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SEplex style build questions (fizz, fuzz, fart?)
SEplex style build questions (fizz, fuzz, fart?)
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Old 30th December 2017, 08:56 PM   #61
Gnobuddy is offline Gnobuddy  Canada
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Join Date: Mar 2016
I forgot to mention, you also need a grid stopper directly connected to pin 7. (Between pin 7 and the 1M grid bias resistor.)

Cathode followers have a tendency to oscillate at very high frequencies. By using the grid stopper (say 22k) and 1k build-out resistor (mentioned in the previous post), you can prevent this unwanted oscillation from occurring.

-Gnobuddy
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Old 1st January 2018, 09:50 AM   #62
jarrodthebobo is offline jarrodthebobo
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So ive been working on some fun things in the amp the past few days... decided on make an extra gain stage, changed the topology to something based of the s.i.r #34 #36 #39 amps and... not to toot my own horn but this is the nicest sounding distorted amp ive ever heard in my life.

Once i get some sleep ill document what i did and get some clips.

Yall are in for a treat!!
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Old 2nd January 2018, 12:13 AM   #63
DrFireBottle is offline DrFireBottle  Montenegro
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Whoo! Happy New year! So... I see you discuss the seplex that I brought up a long ago with my Parallel SE amp. Saw you were discussing putting EL34 and a giant tranny, nah that is not a good idea, I would reccomend putting a lot of smaller tubes in parallel just for fun! Like EL90 or else that has 6.3v filaments in it. Make a similar preamp like SEplex, make it original if you want to. I kinda don't like cranked JCM800 tones because the distorted sounds are alike, and for one to be unique, you have to have a good preamp, for example: if you know your "electronical stuff" you can make a preamp in your head to suit your needs, so I always chased that Fender purity and that "low thump" that it has when strings punched lightly, then I wanted to build an amp with "little tubes" that recreates that fender clear puncy tone whit a bit of that shiny dirt sound when turned up and I managed to do it after all, it was all by my "measurements" as I wanted it to be.

Last edited by DrFireBottle; 2nd January 2018 at 12:22 AM.
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Old 3rd January 2018, 08:39 AM   #64
jarrodthebobo is offline jarrodthebobo
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Been working on this one every single day for the past 2-3 weeks, and it's finally finished!

This amp has been a pain in the *** to get done and has gone through SO many circuit changes until I decided on this current version of the amp.

Thanks to the guys at diyaudio for all the help during these trying times!

STAY TUNED BELOW FOR SPECS:

3 12ax7 tubes in the preamp (Tung Sol, JJ, and Magnavox Vintage Tube)
1 el84 and 1 6v6 in the power stages, run in parallel (can be run separate no problem). These are both JJ's currently. I had tried a NOS Mullard el84 and an old Tesla 6v6 GT, but the Tesla was noisy. The mullard sounded pretty good though, but I'd rather risk the JJ in this amp (you know, in case of explosions!).

Preamp design is based off the S.I.R #34 which itself is a mod of a JCM800, tweaking the preamp stage to cut some more distortion. The addition of all the bypass caps almost 'add' another gain stage with the amount of gain that is added to the circuit with them inserted. All the awesomeness of 4 gain stages without the noise and overt saturation!!

Stage one is biased to 2.7k on the cathode, with 100k on the plates. All triodes have 100k on the plates except for the last triode which is for the second channel; this has a 50k plate resistor. B+ voltages are around 350v at every preamp stage.

Stage 2 is biased at 10k (or variable with switch). Stage 3 is biased at 820ohms.

Stage 3 leads into a cathode follower for the tone stack, and then out into the 'fake pi', which is just another gain stage basically biased to 1.5k or 1.7k (don't remember the exact value; we just wanted something that would bias this stage 'neutral'). Since Phase Inverters in these big amps that we all know in love naturally distort and add to the distorted tone of the marshalls and such, I wanted to be able to get a similar sort of effect in this Single Ended amp, which does not have a PI. Is it the exact same sound? Probably not; but it does sound pretty cool.

The last triode (stage 6... well technically stage 5 because of how I laid out the circuit), is a separate channel with a 68k grid stopper (vs. 33k in the 'normal channel), 1.5k cathode bias, and a 50k plate resistor. This is fed out from the plate through a .002 cap into a 500k pot. The pot connects to V2a's voltage divider network (470k to grid, 470k to ground). This effectively bypasses a gainstage and re-voices the preamp a bit. Effectively, the amp becomes: V1a 1.5k cathode 50k plate into V1b 820ohm cathode 100k plate; or a slightly modified plexi preamp.

Knobs:
Tone slope resistor knob; 1.7k-100k in order to 'select' the mid frequency point (simplest way I can explain it; it does a lot more than just this).
Pre gain 1: 500k gain knob after V1a. 180k resistor to ground from the middle lug. 470k resistor from the plate, with a 470pf bypass cap. Coupling cap is a .0022 cap
Pre gain 2: 500k gain knob after V1B. Coupling cap is a .0015 since I ran out of .0022s... whoops
TMB: Basic Marshall tone stack with a 390pf treble cap.
Presence Knob: Uses a .68uf cap. Boosts mids as well as highs.

