Fender-Marshall together with reverb

[adamG]

Hi Guys,

Could you advice me how to combine those two circuits?
I'd like to build an hybrid amp with clean channel basis on Fender and sec.channel basis on Marshall, together with hot switch as on att.schematic.
Both channels with "full" reverb on/off by relay.
Power stage as 2 x EL34.
Also, it is very tempting to provide FX Loop.

My whole idea is to build warm, soft clean as from Fender or Dumble, but second one as completely different, aggressive tonal character basis on Marshall.
Clean would be with 2-steps bright and mid boost and hot switch within second channel.

Any hints would be appreciated very much.

Regards,

Adam

[tubenit]

OK,  here are some ideas for you to consider. 

Please keep in mind that you will NOT get a pure Fender sound and pure Marshall sound in a hybrid build. Too many differences in LTPI and negative feedback and post LTPI coupling caps, etc .......................

I do think it's possible to get a Fenderish tone and a Marshallish tone with compromises.

This idea would require a simple A/B box into each of the channel inputs.

I personally would lean towards an active FX and then run a reverb effects pedal or delay pedal or both in the active FX

I've attached the ExpressSCH schematics which have a 2nd page which shows the B+ rail and bias.   PLEASE check on the bias that is there because I am not sure if it's for 6L6's or EL34's?   Compare that bias to a Marshall that has EL34's.   Since the SCH is editable, you can easily change it.

http://el34world.com/charts/Schematics/files/marshall/Marshall_1987%20JMP%20Lead%2050watt%20EL34.gif

IF you attempted this, I think you'd have to be sure to have a good layout before starting to help avoid oscillation problems.

With respect, Tubenit

[tubenit]

IF you don't mind not having a "Fenderish" channel, then I'd use a Dumblish style preamp with two tubes and a mid-boost (great feature I use frequently) and a PAB (preamp boost).  Ironically, you can get a pretty overdriven sound with this preamp by activating just the mid-boost and the PAB at the same time.

I think it might be easier to have an effective layout with this design and avoid oscillation issues?

This also uses a simple A/B box for the switching into the channel inputs.  Note that I added a master volume at the end of each channel prior to the active FX to help balance the volumes between the two.

I have something similar to this in my Tweed BluezMeister and it has a beautiful clean channel, IMO.

Note I changed the values of the coupling caps post LTPI.  And again, check the bias on the 2nd page of the ExpressSCH schematic to make sure that it is appropriate for EL34's.

With respect, Tubenit

[adamG]

Tubenit,

Thank you very, very much!
You're the soil of this forum;)

Actually, I was to write about of Dumblish style clean channel ,where it is possible to provide 0,047 coupling caps on power stage.
For now, I do not get two issues you've mentioned. First, what oscillation would I have to avoid? Second, why it is necessary to apply A/B input box instead of a relay(s) that can change over channels? For instance, while first is activated, the second is grounded or isolated?
I prefer this idea because, everything is happening inside the amp.

I also consider power stage with 6L6, that could simplify the whole concept.

Yes, I like mid-boost switching very much ,as well. This switched ON together with PAB gives pretty good overdrive, but I like hot overdrive sound that is given with OD stage in "normal" Dumblish style amps;)

Best regards,

Adam

[tubenit]

Adam,

The .047 coupling caps are after the LTPI and prior to the grids of the power tubes.

All I was referring to is that any reasonably high gain amp or multi-channel amp can have oscillation problems IF the layout is not done well.

Sure you can use relay switching instead of an A/B box.

With respect, Tubenit

[adamG]

Thank you T.,very much.

I just work on the layout.
I'll send it when ready.

Regards,

Adam

[tubenit]

I think maybe I shared this one before? 

It's sort of an AB763 with Dumblish tone stack  and a Marshall/Bassman style with hot switch & mosfet CF.

With respect, Tubenit

[jokn]

Tubenit, would there be any ill effects, having a relay right at the input, before any gain stages? I'm thinking noise from the relay coil, or something of that sort.

