'75 Session 400 upgrade

Brad Sarno · Post by **Brad Sarno** » 13 Mar 2003 2:03 pm

Well I just got my first Session 400. It's a 1975. This is the original model with all discrete transitor circuitry. I see why so many people like these things. It's a different tone than the later, op-amp based models. Very sweet and almost tube-like. Ken Fox explained to me why these amps have this quality in their tone. The transistors in the preamp are called J-Fet's. A J-Fet, although a transistor, has been referred to as a "tube without a heater" because of the way they operate and their harmonic and dynamic characteristics. I also understand that these are also what are in the classic Evans hi-voltage preamp circuits.

Understanding that this amp is a classic, I have no interest in changing any values or doing any "modifications" to the design. Curly Chalker apparently helped develop this amp with Peavey and the process of tweaking was painstaking. Nonetheless, I had to look inside and see what they had going as far as what was in the signal path. This is where the capacitor issue comes into play. The stock signal cap's are all pretty decent looking (and sounding) mylar caps. BUT, at a few critical junctions some relatively high value capacitors (2uF) are used and Peavey chose to use electrolytic capacitors in those places. It's a common cost based choice in the electronics manufacturing world to use the cheaper electrolytic cap's when the values get that high. So, I pulled out the stock 2.2uF electrolytics and put in some good mylar 2uF caps. Just as I expected, the tone improved. It's generally the same sounding amp but with a still sweeter top end and generally cleaner, warmer sound. What I hear is that the better caps help create more clarity and detail throughout the spectrum. The bass is more solid and pitch-defined, the midrange is less cloudy, and the top end is clearer, like cleaning a lens off. I see why some people use the term "string separation" when they talk about gear. This definitely helped create that kind of clarity. What's real cool to me is how the clean signal is easier on the ear, less harsh or "icy" while still remaining crystal clear. Guitar even sounds great thru it.

What a cool amp!

Brad Sarno
Blue Jade Audio Mastering
St. Louis, MO

Bill Terry · Post by **Bill Terry** » 13 Mar 2003 2:47 pm

Does it have the original JBL?

Brad Sarno · Post by **Brad Sarno** » 13 Mar 2003 2:55 pm

No it's a Black Widow with the new basket.

Brad Sarno

Ken Fox · Post by **Ken Fox** » 13 Mar 2003 5:34 pm

Brad, a pleasure to visit with you in Dallas. The whole show was just awesome (my 4th year in a row).
I must confess, I used a Session 400 and a Mace back in the seveties for my 6 night a week gigs. When I got tired of replacing 6L6GC tubes, I bought a Session 400. I was primarily playing guitar and a little steel. What a great amp, very close in warm tone to the Mace (older Mace, transistor preamp). I just got a newer Mace VT and did the Burr Brown chips. I am going to look into those caps and see if I have some in mine to replace. Who makes the 2uf caps you are using?
Another big surprise at the show was the new Nashville amp (80 watts). Wow, what a steel amp with a 12" speaker and only in the 40lb range. Jeff Newman tried one in the Peavey Booth and it blew him and the rest of us away! Warm tone, 3 spring totally awesome reverb and he was cranking it! That amp would be a super nice small club or miked steel amp. I think we will hear a lot about it in the near future. They had another in the Carter booth and it was doing great there as well. Hats off to Mike Brown and the boys at Peavey for another job well done!
Again, I enjoyed our visit and a chance for two "amp geeks" to talk electronics! I learned a lot from you and hope to see you in St Louis this year.<FONT SIZE=1 COLOR="#8e236b"><p align=CENTER>[This message was edited by Ken Fox on 13 March 2003 at 05:36 PM.]</p></FONT>

Brad Sarno · Post by **Brad Sarno** » 14 Mar 2003 1:33 am

Yeah Ken! Great to get to hang with you in Dallas. Not many steelers want to talk about J-Fets and coupling capacitors. The 2uF caps that I put in the Session are some orange drop looking ones that I found locally. Probably mylar. Any 2uF film cap should be great, way better than the electrolytics. You can hear the tone quality of the better caps and it's a good thing.

