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ATG 18 August 2017

Hi All... I am new to the group and hope someone may be able to help. I have an early Rane SM26 on my bench and in need of a schematic. This unit does not use 7815 type voltage regulators but does have the power supply integral to the unit. Since Rane was bought out (by In Music Brands I think) information has been a bit more difficult to obtain. There is a later SM26 posted on their website but it is newer than the one I have, If anyone has a schematic I would greatly appreciate a copy. Thanks

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Boswell Fri, 08/18/2017 - 09:51

If you are talking about an early SM26 rather than the later variants (SM26S etc), then my understanding is that they all used 50/60Hz mains transformers and 7815/7915s or equivalents for their positive and negative power rail regulators. There have been many different product numbers from the various different semiconductor manufacturers for essentially the same 78/79 series parts, although the pinouts were not always identical. What parts do you have fitted in your unit? I'm assuming from the way your post is phrased that it's the regulators that are giving trouble.

ATG Fri, 08/18/2017 - 12:13

Boswell, post: 452166, member: 29034 wrote: If you are talking about an early SM26 rather than the later variants (SM26S etc), then my understanding is that they all used 50/60Hz mains transformers and 7815/7915s or equivalents for their positive and negative power rail regulators. There have been many different product numbers from the various different semiconductor manufacturers for essentially the same 78/79 series parts, although the pinouts were not always identical. What parts do you have fitted in your unit? I'm assuming from the way your post is phrased that it's the regulators that are giving trouble.

thanks for your reply... no as my original post was meant to convey this unit did not use the 78/79 series regulators thus my query.

Boswell Fri, 08/18/2017 - 14:40

The older models used a mains-frequency transformer and linear regulators. The later versions used off-line switching techniques employing high-frequency transformers with feedback regulation. If your unit does not appear to have lin-regs, perhaps it's one of the later DOLS ones.

What does the transformer look like?

Boswell Mon, 08/21/2017 - 04:55

Your photo seems to show a version of the unit that has unregulated power rails. If it is indeed an SM26, it may be some sort of early prototype, as I have never seen production Rane gear where the 120/240V mains arrives via an uninsulated fuse on the main PCB, and the power on/off switch is not in the mains circuit but on the low voltage transformer secondary. Those sorts of things have been a no-no for many years except where the power supply is an external enclosed brick.

I can't tell from the angle of your photo, so could you confirm that the vertical piece of metal screen behind the master output level control is just a tinplate screen and does not have any components bolted to the front of it?

scott2000 Tue, 04/05/2022 - 16:34
Know this is old but figured it may help someone down the road. Found a schematic for a pre-regulator SM26. It's actually 26V after the bridge...dropped by a couple of 680r resistors in parallel. Looks like the power led is actually being used as a regulator.?

tracey82 Sun, 08/27/2023 - 05:23

scott2000 wrote: Know this is old but figured it may help someone down the road. Found a schematic for a pre-regulator SM26. It's actually 26V after the bridge...dropped by a couple of 680r resistors in parallel. Loo

Hi, where did you find this schematic?  I have the same unregulated SM26 and cant find one.

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