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 Post subject: OLD equipment
PostPosted: Aug Mon 19, 2019 12:55 am 
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Joined: Aug Thu 08, 2019 2:07 pm
Posts: 8
Hello all,

I just thought that I'd share with the group some info about my two oldest pieces of audio equipment...

The first is a Heathkit "FM-2" FM tuner. I talked my freshman class physical science teacher out of this tuner
way back in 1966. he had it stored in a cabinet in the class room and when I expressed interest in it, he told
me that if I got straight As throughout the year, he would give it to me. Well, I did manage to get straight As
and he gave me the tuner! It is a monophonic tuner, of course, and it did "work" at one time.

My second "old" piece of equipment is a Dynakit "PAS-3-X" preamplifier, which I bought as a kit and assembled.
I wanted an inexpensive preamp to drive my newly-acquired Crown "DC-300A" power amplifier. The Dynakit
had the same specs as Crown's "IC-150" preamp. I assembled the kit and it worked flawlessly. The Dynakit
preamp uses tubes and it also uses D.C. power for the tube filaments, to keep the AC hum to its lowest possible
level. I since replaced the Dynakit with a Crown "IC-150" preamp, which powers my Crown "DC-300A" amp.

As they say, "Too old to rock and roll; too young to die!"

Brad Anbro
Bluff City, Tennessee


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 Post subject: Re: OLD equipment
PostPosted: Aug Mon 19, 2019 1:41 pm 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 9123
Location: Ohio 45177
Back in the 80s I updated a PAS 3 with modern parts, film caps and metal film resistors. Also with what would be considered expensive euro tube brands, nowadays. It was a great sounding preamp. I also tried a solid state Crown rack mount stereo amp, one of the lower power ones. I forget model but well under 100W per channel. I found the sound of that power amp not very appealing. I stuck with my Hafler amp that I built as a kit for a long time.

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 Post subject: Re: OLD equipment
PostPosted: Aug Mon 19, 2019 4:18 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20564
Location: Utica, NY 13502 (USA)
I'm using a Crown D75 to drive some speakers mounted in the front wall of my shed which is near the house. It is driven by the tape record output of my shop amp which is a Pioneer SA-7100. Crown amps are designed for the commercial sound market and, while bullet-proof, they are not the best sounding among the herd in my opinion. But it is perfect for my application and sounds great.

The thing about driving a solid state power amp with a tube preamp is that you need to make sure the power amp's input impedance is high enough to provide the minimum load impedance required by the tube preamp. In the case of the PAS-3, it requires a load termination impedance of 100 k or higher while the input of the Crown DC-300A , for example, varies from 100 k down to 10 k depending on the input level control setting. At 10 k, (control at maximum gain) this could seriously affect the negative feedback tone control operation of the PAS-3 preamp.

Dave


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 Post subject: Re: OLD equipment
PostPosted: Aug Mon 19, 2019 5:35 pm 
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Joined: Aug Thu 08, 2019 2:07 pm
Posts: 8
Thanks for the informative replies. If I remember correctly, I bought the PAS-3-X
preamp when starting to build my "component" stereo system. At the time, I was
using a Harman Kardon "330A" receiver. The 330A allowed one to "split" the preamp
and power amp sections of the receiver, which I did, and I used the PAS-3-X as a
preamp for the power amp section of the 330A.

This REALLY brings back memories...the 330A was lacking in the available power
output and since I liked to play my rock & roll music loud, I would open up a window
(in the winter time) and let the back end of the 330A hang out of the window, so
that the output transistors could run as cool as possible.

I subsequently sold the 330A to a co-worker, who didn't care for loud music. He
used the receiver for many years and after selling the 330A, I purchased a Crown
IC-150 preamp and a Crown DC-300A power amp, which I still use. The PAS-3-X
sits in a box, in my attic.


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 Post subject: Re: OLD equipment
PostPosted: Aug Wed 21, 2019 4:05 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 4585
Location: Vancouver Island, Canada
Right, when the power transistors get hot, you would get distorted audio.

Back in the 1980's my wife bought a cabinet she liked and we shoe-horned the Toshiba stereo tuner into it, with a shelf on top, which covered the vent holes. Then she complained that the stereo was lousy but I would turn it on and it sounded good to me.
Pulled it out and checked it out over the weekend, sounded great on the bench, stuffed it back, went to work, came home to complaints, "You said you could fix it." :lol:
I figured it out then, cut holes in the sides of the cabinet so the transistors could breathe, problem solved,
Still have that stereo with the custom vent holes.