Brad Sarno

Mike Brown · Post by **Mike Brown** » 14 Mar 2003 6:39 am

I'm glad that you guys got to visit the Peavey Demo Room. It was a pleasure seeing you again.

The Nashville 112 amplifier surprised a lot of players I think. The look on Jeff's face was one that I seldom see as you know that when he comments on a product, you can believe it.

Do you think that an update kit is in order for the Session 400? I have only received about to inquiries about one in the last 4 years.

Bill Fall · Post by **Bill Fall** » 14 Mar 2003 6:48 am

Questions from someone who knows nothing about this stuff . . .

1. If I had my repair guy do the same thing to my Session 400, how many of these 2.2uF caps are we talking about? And would I ask him to replace all that he finds? Or just certain ones?

2. Is this what's at the core of so-called mod kits?

Dennis Detweiler · Post by **Dennis Detweiler** » 14 Mar 2003 6:59 am

The LeMay session 400 repro kits consists of replacing those caps with ones of higher value if I remember correctly? Also, if I recall, there are 18 of them? It's been a few years, but I replaced them in both of my 400s and it made a big improvement in tone, output and silenced background noise.
Dennis

Ken Fox · Post by **Ken Fox** » 14 Mar 2003 7:04 am

The core of the mod kits is the Burr Brown, Texas Instrument, OpAmps (these OpAmps are not in Session and LTD400, but are in teh Session Limited)) and of course some radical changes in the tone caps. The Session 400 upgrade kit that is available replaces power supply filters for sure, not sure if anything else is replaced. What Brad is referring to is an upgrade in quality of caps used in the tone and signal coupling sections for these amp. I have made a similar mod to older Fender tube amps and the results are significant. Just upgrading to Orange Drop caps and silver micas puts a lot of fidelity in a Fender amp. This is not a Fender mod for the "weak of heart" or average blues/rocker, the sound is usually to crisp and clean for their tastes.

Bill Terry · Post by **Bill Terry** » 14 Mar 2003 7:37 am

Brad, sounds like the BW is the deal. I worked for a Peavey dealer when that amp was a new model. We saw a lot of blown JBLs. If you had found one with an original JBL it would be a fairly rare amp, although I suppose some are still out there. I don't remember when Peavey replaced the JBL, maybe Mike or somebody else knows, but as a dealer, we were glad when they did.

BTW, I've done that mod (both Peavey and LeMay) on several Nashvilles and Vegas amps and it is just opamp upgrades, and a few R's and C's. Most of the cap changes are in the coupling stages if I remember, just as you guys said.

Brad Sarno · Post by **Brad Sarno** » 14 Mar 2003 10:48 am

Bill, I believe my '75 Session 400 had about 6 of these 2.2uF electrolytic cap's. They were all on the preamp board. Since they serve as interstage coupling cap's, I presume it's OK to up the value but I wanted to avoid any "modifications" since the old Session 400 is a classic. Like Ken said, the upgrade was merely that, an upgrade in quality of capacitors while keeping the values consistent with the original circuit design. It's a very easy and noticable upgrade, just find some nice 2uF film cap's of proper voltage.

Brad Sarno

jim milewski · Post by **jim milewski** » 14 Mar 2003 9:12 pm

Brad, I agree with you, I have the Session LTD, the transistors offer a sound somewhat between a tube amp and the newer amps using op amps, like Kenny, I upgraded to the mod on my Vegas with the Burr/Brown IC's, so the Vegas sounds great, but the Session is my amp for playing out, the LTD is the smaller cabinet, and the sound in my opinion is nicer still than the Vegas, I will never be without this amp, it did not work when i got it and put some time into it, now I'm kind of bonded to the thing, and love it! I also have a reissue twin with a BW 1501 in it with new Svetlana tubes, a Session 500, so these 4 amps with my old push pull gives me some great tones, I plan to buy every older Session that crosses my path if the price is right though, love those amps.

