music hall 25.2 DAC mod

I've had the DAC25.2 for about a month and it sounds very good. The EH tube not so good. Replaced it with a 60's Tesla (not JJ) E88CC as well as a 60's Amperez 7308. It's a tough choice between the Tesla's better bottom octaves and the Amperex overall Freq. balance which sounds "right", at least to me. Still going back and forth between the two.

It's interesting to also switch to between the 25.2 and the Benchmark USB. Definitely notice subtle differences.

I'm wondering about the mods as well. Keep us posted.

I recently got this DAC too. I have a NOS 60's French Mazda (Philips-owned) 7308 tube en route from Brent Jessee.

I'm also toying with opamp swaps in the RCA tube circuit - replacing the stock (2) OPA2134 and (1) OPA2604.

Not wanting to spend the cash on Burson's at this point.

Does anyone have any opamp swap experiences/recos for this DAC. I've been considering AD8066, AD8620, or LM4562.

Thanks,

Adam

I, too, got a NOS '71 Mazda from Brent Jessee (w/RTC label) and it really transformed this DAC. He said he'd put it up against any EAT valve as they
are reversed engineered replicas built to very high tolerances but can't use
the same metals used in the NOS tubes. Something about the AEC won't allow it.
Now I have no desire to swap out anything else.
I read a blog somewhere else (from '08) that the DACs take about 500 hours
to break in so don't be in any rush to mod this unit. I have about 200+ hrs on
mine and it continually improves. It's like watching a kid grow.
A really good kid.

Nonoise - I got the Mazda 7308 yesterday. It's a Miniwatt/Dario label from 1967. Installed it yesterday afternoon and have been breaking it in since - haven't done any serious listening yet.

As a side note - did yours have the actual Gm numbers on the box label?

Being a noob with tubes, please bear with me.
There is a label from Brent Jessee on the box that has a space for Gm1 & Gm2 and both have a 'check' after them.
Tube type is 6922 and brand is RTC, Mfg. = Mazda. Prod. type = 1971 France.
On the tube itself was a slip of paper with the numbers 27-29 &-18/-18.

Hope that helps and that you get the same results as I did.

On an aside, I tried a '70s Matsushita, from another site, that was touted as a great tube (not from that site but from various sites) with negative results: flat, closed in mids and highs and generally dull sounding and this Mazda is quite the opposite. Open, airy, fleshed out (more body), dynamic, very quiet, with decent bass. Almost organic. The top getter is tilted at a 45 degree (I thought it was damaged at first) and kinda looks like how one would wear a beret.
Fitting for a French tube.