Fosi Audio GR70 Quad Tube Headphone Amp / Preamp

[WaxMaster]

Wondering if anyone has tried the new Fosi Audio GR70 Tube HPA (preamp). I bought one from Amazon to give it a try. Comes in tomorrow. Pure, gratuitous tube madness.

https://www.amazon.com/Fosi-Audio-GR70-Tube-Amplification-Preamplifier/dp/B0FB3P3RZT

My “test” will be to run it as follows:

WiiM Pro (RCA Out) —> (RCA In) Fosi GR70 Preamp (RCA Out) —> (RCA In) Topping L30 II HPA (1/4” out) —> Sennheiser HD 660S2

I’m not sure that the L30 II is necessary, but I read the GR70 can struggle driving some higher impedance cans. If not, the L30 may go back to Amazon. Will have to see how it goes. Thought seriously about picking up the Topping D50 III as a DAC for the L30 II. That may be a next payday kind of thing. Were that to happen, I think the chain would be:

WiiM Pro (S/PDIF Out) —> (S/PDIF In) Topping D50 III (RCA Out) —> (RCA In) Fosi GR70 Preamp (RCA Out) —> (RCA In) Topping L30 II HPA (1/4” out) —> Sennheiser HD 660S2

Would love to hear your thoughts…

Peace…

I am sure you have spent a considerable amount of time with your new Fosi GR-70 by now. Were you as stunned as I was by it's sound quality as both a headphone amplifier and preamplifier? I spent a large sum of money trying to find the right combo of tubes to use with the GR-70, so let me save you some time an money regarding possible tube upgrades. As much as I love the sound of my Raytheon JRP-6AK5 black plate tubes and RTC/Mullard M8100's, nothing compares to the Voshkod 6ZH1P-EV Rocket tubes I purchased from Yen Audio on eBay. With the Voshkod tubes in the input stage and a NOS pair of 1944 RCA JAN-CRC-6AC7 output tubes, I am swimming in a immersive sea of holographic music. I have everything I could possibly hope for with this combination of tubes. The input tubes seem to have the biggest impact on the sound quality of the GR-70. Do not skimp here and just buy the Voshkod Rocket tubes and thank me later. I just did an A/B demo between the JRP-6AK5's, M8100's & Voshkod 6ZH1P-EV's playing music from my Qobuz " Speaker, Cable & System Burn-in Tracks " public playlist through an Eversolo DMP-A6 Master Edition Gen.1 (w/Eddy Pardo Special Edition Linear PSU). This is connected to a Geshelli Labs JNOG 3 (AK4499EX) dac via a Cardas Clear USB cable. The JNOG-3 has Sparko's SS2590 Pro op-amps on the XLR outputs and a Virtual Hi-Fi Hypersonic op-amp on the rca outputs. One pair of AQ water rca's connect the JNOG-3 to the Fosi GR-70 & another run of AQ Water's connect the Fosi to my my Kali IN-5 studio monitors. The headphones that I am using are Verum 1 MKII's, Verum 2's and Sivga SV-021 dynamic headphones. The sound I am hearing from this desktop setup is sublime. The Fosi just makes beautiful music when the right combination of vacuum tubes are installed. After just 10 hours of playing time on Voshkod Rocket tubes, I have absolutely no interest in listening to any of my other 6AK5 tubes. The final upgrade will be a Fiio PL-70 linear psu when it is released in early 2026. This will replace to stock ac/dc wall wart power adapter that ships with the Fosi. I will also purchase a 2nd GR-70 as a backup "spare" in the event that anything ever happens to the one I use now. I have no desire to upgrade any further. The Fosi GR-70 checks all of the boxes for me, and I love the fact that it was super affordable. I wish my other gear offered the same price to performance ratio as the Fosi does.

 

[solderdude]

cool story with lots of impressive name dropping all condensed in a WOT.

 

[Alexium]

Has anyone been able to measure the output impedance? I wonder about its feasibility for IEMs.
This seems to not be an OTL amp, see the two small(ish) transformers:

Spoiler

 

[dvp]

• Is there any chance it will drive DT 880 600 Ohm 96 db?