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 Post subject: Re: OLD equipment
PostPosted: Aug Wed 21, 2019 4:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9079
Location: Beaver Falls, PA. USA
I service that old equipment all the time; I'm just finishing up a Scott 299 amp.

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Tim KA3JRT


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 Post subject: Re: OLD equipment
PostPosted: Aug Wed 21, 2019 5:55 pm 
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Location: Ohio 45177
I don't believe it was the interface of the PAS to the amp that was the issue of why I did not like the Crown amp's sound. I also had a solid state preamp. The PAS apparently did not have an interface issue with the Hafler amplifier that is what I used it with, as I recall. The Crown had a grainy harsher sound than my regular amp. But it was the bottom of their line. The place I worked had some of the really high power Crown amps for some research use, not music. I wish I could have talked them out of those. I think at that time I was either using a Hafler preamp or a G.A.S. preamp most of the time.

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 Post subject: Re: OLD equipment
PostPosted: Aug Wed 21, 2019 7:35 pm 
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Joined: Sep Wed 10, 2014 7:13 pm
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Location: Central Illinois
The first Crown high-power solid-state amplifiers, which arrived on the scene in the early 1970’s, have a great deal of “crossover notch distortion.”

The DC-300, DC-300A, and DC-150 are examples of this.
The earliest versions of the Phase Linear 400 and 700 have similar issues with excessive crossover notch distortion.
But there are also several 1970’s vintage high-power solid-state power amplifiers which do not have crossover notch distortion. The Dynaco ST-400 and ST-416, the Hafler power amplifiers, and the GAS Ampzilla, for example.

Crossover notch distortion causes amplifiers to sound tinny, veiled, and buzzy when played at low volume levels, such as in a home stereo. Amplifiers that have crossover notch distortion sound much better when played loud than when they are operated at quiet listening levels.

Because audio amplifier specifications are measured at or near full power, the quoted distortion % can be quite low, yet there can be audible crossover notch distortion when the amplifier is operated at a power level of 1 or 2 watts.

By 1980 audio amplifier designers had learned ways to reduce or eliminate crossover notch distortion.

-EB


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 Post subject: Re: OLD equipment
PostPosted: Aug Thu 22, 2019 8:04 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Beaver Falls, PA. USA
I have a pile of old amps to work on, after retirement; a Cerwin Vega A-2200, a Crown DC-300 series 2, a Marantz, a couple of Ashly FET-500s, a couple of big Yamahas, etc. Whenever an old one was pulled out, it came home with me.

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 Post subject: Re: OLD equipment
PostPosted: Aug Thu 22, 2019 8:46 pm 
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Joined: Sep Wed 10, 2014 7:13 pm
Posts: 264
Location: Central Illinois
Tim Tress wrote:
I have a pile of old amps to work on, after retirement; a Cerwin Vega A-2200, a Crown DC-300 series 2, a Marantz, a couple of Ashly FET-500s, a couple of big Yamahas, etc. Whenever an old one was pulled out, it came home with me.
If you could post the model numbers, I probably have manuals for all of your Yamaha and Marantz units.

Between 1974 and 1978 I worked for a central Illinois back-line and sound reinforcement company. We owned about 50+ Crown DC-300A units. That was our standard amplifier for traveling sound reinforcement. They were all rack-mounted, 3 amplifiers per rack. Those Crown amplifiers were trouble-free for the most part.

After that I owned and operated a consumer/pro audio and video repair shop from 1980 to 2000. I have so many manuals that I don't know what to do with them. I probably have every Yamaha manual for both their consumer and pro-audio gear of that time period.

-EB


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 Post subject: Re: OLD equipment
PostPosted: Aug Wed 28, 2019 11:56 pm 
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Location: Sunbury, Ohio 43074
Fun Fact about the Crown DC-300..... I was at some long forgotten audio show a few centuries ago, and they had just come out with this gem. The booth display consisted of an HP signal generator, a DC-300, and ...... a toaster.

They were making toast with the thing for the entire show. And it just sat there and worked and worked.

Probably not really being operated at maximum stress that way, but back in those days it wow'd the crowd.

I don't remember if they had a scope or spectrum analyzer on the output. just the toast sticks in my mind....

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 Post subject: Re: OLD equipment
PostPosted: Aug Thu 29, 2019 1:18 am 
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Joined: Aug Thu 08, 2019 2:07 pm
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Another bit of trivia concerning the DC-300 amplifier...the unit used EIGHT
power transistors in the final stage of amplification. I looked up the
specs for those units and at the maximum capacity output of the amplifier,
each transistor was working at 25% of its rated capability.


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