Suggested Dynaco PAS mods

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Postby jukingeo » Tue Feb 03, 2009 9:14 pm

joeriz wrote:It's an old article from the Sensible Sound that outlines various mods to the PAS. I can't recall if this is the whole shootin' match but...

1) The filter switch becomes a tone in/out switch.
2) The accuracy of the RIAA phono eq is increased.
3) I believe an improvement is made to the loudness function.
4) The mod enables it to drive a greater variety of power amps.

If you PM me your e-mail I can send you a copy.

Joe


PM sent your way.

Thanx,

Geo

CpuZapper wrote:If you like the SRPP would it not be better to add tone controls to it?

With a quick google I found some SRPP preamps with tone controls.


Really? I didn't think building a tone control in an SRPP circuit was possible...unless of course you drive the tone controls with the SRPP stage first and then perhaps have additional stages afterward (or even vice versa).

(What I was looking at would be to build the tone controls within a single SRPP stage, so I don't have to use another tube...THAT may not be possible).

I will check it out though.

Thanx,

Geo
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Postby nyazzip » Tue Feb 03, 2009 11:17 pm

...regarding tone controls, i have to agree with the purists: assuming you are listening to professionally recorded, mixed, and mastered music, which i assume we all are 99.9% of the time, then you probably have either a 1)speaker problem, 2) an amp problem, or 3) an ear problem, if you often feel you need to tweak the EQ.
after all, the preamp is simply magnifying a source, and the source (cd/vinyl/tape/fm stream) should be trusted to be sonically AOK.
i'm not saying there is any "Law of Good and Right Sounding Musick" or anything, but IMO it's generally safe to trust the source mix of the very experienced pro engineers, in pro studios, with pro mics, recording pro musicians and their pro instruments, thru pro mastering monitors, all paid for by corporations who presumably understand/understood that one key to selling recordings is having "good" sound. the science of audio reproduction has been done, and that all happened in the 1950s-60s.
the only times i am tempted to tweak mixes is when i am listening at crazy loud volumes and i want to cut a bit of bass lest i wreck some drivers. but then its not about sound quality, its about damage control.
i only chimed in on this because i am a home-hobbyist recorder/musician/engineer, and although i use decent equipment, and am crazy about detail, usually when i bring the recording out of the "studio" and play it in the "real world" (car stereo, friends, any other sound system, etc) to me it sounds sub-par, and i am then reminded to be appreciative of commercially recorded music.
and yes i know what a compressor is Yellow_Light_Colorz_PDT_05

so, i have come to generally trust the fidelity of commercially recorded sources, and if it sounds "bad", i would be inclined to check elsewhere.
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Postby jukingeo » Wed Feb 04, 2009 9:11 am

CpuZapper wrote:If you like the SRPP would it not be better to add tone controls to it?

With a quick google I found some SRPP preamps with tone controls.



Last night I tried looking for some designs. I didn't come up with much.

Do you happen to come across some good links you can post?

nyazzip wrote:...regarding tone controls, i have to agree with the purists: assuming you are listening to professionally recorded, mixed, and mastered music, which i assume we all are 99.9% of the time, then you probably have either a 1)speaker problem, 2) an amp problem, or 3) an ear problem, if you often feel you need to tweak the EQ.


{Climbing up on soap box}

You are missing several other points too. I.E. Room problem, speaker placement, etc. But I do have to disagree with your opening comment about professionally recording music being recorded correct 99.9% of the time, that figure is more like 80%. Perhaps it is higher for those that listen to jazz and classical but as I said, I listen to modern music and production ranges from excellent to down right poor. This is probably the biggest reason of all to have tone controls.

i'm not saying there is any "Law of Good and Right Sounding Musick" or anything, but IMO it's generally safe to trust the source mix of the very experienced pro engineers, in pro studios, with pro mics, recording pro musicians and their pro instruments, thru pro mastering monitors, all paid for by corporations who presumably understand/understood that one key to selling recordings is having "good" sound. the science of audio reproduction has been done, and that all happened in the 1950s-60s.


I listen to music mostly from the 50's to the early 90's. And being that you mention the 50's and 60's let us bring up that point. For one, comparing one era to another warrants some kind of tone adjustment because most of the songs from the 50's and early 60's do sound thin. It wasn't until the mid 70's to 80's where pro audio equipment reached it's full sonic potential. Granted as time moved past the 80's, there is less of a need to use tone controls to take care of "an equipment problem" due to age of the original recording equipment used to create the piece. But I can clearly say that you would need some kind of tone adjustments going from one era of music to the next.

