This post has nothing to do with antique radios, but perhaps somebody here can help.

My hi-fi system has tube-type stereo amp and various input devices such as turntable, FM tuner, CD player, etc.

One of my gripes with FM radio is that the audio is too compressed: fff sounds like f, and ppp sounds like p. FM music broadcasters compress to avoid over-modulating and to make FM music sound OK in a car with road noise in the background. (I was told this by the station engineer of our local classic music station after I complained. He also told me that each program host can adjust compression to his/her heart's content.)

I am interested in finding an audio expander, a "black box" that would go in between my FM tuner and my amplifier. Is there such a thing? I've searched for "audio expander" on the internet, but seem to find only computer software, guitar pedals, and other things that aren't what I want.

If necessary, I would build something, but I don't want to try to design the circuit from scratch.

Any suggestions?

Doug,
My tired old ears welcomes the f's and p's vs the fff's and ppp's, but doesn't solve your dilemna. I'm sure someone will correct me if wrong, but FM broadcasts with pre-emphasis circuitry at the high end of the audio spectrum, and a typical receiver contains the antidote de-emphasis circuits to level the playing field of high's vs low's at your ear. In addition, attack and decay times of both circuits are designed in so to speak. If you can locate these components somewhere near the detector, and do a little research, its possible to de-emphasize the de-emphasis. Modern equip of course would have all this hardware contained in one tiny chip pre-programmed with flash or ROM to control the entire process, but not your vacuum tube set. I would also guess that the pre-emphasis at the broadcast site is run under the control of a PC with a hot line to FCC headquarters. Audio compressor and expander chips are still around too. I suggest you study some of the techniques used with MP3 players and their host PC's where digital audio is compacted, compressed, and expanded from/to different media. RIAA industry standards may also provide clues about audio compression at the recording stage, and encompass the broadcast industry as well.

marv

:This post has nothing to do with antique radios, but perhaps somebody here can help.
:
:My hi-fi system has tube-type stereo amp and various input devices such as turntable, FM tuner, CD player, etc.
:
:One of my gripes with FM radio is that the audio is too compressed: fff sounds like f, and ppp sounds like p. FM music broadcasters compress to avoid over-modulating and to make FM music sound OK in a car with road noise in the background. (I was told this by the station engineer of our local classic music station after I complained. He also told me that each program host can adjust compression to his/her heart's content.)
:
:I am interested in finding an audio expander, a "black box" that would go in between my FM tuner and my amplifier. Is there such a thing? I've searched for "audio expander" on the internet, but seem to find only computer software, guitar pedals, and other things that aren't what I want.
:
:If necessary, I would build something, but I don't want to try to design the circuit from scratch.
:
:Any suggestions?

:This post has nothing to do with antique radios, but perhaps somebody here can help.
:
:My hi-fi system has tube-type stereo amp and various input devices such as turntable, FM tuner, CD player, etc.
:
:One of my gripes with FM radio is that the audio is too compressed: fff sounds like f, and ppp sounds like p. FM music broadcasters compress to avoid over-modulating and to make FM music sound OK in a car with road noise in the background. (I was told this by the station engineer of our local classic music station after I complained. He also told me that each program host can adjust compression to his/her heart's content.)
:
:I am interested in finding an audio expander, a "black box" that would go in between my FM tuner and my amplifier. Is there such a thing? I've searched for "audio expander" on the internet, but seem to find only computer software, guitar pedals, and other things that aren't what I want.
:
:If necessary, I would build something, but I don't want to try to design the circuit from scratch.
:
:Any suggestions?

