Homebrew Audio Amp

[W7SOE]

Hi All,
   I have run my R-390A audio from the diode pickup to the phono input of my SX-42.  It is a pain because the SX-42 is not near the R-390A and it seems silly to run it when I am only using the audio section.

So I am thinking of replicating the SX-42 audio section on a small chassis and place it on/near the R-390a.  This is made easier by the fact that I have all the parts in my sx-42 parts rig except the audio transformer.

Does this seem like a reasonable approach?

Thanks

Rich
 

[N2DTS]

If that is what you want to do.
You can also run all the receivers to one nice audio amp and speaker, one with line outs for recording, etc.
Or you can rebuild an R390 audio module for hifi...

Building stuff is fun, but you dont have to re invent the wheel, good audio amps are not expensive.


Brett

[W3GMS]

Rich,
Be careful running the rcvr audio into a phono input.  Most phone inputs have an RIAA equalization curve built into them.  Its much better to go into an aux input which generally are "flat" from a frequency response standpoint.
Joe, W3GMS     

[W7SOE]

Rich,
Be careful running the rcvr audio into a phono input.  Most phone inputs have an RIAA equalization curve built into them.  Its much better to go into an aux input which generally are "flat" from a frequency response standpoint.
Joe, W3GMS     

On the SX-42 the phono input goes right to the grid of a 6SL7 audio inverter which feeds a pair of 6v6's.

Rich

[K5UJ]

I got a couple of old Heathkit 12 w. (20 w. peak) pp audio amps for this.  they were not prohibitively expensive and give the tube audio sound.  got one at a hamfest, the other off eBay.   Am in the process of recapping one now.  I like the Heaths because of the manuals.  6BQ5 pp.  12AX7 preamp, or that can be bypassed.  enough audio to nicely drive a large bookshelf speaker cabinet.  Fills the house with sound.  Fine to HB unless you want to focus only on things no one makes.   These (models EA2 and EA3) do have the RIAA preamp response but it sounds fine to me.  I just adjust the bass and treble until I have what I'd call full audio.

Rob

[W3RSW]

RIAA, NARB, etc. equalization curves/networks are usually built into only older very low level phono preamps of the day.  Phono inputs on most older receivers are directly to the top of the AF gain pot.

Anyway if I were wanting tube sound these days and couldn't find a decent older amp, I think I'd buy a brand new Hammond retro output transformer, probably screen tapped for the Williamson circuit.  Maybe even buy a new Power xfor and even a choke and build up to just about any power level desired.  Decent poly caps, modern resistors, switch detent volume, bass and treble for a sturdy multi-use audio amp.  Couple it to any decent speaker with at least a woofer and tweeter and you'll have duplicated 95% of the great sound available in the 40's/50's and early 60's.

e.g., pp 6AQ5's all the way up to KT88's, your choice as to power level, damping, feedback circuits, etc.  There are a ton of schematics out there.

[W3GMS]

Good deal Rich on how they feed phono audio into the SX-42 receiver.  I know all my integrated and separate amps around here that have phono inputs have RIAA eq, whereas the aux input is flat audio. 
Joe, W3GMS   

[w1vtp]

I have  Dynaco Mk4 that I have planned for that kind of application.  I plan on building a mixing box that would comvbine all the audio outputs into the amp and perhaps pad each output from the mixing box so that the master control wont have to be messed with

Al

[N2DTS]

If someone transmitter is tubes, and you receive it on a tube receiver, and put it into a solid state amplifier, does the solid state amp somehow filter out the good tube sound?

I use an old Marantz solid state amp, been using it for 30 years, with only dirty switches for problems (deoxit fixed it). Its got bass, mid and treble controls, multi inputs, low and hi filters, speaker on off button, line level ins and outs, its not large, does not get hot or use much power.
I made a rack mount front panel for it, and marked it with the P touch, so when I change receivers, I can peel off the label and put the new name on the input select switch.

I used to have a lot of receivers around, r390a, sx17, Scott slrm, homebrews, 756 pro's, flex, etc.
Nice to have just one good speaker and select each rx I wanted to use at the time.

There are loads of diagrams for tube hifi amps, some are somewhat simple, others are very complex!
They get more complex if you want to add tone controls, line outs, etc...

It would be a fun project to build a nice tube hifi amp.

Brett

[flintstone mop]

I got a couple of old Heathkit 12 w. (20 w. peak) pp audio amps for this.  they were not prohibitively expensive and give the tube audio sound.  got one at a hamfest, the other off eBay.   Am in the process of recapping one now.  I like the Heaths because of the manuals.  6BQ5 pp.  12AX7 preamp, or that can be bypassed.  enough audio to nicely drive a large bookshelf speaker cabinet.  Fills the house with sound.  Fine to HB unless you want to focus only on things no one makes.   These (models EA2 and EA3) do have the RIAA preamp response but it sounds fine to me.  I just adjust the bass and treble until I have what I'd call full audio.