Then there is the issue of the production of the pieces. Production is done by a human being...so right there it is flawed. The hearing of ALL human beings change as time goes on. This is not only true of the listener, but the guy that has been making recordings for over 30 years +. I have seen many well known producers that have made excellent recordings in their early years, but not in their later years. More then likely that was due to hearing changes.

Moving along, sometimes you just get a 'bad' recording, even from professional and well known artists and producers. For example, let me use an example of a very well known band: The Rolling Stones. Perhaps one of my top favorite songs is Gimme Shelter. The recording quality of this song is absolutely horrendous. It has no high end, it has no low end, the middle is thin and the mid-base is VERY peaky. This song DOES require tone manipulation. Now I don't know who was in the booth the day the song was recorded, or if that person was 'stoned' or what have you. But the person clearly ruined an excellent song. Granted there could have been an equipment problem that day or something else because I clearly heard recordings made by the band around the same era that sounded much better.

Now using the SAME band but fast forwarding to the 80's, the Stones recorded "Miss You". This (to me) is an excellent recording. I can turn the tone controls off for this one. Sure you have many more variables when comparing this song to an earlier one and the first thing is better recording equipment. Now you might NOT agree with me that this is a well recorded song. And that brings up the next issue.

Personal Preference: What you hear and I hear as well as what everyone else hears is perceived differently and as such a specific way something is recorded might sound great to you, but horrible to me...even in the event both of our hearing levels would test identical (which wouldn't be the case).

Now going back to the 'reproduction' end of things. The room will play a major role in the sound quality and this is where I find tone controls most helpful. Sometimes you don't have an ideal speaker placement, sometimes the speakers may not be sized right for the room (I ran into this many times). And just a little tweak here or there will help balance things out. When I moved from my apartment to my house, I had a much larger space to fill, but not enough money in the kitty to purchase larger speakers. I had to punch the bass up considerably more. I had more reflective surfaces as I mounted my speakers higher and I also had to reduce the treble. The point is that I was able to do it because of the tone controls.

Now I also have friend that is a purist as well. He is a mostly a 'new age' and jazz listener. He HAS a perfectly tuned room and a very expensive sound system with no controls on the pre-amp. In his case everything sounded fine. But this was because of many factors that attributed to that.

1) Acoustically correct listening room
2) Very high end sound system with speakers that matched the room
3) A very narrow musical interest and cherry picking of audio recordings known to be well recorded.

Granted in his case, he probably doesn't need the tone controls.

But to me this is an 'ideal' system and not realistic. For one I don't have the $20k to buy the system he has (not counting the room alteration costs). Even if I did have that kind of cash outlay, my listening interests are very wide and varied.

The bottom line is that I HAVE gone the purist route and I HAVE built a pre-amp that has limited tone controls. I am overall happy with the pre-amp, but I need something more...something that I can hook up more pieces of equipment too (i.e. a phono and reel to reel deck) and also something that will allow me to have more control over the tone.

Also, just about every modern piece of equipment comes with some kind of tone control...even an Ipod. So what I would like to do isn't something that comes out of the far reaches of the Motaran Nebula.

I do recognize that tone controls CAN do more damage than good, but that is the reason why I posted here so this way I can examine tone control designs and select an option that is 'musical' and will properly correct the sound and not make it worse than it is.

Again, this is all just one persons opinion in lieu of my reasons why I want tone controls. Some may agree with me, some may not. I am just illustrating that there are many many more reasons why one would want tone controls on a pre-amp.

Thank You,

Geo

{Stepping down from soap box}
Last edited by jukingeo on Wed Feb 04, 2009 9:58 am, edited 4 times in total.
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Postby CpuZapper » Wed Feb 04, 2009 9:42 am

I'm no expert so this link said it was SRPP with tone controls.

Not sure if this is any help.
http://www.turneraudio.com.au/preamp-10 ... -2006.html
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Postby jukingeo » Wed Feb 04, 2009 9:57 am

CpuZapper wrote:I'm no expert so this link said it was SRPP with tone controls.

Not sure if this is any help.
http://www.turneraudio.com.au/preamp-10 ... -2006.html


Oh, yes, I did see that one, but remember, I AM trying to fit this in a PAS chassis. This is a 10 tube mammoth of a pre-amp. I DO like the design, but I would have to scale it down to something that would work with far less tubes. But for a larger project down the road, I would consider it.