Doug, I thought I would throw my 2 or 3 cents worth in as I played with expanders in some vintage gear. I have several old sets, two of them using an RCA circuit almost identical to an RCA circuit that first appeared in the RC13 RCA tube manual of 1937 and in several issues later. It used a 6C5 which drove a 6H6 signal rectifier that would control grid three of a 6L7 expander. Audio would be fed into grid one of the 6L7. I have an RCA D22-1 with an expander and four 2A3's found in the trash about 20 years ago. I never redid the cabinet but recapped the thing and it plays well. Most of the early sets only used the expander on the phonograph. I also have a McMurdo Silver Masterpeice 5 that uses the RCA circuit almost part for part and it funtions on both the radio or phono input. The third one I have is in a 1951 Fisher Custom 60 console. I know there generally isn't much interest in early Fisher stuff but prior to about 1954-55, the company really wasn't known outside of New York City and these are quite scarce. Few were made and they were expensive. I found this set in Ohio thanks to a friend of mine there. I saw it with the chassis removed and what attracted me to it was the power amp with four miniature 12AU7's driving push-pull-parallel 6A3's. I never saw commercially built gear still using 6A3's in the 1950's. The set had a cardboard tube location diagram on the back which showed four chassis, a tuner, power amplifier, the amplifier power supply and a volume expander which used three 12AU7's and two 5915's which are non-microphonic 6BE6's. My friend was the second owner buying it in 1964 from his boss. My friend told me the expander stopped working and tossed it in the trash. I had the set 13 years when I found the correct expander on eBay and rebuilt it. I have it in the original cabinet now and can try to describe the performance which is similar on all sets. I found that most records recorded after 1939 are so heavilly compressed that the electronic expanders can't pick a reference point and won't expand. I haven't tried an external FM tuner on the McMurdo Silver but will have to. The Fisher 60 sounds bad on most pop records. Certain 50's instumental RCA red seal LP's sound amazing through the expander. I found the most dramatic on any of the sets are mid 1930's piano music. Most vocals sound bad as they seem to "pump". The Fisher actually has a jack for the output of the phono preamp that feeds into the expander so it too only works on the phono and has the disadvantage that you can't easily bypass it without pulling the set away from the wall.
Will it work for what you want? The RCA circuit is fairly easy to build and the three tubes are not expensive.

Fred R.

Thanks, Fred and Marv.

Fred, I have the RCA tube manual RC-30, which probably came out in the '60s. It has a block diagram of an audio expander, but no schematic. If you could copy or scan your schematic, I'd be much obliged.

:Thanks, Fred and Marv.
:
:Fred, I have the RCA tube manual RC-30, which probably came out in the '60s. It has a block diagram of an audio expander, but no schematic. If you could copy or scan your schematic, I'd be much obliged.

Doug,
The e-mail I sent you bounced. Drop me a line and I will resend it.

Fred

Fred, I received the schematic and ckt description fine. Thanks!

This audio expander is a little simpler than I had imagined. Essentially, it's just an automatic volume control (AVC) in reverse. On loud passages, the grid of the 6L7 amplifier tube is made LESS negative, causing the passage to be even louder -- and vice versa. Hmmm, why didn't I think of that?

All those dead men from the '20s and '30s were pretty smart.

:Fred, I received the schematic and ckt description fine. Thanks!
:
:This audio expander is a little simpler than I had imagined. Essentially, it's just an automatic volume control (AVC) in reverse. On loud passages, the grid of the 6L7 amplifier tube is made LESS negative, causing the passage to be even louder -- and vice versa. Hmmm, why didn't I think of that?
:
:All those dead men from the '20s and '30s were pretty smart.

Doug,
I have thought about your last comment. I work in the RF power transistor field and a lot of the designs are rehash and improvements done to up to 30 year old designs. Having a Radiola 28 with RCA 104 loudspeaker combination which runs on AC, I am amazed that those engineers with in a year of offering the first superhets in March of 1924, by the end of 1925 had a working, improved superhet running on AC power which used series connected 99's and ready to market by RCA. They used the best they had at that time. Now those guys were engineers!

Fred

Doug,
Just rec'd a mail flyer from a place called Guitar City. They got all kinds of tricked out electronic gadgets for musicians. Might even have something useful in your search, but of course it would be solid state, not tubes.

marv

:This post has nothing to do with antique radios, but perhaps somebody here can help.
:
:My hi-fi system has tube-type stereo amp and various input devices such as turntable, FM tuner, CD player, etc.
:
:One of my gripes with FM radio is that the audio is too compressed: fff sounds like f, and ppp sounds like p. FM music broadcasters compress to avoid over-modulating and to make FM music sound OK in a car with road noise in the background. (I was told this by the station engineer of our local classic music station after I complained. He also told me that each program host can adjust compression to his/her heart's content.)
:
:I am interested in finding an audio expander, a "black box" that would go in between my FM tuner and my amplifier. Is there such a thing? I've searched for "audio expander" on the internet, but seem to find only computer software, guitar pedals, and other things that aren't what I want.
:
:If necessary, I would build something, but I don't want to try to design the circuit from scratch.
:
:Any suggestions?

Marv, thanks: what is their website address? I found a couple of different "Guitar City" sites, but none had any such gadgets that I could find.