Rob

That was my very first electronic kit. I waited and waited for the Railway Express truck to deliver the package.
If hi level audio is put into a mag phono input, it would severe overload!!

Fred

[WBear2GCR]

Small toobe audio amps are pretty easy to find... just keep ur eyes open especially at hamfests... or that old tv/radio/phono console that got thrown out on the curb!

They're also not hard to find on ebay (gasp) as random and homebrew for less than the cost of a chassis, output iron and power iron, often in small miniature tubes.

Otoh, a solid state amp is even easier to build, and less expensive overall, smaller too. Forget building, these days used "semi pro" gear or an old 70s or 80s receiver on Craigslist is a best bet.

Rob, you should pull out the RIAA producing parts, it's only a few and make the amp flat - besides the RIAA input has way way too much gain - so maybe just bypass around and move the input ahead of the EQ, or bypass the EQ with a jumper/resistor as required??

If you post the schematic, we can figure that out.

Imho the trick to great AM sound in the shack is not "modern" hi-fi speakers but old paper cone speakers - a 15" paper cone in an enclosure of suitable size will sound terrific and take only a few watts to drive very loud. I know some ops like that low bass response on receive, but I try to avoid the stuff below 100Hz. in general. Nothing wrong with it, but if ur running vintage type drivers that makes for a very large speaker enclosure... ymmv.

                       _-_-bear

[K5UJ]

That was my very first electronic kit. I waited and waited for the Railway Express truck to deliver the package.
If hi level audio is put into a mag phono input, it would severe overload!!

Fred

No overload Fred, you only use the preamp for product detector audio, vy low v., around 10 to 20 mV. right out of the p.d.   Works FB.  For simply boosting the audio from a rx with a too small internal AF amp (modern rx especially usually have only a 1 watt s.s. audio section) you feed that to the input that bypasses the preamp.  The EA2 and EA3 has three inputs, only one is the mag.phono to the preamp. 

Bear, good idea doing a mod to remove the RIAA components.  I never thought of doing that.   I'll study the schematic and see if I can figure it out otherwise I'll scan it and post it here.  I have a day planned to be either operating the rally or working on the audio amp back and forth ham heaven.

Rob

[KM1H]

AM/FM /Phono console sets of the 50's are often free. The better ones have a minimum of PP 6V6's and 2 speakers.

I picked up 3 from one Want ad on Craigslist and the only cost was gas.

My favorite is a 1956 RCA  "Orthophonic High Fidelity" with a pair of 12" speakers and a pair of 5" speakers. It looks as new and is not stereo.
I decided to use one of my restored SX-62A's (same audio section as the SX-42) with this as it has far better control over the audio. I compared this with the other SX-62A that feeds a R-42 bass reflex speaker. While that one sounds OK the one fed into the RCA audio chassis blows it away even tho Im still limited by the IF selectivity on AM. I simply reversed the function of the mode switch and rear phono jack on the 62 and removed the audio tubes.  

Carl

[K5UJ]

If someone transmitter is tubes, and you receive it on a tube receiver, and put it into a solid state amplifier, does the solid state amp somehow filter out the good tube sound?

I bet if it is an old s.s. amp like ur Marantz it is okay.   One of the resident know-it-alls on another ham website tried to tell me once that s.s. AF amps are all noisy.  He wrote that all you have to do is cut all the inputs and turn up the volume to hear the hiss.  I went home and turned on my 35 year old Kenwood 100 w. s.s. audio amp I bought in Korea, when I was stationed there, and cut all the inputs and cranked it up.  Nothing.  Put my ear down to a tweeter.  Nothing.  I never got back to him because you can't teach anything new to one of the Masters of the Universe on this popular ham website, which I almost never visit now.

Rob

[Opcom]

If someone transmitter is tubes, and you receive it on a tube receiver, and put it into a solid state amplifier, does the solid state amp somehow filter out the good tube sound?

It won't take the tube sound out. It will try to reproduce it.

[w8khk]

Lots of good tube amplifier info at this site, MINUS the audiophoolery:

http://www.angelfire.com/electronic/funwithtubes/index.html

Site is run by Max Robinson, K4ODS.

Interesting Valiant Modulator design here:

http://www.angelfire.com/electronic/funwithtubes/Vike_Val.html

[N2DTS]

I think the marantz is quiet.
I know many cheap audio amps are nasty noisy, like all the rice boxes, but I thought the modern hifi stuff was ok.
I have built a few IC chip audio amps that had plenty of noise, but for ham use they were ok.
I put one in the G76 to replace the crazy stuff they did using the modulator driver as the audio output amp.
Fidelity was much better with the chip, even with some background hiss.

