Pre amp & Collins AM864 compressor combined, ideas neede

Hi guys a friend of mine needs a mic pre & compressor, iv made a few tube pre amps & couple of compressors so far with great results, so I said I will knock something up iv got a few bits & bobs lying around but we will have to buys some bits.

He is gonna buy a cheap large capsule studio condenser of maybe that cheap Tbone ribbon mic its for vocals & maybe acoustic guitar.

I was gonna make him an Altec 1566A mic pre & maybe have no output tran, money is very tight you see.

Ive been looking at the schematic for a Collins AM864/U compressor it looks so simple,but I think we would still need a pre amp to drive it.

What im thinking is could I somehow build a pre & the compressor in one lump & try to loose a tranformer or two, don?t want to but like I said money is tight.

Question is the AM864 push pull?

IF so could I insert a part or a whole push pull pre amp after the input tran of the compressor,and loose the pre amps output tran & the compressors input tran & couple it to the input attenuator of the AM864 with capacitors & resistors,was thinking of a RCABA21A push pull mic pre for the job or a mccurdy AU300 PP or maybe just half of one of these, we don?t need too much level, enough to drive the compressor, its for PC based recording by the way

Am I talking crap or has anyone got any ideas

Heres the schematic.

http://www.waltzingbear.com/Schematics/Misc/AM-864.htm

http://waltzingbear.com/Schematics/RCA/BA-21A.htm

http://www.nashaudio.com/DIY/DIY/McCurdy/au300.jpg

Thanks for reading?.Gary O.

Gary


You might want to take a look at the altec 438 compressor. This is basically a 436 with a mic amp stuck on the front end.

Someone here made one (one of the Northern guys I think), & can probably give you more info.

Hey I forgot about that one, yeah that could be the ticket, already have enough bits to make the mic pre part,I wonder if I could loose a transformer perhaps the output, i'll phone my valve supplier about the compressor valves, he has all the valves for BA6A if ya need em Rob 6SK7s are only 4 pounds each.

The AM864 was made by uncle sam so it has the Federal
name with it. Collins did not make the 864.

OK I am letting the cat out of the bag.
I have a FULL Federal AM864 manual that is scanned
and I am hand despoting (cleaning) up each page.
Yes I will post it for the world to see.
But do not hold your breath.
3 pages done 57 to do.
Each page takes about 20 minutes.

Yes I do have a little "OCD" about clean scanned schematics.
But your scanned schematic should allways look better than the orginal.

And in case you were wondering yes it will be a 2 color not grayscale type of scan.

You might be able to lose the output transformer, but the Sowter replacement isn`t that expensive. Just bill your mate for it !!!!!

The whole compressor is cheap to build apart from the iron. You can use the £12 Maplin 250v + heaters transformer for it. the 436 I built a few years back only cost about £50 using surplus Parmeko audio transformers & the maplin mains transformer.

I have already managed to get all the valves for the Ba-6a, I just need £300 for the transformers before I can start.

Sorry uncle Sam federal AM864U good luck with the manual touch up

Yeah could just bill my mate but I no how tight his money is at the mo,as is for myself was gonna use the 28 quid Sowter input tran as it goes,

I just soldered up the electronics for the mic pre part of the 438C & have bin trying it without the OP tran,recorded half a song, sounds brilliant, about the right level for sound card too, great little pre, might just get him up & running with this for now & add compressor later,

I got some of them maplin trans but I have just used an old tape recorder power tran with raw 6.3V AC, not even the slightest bit of humm, unbelievable considering there crock clip wires hangin all over the place.

Those Sowter trans for BA6A didn?t come to quite that much, I have different input tran to the one that says for BA6A its bit cheaper too.

Cheers Gary O.