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Topic: Session 400 EQ analysis |
Brad Sarno
From:
St. Louis, MO USA
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Posted 17 May 2003 11:09 am |
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Well I finally satisfied my curiosity by running my old '75 Session 400 thru some lab tests to see exactly what that EQ is doing. It's a very interesting design, quite unlike the modern Peavey EQ designs that we find with the Mod kits and the Nashville 1000.
First of all I can help shed some light on how the midrange works. It's not as simple as a typical sweepable midrange. The Shift knob selects the frequency. The Midrange knob controls the amount of midrange cut. The circuit WILL NOT boost midrange at all. In fact when the Midrange knob is on 10, the eq is still cutting midrange about -3dB. When the Midrange knob is on 1 it's cutting about -20dB. The flattest you could possible set the amp would be with the Midrange knob on 10 and the Shift (frequency) knob also on 10. If you leave the Midrange on 10 but move the Shift knob to 1, then you get a real wide low-mid dip. This tends to thin out the sound a bit. The Midrange EQ really seems to do its thing when the Midrange knob is between 1 and 5. This is the sharpest and steepest cutting. I've made a chart so you can see how the frequencies line up with the 1-10 scale.
With the Midrange set on 1, I moved the Shift knob from 1 to 10 and marked the frequencies.
Shift settings:
1 = 500 Hz
2 = 525 Hz
3 = 545 Hz
4 = 560 Hz
5 = 615 Hz
6 = 710 Hz
7 = 800 Hz
8 = 940 Hz
9 = 1120 Hz
10 = 1200 Hz
I often see people with this knob set at or around 6.5 or just under 800 Hz. This seems to be the most offensive frequency range on a steel guitar. It's interesting to me how this amp is voiced with a permanent midrange cut no matter what you do to it. The newer model Peavey amps like the Nashvilles have a more traditional mid-sweep EQ where you can both boost and cut midrange. I think this mid circuit is really the heart of the Session.
For the treble control, the frequency is right around 2.7 kHz. It's a powerful control that will boost and cut +/-20dB. Careful boosting this one or it'll really hurt. I think that part of the sweet, warm Session 400 tone comes from a pretty healthy amount of treble cut, like with the knob at or around 2-4. It's interesting again how the Peavey mods have moved the treble control from this 2.7kHz range to up around 6kHz to give control over the pick attack. Personally I like having control over this critical 2.7kHz range.
The Presence control appears to be a high boost around 10kHz. This brings in air or "sweetness" and a little pick attack. It does little below settings of 5. Above that it starts to bring in the "presence".
The Bass appears to be either a low-shelf or a wide bell centered at 45Hz. This control has a range of about +/-15dB.
I've been fascinated by the old Session 400 at how it's so perfectly voiced for steel guitar. The midrange section is the most mysterious for people because it's kind of hard to understand what it's doing when set on 10. When it's on 1 it's pretty obviously a simple sweepable dip. But on 10 it aint boosting at all, it's still cutting but a wide and gentle cut. Even more strange is how with Mid on 10 and Shift on 1, the cut is a real wide and gentle low-mid dip centered around 350Hz helping to thin out the sound. Again with Mid and Shift on 10, that's as flat as you can get the amp.
If you want to hear the Session 400 set as "flat" as it can possibly be, try these settings. Then compare that to what your usual settings are.
For near flat EQ:
Presence 5.5
Treble 5.5
Midrange 10
Shift 10
Bass 6
My usual settings are:
Presence 8
Treble 2.5
Midrange 2.5
Shift 6.5
Bass 8.5
My typical settings were shockingly extreme when viewed on the analysis screen.
If anyone has any more in-depth geeky questions about this data, just drop me an email. I hope to get some screenshots on the web so people can view the EQ in action.
Brad Sarno
Blue Jade Audio Mastering
St. Louis, MO |
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Bill Moore
From:
Manchester, Michigan
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Posted 17 May 2003 1:02 pm
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Pretty interesting, Brad, I just looked at my Session, here's what I've got it at:
presence 3
treble 3
mid 9
shift 9
bass 10
It sounds good to me. Maybe I'll try your settings and see how it sounds.
