Thanks. I have indeed looked into ACA, since it is the hottest thing right now. But my assessment is that, among the more powerful amps (i.e., not the WHAMMY), F5 is the higher performing one, especially in the area of noise (which is relevant in powering headphones).

How would this compare to an F5 in driving Hifiman HE6 (i.e., hard-to-drive planars)? Trying to decide whether to build an F5 customized for headphones or WHAMMY. My headphones are all pretty hard to drive (HE6, Pioneer SE700, etc.) -- I need both voltage swing and current. I have been using a...

Many thanks. Received Caddock MP925 yesterday, put them in with big heatsinks, and they actually make a big difference over the (1) the old carbon comps and (2) the metal oxides that I installed earlier.    I will add in a 2-resistor attenuator. It sounds like the most sensible and easy solution. 

Anyone? It would be especially helpful to know how the gain could be modified. Thanks.

Happy holidays!   So the old potentiometer has become very scratchy. My solution was to bypass it and use an outside digital potentiometer instead (I also changed R102 and R202 from 910k to 50k). The problem, however, is that my DAC outputs a healthy 2.1v and so the amp is already very loud...

Question regarding the 2pf capacitors, C101, 102, 201, and 202. I am trying to find replacement parts, but they don't go as low as 2pf. What would be the highest value I could use there? It's much easier to find, let's say, 0.01uf/1000v parts, but that's thousands times of the original value...

I will be there with my:   Stax Lambda original Koss ESP6/9 with Stax's 6-pin plug Stax SRD-7 Koss A250 Pioneer SE700 MB Quart QP95 DIY amp with mass regulated power supply (and may be some other vintage phones)   All modified.

Quote:   Thanks. I have compared these against the circuit board of my SRD-7SB and the SB seems quite dissimilar.    I googled everywhere, and nobody seems to have posted a schematic for the SB. 

Does anyone has the schematic for SRD-7SB? 

SRD-7SB is just a transformer box -- you need to connect it to a speaker amp with a fair amount of power (or a very strong headphone amp with high gain). The bare wires are for connection to the speaker amp. 

Quote: I agree about the metal box and good power supply. But you can always buy/build a 9-12v linear power supply with minimum cost. I am also thinking about fitting the amp in a metal box, but I need to plan it well so that I can easily put the amp back in the plastic box for any...

Just got my new pair of Koss ESP 950. Compared to my old Stax Sr-Lambda normal bias (which broke down a few weeks ago), the Koss is must more linear with a flatter frequency response. The sound is also more immediate -- things are happening near ears with greater detail.    On the other...

Quote: Thanks. I will keep that in mind when I get a Pro phone. 

Quote: Thanks!