For music, I am still using an old pioneeer receiver with the brushed alluminum front and the flywheel tuning (analog), as it just keeps working.
I would like to get something with FM presets rather then tuning, but the xyl says just keep the old stuff...
I should fix the scratchy tuning cap and correct the dial which is off...
Got a load of records and a nice direct drive turn table.....

I think it would be really easy to build a nice tube hifi amp using something like a pair of 6L6's in Williamson, 20 watts out, Hammond iron....


Brett



[/quote]

I bet if it is an old s.s. amp like ur Marantz it is okay.   One of the resident know-it-alls on another ham website tried to tell me once that s.s. AF amps are all noisy.  He wrote that all you have to do is cut all the inputs and turn up the volume to hear the hiss.  I went home and turned on my 35 year old Kenwood 100 w. s.s. audio amp I bought in Korea, when I was stationed there, and cut all the inputs and cranked it up.  Nothing.  Put my ear down to a tweeter.  Nothing.  I never got back to him because you can't teach anything new to one of the Masters of the Universe on this popular ham website, which I almost never visit now.

Rob


[/quote]

[K5UJ]

For music, I am still using an old pioneeer receiver with the brushed alluminum front and the flywheel tuning (analog), as it just keeps working.
I would like to get something with FM presets rather then tuning, but the xyl says just keep the old stuff...
I should fix the scratchy tuning cap and correct the dial which is off...
Got a load of records and a nice direct drive turn table.....
Brett

That's almost exactly the same setup that I have except for brand names.  I have an old analog Technics flywheel tuner and Pioneer direct drive turn table.  The tuner is connected to 75 ohm coax that runs outside to a mast next to the house holding a 5 el. FM bc yagi.   About 8 or 9 years ago I needed a tuner and I was so out of it I went to Best Buy and quickly learned that the audio market had devolved into getting one big black box for everything, and if you wanted a separate component system you now had to blow thousands of bucks on gold plated components sold in audio salons.   So I went to a hamfest a few weeks later and there in the flea market was a Technics tuner for $20 which I bought and have used ever since.  I'm still using these big old Sansui speakers that are around 30 years old.   

[N2DTS]

I need an outside antenna as some of the stations I like are not real strong.
My speakers are old marantz 12 inch woofer 3 way jobs.

The new stuff is very light, made of plastic, has crappy displays, and is just a few chips inside.
It would be fine if they had nice displays and so on, no menu's, many don't even have tone controls just different eq curves, yuk!
I never looked at the real expensive stuff, maybe its better.
My old pioneer has watt meters on the front, and the center tuning/signal strength meter, metal knobs, etc.

Brett

 

[KC4VWU]

Brett, in the shack I use my old Sears LXI receiver bought when I was a teenager. Analog tuning, somewhere around 30w./ch., brushed aluminum faceplate. Nice weighted flywheel tuning. I was wanting to try out an outboard setup for my National, and had misplaced a couple small PA amps; so I just sat there and scratched my head... " What do I have to do this?" I remembered the old rx and drug it out. It had been poorly stored for quite a few years, not in direct exposeure to the elements, but in an old barn if you could actually call it that. Looked and smelled pretty rough, but I took the top cover off and gave it a water hose bath with some Totally Awesome, let it dry for a week, lube and cleaned everything, and applied power. Now, I have a BA rx. input to the AUX, and I can listen to the FM BCB: but I can't seem to find any Van Halen, Judas Priest, or Ted Nugent anywhere across the dial. Just some jokers wanting a nickleback in change and a few other losers. Maybe it's still broken!

[N2DTS]

They sure don't seem to make stuff like this anymore.
Who would think these pieces would still be working so long after they were made.
(without any repair)

Brett

[WBear2GCR]

http://www.angelfire.com/electronic/funwithtubes/Amp-Monoblock_Triode.html

This happens to be a very nice design...

I'd not use 6L6s... and one ought to be able to do more than 18 watts I think out of a quad... but... the circuit is quite nice, only one aspect I'd alter and it is minor. A good one to build. Far nicer than a Willamson in all regards, imo. Btw, it seems this is running in Class A2, if you ran it in AB2, it would likely do more like 60+ watts. A switch to 807s at >750vdc on the plates, and with a fixed screen voltage, and you'll make 200 watts, 6550s in AB2 will likely do >100watts with around 500vdc on the plates... of course you can scale back down and use 4 x EH300B (Electro-Harmoinix ruskie 300Bs, nice) and do the same 18 watts or better DHT triode style.

                _-_-bear

                    _-_-bear