SWITCHES: each switch changes the cathodes of V1a, V1b, and V2a. I misspoke in the video; V1b has the cathode resistor at 10k stock; but can be bypassed with .1uf or a smaller resistor for a total resistance of 2.2k, making it much hotter than 'stock'.

The other switches change V1a's cathode bypass cap to either none, .68uf, or 20uf. The last switch changes V2a's cathode bypass from none, .68uf, and 10uf.

Speaker: A single WGS Veteran 30 speaker (16 ohms); WGS's take on the Vintage 30 but without the huge mid-spike Vitnage 30s are known for. There is still a mid hump, but much less so. It's a nice speaker; but I want to throw some creambacks in the cab!

(This was the description of my video which refuses to upload... soon.... sooooon)
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Old 3rd January 2018, 08:39 AM   #65
jarrodthebobo is offline jarrodthebobo
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Nevermind; here it is!

YouTube
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Old 3rd January 2018, 06:25 PM   #66
Michael Koster is offline Michael Koster  United States
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Wow, thanks! This whole thread has been quite entertaining and I'm happy to see your success! Happy New Year!

"Lynch tones" ;-)

Last edited by Michael Koster; 3rd January 2018 at 06:26 PM. Reason: more info
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Old 3rd January 2018, 10:27 PM   #67
Gnobuddy is offline Gnobuddy  Canada
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The playing is less skillful, and the EQ is slightly different, but this clip ( http://www.diale.org/mp3/v1.mp3 ) sounds a lot like Jarrod's amp to me. In particular listen to the clip starting about 40 seconds into it, when the player switches from single-note lines to (power?) chords.

Five valves, two hefty transformers, a slew of pots and knobs and passive components, a large chassis, and a bunch of time and trouble went into creating Jarrod's amp.

And the MP3 clip? Shockingly, it came from two dirt-cheap small signal transistors (BJTs) in a circuit as simple as a fuzz-face: 2BJTE - 2 BJT triode emulator

Now there's a headache inducer!

(To be clear, the BJT circuit and guitar clip are not my work; both the circuit and the guitar clip are from Tiago Charters Azevedo).

-Gnobuddy
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Old 3rd January 2018, 11:11 PM   #68
jarrodthebobo is offline jarrodthebobo
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Quote:
Originally Posted by Gnobuddy View Post
The playing is less skillful, and the EQ is slightly different, but this clip ( http://www.diale.org/mp3/v1.mp3 ) sounds a lot like Jarrod's amp to me. In particular listen to the clip starting about 40 seconds into it, when the player switches from single-note lines to (power?) chords.

Five valves, two hefty transformers, a slew of pots and knobs and passive components, a large chassis, and a bunch of time and trouble went into creating Jarrod's amp.

And the MP3 clip? Shockingly, it came from two dirt-cheap small signal transistors (BJTs) in a circuit as simple as a fuzz-face: 2BJTE - 2 BJT triode emulator

Now there's a headache inducer!

(To be clear, the BJT circuit and guitar clip are not my work; both the circuit and the guitar clip are from Tiago Charters Azevedo).

-Gnobuddy
Hahah, I'm sure the biggest problem is my horrible laptop mic! I gotta get it actually miked up; it's a lot fuller in person and doesn't have that harsh beesnest tone that the video shows. Also I think I overloaded the mic at points.... whoops, hahah!

I'll be sure to get a proper demo in soon!

EDIT: But that transistor amp does actually sound pretty good too . Sometimes its about the journey rather than the destination though, haha!
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Old 3rd January 2018, 11:53 PM   #69
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by jarrodthebobo View Post
EDIT: But that transistor amp does actually sound pretty good too.
Doesn't it? That clip and circuit shocked me, because I'm used to transistor distortion circuits pretty much always sounding awful. Various shades of awful, maybe, but always awful.

Except for this one. I've never heard any other transistor distortion circuit that sounds that close to an overdriven Marshall. More importantly, that actually sounds good in a very "rawk" sort of way!

Quote:
Originally Posted by jarrodthebobo View Post
Sometimes its about the journey rather than the destination though, haha!
True enough!

-Gnobuddy
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Old 11th January 2018, 06:51 AM   #70
jarrodthebobo is offline jarrodthebobo
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S.I.R Amp Build Direct in Test by Jarrod Beauchemin | Free Listening on SoundCloud


Built a simple effects loop into the amp right before the final stage, so the amp is now usable as a preamp if I so fit!

Unfortunately my soundcard doesnt have its own volume control so I had to tweak the padding via vst as the output was overloading the soundcard from the effects loop send.

I'm using a few different cab models the responses of an SM57 miking a v30 and a greenback) to try and emulate the tone of how the amp sounds in person. There is a dab of reverb added in post as well in order to make it sound a bit less 'dry'.

No eq tweaking has been done. I should be able to have a better demo in soon when my new recording box arrives, which has independent volume controls AND a mic pre, so I can finally record an actual clip of the amp in person.

The long pause towards the end indicates that I've changed the channel on the amp.

hope you like it!
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