Yet Another Roberts 770 mono block conversion
- Thread starter Omegaman
- Start date
brendandoher
Active Member
wait- those were speaker cabs? what kind? FABULOUS
All complete and ready to go
Here is the completed project:
Put feet on the cases which really turned them from speakers to cases
Wired the RCA input and speaker outputs to the existing connections on the back
I painted the grill 24k gold for some Bling factor
I am going to take 1.5 inches off the back plate to give it more air flow
Here is the completed project:
Put feet on the cases which really turned them from speakers to cases
Wired the RCA input and speaker outputs to the existing connections on the back
I painted the grill 24k gold for some Bling factor
I am going to take 1.5 inches off the back plate to give it more air flow
Attachments
brendandoher
Active Member
are those fisher cabs? (http://stockton.craigslist.org/ele/4177858527.html) or harmon kardons?
Cabinets are Realistic solo 4B
These speaker cabinets were "Realistic solo 4B". Probably from the 60's. They had a single 5 inch driver in them. I had them lying around for years, one of those "I can't bring myself to toss them" kind of things
There are some on the bay sold listings
I guess they have a following but they were a good choice for my DIY project
I googled and found some info on them. Some say the 4b did not have wood veneer but these do. They sounded ok and I kept the drivers
These speaker cabinets were "Realistic solo 4B". Probably from the 60's. They had a single 5 inch driver in them. I had them lying around for years, one of those "I can't bring myself to toss them" kind of things
There are some on the bay sold listings
I guess they have a following but they were a good choice for my DIY project
I googled and found some info on them. Some say the 4b did not have wood veneer but these do. They sounded ok and I kept the drivers
Thanks for the response Derek
I'll probably end up routing slots in the top
I am concerned about heat also, but I am hesitant to cut into the tops. I have a router, but I am not skilled on it yet. I can get advice, as I know real craftsmen. Its 1/4 thick on top
The fronts do have the grills and these amps were in a kind of tight spot in the original tape decks. I am monitoring the heat as I enjoy these clean Hi-Fi low watt amps
I am putting flashing on the inside top to try to keep the heat off the top wood and to vector the heat to the rear where I have drilled seven 7/8th inch holes in the back plate nearest to the top.
I thought of just taking 1.5 inches off the the back plate also but the holes are easier to do than get out my table saw.
The holes in the back and the grill in front should allow for convection
Then there are micro fans
Can I power a micro fan with the 6.3 volts from the heaters?
I'll probably end up routing slots in the top
I am concerned about heat also, but I am hesitant to cut into the tops. I have a router, but I am not skilled on it yet. I can get advice, as I know real craftsmen. Its 1/4 thick on top
The fronts do have the grills and these amps were in a kind of tight spot in the original tape decks. I am monitoring the heat as I enjoy these clean Hi-Fi low watt amps
I am putting flashing on the inside top to try to keep the heat off the top wood and to vector the heat to the rear where I have drilled seven 7/8th inch holes in the back plate nearest to the top.
I thought of just taking 1.5 inches off the the back plate also but the holes are easier to do than get out my table saw.
The holes in the back and the grill in front should allow for convection
Then there are micro fans
Can I power a micro fan with the 6.3 volts from the heaters?
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You could try a PC fan - just figure out which ones will run when undervolted to 6.3VDC (they are designed to run on 12VDC). SilentPCReview.com is a good reference in figuring out which ones are best. Just make sure the fans don't introduce noise into the signal path.
-D
Wow! Nice job. Love the re-purposed cabs!
I believe the green wire around the cap was to cancel hum induced by the motors... or something like that.
You mentioned the 770x going so well, you didn't put it under the knife? Nice.
Was gifted a 770, and thought I'd pre-amp/mono block it. Completely changed my mind after listening to a few reels. It sounds pretty damn good as is(guessing that was your take, as well.) If I only had a friend that had the blocks sitting under a tarp, or with a crumbling deck! Until then... Nice job with a save, and a score!
I believe the green wire around the cap was to cancel hum induced by the motors... or something like that.
You mentioned the 770x going so well, you didn't put it under the knife? Nice.
Was gifted a 770, and thought I'd pre-amp/mono block it. Completely changed my mind after listening to a few reels. It sounds pretty damn good as is(guessing that was your take, as well.) If I only had a friend that had the blocks sitting under a tarp, or with a crumbling deck! Until then... Nice job with a save, and a score!
