CheffDeGaar UGS preamp vs other or Borbely

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I bought the boards to make the CheffDeGaar UGS preamp. In reading through the threads, I came across a few people that didn't like the preamp compared to:

Borbely SE JFET final.pdf

Or the Choky and Oly Pumpkin Pumpkin & Shunty.pdf

Before I spend the money on the build (the UGS with the shunts will run a fair amount), do folks have experience with the other preamps I've noted?

I'm running an F5 amp and need gain.

compared to: Borbely SE JFET

Balanced designs only work if they're balanced. :clown:

Balanced also implies that the left and right part (aka inverting + non-inverting) operate identical (step two is building left and right channel as close as possible).
Which means that you have to invest in a lot of parts to build a proper one, especially those with local NFB only (Burbely rear ended).
The main reason why commercial products of relative simplicity are very costly, (sale tag also pays for the rejects and the time invested in them)

Nice example is the current Goldmund folly at the SS forum.
Original parts are hard (expensive) to come by, and a Lateral MOSFET output stage of 3-4 complementary pairs without source resistors obligates buying a lot of them for proper matching.
Name something Swiss that cost $25K in 1994, the hurd will scream for boards.
MSRP of a '90s Rolls paid for the hand-painted Golden line on the sides, a dozen scar-free Connolly leather hides, a flashy bird on the radiator.
It also paid for a hand-assembled and blueprinted engine, including the mechanic's signature.
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Nagging questions as I build preamp(s)

It's taken longer than it should have, but I think I'll have all the parts for a fully balanced system in a few days.

As you may have surmised, I'm new to DIY audio. I found the most difficult part was getting specifics from people that have done it before. I certainly understand a commercial enterprise keeping trade secrets. I seem to have encountered an issue around not being expert enough to warrant specific answers to real questions, or being told to "read the thread". I can tell you, I've read some of these threads 20 times. When you don't understand something new, reading over and over again is not the answer.

Some examples:
I still don't know what the distortion figures are for an F5 with different feedback resistors. Folks point to feeback resistors of 75 ohms and 100 ohms (instead of 50 ohms) as ways of getting more gain, but I haven't seen any analysis of the distortion using those parameters. I don't have access to the equipment to check it myself.

I still don't know how to refigure resistors for a balanced version of the F5 using the IRF outputs. If anyone knows, I'd appreciate a heads up. The electronics expertise to answer this question is beyond my abilities.

And getting back to this thread, I've read about a number of people seeking preamps for their F5. The one's I've listed in this thread seem like naturals for the F5. I would have guessed many people have tried these out and have A vs. B thoughts.

Any input is appreciated.
Official Court Jester
Joined 2003
Paid Member
well - I can say that you're given with answer to your question , asked in this thread ;

build Papa Borbely's preamp and enjoy ; it's on par with two other you mention .

regarding other questions ...... ask them one by one ........ here or in any other thread ;

just one thing - do not bother with F5 distortion ; it's certainly better than most amps you can buy for sane amount of greenies ;

distortion numbers will not tell you what's important , on this level of game .
more important thing in changing feedback ratio in F5 , or changing type of outputs is , say , damping factor change , same as distortion harmonics distribution ;
long but short story ;
if you say that you don't have enough electronic knowledge - you can't be filled with knowledge in short ..... you must trust someone to tell you differences in simple terms

speaking of which ...... (game) you didn't tell what speakers you have , room , listening habits ( meaning on SPL ) ;
ZM -

Thanks for the responses.

From reading the forum, I'm trying to build:

XF5 Balanced (already have "regular" F5 - first build)
Preamp - UGS, Borbely SE Balanced JFET, or Pumpkin
Speakers - OB FF85K and Alpha 15" ala Martin King

Except for the F5, I'm ordering parts and building everything else. In fact, I'm just finishing measuring 220 transistors for their Idss to make matched sets of 8 for each balanced item (amp and preamp).

I guess my most burning question is if anyone is running an "XF5" balanced with the IRF output devices. If so, what resistors are they using? I'd like to see how folks optimized the IRFs in a balanced configuration. I suppose it's possible no one is using the IRFs in the "XF5", but I'd be surprised.
Joined 2003
Paid Member
I would also like to see F-5X as well. As far as preamp, I'm going to try the Pumpkin, once banks wake up. I've got IRF devices, also have Toshiba, which is what I'm using on next build.

I'm going through the entire F-5 thread again, taking notes as to interesting info, straining out the babbling....

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