Akai M8 Amplifier Mods

[kylej1050]

I know this is a long shot but does anyone have an archive of at least the images from:

http://briarsfield-hifi.co.uk/akai_m8.htm

I was going to save them and wouldn't you know it in the week between when I found and read the site and was going to save the images 'just in case the site went down', the site gets closed down...

I can wayback the text but the schematics were what I'm really looking for.

Or if someone else has a good link to information about converting these for use without the R2R parts.

Thanks!

 

[Wigwam Jones]

I tried this but did not see the images. I don't know if it will help you or not, but just in case:

https://web.archive.org/web/*/http://briarsfield-hifi.co.uk/akai_m8.htm

 

[planet10]

I hadn't seen that website before, but i have 3 pair of the M8 amplifiers (untouched at the moment). My intent was to start by stripping a pair down and make a set of RH84 variants.

I have no need for tone controls and as to preamp duty that really only involves adding a 100k pot at the front.

I also figured out how to repurpose most of the holes on the front, and to connect the VU metets as output level feedback.

I have the schema and a few other pieces of info, what were you looking for?

dave

 

[kylej1050]

That's actually exactly what I'm looking for. I want it to have the ability to do line-in and phone in while keeping the chassis they currently have since I think the look is cool as heck.

 

[Eli Duttman]

You can certainly set yourself up for both line and phono I/Ps, using the existing chassis.

For all practical purposes, 6267 = EF86 and 12AD7 = 12AX7.

I'd set the phono preamp up to use an 'X7 section in the 1st gain block and the EF86 in the 2nd gain block. Both the 12AX7 and EF86 are quite wimpy and very poor at driving loads. I suggest you add a MOSFET buffer, as illustrated by the tweaked RCA setup. If you are going to retain the AC heating shown, definitely use the Sovtek 12AX7LPS, which is a genuine 7025 equivalent containing a hum bucking, spiral wound, heater.

Use the 2nd 'X7 section as the voltage amplifier for the 6BQ5 power O/P stage.

 

[limpet]

I remember that site, unfortunately this was the only image I seem to have saved from it.

 

[jazbo8]

Here is another good resource for modding the Akai.

 

[kylej1050]

Thanks so much! The saved schematic helps a lot.

I was wanting to preserve the pentode phono stage because I really like it as-is. When I have my workshop finished in a couple of months I plan on getting these on the bench and updated.

 

[Eli Duttman]

An EF86 in the 1st gain block role of a phono preamp is marginal, from a S/N perspective. That's why I suggested using a 12AX7 section in the 1st gain block role. OTOH, you can get "gobs" of gain from an EF86 in the 2nd gain block role, without any S/N degradation worries.

JMO, use a tool appropriate to the job at hand.

 

[kylej1050]

Eli,

I'll do a bit of research on that. I'll need RIAA eq so I'll have to make sure I have enough gain in the phono amp to drive that stack. Or I could toss a unity gain RIAA circuit between the two 12AD7 stages.

 

[planet10]

Full schema attached.

The EL84 really only needs 1 stage in front of it. I'd be tempted to try the EF86 in a Schade arrangement.

dave

 

[kylej1050]

Full schema attached.

The EL84 really only needs 1 stage in front of it. I'd be tempted to try the EF86 in a Scade arrangement.

dave

Scade?

 

[planet10]

Sorry Schade.

Plate-to-plate feedback.

Like the RH84 (lots & lots on that amp here).

dave