Cooling vents routered
I knew I needed vents on these amp cases and I wanted to learn how to router
So I got out my GW Craftsman router and read the manual, then I practiced on some similar material, and GOOD THING as routing is a SCIENCE and an ART
After learning all the mistakes and the lessons, I had a go at it
It should stay cool now without a fan
I knew I needed vents on these amp cases and I wanted to learn how to router
So I got out my GW Craftsman router and read the manual, then I practiced on some similar material, and GOOD THING as routing is a SCIENCE and an ART
After learning all the mistakes and the lessons, I had a go at it
It should stay cool now without a fan
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janikphoto
Lunatic Member
I really need to do something with my amps. Why didn't you re-route the inputs and outputs to the back? I've seen other conversions that did it. Are you just trying to keep things simple? I understand that methodology!
See post #23
The Realistic Solo 4b speaker cabinets I used to make the cases had +/- screw terminals for the speakers and also an RCA for alternate speaker connection. I used the RCA for line input and the screw terminals for speaker output. I also retained the 1/4" jacks in front for quick auxiliary access
But yes, I try to keep it simple
I might buy another pair or Solo speakers and do this again
janikphoto
Lunatic Member
Ahhh, ok. So you kept the front inputs, and simply connected some on back, as well.
janikphoto
Lunatic Member
I got tired of these things sitting around, so I pulled them out and worked on them some tonight. Not counting the Akai that won't get parted out (my father brought back one from Vietnam that I now have), I've got two pairs of these little guys. A pair of Roberts and pair of Akai. The Roberts worked perfectly, and I probably should've kept it together. The akai was picked up of CL for $40, but one channel doesn't work. I was thinking about using the good one for a guitar project and the bad one for parts.
Anyway, I worked on the Roberts pair tonight, disconnecting the Phono/Radio plug and soldering its wires I to an RCA plug I mounted on the side of the chassis. Then I disconnected the speaker plug and soldered in wires, which will eventually go to binding posts under the RCA plug... I just didn't have any binding posts in my parts pile to use, so I'll have to buy some.
I haven't done the resistor/cap mod yet... The one that smooths out the frequency response. I'll have to track down that thread again. I also need to build a case for each. These are quieter than I remember them, but maybe I was using more efficient speakers during my last test? I'll post pics tomorrow. Not much to see, but maybe my pics will encourage others to post their finished amps.
Anyway, I worked on the Roberts pair tonight, disconnecting the Phono/Radio plug and soldering its wires I to an RCA plug I mounted on the side of the chassis. Then I disconnected the speaker plug and soldered in wires, which will eventually go to binding posts under the RCA plug... I just didn't have any binding posts in my parts pile to use, so I'll have to buy some.
I haven't done the resistor/cap mod yet... The one that smooths out the frequency response. I'll have to track down that thread again. I also need to build a case for each. These are quieter than I remember them, but maybe I was using more efficient speakers during my last test? I'll post pics tomorrow. Not much to see, but maybe my pics will encourage others to post their finished amps.
janikphoto
Lunatic Member
Pics...
It might not show in the pics, but I pulled the record bulb from the M8 and added it to the second Roberts, so they'll both have a bulb. My plan is to eventually hook it up to turn on with the power switch. I know the meters already light up when these power on, but I like the idea of the bulb doing something, and not just sitting there.
It might not show in the pics, but I pulled the record bulb from the M8 and added it to the second Roberts, so they'll both have a bulb. My plan is to eventually hook it up to turn on with the power switch. I know the meters already light up when these power on, but I like the idea of the bulb doing something, and not just sitting there.
BrokenHill
Well-Known Member
Go to this link > http://www.audiokarma.org/forums/showthread.php?t=79384
I think post NO: 9 will give you the details on the proven tracker X mod for the tone control mod.
Keep up the good work, I think when you get them done you will be very pleased at the sound quality of these mono amps.
The resisters are wire wound and should not need replacing, I did replace them all when I was experimenting with my pair and
it altered the way these amps sounded, killed the awesome soundstage these amps are known for.
I put the wire wound resisters back in and all is good again.
I think post NO: 9 will give you the details on the proven tracker X mod for the tone control mod.
Keep up the good work, I think when you get them done you will be very pleased at the sound quality of these mono amps.
The resisters are wire wound and should not need replacing, I did replace them all when I was experimenting with my pair and
it altered the way these amps sounded, killed the awesome soundstage these amps are known for.
I put the wire wound resisters back in and all is good again.
jaymanaa
RIP 1961-2018
That's a good thing to know, thanks for sharing that. I've got about 6 pairs of these darn things, and a couple complete units. I hope they sound as good as everyone says.
Did they have a special tap on the OPTs for high Z headphones like certain Sonys did (600 ohm)?