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Bose 1801 Monster Power Amp Restoration!

Great thread, I remember back in High School a traveling Science show came to our auditorium. For the PA they used Bose 801's and the 1801, I remember being mesmerized by the meters.


:worthless
 
ok I did see them pics sorry. I have used the 200's in a project and ordered the stud on bottom by mistake, I returned mine for the regular style.
 
I had a look at the data sheet for the UA604, and I think you can use it as a plug in replacement. You may have to remove C5, the stability cap, it may not be needed. Leave it in and check for oscillations, then if everything is working ok, run a 20KHz square wave in, adjusted for a 10V p-p output and look at the output with a scope. You want very little overshoot and no or minimal ringing. If it looks good, you're done.
 
dr*audio said:
I had a look at the data sheet for the UA604, and I think you can use it as a plug in replacement. You may have to remove C5, the stability cap, it may not be needed. Leave it in and check for oscillations, then if everything is working ok, run a 20KHz square wave in, adjusted for a 10V p-p output and look at the output with a scope. You want very little overshoot and no or minimal ringing. If it looks good, you're done.
Click to expand...

I found a part at digikey (7-1437529-6-ND) I could use as an adapter for the new opamp. It was just a DIP socket with long legs that I could bend to fit the TO99 pattern. See picture 1.

Second picture is a squarewave at 1Hz 10Vpp. Third picture is the 20kHz wave at 10Vpp. It doesn't look too square. But the other channel with the original opamp looks the same.

No signs of oscillations. Offset is -18mV with no adjustment in place. I'm thinking time to do the other channel the same?
 

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There must b e some bandwidth limiting in the circuit that is rounding off the square wave. That's fine. The 1Hz square wave looks great, not much slope to the flat parts. You're done!
 
dr*audio said:
There must b e some bandwidth limiting in the circuit that is rounding off the square wave. That's fine. The 1Hz square wave looks great, not much slope to the flat parts. You're done!
Click to expand...

I did the other channel the same and it is playing now. Offset looks good too, and it compensates for a DC offset from my signal gen fine.
 
On Wednesday night, I went to visit Racoon1400 to pick up my newly restored Bose Monster Amp. The night before had been a disaster for me, as I prepared for my new baby. I wanted to change the table the Bose was going on with a longer lower TV stand that I figured could hold both my restored 1801 and my road trip 1801 with the 4401. It is on wheels so that would help in changing things around.

Unfortunately, I made a mistake, and now my road trip amp no longer outputs from the main output. Surprisingly, the remote outputs are fine! I also thought I took out my Kenwood Supreme 600, but it seems to be fine. I had also thought I might have killed my ESS AMT 1aMs, but they are fine.

So I started off by trying the restored Bose by connecting directly to the airport express outputting to the AMTs. Wow! Did they ever sound great! But I wanted to compare it with the road trip 1801. So I did the same thing on it, however still no output. Then I moved the output to Remote, and they sounded great too. I couldn't tell if they were better or worse, because I was so relieved to hear good sounds coming from the amp. Sade 'Pearl' was playing, and it sounded good. I went back to Racoon's restored version and Wow! Really Wow! Huge difference! All the mods and work he has done has really paid off! I am getting closer to audio nirvana!

Thanks Racoon1400! You did a great job bringing this back from being totally dead, and missing half the power transistors! :)

Now I just have to figure out what I did on Tuesday night to the other one. Hard to do because I am enjoying listening to the restored amp so much through the AMT 1aM towers.
 
It's a cool amp, I listened to it the day before you picked it up when I went over to pick up some parts- Duncan did a really good job on it, nice and clean rebuild.

Enjoy!
 
bktheking said:
It's a cool amp, I listened to it the day before you picked it up when I went over to pick up some parts- Duncan did a really good job on it, nice and clean rebuild.

Enjoy!
Click to expand...

Yes, he did do a fine job. I'm extremely happy with it.

I put the 4401 back into the setup, and although there is a bit of fuzz on the edges, it still sounds better than the Supreme 600 as a preamp, or the Sony TA 2000F. They sound really good, but it sounds better. I guess thats the price of buying vintage. Most will need some work to be at their best.

One thing I've discovered is that these are very revealing speakers. If the source isn't good, you will hear it. I've been looking for remastered versions of my favourites.

Sound wise, I am really impressed with the 3D image I get from this setup, and feeling right in the middle of it. The AMTs have more presence with the restored 1801. I've been telling my friends it is like home theatre with only 2 speakers! It really is! Except it is so much cleaner, clearer, and balanced!

I really love the versatility in the controls on the 4401. And the phono section is really nice! This is the right direction for me! :music:
 

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BilboBaggins said:
Yes, he did do a fine job. I'm extremely happy with it.

I put the 4401 back into the setup, and although there is a bit of fuzz on the edges, it still sounds better than the Supreme 600 as a preamp, or the Sony TA 2000F. They sound really good, but it sounds better. I guess thats the price of buying vintage. Most will need some work to be at their best.

One thing I've discovered is that these are very revealing speakers. If the source isn't good, you will hear it. I've been looking for remastered versions of my favourites.

Sound wise, I am really impressed with the 3D image I get from this setup, and feeling right in the middle of it. The AMTs have more presence with the restored 1801. I've been telling my friends it is like home theatre with only 2 speakers! It really is! Except it is so much cleaner, clearer, and balanced!

I really love the versatility in the controls on the 4401. And the phono section is really nice! This is the right direction for me! :music:
Click to expand...

Yes, in their time the Bose 1801 and 4401 were among the finest electronics the audiophile could buy. Enjoy your new setup, I have mine since over 30 years now and I still love it.


Thierry
 
This thread reminds me of all the Phase Linear's that I have read that were being rebuilt. It seems things never go smoothly but the end result is the same, audio bliss congrats!
 
Hi Guys,

I am also the prought owner of a restored Bose 1801. Although 80% of the restoration has been done by the guy I bought the amp from, I have done some fiddling myself.

The front has been completly modified to give it a completly differend look.

Latest modification was adding an 12v trigger by using a solid state relay.
I've added some pics for those who like it :)

The only problem I am running into is that I often need to replace the light bulbs.
They last about a year or 2 and then burn out. Removing the almost 40kg from my setup to replace them is a pain in the ass....

Now I found these 6volt leds for replacement.
http://www.leddel.nl/a-22048/ba9s-5-smd-led-/
Has anyone got experience with replacing the bulbs with leds?

Thanks!!!
 

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Bilbo,
This is late in the game but the road trip 1801 has the outputs fused,open up the top
and you will see the fuse holders.I had put in lower value ones to protect my low watt speakers.You should be able to bump up the values with your speakers.
 
Hello,
Love the info everyone has posted. I was curious as to how much it would cost in parts and labor to have my 4401 and 1801's tuned up. They work now but would love the improved sound a tune up would bring. thanks Jerry
 
I think it really depends on what you need/want done on them. Both of mine were full restores. So top dollar went into each of them. And that included replacing all the RCA connectors on the 4401, installing speaker protection in the 1801, all the safety mods, etc. I would suggest you contact Racoon1400 for a quote. The 1801 might be a bit big to ship, but the 4401 is pretty light.
 
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