Rockhopper M^3 - The Review - Page 4

So you bought that SFT built balanced M^3. I remember thinking really hard about picking that up when it went up for sale. At that price, this amp was a friggin' steal. Congrats!

Whatever happened to SFT? His amps were nice.

Thanks, I really enjoy it. From memory I remember the seller saying that this was one of SFT’s last builds.

nice. i'm not sure how i missed that deal. if i had seen it, it would have been gone immediately. that's seriously an amazing price.

Fair enough.....I'm not sure the last sentence is necessary though....the module schematics and that info you require is but an email and a glance away...including square wave test results. Shrugs shoulders....


Peete.

Is the schematic on their website? I tried looking but the site is so slow, that after 10 minutes staring at a blank page I simply gave up.

Thanks, they look decent. One of these days I'd like to test them. A full set of specs would still be good. Their site shows an extension cable for the module, which I would strongly suggest not to use. The added inductance is not good when you consider that the wires carry the negative feedback loop as well as the power supply rails. The schematic shows no additional rail decoupling onboard.

You might wanna check this one out too. Lol.

Burson Opamp

i was just thinking of posting that.

The Burson modules are made by audio-gd

Here read this from the audio-gd OPA page

We are the first to made and sale HDAM (OPA): We are the first made and sale OPA-EARTH or name calls " HDAM " in China and oversea market . Through below links , can know we have design and made original HDAM begin 29-6-2005 , although these links were Chinese , but have pictures and post date . Begin at 2006 year , we OEM a lot of HDAM for a agent . In whole world , only we have the PCB files of original HDAM .
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I have some specs pulled from the OPA page that may help AMB....Kingwa is the designer and is more than happy to go into details on anything he makes...he's a pretty cool guy that seems to work 24/7....(well almost 24/7).

OPA – Earth : Our first generation discrete opamp has been sold throughout the world by other marketing means. This discrete opamp utilizes integrated cascode circuit with the schematic based on single channel circuit which is an improvement based on new improved parameters and technology. The sound characteristics is neutral and natural . THD Less than 0.0005%(1KHz), Operating voltage：±9 TO ±25V，Open loop gain：35DB，Operating current：Approx. 28MA（Single OPA），Approx. 56MA（Dual OPA）.(Products have upgrade to Cap Model, use EVOX MMK capacitors. )

OPA - Moon : This discrete opamp uses dual differential gain stage and single ended output stage circuit design , we try and listen long term . The OPA-Moon sound characteristics is had a bit tubelike taste (vacuum valve) , soft and slight thick, and full of sentiment . THD Less than 0.0008%(1KHz), Operating voltage ：±9 TO ±25V，Open loop gain：33DB，Operating current：Approx. 28MA（Single OPA），Approx. 58MA（Dual OPA）.(Products have upgrade to Cap Model, use EVOX MMK capacitors. )


OPA-SUN (Version 2) : This discrete opamp uses full balanced circuit design which is widely accepted by our Hong Kong and American followers among our other products. THD Less than 0.0003%(1KHz), Operating voltage ：±12 TO ±20V，Open loop gain：36DB，Operating current：Approx. 25MA（Single OPA），Approx. 50MA（Dual OPA）.(Products have upgrade to Cap Model, use EVOX MMK capacitors. )


I fully agree the extension cable is not the best way to go....I avoid that if I can. Once I settle on a module for good I pull the socket and solder in the modules permanently if I have the room/clearance in the chassis. That is there main drawback, size. They do require a good steady supply of clean current but most applications with a 25VA transformer should have no issues I would think.

That's why I piped in when Grawk said he had the bulked up PSU.....these might be a match made in heaven with the souped up M 3. Certainly worth a try IMO.

Peete.

Those are very scant information, but nonetheless illuminating.

The open loop gain for all three variations are very low, which means that the modules are not appropriate for all places where an opamp is used for audio. Applications requiring high closed-loop gain (i.e., phono stages, mic preamps), or those with certain special topologies designed with a high open loop gain opamp in mind (i.e., amps with Jung multiloop such as PPA or Pimeta) are not good candidates for these modules.

Also, the supply current is high, and may be an issue in certain designs. For example, in a PPA with JFET rail isolation. Even high-Idss JFETs like the PN4392 might be marginal and could starve these modules of current.

The moral of the story is, the modules might be fine products, but you can't just roll one into anything that has an opamp and expect it to work well.

I never said you could roll them into anything (nor do I go around suggesting that with every damn amp that has opamps, in fact I rarely suggest putting these into anything without checking out whether the unit can handle the current needs or is compatible) furthermore....there is a list of opamps on the web page that are compatible (not all have been tested...but there are quite a few that are similar to the AD opamp specs/needs Grawk IS using currently)...of course as you point out there are other parameters to take into consideration....it's fairly likely that the M3 with the beefed up PSU would be a "possible" candidate since it's neither a mic preamp nor a phono stage....I'm glad you pointed that out to me...you saved me from asking where the MIC input is......

Peete.

OK guys. I just want to make sure I am ordering the right thing. The AD8610 are mounted on what I believe is a DIP adapter so this is the main source of my confusion. So....

Should I get these two:
OPA627BP
OPA637AP

Or will these destroy my amp?