all good. I've just spent a couple of hours listening with it driving the Sony VFET follower I recently built. The pre-amp is phenomenally good, so much resolution and delicacy, it is a delight with the VFET, even just using my cheap Ariston bench speakers.

This pre-amp is an absolute keeper and I'll work on rehousing it and making a few improvements - It has, probably starting with bypassing all the relay input/mute stuff (I only need one input) and replacing the Alps Blue pot with a better volume control, maybe with a Slagle autoformer I've not used.

[Ray P]

I took the plunge and cut down the pre-amp PCB to remove all the input switching and Alps volume pot - it will be a single input build with a better quality volume control and no remote control. I'm leaning towards using my Slagle autoformer attenuator.

[Ray P]

So a bit of a change in that I've decided to keep the Slagle autoformer for it's original VFET preamp project and I've ordered an Academy Audio Muses volume control board to use with the Borbely project. The Academy Audio purchase includes a power supply similar to Jan Didden's 'Silent Switcher' - 5V in for +/-14V out. To supply the 5V I'm repurposing the power supply on the preamp board that was used for the input relays, replacing the 12V transformer and 7812 with 6V and 7805 items.

https://www.academyaudio.com/product-pa ... -low-noise

[Ray P]

I've been hacking the Borbely pre-amp PCB today, preparing to install it in a chassis and hook-up the Academy Audio Muses volume control module.

The components on the right and the small transformer are now a floating 5V supply that will power the Academy Audio switcher supply (5V in, +/-14V out) - it's floating because the switcher has an isolated grounding arrangement.

Having discarded all the input switching relays and powered Alps blue volume control, I've had to connect some of the hookup wires to PCB tracks that I've scraped the solder resist from, so I've drilled some holes and used cable ties to provide some strain relief, lest I accidentally peel the tracks off the board.



Waiting for a chassis to be delivered from Aliexpress now.

[Ray P]

I've received the preamp chassis from AliExpress and have started work on it. I've started with the front panel for the Muses volume control module.

Step 1 - Make the opening in the front panel



Step 2 - Insert the 3D printed bezel



Step 3 - Install the Muses Volume control module and test.

[simon]

Impressive Ray, looks like a commercial unit.

I can't remember, did you use Front Panel Express to 3D print the front cover?

[Ray P]

Impressive Ray, looks like a commercial unit.

I can't remember, did you use Front Panel Express to 3D print the front cover?

Cheers Simon. I did most of it in front panel designer then exported it to .stp format and tweaked it in Fusion 360. I got it 3D printed at JCB, very reasonable cost.

[simon]

[pre65]

I got it 3D printed at JCB, very reasonable cost.

It should have been yellow then.

[Ray P]

It should have been yellow then.

Hmmm....

I meant JLC, of course.

[Ray P]

Borbely preamp is coming together nicely.

[Ray P]

I just need to install the input/output RCAs now.

[Ray P]

After resolving a ground loop noise issue I've now finished by Borbely pre-amp project and it is sounding very good driving my Nelson Pass Sony VFET follower. The pictures are of the pre-amp under audition, into my Sony VFET and driving my Lowther horns and it is sounding very good against a silent background. The lid is now screwed down so job done.

If anyone is interested, the bezels for the RCA sockets are 3D printed (by JLCPCB), the same as the front panel bezel.

[andrew Ivimey]

Yuk, is it possible to say 'yuk' in a non judgemental kind of way? It looks so already neatly built micoelectronically controlled/ built that all that's left is to screw down the outputs. If so - who cares!?

[Nick]

I did a design a couple of years ago using the 72320 volume chip. I wonder of they followed the same standard design. If so, may be worth checking the 10pf cap across the output op amps. I found replacing what I had originally used (a ceramic) with a leaded polystyrene may make a huge difference (in a good way) to the sound.