[tubenit]

I don't know?

[adamG]

It's sort of an AB763 with Dumblish tone stack  and a Marshall/Bassman style with hot switch & mosfet CF.

Tubenit,

Thank you very much;) This schematic is pleased to me of all.
Silly question, if I may. Could you explain me what is the meaning of V2b in Fendery reverb circuits? Does it additionally charge D-style channel after its TS?

Regards,

Adam

[tubenit]

I have something similar in my Carolina Overdrive Special 5879 plus amp.  That same amp previously had two stages for clean prior to adding the 3rd one.  It doesn't change the Fender/Dumblish hybrid tone very much going from 2-3 gain stages.  It may be just a tiny bit more touch sensitive.

The high plate Dumblish style amps typically have 220k/3.3k and 150k/2.2k   plate/cathode stages.  Going to lower stage 100k/1.5k and adding a 3rd stages that similar in plate/cathode values doesn't seem to change the tone much to my ears.

http://el34world.com/Forum/index.php?topic=21803.msg231617#msg231617

With respect, Tubenit

[adamG]

Thank you T.,very much.

I've been workin' on the layout. It's almoust ready, but I need to consider whether reverb or FX loop,yet.
Till now, I am decided for IRF CF. It's time to try it on.

Best regards,

Adam

[guitardude57]

Tubenit, would there be any ill effects, having a relay right at the input, before any gain stages? I'm thinking noise from the relay coil, or something of that sort.

You can have a relay or optocoupler at the input.  The Randall RD 45 uses a few Optos for channel switching,
and there is one, at the input.


But that is a very gainy amp.


If you are to channel switch between the F and the M side, there are better places to make and break the channels.

[adamG]

It's sort of an AB763 with Dumblish tone stack  and a Marshall/Bassman style with hot switch & mosfet CF.

Tubenit,

Did you buid this amp? If so, I can act boldly, right?
My question is, may I follow the coupling caps as on schematic? Especially, I consider two input ones 0,47 and 0,022? Previously, My Plexi 18 based on Sluckey's project, had 0,0022. But that's not the main issue now.
Wouldn't be amp too dark with them? I am concerned about 0,47. Isn't it too big?

Regards,

Adam

[jokn]

Thanks for the input, Guitardude. It's good to know that it's possible to have to completely different preamps. In my current project the two channels share the input stage and are then split by a relay to go their separate ways, only to meet again at the PI. My apologies for the thread hijack, adamG.

[tubenit]

Adam,

No I have NOT built any of the four amp schematics that I've posted.  Regarding the .47 cap, it might be too big ....... I don't know?  You can build everything else and leave that cap unsoldered and use insulated alligator clips to try different values OR a decade box with capacitors.

PLEASE keep in mind that caps in series will change the "value" to the next gain stage.

http://www.kusashi.com/series-capacitors.php

I always view amps like this as something that you plan on building and then tweaking.  Since I typically use paralleled turrets with my layouts, tweaking is reasonably easy to do.

With respect, Tubenit

[adamG]

My apologies for the thread hijack, adamG.

It's ok. Thank you for visiting this thread:)

Regards,

Adam

[adamG]

PLEASE keep in mind that caps in series will change the "value" to the next gain stage.

Yes, you're right. I completely forgot it.

Thank you T., very much.

Best regards,

Adam

[adamG]

The high plate Dumblish style amps typically have 220k/3.3k and 150k/2.2k   plate/cathode stages.  Going to lower stage 100k/1.5k and adding a 3rd stages that similar in plate/cathode values doesn't seem to change the tone much to my ears.

Tubenit,

One more question, if I may?
If I reduce 12AT7 and third step within Dumblish channel, than do I need two resistors 220K in the way to PI?
Of coure, reverb would be only with one tube 12AX7.

Regards,

Adam

[tubenit]

do I need two resistors 220K in the way to PI?

