SSS/JM Sig amp/Overdrive reverb Hybrid idea

[valveandsound]

Greetings all!

I've really enjoyed watching the Dreric, Mhartman and Manning projects and ideas on TAG lately - And it's inspired me to dream up a fun concept.

I've heard of a few folks who built the SSS with an integrated OD stage - I like the idea of this. It's somewhat similar to the Overdrive Reverb but minus the Filter switches, CF driven PI, and local negative Feedback choices.

Having built a few JM Sig amp clones ages ago, I really love the clean preamp in that amp.

So, I drafted up a schemo that integrates the JM Sig amp clean, Low Plate Classic OD section, Overdrive Reverb/SSS Reverb circuit, and the SSS Filters (with Martin Manning's excellent updates)/Post PI Cathode Follower driver circuit.

I've tweaked some stuff in the Reverb circuit that I gleaned from the Overdrive Reverb - The ODR Verb potentially has a hotter signal going in than the SSS, so you'll see a slightly different Verb entrance with the OD circuit tacked in. Also it's entrance is placed at the end of the Clean/OD relay, as opposed to the SSS where the Verb splits off after the first gain stage.

Iron i'm using is a combination of an Thordarsen PT capable of roughly 560vDC on the plates. Seeing how successful Dreric's build was with the pair of 6550s, I opted for that power section with the UL setup and a Dynaco OT. I'll initially opt out of Global NFB, but may play with adding it in once the actual build get started. having just a pair of 6550s might save me a little chassis space.

I opted to place the Filters post OD, at least initially.

And to put icing on the cake, Instead of the typical Dumble FET input stage, I opted for the Echoplex EP3 preamp FET input. I have built several of these in pedal form and they work great for Dumble style amps. I find they trim more lows than the stock FET boost (which is typically a full range flat-ish boost) and work well even pushed pretty hard, thanks mostly to the higher voltage swing I reckon.

Schemo is a draft, so will likely contain errors, although i've tried to be dilligent. localized grounding is color coded, and is there mostly to help me keep solid grounding practice once I start working on a layout.

I want to give a big thanks to Martin Manning, Jelle, Dreric, M Hartman, M Fowler, and all the others who have contributed greatly to the wealth of knowledge here, especially on the Dumble stuff.

Any thoughts, comments, suggestions or concerns would be encouraged. I've left out Dropping string values in the PSU on purpose, as I have no clue what those are going to be as of yet.

[dreric]

WOW! Ambitious project, I would totally build your amp, especially if there was a layout

I thought about doing something similar for a while now. I think Shad did a SSS with a ODS channel before he went off the deep end.

I think that a EF86 pre-amp with your build could be very cool. Check out this thread:
http://ampgarage.com/forum/viewtopic.ph ... sc&start=0

[dreric]

I think you'll like the Dynaco UL 6550 set up it's very "beefy"

[dbeasley]

Dreric,

I do recall seeing that schemo ages ago. I'm kind of amazed that more folks don't chase the EF86 dumble rabbit hole. I guess that was more of another generation's efforts.

There will be a layout for this one eventually. My layout skills have come a long way from the JM sig amp stuff I posted here several years ago! I enjoy seeing folks taking the old ideas and mixing them up a little bit, as opposed to all the straight cloning.

I'm most curious about how the filters are going to effect the OD tone. I've played around with HF taper controls in the past and never really liked them. Truth be told the filters could sound like crap with the OD engaged - so in the back of my mind I'm thinking of leaving space in the build for a relay controlled Filter bypass, maybe set it up to disengage the filters when the OD is engaged. Luckily that shouldn't be a problem.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[dreric]

Dreric,

I'm most curious about how the filters are going to effect the OD tone. I've played around with HF taper controls in the past and never really liked them. Truth be told the filters could sound like crap with the OD engaged - so in the back of my mind I'm thinking of leaving space in the build for a relay controlled Filter bypass, maybe set it up to disengage the filters when the OD is engaged. Luckily that shouldn't be a problem.

Sent from my SAMSUNG-SM-G920A using Tapatalk

Now that I've played with the filters a bit more I'd say that they are going to be very cool with the overdrive. I've been wanting to try that for a while. What I have found in the SSS is that they filters really affect the signal when the gain is very high, the FET is used or with effects. They create and enhance over tones that really are fun to play with. Also they are very helpful in zeroing in on the resonance affect, when the room seems to fill with the amp and or you cut through the band mix.

[martin manning]

Looks like a very interesting project! A couple of things to consider are that the filter bypass will boost the signal a lot, so maybe some kind of attenuator will be needed. As an alternate approach, a PAB-like ground lift could be tried. Also, note you have an extra cap in front of the filter, but I don't think that will make too much difference.

With 560V on the plates the bias-balance network will need some adjustment (the 56k will have to be reduced) to recenter the range. This depends on the input voltage from your bias tap, of course... what is that voltage, BTW?

Dreric, did you ever try disconnecting the GNFB? Good to hear you are still enjoying your amp, still liking the new filter design, and that there are no issues with the CF power supply!

[dbeasley]

Actually, I've just realized that my PT does NOT have a bias tap. I'll go ahead and use the small transformer like the Traynor conversion does.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[Aaron]

Maybe bias tap it like #0121.

Thanks,
Aaron

[pompeiisneaks]

Actually, I've just realized that my PT does NOT have a bias tap. I'll go ahead and use the small transformer like the Traynor conversion does.

Sent from my SAMSUNG-SM-G920A using Tapatalk

You can also quite often easily get the bias voltage with a dropper resistor of decent size off of 1/2 of the main secondary, look at the fender princeton b1270 for an example: https://tubeamplifierparts.com/schemati ... ematic.gif

~Phil

[valveandsound]

Also, note you have an extra cap in front of the filter, but I don't think that will make too much difference.

Martin, Are you referring to the .001uF or the .012uF cap?

[martin manning]

The extra cap I’m referring to is the coupling cap at the clean or OD output, depending on which mode you are in.

[Bombacaototal]

Just a suggestion of an idea I have been contemplating for some time. I always thought that adding the OD in parallel to the Dry + Wet signal would be sensible approach.

One would use the "standard" Overdrive Reverb/SSS type Dumble Reverb. The dry signal affected by the filter would mix with the Reverb ...and then the dry+wet signal would mix with the OD (which signal is not affected by the filter and does not have reverb). The OD would be added with 2 mixing resistors like a Fender Blackface adds the Normal channel after the reverb of the Vibrato channel.

This is just a quick illustrative drawing. Of course the overdrive bit is missing the OD trim, OD drive, OD level, etc.

Any thoughts?

[norburybrook]

in theory that sounds like a great idea. I quite often when tracking guitars in the studio will mix a 'clean' guitar tracked with the OD guitar to give some definition.

This sounds like the same concept but in an amp.

M

[Guy77]

Sounds like a great idea valveandsounds. However you go about doing it ( and if your interested in retaining the original clean tone) I have discovered that the 4th tube in the JM Sig circuit adds a nice richness to its clean tone. I tried bypassing that on another project and did not like the clean tone as much.

Cheers

Guy

[dbeasley]

That idea is somewhat similar to ODSR#13 I believe. It's reverb is pre OD. It's an interesting idea, but I wasn't a huge fan of the pre OD reverb tone.

Martin, I've omitted the .012uF cap leading into the Filter network in lieu of the .02uF coupling cap coming from the clean channel/OD ratio out.

I've redrawn to replace the bypass toggle with a relay. Will make it easier to control should I decide to make the filters exclusive to the clean mode or OD.

Sent from my SAMSUNG-SM-G920A using Tapatalk