Restek Fantasy amp cap upgrade + opamps and Bursons!

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Hi Guys,

I thought I’d 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, I’ve 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 wouldn’t 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 ZA’s) I’ve 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 2604’s for LME49720HA’s decoupled with Rubycon ZA’s. I wasn’t convinced the pre section was particularly good even with the different opamps. I’ve 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. I’ve now swapped out the LME’s for Burson discrete opamps and bypassed the buffer stage. These discrete opamps are expensive but well worth the money (it’s also what I use for I/V on my TDA cdp).
The results are unbelievable! This amp was already punchy and dynamic now it’s 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 I’ve ever owned!
The cost of the caps totalled approx. £80, the 2 LME49710HA £26 and the Burson £90. I hadn’t initially planned to upgrade to Burson so the cap swap wasn’t 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
before.jpg


in the middle!
during.jpg


After :):)
Final.jpg


output stage with FM's
Outputstage.jpg


More FM's
FMdecouple.jpg


F&T Smoothers
FTsmoother.jpg


More F&T Smoothers - all 80,000uF!!!
80000uFFT.jpg


Bursons up close
Brusons.jpg


Bursons2.jpg


Cheers!!!

PS I've asked here before but if anyone happens to have a diagram, I'd really appreciate!
 
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!!!
 
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!!!
 
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!!!! :D:D:D
 
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!

Regards
 
This guy thinks Arcam make good amps, hmmm. Arcam CD players are good, but their amps were the worst I heard when I last bought one new a few years ago. They sounded dull and shut-in compared to offerings from MF, Rotel and Roksan.

The point made is maybe why we don't see many Resteks.

But that's beside the point really, yours is totally un-standard now and clearly loads better for it!!!
 
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!

Regards

So, I have an amp that cost approximately £2000 which sounded pretty good to my clearly untrained ear when new. I have now changed all the caps and effectively rebuilt what was admittedly a poor pre-amp stage. I have shared my proud achievement with the rest of the DIY community.

My Thanks are
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!

Regards

1 I am not fumbling
2 nasty music-killer-rip-off-amp (your very offensive opinion)
3 Arcam, Creek, MF, Mission,Sugden - in the most part the later amps are very poor. (note I said in the most part)
4 Offense is not intended here but Restek is one of the worst manufacturers I know - it sounds even worse than Burmester!
How the f*ck can that not be offensive when i'm proudly displaying my achievement.

Regards to you too:confused::confused::confused::confused:
 
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Well, the parts are squeezed together a tad too much. The input sockets are nasty cheap. The cabling looks chaotic and an Alps pot at that price range...

Restek generally has a tendency to sound 2D and sharp - quiet unbritish. I would strongly recommend to use Nichicon Fine Gold and/or other Nichicon & Elna caps. Rubycon is too open and bright for this amp. I guess Panasonic FC or FM is not enough to tame this amp. Please use british caps for the large ones maybe Nichicon or Epcos will do too. More bias for the output stage! Panasonic pot instead of the nasty muddy dirty & nervous sounding Alps. Cardas Silver/Rhodium RCA sockets will bring back some body & authority if you want it darker than you can use WBT (speed loss). I would be careful with doubling the cap values, this has a tendency to sound slow and shut-in. Even technically seen - this can be a disadvantage.
Good luck.
 
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Just forgot, the big white ceramic resistors are really nasty. They are in the 0.1 - 1.0 Ohms range I guess.

At this price range...:cannotbe: Sorry but even the cheapest british amps do have better parts - fact. German HiFi does have a strong tendency towards rip-off. Please don't get upset, I'm just trying to be realistic.

I would change the ceramic resistors to MPC or Rosenthal or Isabellenhütte or the big black US resistors with silicone coating - forgot the name.
 
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Just forgot, the big white ceramic resistors are really nasty. They are in the 0.1 - 1.0 Ohms range I guess.

At this price range...:cannotbe: Sorry but even the cheapest british amps do have better parts - fact. German HiFi does have a strong tendency towards rip-off. Please don't get upset, I'm just trying to be realistic.

I would change the ceramic resistors to MPC or Rosenthal or Isabellenhütte or the big black US resistors with silicone coating - forgot the name.

I will take a look at those resistors for sure.

All of the internal power stage caps have been changed to FM (were BC) and the results are very good. The opamp on the power stage (I'm unsure of its function without a diagram) has been changed from BB604 to LME47910HA and this has been decoupled with Nichicon. I also repalced the elco's for DC blocking with Wima MKS2.

The main smoothers are replaced with F&T SI and been changed from 10,000uF per rail to 20,000uF per rail. I beleive this has been responsible for the huge leap in dynamics!!!:D

The origianal preamp consisted of a Buffer (BB2604) and gain stage (BB2604) the Blue Alps pot and a final gain stage (BB2604).

I have bypassed the 1st buffer stage and replaced the remaining 2 BB2604's with Burson discrete opamps. The result is that the entire preamp stage is now discrete. The Bursons are decoupled with a mixture of Black Gate and ZA. I have to say I'm very happy with the results so far.

It is indeed on my list to replace the horrid input phono sockets with something like CMC silver over copper for the 1st 2 inputs at least

You seem to be very well informed on this amp. Do you have a schematic in particular of the power stage? You also say that I should raise the bias. Can you provide details of how I can do this.

All in all, I really like to look and feel of this amp. :)

Many thanks

Ian
 
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