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Bill Moore...
my steel guitar web page
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Gino Iorfida
From:
Pittsburgh, Pennsylvania, USA
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Posted 17 May 2003 2:43 pm
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Brad,
Thank you for doing all the legwork in this!!! Saves me the effort!. Did you test the output after the power amp, after the voicing of the speaker, or strictly from the preamp itself?
I guess why I'm asking is, if it was from the preamp itself, I'm wondiering if the midrange dip you are noticing is through the whole chain, or is ther to o****eract the voicing of the power amp and the speaker. Could get some very different results.
What amazes me is how WELL the Session is, and how well it works with modern humbuckers (BL-710 etc), which have a natural midrange emphasis, as opposed to the single coils that were more prevalent at the time. Granted, you dont have the range of control that you would have with the modern Nashville 1000 or modded Nash 400 tone controls, the controls seem to be voiced perfectly (Ironically, checking out Miracle Audio's webpage, it seems that LeMay does not have a 'mod' for the old sessions, but just a simple cap upgrade kit for replacing the tired old worn out electrolytics)
It may be my ears, but to me the Session seems to be a bit better in the signal to noise ratio than the Nashville 400 was (don't have one here to do a direct comparison, mind you). THe reverb also seems a bit less sensitive to picking up hum, which I more than likely attribute to the larger cabinet, but could also be that Peavey was driving the tank harder in the session, with a lower gain recovery stage, vs less drive and more gain in the recovery, which will change the way the reverb reacts, but will also help in the signal to noise ratio... granted the Session reverb would be more likely to 'boing' out, but it does sound very close to the old Fender reverb to my ears. Playing my first gig with my Session this evening....so I'll let ya'll know how it performed in a live setting (incredible at practice, so I'm sure it will be just as well in a bigger room) when I get back from vacation. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 17 May 2003 3:51 pm
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Gino, the only voicing of the Session is in the eq section. The power amp section is just a plain old flat response power amplifier. The preamp input section is also flat. It's likely ruler flat from 20Hz-20kHz. I measured the audio at the "booster" output which is actually tapped off the power amp output in a Session 400 so it was a true reading of the amp as a whole. It's rare to see a power amp section that is anything but flat response. The EQ does any and all voicing and was quite likely designed to cover the range required for a 12" or a 15" speaker. I think there were actually some early Session 400's that came with 2-12" speakers instead of 1-15". Jerry Reed was an endorser at the time and being a guitar player I bet he used a 2-12" model. From what I understand, Curly Chalker played a major role in the tweaking and voicing of the eq, so I bet the bulk of the design was for steel and 15" speakers, likely JBL D-130 at the time. Since the Black Widow is so similar in voice to the JBL, the EQ could cover the variables.
And regarding the noise issue, after replacing the filter caps in my Session 400, it is MUCH quieter than my modded Nashville 400 was. The Session is a surprisingly quiet amp.
Brad Sarno |
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jim milewski
From:
stowe, vermont
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Posted 17 May 2003 3:55 pm
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| Brad, seems you like your Session as much as I like mine, what do you have in yours for a speaker, mine is a 1502 4 ohm |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 17 May 2003 5:14 pm
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Jim, I've got a brand new 1501-4 basket in it. I think they often had the 1502-4 but I think that's a ribbed bass speaker. The 1501 seems to have more of that JBL voicing that I like on steel.