Brad Sarno · Post by **Brad Sarno** » 17 Mar 2003 1:53 pm

I just set up my rig with the Session 400 side by side with my '69 Twin with a 1501-4 BW speaker. It's amazing how "tubey" the old Session 400 sounds. The amps are voiced differently and the EQ sections are quite different, but I was able to get a very similar tone from the two amps. The Twin will always be my baby but my recent discovery of these old transistor Session 400's (and LTD's) has my Twin a little jealous. The Session, afterall, gets a lot louder, especially in the low end, and it's so sweet sounding.

Brad Sarno

Gino Iorfida · Post by **Gino Iorfida** » 8 May 2003 4:46 am

I just fell across an old Session 400 ('78 model, Thanks again to Mike Brown for the assistance in dating this amp!). And I agree, the tone is INCREDIBLE. It's not the gritty modern tone coming from Nashville these days (then again, most of what is coming out of there is Paul Franklin using Mesa tube preamp which is probably adding some of the grit, then the whole 'digital recording etc' is probably giving the rest of it-- the Vox Valvetronix can get that tone VERY easily btw!). Just very sweet tone. I do think it sounds better than the Nashville 400 I had before. Feeding this amp with the signal from a Lawrence 710 equipped push pull emmons, I can't get a bad tone from the amp, just a lot of DIFFERENT sweeet, warm tones.. Even though the enclosure is bigger than the Nashville 400, for some reason, it SEEMS lighter to me, could be my imagination, but hey maybe the tone makes me forget the weight!.
Brad, I'd definitely be interested in talking to you about the mods/updates you did to your Session, though, since I'm sure this amp is way overdue for a cap job anyways, and while I ahve it open, and replacing the electro caps, definitely would nt' mide putting in the best components I can!
I agree with Ken, that using the mica caps instead of ceramics in a Fender is not for the bluse man. For 6 string, the tone is way too harsh/sterile sounding (once again, what proves best for fenders for steel and what is best for 6 string are in most cases not the same... I LOVE the silverface phase inverter and silver mica caps in a fender for steel, but prefer the blackface PI and ceramics for 6 string... go figure...)
Again, though, thanks again to Peavey for being the ONLY big manufacturer of musical equipment for caring about the steel guitar. Yes, we have guys like Webb, Evans and LeMay who care, but they are in my opinion the 'boutique' guys... Fender gave up on the steelers, Marshall never cared, Vox never cared (although for lower power needs, the Valvetronix line sounds REAL nice with their Fender and 'boutique' models!). Randall Cared for a couple years, then felt that guys like 'dimebag darrel' of pantera would better suit their business model than someone like John Hughey, Buddy Emmons etc. Mike and the rest of the folks at peavey, keep up the good work!! (Hint: an idea ya'll may want to try with some of the newer steel amps-- 2 switchable channels-- 1 beign the classic Nashville 400 style preamp, and the other a TransTube/Fenderish preamp, add in digital reverb and those of us who dont like to use a lot of effex could be happy... we could get the classic tones, and the modern tones all in one amp..)

Shoe · Post by **Shoe** » 12 May 2003 4:23 am

I bought a Session 400 w/JBL M35-4 in 1975 at the Chicago Store in Tucson, AZ. I have played it over these many years and the tone seems to have deteriated somewhat. So, I bought a Session 500 w/BW. Result, I still prefer the 400 tone quality over the 500. But I would like some reccomendation on upgrade to get the original sound from the Session 400. Thanks, Edwin Shoemaker.

------------------
Edwin G. Shoemaker
ZB Custom D10 8/5
'75 Session 400 w/JBL Session 500 w/BW

Brad Sarno · Post by **Brad Sarno** » 12 May 2003 8:39 am

The old Session 400 shouldn't need too much other than a good cleaning. Open it up and with a good electronic contact cleaner spray clean all the points where wires can be unplugged. Spray all the pot's and turn the knobs a few dozen times to clean them. Spray the input jacks from the inside. Spray the speaker jacks too.

Check and see also if all the rivets that hold the circuit boards are tight. If loose, then have someone re-rivet them. It's super easy. If the amp is electronically working with no real problems, it should come right back to life. Peavey's are great like that. Keep that old Session 400, it's a true classic that will only increase in value.

Brad Sarno
Blue Jade Audio Mastering