Genera mods...
Printed From: Graham Slee Hifi System Components
Category: DIY AUDIO
Forum Name: DIY Audio questions and answers
Forum Description: www.diy-audio-kits.com ... superb audio kits for experienced constructors
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=2290
Printed Date: 27 Mar 2026 at 4:04am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Genera mods...
Posted By: TIM
Subject: Genera mods...
Date Posted: 09 Jul 2014 at 10:36am
|
Hello all! I've been using my Genera phono preamp for over 2 years now and it's brought me a great deal of pleasure - many hundreds of LPs have coursed through it's little components and I've enjoyed every moment. Recently, I read through my copy of the notes that Graham sends out with the Genera kit and there's a couple of things he mentions that have piqued my interest and started me wondering if there's any mods I could carry out that would elevate it's performance even further... Firstly, he writes that the electrolytic capacitors should be of at least 35V DC working value, but using capacitors of 63 to 160V will lead to improvements in clarity. Secondly, there's mention of using film bypass capacitors to effect a further boost to sound quality. Has anyone tried this? Surely we'd be silly to ignore such a tempting carrot dangling right there! I'd be really interested in any thoughts on this, and as I'm no expert on electronics does anyone have suggestions as to makes/values for the capacitors that may be suitable for such a modification. Regards, Tim. |
Replies:
Posted By: LOINER
Date Posted: 09 Jul 2014 at 12:47pm
|
Oh Dear I suspect your going home with note ------------- STUART SOLO ULTRA LINEAR DIAMOND EDITION LAUTUS DUAL MONO 1.5M INTERCONNECTS GRAM AMP 2SE |
Posted By: TIM
Date Posted: 09 Jul 2014 at 2:34pm
Is going home with a note a good thing or a bad thing? 
|
Posted By: ICL1P
Date Posted: 09 Jul 2014 at 5:55pm
|
It can be entertaining as well as educational. ------------- Ifor ===== Reflex M & ACCESSION M, CuSat50, Majestic DAC, a Proprius pair. |
Posted By: Fatmangolf
Date Posted: 09 Jul 2014 at 10:04pm
|
I modified my Genera with switchable input capacitors so I had 100pF, 220pf and both as options. Graham was very helpful. ------------- Jon Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
Posted By: TIM
Date Posted: 14 Jul 2014 at 7:51pm
| Jon - did you ever try the bypass capacitors on your Genera? Last night I read back through the whole topic on the Genera design (all 46 pages, took ages) and I noticed that you'd asked Graham about capacitor types, values etc for bypassing. It sounds so good currently that I wonder if I'd be best to leave it alone, but you know what it's like... My turntable is going away in a few days for a bit of TLC and some upgrades so now seems like a good time to look into any possible tweaks to the phono amp. |
Posted By: Fatmangolf
Date Posted: 14 Jul 2014 at 8:41pm
|
I didn't get round to bypassing the input and output capacitors. If you leave the preamp alone and powered up, you'll be able to judge the impact of the TLC on the turntable better. ------------- Jon Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
Posted By: Graham Slee
Date Posted: 14 Jul 2014 at 9:44pm
|
Hi Tim, bypassing can work, but can easily be "overcooked". The combinations of series inductances can unite to create spikes. It's not too bad however, because series impedance is usually high enough on electrolytics to dampen spikes. To calculate a suitable value the impedance of the circuit the capacitor is working to must be found. I think on the negative feedback the grounding resistor is 330 Ohms? (I'm going on memory), so the series DC blocking capacitor sees this as its load. To get an in your face result the bypass capacitor would need to have a turnover frequency with that resistance of around 1kHz - 3kHz. A more subtle rendition would require a turnover frequency in the region of 8kHz - 12kHz. If you can do the math with C=1/2pi*f*R then you won't need any further help. If not I can suggest some values. ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |
Posted By: TIM
Date Posted: 14 Jul 2014 at 11:01pm
| Thank you for your replies Jon and Graham. I think you're right actually Jon, it would be wise to leave things unmodified until the turntable returns else I risk having no familiar reference to work from. |
Posted By: TIM
Date Posted: 18 Jul 2014 at 9:33pm
|
When my turntable does return, and the time comes to maybe do a few modifications to my Genera, I've been considering rehousing it in a slightly more roomy case - don't get me wrong, the case that comes with the kit is lovely, but it'd be nice to have something a bit bigger (and heavier) so my interconnects don't pull it around. Now, pardon my ignorance - but does the case need to be metal? Is it providing shielding or grounding, is there any reason why the case couldn't be plastic or even wooden - in fact could there be any benefits? I'm thinking of DNM and their plastic amp cases and the claimed benefits... |
Posted By: Graham Slee
Date Posted: 19 Jul 2014 at 9:55pm
|
I'd read this and then consider such claimed benefits: http://www.compliance-club.com/archive/keitharmstrong/design_techniques4.html - http://www.compliance-club.com/archive/keitharmstrong/design_techniques4.html One proponent of zero shielding argues that shielding reflects the magnetic field back at the conductors, thus causing feedback (negative and positive) which interferes with the signal... In which case a printed circuit board is absolutely useless, and signal traces should be separated by massive distances... just picture your amp being the size of your room! Also, you would not be allowed in it whilst wearing a metal zip fly, watch, or any other metallic article... Neither would your speakers, turntable, any other signal source... or even any mains wiring! All of these items could reflect back the magnetic field surrounding one of many signal conductors which make up a circuit. But none of this is necessary because the magnetic fields are so tiny, and this is why sub-miniature items such as smartphones, tablet computers, sat-navs etc work, even with all their conductors so tightly bunched together. The metal case being a conductor (the ground conductor - or even a "floating" one) is a considerable distance away by comparison. Further info on this can be found here: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html - http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html and by plugging in real world values like 0.00001 in the "I1" box and 0.0005 in the "r" box you should get the result which is an extremely weak magnetic field of 4e-9. Then, by all means, have a go with part two. Let me tell you a short story... when I was aged 10 at school, we had to do a presentation on something we were interested in. I'd not checked my facts and told it the way I imagined it to be... it was met with howls of derisive laughter from the boffins of my class. Some "grown ups" in hi-fi seem to be doing exactly what I did at the age of 10. I learnt a valuable lesson that day: not to look like a complete tit! "Materials technology in amplifiers: The DNM Series 3 Pre-Amplifier designed in 1984 saw the first use of construction materials that do not interact with the amplifier's magnetic fields. DNM are still the only ones doing this over 20 years later! " I wonder why?  ------------- That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps |