bada bing

Just the standard NFB loop from "+" output to "-" input as documented in the project files. No NFB on the "-" side. I have my dynamid gain set at 3 (10k & 5K resistors I believe). Servos set-up as in the project files for balanced bridged. I haven't had this bridged version on a scope yet but no audible signs of bad behavior. Sounds better I think than the same boards did configured as 4 full channels. Are there tweaks to try for feedback loop(s) ? Is there an improvement by adding a second feedback loop ? Any hints or a link ? I've done some due diligence with search engines and reading, but I've never found much on adding the second (-) feedback loop beyond the observation it would require major mods to the circuit. I'd be very interested to read of practical methods to address the potential non-linearities on the "-" side of the amp. It does seem to be the biggest theoritical downside to a pretty elegant circuit.

I don't think there is any doubt Fitz can handle this one, I'm not reading where I wrote anything even slightly contrary to that. Maybe there's a translation error from Alaskan and Texan. Happens to me all the time at work as well. Not seeing the insides of one version of the many Gilmore Dynamic variants doesn't seem to invalidate my post in any way. Anyone spending the money to mod a Gilmore Dynamic variant to balanced ought to consider the balanced bridged option. I think maybe it gets less consideration than is due because SE input to Balanced output seems funky. It's cheaper, easier, less complex and aurguably a cleaner implimentation than full four channels in a Dynalo because of the unique servo arrangement and the differential signal created at the inputs. Maybe in this case it's been considered and rejected or there's some other tweak going on. That would be interesting to see discussed, at least to me. I'd love to learn something about the dynalo/Gilmore dynamic or be given a new tweak or tangent to try. I've spent quite a bit of time on dynahi/dynalo projects, partly because they make good HD800 amps to my ears.

What are you using for the PCB for the additional channels ? The balanced bridged configuration of the Dynamic/Dynalo amp has some advantages over full balanced end-to-end. You don't get to use all 4 wires of a balanced source, but it runs off a two channel pot and avoids the added complexity and potential for component mismatchs by having a 2 channel verses 4 channel front end. I messed around with a couple versions of fully balanced Dynalo before I went with the balanced bridged configuration. The trade offs work better for me and it makes an almost perfect amp for a "balanced" HD800. Eventually I'm going to do the same retrofit to a Dynamite. I've never seen the innards of a Reference, but it must be as easy, and somewhat cheaper, to balance bridge as opposed to clone two entire channels.

If lurkers are eligible, I'd love a boardset and whatever stuff gets offered as a package with it. If 2SA1968 are sourced and available for anything close to $.70 ea, I will commit to buying couple hundred extra to bump up the volume discount. Back under my rock now ....