The Schiit Freya+ Multi-Mode Preamp
The Schiit Freya+ is a new breed of chameleon-style preamp. It does whatever you want: Unbalanced to balanced conversion or vice versa, tube or transistor, buffer or amplifier with gain, relay switched volume, remote control, the Freya+ has it all.
Part 1: Tube Rolling
Of course you can roll in or roll out all existing 6SN7 variants of the world. But if you are not really an aficionado of the 6SN7, which applies to me, there are other tube types which you can use with the help of ready made noval/octal tube adaptors.
But one thing you have to keep in mind: The 6SN7 has 0,6A heaters and the heater power supply is providing unregulated DC using passive RC-filters, which I do like as an engineering approach in general. But if you select other tube types you have to take care that the sum of heater currents of all 4 tubes is 2,4A. Otherwise the heater voltage will be too high or too low. Also the tubes you select for the voltage amplifier stage (tubes to the right if you look from the front of the preamp) which run at appr. 7mA need to be medium-µ, which means 15 to 20. The cathode follower tubes run at appr. 2mA and need to have high transconductance at this relatively low anode current. µ doesn’t matter for a cathode follower.
The high voltage power supply is also based on RC-filters. But you don’t have to worry about tube currents as they are determined by constant current sources. Whatever tube type you roll in the tube will allways run at the same current.
My idea was to use the 5687 in the differential amplifier and the ECC81 as cathode followers. There are many very different sounding variants of the 5687 and I’m still not settled regarding this tube. The Tung-Sol sounds slightly too rich at the bottom and General Electrics are adding somewhat too much of emphasis on the mids. But I love what the 5687 tube does in all other areas. An alternative at this position could be the Russian 6H30 or 6H6 but I have not tried those types in the Freya+.
The 5687 consumes 0,9A heater current which leaves 0,3A heater current per channel for the catode-follower tubes. Perfect conditions for the ECC81 tubes. The ECC81 has a relatively high transconductance which leads to low output impedance and works at relatively low currents. I settled on the Telefunken ECC801S which for me is a sort of blameless ECC81. An alternative at this position could be to use the ECC88 (or 6922, 6dj8 etc.) which has even higher transconductance. I have tried that but I found the ECC88 hides details which I hear with the ECC801S.
Part 2: Modding
The WIMA MKP10 are decent audio capacitors but they are not really close to the quality summit of audio capacitors. Freya’s PCB leaves enough room for installing 4 V-Cap ODAM 2,2µF / 400V capacitors instead of the WIMAs. The ODAMs are not cheap but their biggest advantage apart from the sound is their small space requirement. I have used ODAMs in some other projects and for me they sound as they are not really there. A very close to ideal audio capacitor. The WIMAs in comparison appear to me as driving with a slightly applied handbrake.
The second modification is to replace the 8 pieces of 2W Dale metal film resistors with 2W Audio Note Tantalum types. There are 4 pieces of 22k resistors in the differential amplifier´s anode connection and 4 pieces of 47k resistor in the cathode follower´s ground connection. These tantalum resistors are also not cheap but their impact is easily heard. There are even two other even more expensive resistor types from Audio Note available. Still, they need some significant time to break-in and results right after installation are quite poor. The sound difference from the Audio Note to the Dale is not as big as the difference in capacitors from MKP10 to ODAM.
And yes opening Freya’s case can be a pain. You have to pull off the volume control knob and release the 11mm nut from the potentiometer. Then give the Freya a few mindful blows with a rubber mallet on the edge of the top plate from the back side. The top plate will come of and release the 3 push buttons to fall out. Reinserting those buttons is fun too.
Keep in mind that performing these mods on your Schiit Freya+ voids your guarantee!
So how did the upgrades / mods sound after the break-in ? I’m interested in doing the same mods to my freya+.
I find sound differences of mods/changes quite difficult to describe without mentioning all side conditions. Of course as always veils have been lifted and my wife asked from the kitchen how I possibly achieved such an improvement of the sound of my system.
Now seriously, I would rather describe the differences between the components.
1st WIMA MKP10 vs. V-Cap ODAM: The MKP10 surely is not a bad capacitor but leaves a certain haze between sound sources like voices or instrument. The ODAMs remove that haze and clear the way for a load of details which were unheard with the WIMAs. They are capacitors with the sound of a wire of very decent quality.