I didn't see anything simpler though.

I did think of just adding a tone stack to the Rosenblit pre-amp design. But I don't know if I should put the stack before the amp, after it, or if I need additional amplification.

Thanx,

Geo
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Postby EWBrown » Wed Feb 04, 2009 10:05 am

The PAM and PAS series of tube preamps were engineered to get as much "bang for the buck" as was humanly possible back then, and Dynaco did an admirable job.

Compare the price to that of McIntosh or Marantz systems of the time. :o

A passive Baxandall (as in the RCA tube manual,and in the PAS series) tone stack does attenuate the audio signal levels, so some amplification is necessary in order to restore the audio signal back to pre-tone stack levels. The amplification can be before, or after the tone stack.

In the PAS3X, the tone stack splits the treble and the bass controls as shown here:

http://www.geocities.com/vintageaudio/pas3xb.JPG

In the RCA tube manual's tone control design, the bass and treb are simply lumped together with a gain stage before and after.

similar to this approach:

Image

On a second look, it appears that this circuit does appear to have fedback throuth the 0.25 uF cap, so, as Rosanna Roseannadanna used to say...

never mind ........ Yellow_Light_Colorz_PDT_02 Yellow_Light_Colorz_PDT_09 Yellow_Light_Colorz_PDT_05

An active tone stack (in which the circuitry involves fedback as part of its operatiom) may or not need additional amplification after the fact.

The loudness compensation is part of the volume control, and doesn't attenuate the audio signal level.

/ed B
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Postby Slartibartfast » Wed Feb 04, 2009 12:04 pm

jukingeo wrote:
CpuZapper wrote:I listen to music mostly from the 50's to the early 90's. And being that you mention the 50's and 60's let us bring up that point. For one, comparing one era to another warrants some kind of tone adjustment because most of the songs from the 50's and early 60's do sound thin. It wasn't until the mid 70's to 80's where pro audio equipment reached it's full sonic potential. Granted as time moved past the 80's, there is less of a need to use tone controls to take care of "an equipment problem" due to age of the original recording equipment used to create the piece. But I can clearly say that you would need some kind of tone adjustments going from one era of music to the next.



And I would disagree with you. My refurbed PAS, minus tone controls, plays music from the 50s to present.

Music from the 50s may sound "thin" to you, but that does not make it "wrong" and in need of adjustment, at least not for every one.

Every one does not hear the same, so to make a blanket statement as you did, is flawed.

My goal is to listen to the music as it was recorded. If it sounds bad, I will not continue listening to it.
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Postby CpuZapper » Wed Feb 04, 2009 12:26 pm

Slartibartfast, you have your quote wrong, I think that was from a jukingeo post. The CpuZapper wrote: had me a little confused.
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Postby Slartibartfast » Wed Feb 04, 2009 12:36 pm

CpuZapper wrote:Slartibartfast, you have your quote wrong, I think that was from a jukingeo post. The CpuZapper wrote: had me a little confused.



not the quote but the inline HTML... Yellow_Light_Colorz_PDT_09 :o Yellow_Light_Colorz_PDT_08 Yellow_Light_Colorz_PDT_02
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sometimes better isn't

Postby EWBrown » Wed Feb 04, 2009 1:56 pm

Back in the 50s / 60s, all of the music I heard was mostly through a small 4 or 5 inch speaker in a "5 tube AC/DC" table radio, often with local electrical noise, thunderstorm static, etc, in the background. Limited bandwidth, not only from the AM station, but add in the table radio's limited response, and often the received stations were at a distance, expecially at night, when they could be heard from halfway across the country. And of course all of this was in glorious mono.

WHen I hear "oldies" on a good system, and in stereo, it definitely sounds a LOT better as far as audio quality, but it still doesn't sound quite "right" to me...

/ed B
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Re: sometimes better isn't

Postby jukingeo » Wed Feb 04, 2009 3:11 pm

EWBrown wrote:Back in the 50s / 60s, all of the music I heard was mostly through a small 4 or 5 inch speaker in a "5 tube AC/DC" table radio, often with local electrical noise, thunderstorm static, etc, in the background. Limited bandwidth, not only from the AM station, but add in the table radio's limited response, and often the received stations were at a distance, expecially at night, when they could be heard from halfway across the country. And of course all of this was in glorious mono.


