Restek Fantasy amp cap upgrade + opamps and Bursons! - diyAudio
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Old 15th May 2010, 06:41 PM   #1
UV101 is offline UV101  England
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Default Restek Fantasy amp cap upgrade + opamps and Bursons!

Hi Guys,

I thought Id share my latest round of mods here! I usually hang out in the digital domain but thought it was about time I treated my amp to the same treatment my CDP's have been getting!

I've had my Restek Fantasy MKI amp for a few years now and knowing its about 13ish, Ive been thinking about recapping it and changing a few opamp and having a general poke about. I struggled with Restek and although they've emailed me just about piece of paperwork on the unit they produced, no schematic was forthcoming!

The design is very good. Fully dual mono power sections running from separate 100VA transformers, recs and caps (10,000uF per rail). This was my 1st upgrade! I swapped out the tired Philips LL caps for replacement F&T of equivalent value. I then added the same again off board bring the total smoother capacity to 20,000uF per rail (a whopping 80,000uF in total). There are a handful of similar Philips local decoupling caps around the power stage ranging from 220uF to 470uF. These were swapped for similar value Panasonic FMs with the exception of the main op device caps, here I changed from 2x470uF to 1x470uF and 1x1000uF.
There is an opamp in the beginning of the power stage. This was originally a BB604. I had previously tried to swap out for single Burson discrete opamps but the amp wouldnt come out of protect mode. I would love to know why but without the diagram...... I swapped this for LME49710HA decoupled with Nichicon ( I may swap to Rubycon ZAs) Ive also swapped the input DC blocking set up here from a 22uF elco bypassed with a 1uF MKP to a WIMA 22uF MKS2-XL cap. Both the signal and signal ground are decoupled. I guess this is for complete isolation.
The preamp section is pretty basic (it looks like the went into the power stage!!!). It consisted of an opamp buffer into an opamp gain stage followed by a Blue Alps volume control and finally another opamp gain stage. I had previously changed the standard BB 2604s for LME49720HAs decoupled with Rubycon ZAs. I wasnt convinced the pre section was particularly good even with the different opamps. Ive now recapped the LM317/337 regs supplying the pre section and have some Avondale tracking regs boards on the way to try here (Thanks Chrism/Les) and I may run separate TX and PSU when I build them. Ive now swapped out the LMEs for Burson discrete opamps and bypassed the buffer stage. These discrete opamps are expensive but well worth the money (its also what I use for I/V on my TDA cdp).
The results are unbelievable! This amp was already punchy and dynamic now its off the scale! The components have been in for about 50hrs now and as such should be starting to burn in nicely. I would now describe the amp as massively dynamic. It was quite a forward maybe harsh sound before but this has subsided without loss of detail. It sounds very capable easily the best amp Ive ever owned!
The cost of the caps totalled approx. 80, the 2 LME49710HA 26 and the Burson 90. I hadnt initially planned to upgrade to Burson so the cap swap wasnt going to be that expensive! In the end, it was no cheap upgrade but considering the gains, I consider it to be well worth it.
I would definitely recommend a cap refresh to anyone with 10+ year old amp. Those low ESR F&T caps (10,000uF/63v) are excellent value for money @ 7 each. The Panasonic FM caps are also great value for the elcos in the amp stage itself!

I still need to fit the Bursons properly and get it all back together here's the pics cos I know we all like pics!!!! :lol:

Before
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in the middle!
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After
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output stage with FM's
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More FM's
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F&T Smoothers
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More F&T Smoothers - all 80,000uF!!!
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Bursons up close
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Cheers!!!

PS I've asked here before but if anyone happens to have a diagram, I'd really appreciate!
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When Bitstream came out, I thought, my God, what are we going to do...? Ken Ishiwata http://www.hifisounds.co.uk
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Old 16th May 2010, 10:48 PM   #2
SimontY is offline SimontY  United Kingdom
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Looking good Ian, but those Bursons are on STILTS! I've never heard of Restek before, is it a UK company?

Any further mods planned for it?

Simon
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Old 17th May 2010, 11:26 AM   #3
UV101 is offline UV101  England
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Restek is German. For some reason its not that popular overhere. It has a reputation for being very powerfull but a bit sterile. In this case, i'd put that down to the use of multiple opamps as a pre. Its certainly not sterile with the Bursons in!

Those Bursons were only hooked in to test btw!!! I'll be fitting them properly as soon as the DHL man arrives with the final couple of caps for the pre stage!!!
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When Bitstream came out, I thought, my God, what are we going to do...? Ken Ishiwata http://www.hifisounds.co.uk
JA-88D Class A, Audio Aero Capitole MKII, Focal and Kimber "Leave Nothing as Standard"
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Old 17th May 2010, 11:39 AM   #4
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Looking good. I am suprised those normally efficient Germans used so many opamps!

Brent
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Old 17th May 2010, 06:17 PM   #5
SimontY is offline SimontY  United Kingdom
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Probably got them 0.00001% lower THD

Some people design amps based on numbers, not sound. Then the marketing people come and stick a pretty front on. Or something like that
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Old 17th May 2010, 07:12 PM   #6
UV101 is offline UV101  England
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indeed! I would have thought a buffer and a gain stage would have been enough for anyone!!!

All I can say right now is that those 2 Bursons and removing the buffer opamp have made this preamp section fully discrete and fully awesome. Those Bursons went in on Friday afternoon and the amps been on since. I had a listen this morning and there is so much more going on. The sound is bigger and faster and tighter. The Bursons have removed any trace of shrill and sound more balanced with bags of micro details coming through. Obviously changing all the caps and adding the Bursons was a major upgrade but boy what a difference. I'd stick my neck on the line and say this amp is now possibly one of the best I've heard. Pleased as a pleased thing on a pleasing day out in please town I am!!!
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When Bitstream came out, I thought, my God, what are we going to do...? Ken Ishiwata http://www.hifisounds.co.uk
JA-88D Class A, Audio Aero Capitole MKII, Focal and Kimber "Leave Nothing as Standard"
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Old 18th May 2010, 07:17 AM   #7
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Don't forget the Bursons take approx 100hrs to burn in so you will get more improvement.

You can't beat discrete

Brent
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Old 18th May 2010, 08:43 AM   #8
SimontY is offline SimontY  United Kingdom
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I bet it's a nice match for your Philips CD960 as well Ian
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Old 23rd May 2010, 07:24 PM   #9
UV101 is offline UV101  England
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Indeed the 2 do seem to play nicely together Simon!!!

I've now been running in for about a week. I've tidied those 'stilts' and sorted some caps. The 1st Burson is now ZA decoupled and the 2nd one is Black Gate 470uF decoupled.

Its really very good now. Very revealing and accurate sounding with the most amazing pace and stamina. Possibly one of the best upgrades I've carried out!!! (well the most recent lol)

I've also treated myself to an upgrade from 4tc to 8tc! yay!!!!
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When Bitstream came out, I thought, my God, what are we going to do...? Ken Ishiwata http://www.hifisounds.co.uk
JA-88D Class A, Audio Aero Capitole MKII, Focal and Kimber "Leave Nothing as Standard"
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Old 24th May 2010, 04:14 AM   #10
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It is frustrating to see Brits fumbling with a nasty music-killer-rip-off-amp like Restek. You have Arcam, Creek, MF, Mission, Sugden etc. Offense is not intended here but Restek is one of the worst manufacturers I know - it sounds even worse than Burmester!

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