2nd Dale vs. Audio Note Tantalum: This difference is harder to describe because the biggest improvement has already been achieved with the change of capacitors. It is more like the icing on the cake. AN Tantalums need very long time to break-in. First they sound quite dissapointing like a step or two backwards but after about 200 hours they reveal even more tiny musical details I have not noticed before.
Provision for everything said is that you have found your set of tubes which give you the desired sound signature.
Thanks I appreciate the response,
what tubes are you currently using?
I’m using Sylvania GB5687WA in the differential voltage amplifier position and Telefunken ECC801S as cathode followers.
Great article! But how did you take the cover off the case? I also want to do the modification myself, but I’m worried about breaking something.
It sounds a bit rough but it is definitely worth investing into a decent rubber mallet to work the edge of Freya’s top panel from the back. I don’t know any other solution. Follow the instructions above!
Hi I have ordered the VCaps. Do you recommend any other resistors besides the Audio note ones as they work out quite expensive.
Would you recommend any other mods to the preamp.
Thanks
Blair
Hi Blair,
I personally would not put more money into the Freya+ besides for ODAM capacitors, AN resistors and decent tubes.
Of course one could go further and replace some of the electrolytics etc. For me the next step would be to replace anode and catode resitors with current sources but that’s a much more effort approach …
Regards, Norbert
I see 12AU7-to-6SN7 adapters in your photos. I also noticed your description of how the heaters are powered. Seems that each heater may have a series resistor fed from a regulated supply but not sure. If so, that arrangement would expect a specific heater current draw such that the final voltage at the fully hot heater would land at 6.3V at that particular tube – if it were indeed a 6SN7 drawing 600mA. But you have inserted tubes which draw 900mA each. So that “passive unregulated… RC filter” statement doesn’t fly right to me. If a series RC is there then those Sylvania GB5687WA would be under-voltaged. And then the warning to stay at 4 x 600mA = 2.4A total is very confusing … ” which leaves 0,3A heater current per channel for the catode-follower tubes”. Now that sounds like you are saying that the four sockets share a common 2.4A pool, no matter what the individual tube requires. Can’t be under – can’t be over. Hmmm? Clarify please. I would like to try 12AU7s which require 1/2 the heater current of the 6SN7 (i.e. 300mA each). What’s the worry?
Hi JRA,
In fact you nailed it already: The four sockets are using a common RC filter and not individual filters per socket. That’s why I was saying “take care that the sum of heater currents of all 4 tubes is 2,4A”. In my example it is divided into 2 x 900mA for the 5687 and 2 x 300mA for the 12AT7 which sums up to 2,4A.
Using 4 x 300 mA for 12AU7 will result in a too high heater voltage due to the total current being only 1,2A!
Regards, Norbert
Do the ODAM capacitors influence the stage without gain (direct) or only for the gain part with tube? (Sorry, I don’t know much and I only use my Freya+ without using the tubes) THANK YOU!
Hi tutonunez, The ODMA capacitors are solely used in the tube output circuit. AFAIK in earlier Schiit marketing material you could read that the transistor buffers are using DC-servos to maintain 0V DC at their outputs. Regards, Norbert
@Norbert
The V-Cap ODAM’s you fitted to the Schiit Freya+ should be oriented for best use (outer foil).
Did you do this when you fitted yours?
If so, can I take it that the correct orientation, is that used in your photograph?
Thanks
Yes, they should be oriented the best way on those photos, outer foil to low impedance side (cathode of 6SN7). But please verify with the VCAP website to be absolutely sure!
Great, thanks for responding.
I wasn’t sure if the tracks would be visible on the PCB, to trace their path. I will try and trace, but as a last resort I will just orientate as in your picture. The short lead is at the outer foil and the lettering on the ODAM’s is orientated toward the outer foil, so its obvious from the photograph which way round they should be fitted.
My ODAM’s are expected this morning, still weighing up whether to change the resistors as well. I’m considering the A.N. Tantalum – Non Magnetics, these are supposed to be a step up from the magnetic version you used. But its a lot of cash for a small improvement, compared to the Cap change.
I’ll come back with my thoughts after the mod/mods.
Just a tip for anyone reassembling a Freya.
The 3 push button caps fall out and don’t tend to stay in place when putting it back together.
Stick a piece of masking tape across the front face, over the holes and position the push buttons, pressing them against the tape.
This holds them in place while locating the lid.