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Genetically Modified: Roberts 770X -> SE Bamboo Mono Blocs

Imready - your 997 (similar to the 990 and to the Akai M-6) if I understand well, would make good candidates for these neat amps.

On the speakers, well I really am out of my depth when selecting speakers. Being these are small amps, I found some old, small, low power speakers that I put new grills on, recapped the crossovers (no audible change) and deox'd the pot (has a definite audio affect). No real brand name that I can associate with the tag on the back but they sound OK to me.
 

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I just sold a pair of the AKAI M-8 versions of these to Jay to fiddle with bet he will be interested in reading this thread.

As to my other M8 Touch it and suffer greatly. Of my 4 R2R decks it's my second favorite behind my RT-707. And will end up in a drawer type installation in my Tube system Rack I hope to get to start putting together this winter. Right after 20 other projects are done.
 
Can't stop a good thing

I really like these little single ended mono blocks. So I was able to acquire a pair of Akai M-8 R-2-R which I then disassembled and made into two pair of mono blocks for my sons for Christmas. This time I made one of the sets of cases out of American black walnut. The other set is bamboo like the original set that I did. They sound equally as good as the Roberts 770X and in fact inside are almost identical except that there was an additional transformer so that it would run mains voltage from 100V to 240V. That transformer was mounted up in the tape deck. One other small difference is that the Roberts has a shielding plate under the entire amp. The Akai has it only under the preamp tubes.

Happy Holidays to all!

Bill
 

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Bill-Thank you for the detailed photos and work list. I am in the midst of a similar conversion on my M8, and was struggling with the reed phono- line in switch, wanting to maintain functionality of both CD and phono inputs. Your solution is elegant.
Did you ever develop a schematic?
 
Missed this thread when it was first posted. I've heard about the conversion of these r-r amps but hadn't seen any completed. Very cool and nice work!
 
Hi Fi Engine Schematic

QUOTE=Raul;3320326]Here is a Roberts 770X schematics that I found on hifiengine.com[/QUOTE]
Thanks (Grazie) Raul- I found that too.That is the only readable Akai/Roberts schematic I have found, even after spending $ for a poorly reproduced copy of the Service manual for the M8. Hint-If you print the PDF schematic using "Print current page" and "Tile" at 32%, you can print that schematic onto 2 pages and overlap them, for a nice big working schematic. I tried to attach it here, but I think the PDF is copy protected.

I would love to see Bill's modified schematic, with all of the extraneous components omitted from the R-R units. I play vinyl and CD/MP3, so Bill's solution, to allow selection of Phono in vs. line/mic in, is just what I needed.
 
Last edited:
cubby01 said:
Very nice. Is that a metal case with look of bambo or is it bambo? I have my M-8 still in tact but plan to break it down some day. Would be interested in your mods and impressions.

Oh, another question. Is there an RIAA equalization circuit when using for phono input? I recall mine sounded fine with phono but thought it sounded like there was no RIAA. It's been a while.
Click to expand...

The manual I have on the Roberts says there is no RIAA, and an external phono amp should be used.
 
jaymanaa said:
The manual I have on the Roberts says there is no RIAA, and an external phono amp should be used.
Click to expand...

Interesting... I have the M8 Service manual, and it shows a hook-up diagram showing RCA from Turntable directly to 1/4" Phono input, with no phono amp in between. I have attached it here- a bit blurry as the repro I received was marginal.
 

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Missed this thread as well.

I have a Roberts 990 set aside for conversion. That you can still find these for next to nothing is amazing. With so much info online about mods to them you'd think there would be more demand? One site has a run through on the Akai M-8's that is terrific in the amount of detail it provides.
 
Befor and After Schematics

This is the Roberts 770X / Akai M-8. One is of the amps with all the connectors etc that it came with. The other shows the components crossed out that were removed. The connecting wires were taken out with white out so you have to refer to the original to see where they were connected.
 

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LATE to this thread - got the same amps

Yeah i am looking to do a similar project - i have a working roberts 770x - reel mechanism and everything else works but i have been running my audio through the amps and love the sound. I don't want to make the entire unit unusable but would like to remove the amps for convenience. The entire unit weighs well over 50 lbs.

I would like to do the mods mentioned in this post but i know that will prevent them from being able to be reinstalled... Looking to use the amps for either a home receiver or maybe a guitar amp... or mic preamp...

ANyone got any tips on how to remove the amps so that they can be put back in without ruining the entire unit? I have read that the amps disconnect rather easily and have opened it up to take a look and it looks pretty straight forward...
any input appreciated..
thx - mittenTuber
 
mittenTuber said:
Yeah i am looking to do a similar project - i have a working roberts 770x - reel mechanism and everything else works but i have been running my audio through the amps and love the sound. I don't want to make the entire unit unusable but would like to remove the amps for convenience. The entire unit weighs well over 50 lbs.

I would like to do the mods mentioned in this post but i know that will prevent them from being able to be reinstalled... Looking to use the amps for either a home receiver or maybe a guitar amp... or mic preamp...

ANyone got any tips on how to remove the amps so that they can be put back in without ruining the entire unit? I have read that the amps disconnect rather easily and have opened it up to take a look and it looks pretty straight forward...
any input appreciated..
thx - mittenTuber
Click to expand...

If you can find a service manual -- there is one oneline somewhere it has instructions on removal. But you can probably figure it out. You take out some screws and the chassis slide out. You need to disconnect some mechanical linkages and power and wiring harness connectors. Once you have them out you need to get power to both amps as only one wall plug is supplied. I think that was simple but don't quite recall how the power cables run. There are some other threads on the M-8 and 770x that probably have more detail. Do some google searches using search in the above menu and select "search AK with Google"
 
mittenTuber said:
Yeah i am looking to do a similar project - i have a working roberts 770x - reel mechanism and everything else works but i have been running my audio through the amps and love the sound. I don't want to make the entire unit unusable but would like to remove the amps for convenience. The entire unit weighs well over 50 lbs.

I would like to do the mods mentioned in this post but i know that will prevent them from being able to be reinstalled... Looking to use the amps for either a home receiver or maybe a guitar amp... or mic preamp...

ANyone got any tips on how to remove the amps so that they can be put back in without ruining the entire unit? I have read that the amps disconnect rather easily and have opened it up to take a look and it looks pretty straight forward...
any input appreciated..
thx - mittenTuber
Click to expand...
You might also try in the Tube forum. AKer Sloober has recently worked on a few of these. If you do a search in the Tube forum you'll find some threads there, for example:
http://www.audiokarma.org/forums/showthread.php?t=296546
http://www.audiokarma.org/forums/showthread.php?t=320289
http://www.audiokarma.org/forums/showthread.php?t=322318
http://www.audiokarma.org/forums/showthread.php?t=301665
 
bill,

any chance on getting the modded schematics in better resolution? i just picked up (2) monos and (2) stereos. still on the fence on whether to gut and start fresh reusing old iron or to mod the way you did yours on the monos.

for anybody interested, i did get full schematics on my units. could scan and post up somehere.
 
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