On Dell Viking's Come Go With Me you can hear the the squeaking of the drummer's bass pedal :). But I know what you mean, it is amazing what you hear in the background when you play these older songs on a 'modern' system.

Come Go With Me also seems to sound the best on my 1959 jukebox, AND the bass pedal squeak isn't as noticeable. But then again too, the jukebox doesn't have as an articulate high end.



WHen I hear "oldies" on a good system, and in stereo, it definitely sounds a LOT better as far as audio quality, but it still doesn't sound quite "right" to me...

/ed B


I know what you mean. A modern system does make the music sound "better", but something still doesn't seem right (until I start playing around with the tone controls). But I have found that music from this era seems to play the best on my jukebox than anything else. If I play modern music on my jukebox I actually have to turn the bass DOWN.

The jukebox amp is vacuum tube based BTW. It has a really nice sound and makes old 45's sound great.

I do have many old records as well which are not replaceable and they are a bit worn from age, so on a modern sound system, I have a tendency to turn the treble down a bit to mask the high end crackles and pops.

However, I will say that much of the old 50's and 60's music I like I do have on a CD so it is not plagued by problems such as record noise. Many times the sound is fuller on the CD as well. Yet compared to 70's and 80's music, I do find myself fiddling with the tone controls.

Slartibartfast wrote:Every one does not hear the same, so to make a blanket statement as you did, is flawed.

My goal is to listen to the music as it was recorded. If it sounds bad, I will not continue listening to it.


And this also proves what I was saying. If a song has a minor issue that could be corrected, you would dismiss it simply because your system can't adjust for the deficiency. Sometimes listening to something 'as it was recorded' is not always ideal. This is what I stated in my example with the Stone's Gimme Shelter. It is a fantastic song that was just badly recorded. BUT with a bit of a fix on the high and low end, it does make the song more listenable. I certainly am not going to reject this piece of music even though it isn't the best recording.

While I am not totally against pre-amps without tone controls...having been there, I would like the OPTION to use them or not.

Geo
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Postby TerrySmith » Wed Feb 04, 2009 3:23 pm

I never was really satisfied with the PAS phono stage, even with the curcio mods, so I repopulated an old board as per the circuit in the RCA tube manual as it's almost the same. Tubes are 6N2P-EV, eqiv to 6AX7.

The sound is much fuller, NO HUM, and the output level is a lot closer to other line inputs so I don't have to crank the volume way up.
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Re: sometimes better isn't

Postby Slartibartfast » Wed Feb 04, 2009 4:42 pm

jukingeo wrote:
And this also proves what I was saying. If a song has a minor issue that could be corrected, you would dismiss it simply because your system can't adjust for the deficiency. Sometimes listening to something 'as it was recorded' is not always ideal. This is what I stated in my example with the Stone's Gimme Shelter. It is a fantastic song that was just badly recorded. BUT with a bit of a fix on the high and low end, it does make the song more listenable. I certainly am not going to reject this piece of music even though it isn't the best recording.

While I am not totally against pre-amps without tone controls...having been there, I would like the OPTION to use them or not.

Geo



Speaking of music from the 50s, take Elvis recording at Sun Records for instance. They had at most a two channel board, so that meant two mics for him and the musicians. There is not much to work with, even with tone controls.

Now your Stones example, when I said I would not listen to it, I meant I would look for a different recording of that song. This is easier to do for music of the late 60s and beyond.

For critical listening in the late 50s I limit my selection to Jazz. Most of the music I like is 60s and beyond.
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Postby TerrySmith » Wed Feb 04, 2009 5:16 pm

Here are some pics of my modded PAS3. It has slight hum in the linestage, most likely because of my wiring. There are no tone, filter, loudness, etc circuits, just a barebone linestage. Tubes in the linestage are 7AU7's.

Image

Image

Image

PS: I'm trying out my new camera, whaddayou think?
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Postby nyazzip » Thu Feb 05, 2009 2:31 am

sorry for stirring up a hornets nest gentlemen. i can be a bit opinionated at times, and indeed i am not qualified to comment on virtually most of the things i do comment on.
nevertheless, it is entertaining.
back to the thesis of: dynaco PAS mods which retain the tone control circuitry.
i too own a PAS 2, and one channel of the phono section is seemingly weak, and the balance pot is crap, thus i also dream about some mods some day.
for me step one is that selenium rectifier Yellow_Light_Colorz_PDT_09
cheers
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