(re)searching for a better preamp

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#584
rudi said:
Hi Leo

the only valve based pre that I think that can came close will have to be a 6h30 based one.

but we know that Carlos will never be able to do the comparison because. " the tube, she is still comming to portugal" :devily:
Click to expand...

Hi Rudi,

I'm not exactly sure which one to try out to be honest, nearest I have to 6h30 is 6C45PI😀 the gain on those would probably be overkill

So in your honest opinion would you say the AD815 is as good or even better than the 6h30?
I've heard a few valve pre's but unfortunately not in my own system
 
#585
t. said:
Yes, Morphine is great and that sax😎 it does like to be played loud though so I normally only listen to it when the neighbours are out, it also gives the speakers a good work out
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I remember an unforgettable concert from Morphine here in Lisbon, the guy put two saxes on his mouth, grabs one on each hand and plays. 😱
You know, there's also something fantastic about that out of tune two string bass ("the other strings are not needed..." - Mark Sandman).
Mark Sandman is missing. :xeye:
 
#586
t. said:


So in your honest opinion would you say the AD815 is as good or even better than the 6h30?
I've heard a few valve pre's but unfortunately not in my own system
Click to expand...


It is difficult to say. properly setup I think the AD815 is better (but only by opinion). but then the 6h30 have a sweetness and balance that I am still chasing (I am close with the use of the OPA627 on the Walt Jung design).
the 6h30 strong points: more weight in the mids and tops.
the AD815 have this to a lesser extend (more clinical), the OPA627 does rectify it to some extend. but then the bass is mind blowing

When i tested the pre on a valve amp on saterday it had some weird artifacts in the tops but then again the preamp only had 4 hours of break-in at that time. will test it again with a valve amp to see how it matches. It is a perfect match with the X-calibre.

the best amp i have ever heard is a hybrid using 6h30's and exicon output mosfets. with 650VA per rail (One toroidal for every rail)
 
#587
Tube Pre

I have a couple of the supertubes, but have not used them yet. They have great specs.
I do have a linestage that uses a single 6080 as the voltage amplifing device. It operates at 60 volts on the plates and 80 ma per side. With the 2.5 ampreres heater draw it gives off a lot of heat.
Even that monster is not in the same league as the AD815 as far as dynamics and power. This one is special.
I found an issue with my implimentation of Carlos' design. There is some breakup at elevated volumes at certain frquencies. I reinstalled my cascoded, current sourced, single ended, dc coupled jfet line and it shows the issue is MY version of the AD815.
Suspected it is the high impedance supply I am using for the +/-15 volt rails. Planned to build another supply using a discrete low feedback, widebandwidth pair of regs.
Last night while falling asleep it hit me where the most likely cause of this distortion is. I have small input transformers inbetween the source selector and volume pots.
I have measured around 1 mv on the input of the preamp. I think that as the volume level is increased this may increase also. This is saturating the transformer cores and causing this distortion. The dcr of the transformer is 1800 ohms, so this works out as half a micro amp. I did not think it would be a problem.
Plan on measuring the input dc and nulling the voltage to minmize this. Right now the nulling circuit was set to minmize output offset. The input offset did not seem to vary as much as the output when I checked it on another circuit board and rotated the volume pots
If it cannot be reduced to less the a couple tenths of a millivolt, guess the input transformers will have to go. Sad to maybe lose them.

George
 
#588
carlosfm said:


I remember an unforgettable concert from Morphine here in Lisbon, the guy put two saxes on his mouth, grabs one on each hand and plays. 😱
You know, there's also something fantastic about that out of tune two string bass ("the other strings are not needed..." - Mark Sandman).
Mark Sandman is missing. :xeye:
Click to expand...


I'd love to watch them live Carlos, no matter how good a Hi-Fi you can't beat that live experience🙂
Its hard to imagine the guy playing two saxes at once, quite amazing really how well it goes together.
A lot of my friends have never heard of Morphine😕
 
#589
rudi said:



It is difficult to say. properly setup I think the AD815 is better (but only by opinion). but then the 6h30 have a sweetness and balance that I am still chasing (I am close with the use of the OPA627 on the Walt Jung design).
the 6h30 strong points: more weight in the mids and tops.
the AD815 have this to a lesser extend (more clinical), the OPA627 does rectify it to some extend. but then the bass is mind blowing

When i tested the pre on a valve amp on saterday it had some weird artifacts in the tops but then again the preamp only had 4 hours of break-in at that time. will test it again with a valve amp to see how it matches. It is a perfect match with the X-calibre.

the best amp i have ever heard is a hybrid using 6h30's and exicon output mosfets. with 650VA per rail (One toroidal for every rail)
Click to expand...

Thanks Rudi,

Well I'll let you know what I think as soon as the latest AD815AY board is up and running, I like the idea of being able to swap the boards, I wonder if Carlos nulling circuit could be added too to try out with your board😉
 
#590
Hi t.

you would have no problem adding his nulling circuit. we can design it on the daughter board. then you can just swap it out. (that is if you build his version onto the board.) you will see that the pins have different functions
 
#591
Snubbers

Hi T,

Have you tried the snubber (0.47 ohm etc) after the ALW super reg or just after the double reg. I know Rudi got great results after the double reg.

Rudi, have you built the straight 815 to compare with Jung yet?😀
 
#593
Re: Snubbers

Dr.H said:
Hi T,

Have you tried the snubber (0.47 ohm etc) after the ALW super reg or just after the double reg. I know Rudi got great results after the double reg.

Rudi, have you built the straight 815 to compare with Jung yet?😀
Click to expand...

Hi Ryan,

I only tried the snubber with the double reg on Rudi's smd AD815 board, as soon as I get the rest of the parts for the AD815AY board I intend to try the double regs,ALW super regs both with and without snubbers and the different nulling including the Jung version, Rudi's board should be ideal to try all this out😀
 
#596
carlosfm said:


Huh... try it.
I'm out of time to test brands of caps on the snubber:clown:
I don't have anything nasty on my parts box, I'm very picky when buying caps.
No need to spend a fortune, Philips/BC 037 does it for me.
No green Lelon caps, please. :devily:
Click to expand...


Did you like the Frako Caps ? 😎

Now I am using Frako, Siemens, Philips, Daewoo, Rubycon, G-luxon and JD(cheap).
I also have a pair of Blue Lelon.... didn't tried yet!
Buf if they are like the NA caps.... it's rubbish :dead:
 
#597
XELB said:
Did you like the Frako Caps ? 😎
Click to expand...

I have some around, I used some of them on a super-reg, but I can't say for sure if they are good or not.
They remind me Roederstein caps (which are IMO very good), and I like their "retro" look & feel. 😎
 

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