Brad Sarno
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Earnest Bovine
From:
Los Angeles CA USA
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Posted 17 May 2003 7:00 pm
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| My Session 400 from 1975 required lots of mid-range cut at about 800 Hz. Maybe it was the Electro-Voice SRO speakers. |
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jim milewski
From:
stowe, vermont
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Posted 18 May 2003 2:16 am
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| For me the 1501 is the best speaker for any amp, I have one in a Twin, I'm looking for another 1501, my buddy has a fellow worker that found a Session 400 in the dump, his son is using it for a bass amp (after getting it fixed) I think I'll search for a bass amp for this guy and see if I can buy the Session, then put a 1501 in it, I think the speaker is a Radio Shack replacement, I have to say that my Session 400 LTD with a 1502 is my best sounding amp right now. My first Session had the 2 EVM speakers in it, they were not as common as the ones with the JBL, but was all that was available back in 1975 when I bought it new at $500 [This message was edited by jim milewski on 18 May 2003 at 03:19 AM.] |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 18 May 2003 4:40 am
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Great topic Brad. And thanks for detailed analysis of the frequencies. I've always been curious about the frequency range of the session 400. I have a 1974 that I bought new and a 1975 that I picked up about 15yrs ago. I've tried the Nashville and the 500 several times since they were introduced and always like the tone of the old 400s better.
This info will help me zero in on close settings on my Furman PQ-3 while experimenting with a Classic 50/50 tube head. 
Dennis |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 18 May 2003 8:40 am
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Ernest, I think many players do that steep cut at 800 Hz, regardless of the speaker type. Steel pickups are loudest at that frequency. Cutting at 800Hz is merely trying to smooth out the response of the pickup. Bill Lawrence once explained to me how steel pickups, whether wound high or low, will be loudest around 750-800 Hz. When I hear Curly Chalker's tone on his Session 400's, I hear that same steep cut at or around 800Hz.
Brad Sarno |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 19 May 2003 7:40 am
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Tom Mortensen
From:
Nashville TN
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Posted 3 Jul 2003 7:32 am
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The older session 400's have a "Booster" output.
Was this ever meant to be a line out suitable for recording?
I wonder if you could describe the location of the pin on the circuit board that connects to the wire to the 1/4" jack for Booster output.
At some point in time I must have reomoved this wire and would like to restore it.
Thanks |
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Nicholas Dedring
From:
Beacon, New York, USA
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Posted 3 Jul 2003 8:12 am
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| A question: is the EQ set up the same way on the "Session 400 LTD"? I was given to understand that it's basically a reissue of the Session 400, same wide cabinet, wide baffle thing... I still haven't gotten a clear answer from anyone on what exactly is the difference between it and the Nash 400, and it and the Sess. 400. I know the Limited was yet another amp, with a different cabinet etc., but I am a little confused. |
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Bill Terry
From:
Bastrop, TX
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Posted 3 Jul 2003 9:22 am
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Tom, I don't have the power amp schematic with me, but I seem to remeber the booster output is a wire from a voltage divider off of the speaker jack output over to the booster out jack. On my amp, the voltage divider resistors are wired right to the speaker jack, but I'm not sure that's stock.
Some previous owner of the '76 Session that I have, modified the booster out by changing the voltage divider values (I think the resistors are different than stock value) and adding a balancing transformer and XLR connector in place of the 1/4" booster output jack. I haven't actually tried it yet, but if it works pretty well, I can post the schematic for the mod if anyone is interested.
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Tom Mortensen
From:
Nashville TN
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Posted 3 Jul 2003 10:22 am
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I'm sure that in my 74' model Session 400 the wire was connected to a pin that protrudes upward from the circuit board.
There are three pins that have nothing attached at this point.
One is toward the front of the amp between the Reverb and Tremelo Depth pot.
There is another between the Tremelo Rate pot and the Sensitivity pot.
The third pin is front and 1 and 1/2" to the left of the right hand corner of the back circuit board. 
Bill, I would like to see the schematic for the xlr hookup if it is available.
thanks[This message was edited by Tom Mortensen on 03 July 2003 at 11:27 AM.] |
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Bill Terry
From:
Bastrop, TX
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Posted 3 Jul 2003 11:28 am
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Tom, based on what you say yours looked like, somebody has likely modified that whole circuit on my amp. It didn't really seem to be a 'Peavey' thing to fly a wire over to the booster out jack and hang resistors on a jack.
I'll have to reverse engineer the Lo-Z out and figure out what they've done. I don't see any numbers on the transformer either, but maybe I can figure out what it is. Give me a day or two and I'll drop you an email when I figure it out.
