Recording Studio Design 800B

[laatsch55]

I have found XLR male to female RCA connectors, but I'm having a problem finding any converters for the XLR male to banana or other speaker connectors. I guess I can just buy some XLR connectors and make a solid connetcion to the XLR posts with the speaker wire, but which ones would be positive and negative? And what about the third connection? I'm sorry I'm so stupid when it comes to this stuff..but someone help me figure out how to determine what is what. I probably will wait for the amp to see if I'll need a fan and any other parts, and then I can open the chassis to see how everything is wired, but I'll probably need help in determining what is what...I have a multimeter, if someone can tell me what I'm looking for...sorry I'm such a neophyte

We're all neophytes, just different pay grades.

 

[ksrigg]

I wonder if pin 1 or pin 2 is hot? After reading the material you sent along, I wonder if the MCM converter would work if the incorrect pin is hot? Maye the best thing for me to do is post a nudie, and see wht you guys think. It might be safe to do that and then change the hot to the proper pin in the amp itself....I assume I'd need to change inputs and ouputs to the proper pinout? Sorry I'm so non-amplifier internals savy.......

 

[laatsch55]

EIA Standard RS-297-A describes the use of the XLR3 for balanced audio signal level applications:


Pin Function
1 Chassis ground (cable shield)
2 Positive polarity terminal (hot)
3 Return terminal[5] (cold)

Prior to the introduction of this standard, the wiring of pins 2 and 3 varied. The pin 2 "hot" and pin 3 "cold" convention was typically used by

 

[ksrigg]

I have finally gotten this amp out of the box, and have taken some pictures. It is very dusty on the inside, but have been able to determine the transistors ued in the output stage. It has 4 RCA 410 and 12 2N3773 output devices. I would like to replace them all as they all have manufacture date of 1974. From talking with Mark, he thinks go back with the original outputs, and change the drivers to MJ15024G.What do you all think? This thing is built like a tank. The transformer is as big, if not larger than the one in a Phase Linear 700B. The thing is huge. Please feel free to comment on the amp. I am planning on leaving all the inputs and ouputs as they are, but must address the pro vs home audio obalanced vs unbalanced input and output. Should I buy the little converter mentioned earlier in this thread? If everyone would tell e what they would do with this amp, I'd really appreciate it. I may use it for sub duty, or I may use it in a system. I depends on how good it sounds when I get through with her. Probably should change the Bridge Rectifier with a 50 amp one, and bypass it with the small caps? Your thoughts please..

Oh, if I do stay with the 2N3773, should I go with the On Semi or use a different one? NPN? Looks like it is a 400 watt amp and not the 800 watts it hints at...(into 8 ohms anyway...

Thanks a lot, guys.....

 

[laatsch55]

Do the meters act the same as the 400's??

 

[ksrigg]

Here is a close-up from inside the amp of the inputs and ouput (the inputs are female XLR and the outputs are male XLR). After looking, I don't think these are balanced connections after all. I think they are unbalanced with just two connections per input and two per output. Does anyone see something that I am missing? The switch to the right of the inputs (the little red switch) is a stereo/mono switch, and has only two wires running to it. I am assuming that they are the + connection from each left and right channel. If all this is correct, the pin at the botom of ther XLR cnector would be + or hot and the other one would be negative? Before I make up the XLR cables, someone let me know if you are seeing something different. If you look at the pictures at the top of the thread, you can see the front of the amp showing those inputs and outputs. If you'd like another pic from inside the amp better showing the inputs, let me know.

Also the blue caps are 75VDC. I can't read the number for the uf rating, but I have some 35,000 uf 80VDS that have been looking for a home. I may have finally found one for them...

 

[mlucitt]

Have you figured out the input and output wiring yet? Here are some hints:
Lee is right for balanced cables but this amp is from the UK and things are different over there. Plus this is not a balanced output. There are no connections to the shield or to the cold contacts.

Follow the wire colors:
Red = input on pin 3
Red shield = input ground on pin 1
Green = output ground on pin 1
Pink = right output hot on pin 2
Purple = left output hot on pin 2

The top lug is the shield and it is connected to nothing but you may find it is at the chassis potenial because the connectors are rivited to the front plate.

Have fun.

 

[ksrigg]

The amp lives. I finally made all the cords and ran a little CPD through a tube preamp as source and the thing sounds amazingly good with the old transistors in it. It is probably a 400 watt amp. The meters work almost like a Phase 400 meter. It is a little sluggish, but not quite as much as a PL meter. The top end is not as pronounced, so perhaps it will make a great sub amp. Or maybe the electronics are "tired" and putting fresh outputs and drivers in her would brighten her up a bit, but still, for the $150 she costed, she is a bargain. A big beautiful girl. She neeeds new meter lamps and that probably will be the next thing I attempt to do. But I did want to report that she is working....And the wiring to the XLR's in NOT to standard. It must be the way they wired XLR inputs and outputs in England in the early 70's...

