Comments on: Federal AM-864 Limiter Clone: Build Notes: update 1

By: Gavin Pursinger

Gavin Pursinger — Fri, 05 Sep 2025 17:33:42 +0000

I have tweaked and fine tuned my build and use it alot during mixdown on lead vocal…especially on material that has alot going on. It puts a force field around the vocal and a 50’s edge to it and cuts thru the mix. I love this unit. Transformers are old Merits unshielded…so I devised a blocking metal plate from a printing press and experimented with placement…wrx great.
Chassis is from a rackmounted air compressor regulator. It had 2 holes on front so I metered it like the old bc730…separate output and comp. Man does this unit have gain…20 db pad on input. You can di a bass into it…with pad defeated…killer…COULD NOT HAVE BUILT THIS WITHOUT YOUR GUIDANCE…MILLION THAMKD

By: saul

saul — Fri, 28 Jan 2022 16:12:27 +0000

dude do you know how good this is:

you literally macguivered the whole thing like a pro and saw all the angles

16hours??? to build???

dude and the rear panel shot is clean like it just came from the apple store

Best, Friend!
Saul

By: Gavin Pursinget

Gavin Pursinget — Thu, 30 Dec 2021 20:07:50 +0000

Thx for this am864u article. I built a single ended comp with 6L7 and tried connected 6L6 output…unit works great and sounds good….I AM READY TO TRY AN 864U BUILD…YOUR INFO HAS ALSO BEEN HELPFUL IN CLEANING UP PROBLEMS IN PREVIOUS CREATIONS…YOU ROCK!!!!
THX
Gavin

By: LandFill Sessions

LandFill Sessions — Thu, 04 Jun 2020 17:01:42 +0000

In reply to Randall Ball. Sowter UK makes all of the transformers applicable to the AM864.

By: Randall Ball

Randall Ball — Tue, 27 Aug 2019 04:01:22 +0000

Hello, great thread! I am in the very early stages of starting to translate the schematic into a wiring diagram. For mine, I would like to use the tube rectifier like the original. But I seem to be having trouble finding a transformer that matches the specs on the schematic. Any advice would be greatly appreciated.

By: directdriver

directdriver — Thu, 04 Oct 2018 13:50:17 +0000

“The release timing is apparently dictated by C1 and R1. I tried changing C1 to a .1, a .2, and a .5, but they all caused some degree of motorboating weirdness. ”

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The motorboating is caused by the lack of a dropping resistor and a decoupling cap between 6SN7 stage and 6SK7 stage in the power supply. Notice the output transformer center tap is also directly connected to R2, 6SK7 plate resistors. Since there is no separation between the two, it is easy to have crosstalk between stages, hence motorboating. Adding a dropping resistor and a decoupling cap can remedy that and then you can change the value of C1 to adjust release time.

By: Danny Knapp

Danny Knapp — Sun, 05 Aug 2018 17:22:13 +0000

kudos, great work!!

By: Jake

Jake — Sun, 17 Sep 2017 18:43:58 +0000

Excellent thread! Thanks for sharing. Plan on building one soon.
Any idea where i can find face plate handles like what you used?

Thanks,
Jake

By: Andres Luraschi

Andres Luraschi — Wed, 25 Jan 2017 02:18:03 +0000

In reply to chris. no image ... ooopsss! need your help again chris !

By: chris

chris — Sat, 14 Jan 2017 13:38:24 +0000

In reply to Devon. Hi Devon. I did build a second one after finishing this one. I did it in two rackspaces - thordarson input, motorola output (from onna those classic HP oscillators) and solen caps. Next time gonna make a stereo version.