I'm not sure if you need both 220k resistors, but I would build it that way first.  Then you can jumper across one of the 220k resistors if you want & see if that changes it to your liking?

Again,  this is NOT a proven design (that I know of) & IF you build it ........... I would definitely plan on some tweaks to have it become the amp that you truly want.

With respect, Tubenit

[adamG]

Thank you T..
As always, you suggest reasonably.
What do you think about the reduced tube/steps idea?

Regards,

Adam

[tubenit]

What do you think about the reduced tube/steps idea?

Adam, please accept my apology .......... but I don't know what this means?  Can you explain?

With respect, Tubenit

[DummyLoad]

see attached - no reverb on plexi channel, wouldn't be a plexi then. super reverb and plexi preamps. super/plexi LTPI.

FX? what *&%$% FX!! that crap belongs in movies! put that stuff in front of the amp. :p

R24-25 could be replaced with a 1M-A pot (or a fixed R and pot under the R) for fender channel master volume.

bias range should be adequate for 6L6Gx or EL34 - remember to strap pins 1 & 8 together on the sockets of both V7 and V8 if you use EL34.

8 valves, 61 resistors, 36 capacitors, 14 diodes, 4 inductors, 12 controls -  that's gonna be a big *&%^$* chassis.

schematic passes ERC so assuming no glaring errors, you should be able to layout a PCB: P2P purists, don't be h8n... 

--pete

[adamG]

What do you think about the reduced tube/steps idea?

Adam, please accept my apology .......... but I don't know what this means?  Can you explain?

With respect, Tubenit

I'm sorry, I wasn't clear with those steps.
I mean to reduce V2B, to replace V4/V3B by single 12AX7.
So, in this way, I would receive only 4 tubes;)

Regards,

Adam 

[adamG]

see attached - no reverb on plexi channel, wouldn't be a plexi then. super reverb and plexi preamps. super/plexi LTPI.

Thank you Pete, very much;)

Regards,

Adam

[adamG]

FX? what *&%$% FX!! that crap belongs in movies! put that stuff in front of the amp. :p

R24-25 could be replaced with a 1M-A pot (or a fixed R and pot under the R) for fender channel master volume.

...P2P purists, don't be h8n... 

Pete,

I'm afraid I don't get above. Could you expand them a little?;) Especially ,MV for Fender channel.

Regards,

Adam

[DummyLoad]

FX? what *&%$% FX!! that crap belongs in movies! put that stuff in front of the amp. :p

R24-25 could be replaced with a 1M-A pot (or a fixed R and pot under the R) for fender channel master volume.

...P2P purists, don't be h8n... 

Pete,

I'm afraid I don't get above. Could you expand them a little?;) Especially ,MV for Fender channel.

Regards,

Adam

see schematic attached in reply 22.

if you are a novice amp builder, this not a good first project.

if you're new to amp building, please build something proven and that will work - champ, stout, etc. first. 

respectfully,

--pete

[adamG]

if you're new to amp building, please build something proven and that will work - champ, stout, etc. first. 

Pete,

Actually, I'am not an electronics man, but it happened to build something before...
What I asked you for is not how to read schematics, but you've mentioned:"FX? what *&%$% FX!! that crap belongs in movies! put that stuff in front of the amp. :p" and this :"(or a fixed R and pot under the R)", which is not clear to me, at least.
Anyway, thank you for visiting this thread and assistance.

Regards,

Adam

[adamG]

Again,  this is NOT a proven design (that I know of) & IF you build it ........... I would definitely plan on some tweaks to have it become the amp that you truly want.

Tubenit, if I may ask you for your opinion, could you explain me the difference between mosfet and tube on CF, please?
I intend to apply mosfet in this build.
Thank you in advance.

Regards,

Adam

[tubenit]

Adam,

I can NOT tell any difference at all in tone between a mosfet CF and a tube CF.

http://www.geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm

With respect, Tubenit

[adamG]

Thank you T., very much!

Best regards,

Adam