If you ever see one of these amps, pick it up. It is a brute..

 

[speakerman1]

The brits build different sounding amps and speakers. On the speakers they are pretty detailed sound. You have to like the sound. It is sort of a dry. If you ever see a used Creek come up for sale grab it.

Larry

 

[ksrigg]

I think I might replace the transistors too. Just for giggles, I have some 3773's to replace the ones from the 70's and I have some MJ15024 to replace the RCA 410. I think this should give the amp a different "voice", but I don't have enough experience to know what that voice will be. I suspect it will be less "dry" and more dynamic. It would seem that the On-Semis's as drivers would set the ouput stage with a slightly different timbre, and give her a little more "punch". Tell me if I'm wrong...or if you have other suggestions. I like the amp as is, but it seems to lack any really punch in the lower registers, and just doesn't have the "sparkle" in the top end that a Phase Linear has. I realize a lot of that has to do with Joe's PCB, and the newer larger caps in the power supply, but it might get me a little more definition.

I also may try to see if I can get some of the 35,000 uf 80 VDC capicators in her. I'm not sure if I can get them to fit, but I think I can. They are 2 1/2' in diameter....and the length is about the same. The caps in the amp are 80 VDC, so I don't see a problem there. If I can get them to fit, that should take the amp to a new level combined with the transistors... I need some clamps for the caps though, unless the ones in the amp will accomidate the larger diameter caps.....

Then I'll have to figure out bias...Anyone have a clue? Before I start messing with her, where would you suggest placin the leads to get the bias as it exists now?

I appreciate anyone's help. Thank you..

 

[speakerman1]

To me dry means that they seem very accurate. Did you listen to the PLs before they were modded for any time? I have not heard Joe's boards. So I have nothing to compare. I know I have gotten more bass from Bi-wiring.

Now for my PL I have a pair of bar speakers. Don't really care if I blow them. I can rebuild them. For the mach levels you guys play them the horns are a very good match.

Larry

 

[ksrigg]

Lrry...I did not listen to the unmodded PL. I don't know that I've ever received one that worked before the mods....but I imagine they probably sound similar to this unmodernized RSD. I've been listening to it some more, and the high end is there. Just lacking in the basss department, and just doesn't have much "punch". It is built like a tank. I mean really well put together. Solid as a rock....BIG transformer...well thought out and beautifully built. I'd like to have a mate for it. All the lights ae burnt out in it though. The power switch lamp and the VU meter lamps.....all gone...but they are some big meters, and I think they are a little faster than the PL meters...The fan in it is loud, but the transistors don't get even warm. That fan is moving some air.. I think if I can get the larger newer caps and new appropriate transistors in her, I'll bet she will really sing...We need to buy a boatload of these from Great Britain and let Joe have at them. I'll bet they could be the stuff....

 

[laatsch55]

Run the MJ 15024's as drivers and the MJ 21196's for outyputs. Need a pic of the inside of the amp showing the wiring of the outputs to tell you about biasing.

 

[ksrigg]

Hw do the 3773 that originally cme in the RSD as outputs compare to the MJ 21196's? I already bought a dozen new 3773's to repopulate the wall, so I may stick them in there for now. Should I expect any difference with the new 3773's and the MJ 15024's as drivers? What will the MJ 21196's add to the mix, when and if I change them out?

 

[laatsch55]

Maybe less distortion overall and a lot more reliability. Nothing to change course on yet there Sutton. Where's the pic of the outputs and output wiring??

 

[ksrigg]

I'll get some pics in the morning. It's after midnight here, and gotta go to bed.... I'm just happy to have the amp up and running. It sounds really good except the low end is weak...and a little distortion throughout. I finally got to the caps and they are 10,000 uf 75 VDS caps...I gotta see if I can get the 35,000 uf 80 VDC's to fit, and I think I'll need new clamps to make it work..

 

[laatsch55]

Looked like there was room.

 

[ksrigg]

It is kinda tight with some nuts being in the way..PlusI don't want to have to drill new holes for the clamps. I hoep the 2.5" clamps will fit in the existing holes or at least one of them...that will work for me..

 

[Skratch]

Sutton, How are you doing on your active crossover

 

[ksrigg]

Pictures "under the hood" showing the placement of all the boards, caps etc. I'm trying to figure out where to take a bias reading, and as you can see, the back of the wall where the output sockets are located are covered with boards, all with soldered tabs locking them in place...Buttoned up pretty well...