Please look at this thing on eBay and tell me what it does: 190018560280

I'm not hung up on a tube-type expander. (Even though my hi-fi amp is tube-type, my tuner is solid state.)

I'm sure I could build the tube-type expander that Fred sent me info on. However, if I build it the way it was designed by RCA back in 1937, or so, it would take six tubes to have expansion for two stereo channels.

I definitely intend to do something, because I can no longer live with classical music on FM. The chief engineer at our local classical radio station in Chicago, WFMT, was very frank in admitting to me that they over-compress their audio, but that it was out of his control.

:Doug,
:Just rec'd a mail flyer from a place called Guitar City. They got all kinds of tricked out electronic gadgets for musicians. Might even have something useful in your search, but of course it would be solid state, not tubes.
:
:marv

Doug here's what you need lol:
a 1927 Grebe Synchrophase... at least according to this ad:

http://www.pbpix.com/grebe.jpg

Peter, I happen to own one of those Grebe sets, but I can't seem to pick up FM on it.

:Doug here's what you need lol:
:a 1927 Grebe Synchrophase... at least according to this ad:
:
:http://www.pbpix.com/grebe.jpg

Doug,
Not familar at all with this item, but the brief description shows it may have some promise in your application. I just typed in DBX 228 on Google, and a number of sites came up. It may take some time, but suggest you try the Google thing, and you'll find reviews (both pro and con) in addition to complete specs.

marv

:Marv, thanks: what is their website address? I found a couple of different "Guitar City" sites, but none had any such gadgets that I could find.
:
:Please look at this thing on eBay and tell me what it does: 190018560280
:
:I'm not hung up on a tube-type expander. (Even though my hi-fi amp is tube-type, my tuner is solid state.)
:
:I'm sure I could build the tube-type expander that Fred sent me info on. However, if I build it the way it was designed by RCA back in 1937, or so, it would take six tubes to have expansion for two stereo channels.
:
:I definitely intend to do something, because I can no longer live with classical music on FM. The chief engineer at our local classical radio station in Chicago, WFMT, was very frank in admitting to me that they over-compress their audio, but that it was out of his control.
:
::Doug,
::Just rec'd a mail flyer from a place called Guitar City. They got all kinds of tricked out electronic gadgets for musicians. Might even have something useful in your search, but of course it would be solid state, not tubes.
::
::marv
:
:

:Marv, thanks: what is their website address? I found a couple of different "Guitar City" sites, but none had any such gadgets that I could find.
:
:Please look at this thing on eBay and tell me what it does: 190018560280
:
:I'm not hung up on a tube-type expander. (Even though my hi-fi amp is tube-type, my tuner is solid state.)
:
:I'm sure I could build the tube-type expander that Fred sent me info on. However, if I build it the way it was designed by RCA back in 1937, or so, it would take six tubes to have expansion for two stereo channels.
:
:I definitely intend to do something, because I can no longer live with classical music on FM. The chief engineer at our local classical radio station in Chicago, WFMT, was very frank in admitting to me that they over-compress their audio, but that it was out of his control.
:
::Doug,
::Just rec'd a mail flyer from a place called Guitar City. They got all kinds of tricked out electronic gadgets for musicians. Might even have something useful in your search, but of course it would be solid state, not tubes.
::
::marv
:
:

OOPS!!! FORGOT!!!Its www.guitarcenter.com

marv

:Marv, thanks: what is their website address? I found a couple of different "Guitar City" sites, but none had any such gadgets that I could find.
:
:Please look at this thing on eBay and tell me what it does: 190018560280
:
:I'm not hung up on a tube-type expander. (Even though my hi-fi amp is tube-type, my tuner is solid state.)
:
:I'm sure I could build the tube-type expander that Fred sent me info on. However, if I build it the way it was designed by RCA back in 1937, or so, it would take six tubes to have expansion for two stereo channels.
:
:I definitely intend to do something, because I can no longer live with classical music on FM. The chief engineer at our local classical radio station in Chicago, WFMT, was very frank in admitting to me that they over-compress their audio, but that it was out of his control.
:
::Doug,
::Just rec'd a mail flyer from a place called Guitar City. They got all kinds of tricked out electronic gadgets for musicians. Might even have something useful in your search, but of course it would be solid state, not tubes.
::
::marv
:
:

A Simple DBX expander will do the job. They are quite cheap on eBay search for DBX expander. They go for 20-30$ for simple units, just what you need.

Or search for Dynamic Expander.