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Tom Mortensen
From:
Nashville TN
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Posted 3 Jul 2003 3:47 pm
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Click Here to see a picture of the pins in my session 400 that I have referred to in previos posts.
Which pin should be connected to the 1/4" Booster out jack.[This message was edited by Tom Mortensen on 03 July 2003 at 04:49 PM.] |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 3 Jul 2003 4:16 pm
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| Well, IMHO, they plainly knew what they were doing in having no mid-range boost in the thing. Most steels already have more mid-range than anyone in their right mind would ever use! And the mere thought of playing a steel "flat" (let alone "boosting" the mids) makes me cringe, anyway. |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 3 Jul 2003 4:41 pm
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Not sure about this...but I think the booster out was meant to run into a slave head for more power. The booster out signal is too hot for patching into a board. However, with the advent of attenuation controls, maybe it is now possible to cut the signal into the board?
Dennis |
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Dennis Detweiler
From:
Solon, Iowa, US
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Posted 3 Jul 2003 4:46 pm
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Since the original Session 400s came out, active circuitry was added to the newer 400s. Zero being at 12 o'clock. However, I played through a Nashville 400 soon after they were introduced. Without looking at the control panel, I adjusted the tone on a Nashville to duplicate the tone on my Session 400 and ended up with the knobs adjusted to the same settings (o'clock) on the Nashville as on the Session.
Dennis |
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Bill Terry
From:
Bastrop, TX
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Posted 3 Jul 2003 5:16 pm
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Tom, according to the schematic I have, and after looking at my amp, it looks like it has to be the pin on the power amp board (the one toward the back of the amp).
You might want a second opinion from Brad or Ken or one of the other Session gurus, but I'm 99% sure that's it.... |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 4 Jul 2003 10:34 am
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The pin on the power amp board, as I remember, is where the booster connects. It's just a single wire with a molex plastic connector that fits over the single pin on the board. I'm not positive though. I'll have to pull a head out of the chassis and peek.
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Brad Sarno
Blue Jade Audio Mastering
St. Louis
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Terry Downs
From:
Wylie, TX US
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Posted 4 Jul 2003 6:25 pm
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Brad,
Thanks for you effort in testing. I have always been perplexed about the Session 400 EQ. I have a great life long friend in N.C....the guitar doctor A.C. Lail. He happens to work on Redd Volkert's teles. He swears by the Session 400 for Telecasters. When I visit, they always want me to play, and I always have a hard time setting it right. Knowing that the midrange is a "cut only" will totally change the way I approach setting that amp.
The Session 400 preamp and mid EQ section is a strange circuit topology. The bass and treble EQ section (folllowing the mid section) is very classic and straightforward. I may Pspice that section to see how close it comes to your experimental data.
Regards,
Terry |
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Rick Aiello
From:
Berryville, VA USA
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Posted 4 Jul 2003 7:12 pm
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Thanks Brad ... I love to analyze stuff and read about others work.
I certainly have improved my sound readin' stuff from here ... I have a Peavey Jazz Classic that I understand is related to the Nashville 400 (?) .. your work seems to fit it as well.
I have "picked up" on the 800 Hz cut ... and it really makes a big difference. Doesn't seem to really matter which steel and/or amp ... a cut at 800 really is nice.
I also read that somewhere in the 250 Hz range can be reduced with good results.
What other frequencies do y'all think are "influential" ??
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Joe Alterio
From:
Irvington, Indiana
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Posted 4 Aug 2005 12:30 pm
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I know this thread is nearly two years old, but I really enjoy looking back at the analysis Brad did and thought some others might like to see it as well (that missed it the first time).
One thing I find odd....it seems that most people that have posted their settings here on the Forum have their Shift settings set at 7 or higher. Both Buddy Emmons and Lloyd Green have reportedly set their Shift at 10 (which, per Brad, is 1200Hz!!!). Perhaps the Hz settings Brad listed are only valid when the Mid is at "1" as he described??
All very interesting......
Joe |
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