Best effects loop circuit?

[Mark]

I want to put an effects loop into my Mesa Boogie SOB and was wondering what people have had good results with.

Thanks for your assistance.

[Reeltarded]

https://grangeramp.com/product/ultimate-fx-loop-2/

I don't like tube loops. This is = to zero loss design and it's great.

[Mark]

Thanks for your reply Miles, I want to use the existing holes in the amp. I was intending to use a valve too.

[Reeltarded]

One dual triode? What is the circuit you have in there now?

Asking to know insertion point.

[Stephen1966]

The one mitigating factor I ran into when I faced a similar conversion was the power transformer. Do you know how much current it can feed from its filament coil? A tube (12AX7) is going to draw 300mA. A solid-state board is likely to be a safer bet if you can't be sure. Those jacks on the solid-state board can be removed. You might be able to remove just one and run some cables to a chassis jack, keep the other on the board and use it to mount the board.

[Mark]

Thanks for your interest Miles. The insertion point will be after the master volume.

http://guiguijones.free.fr/Electronique ... e/mk1b.gif

http://guiguijones.free.fr/Electronique ... irga_1.jpg

Hi Stephen, thanks for your reply, The power transformer is the 100 watt version I suspect and I’m thinking the filament current won’t be a problem. The amp can run reverb which is an additional 12AX7.

My amp doesn’t have reverb.

[Stephen1966]

Thanks for your interest Miles. The insertion point will be after the master volume.

http://guiguijones.free.fr/Electronique ... e/mk1b.gif

http://guiguijones.free.fr/Electronique ... irga_1.jpg

Hi Stephen, thanks for your reply, The power transformer is the 100 watt version I suspect and I’m thinking the filament current won’t be a problem. The amp can run reverb which is an additional 12AX7.

My amp doesn’t have reverb.

A Dumbleator will work fine in there. You can take a look over at my schematic for my 183 to see how I implemented it. Same insertion point, between master and PI. Depends what you're after though. The DL is not a transparent circuit. Some like it, some don't. Also, Tube Town do a solid state FX loop as well, about 30 Euros.

[TUBEDUDE]

I want to put an effects loop into my Mesa Boogie SOB and was wondering what people have had good results with.

Thanks for your assistance.

After trying several I've settled on this for my builds.
The 12DW7 "AU"half is the cathode follower send. The "AX " half is the common cathode return gain stage. It has send and return level controls and a series/parallel switch and sounds great.

20220216_123421.jpg

Here is a sketchy sketch of the PtP layout.

[Ten Over]

The insertion point will be after the master volume.

Placing the effects after the Master Volume means that the effect device will end up controlling the output volume of the amp. This doesn't keep a lot of people from doing it and even production amps have done it.

[Ten Over]

If you put in a Send Level control, then the Master Volume can resume its usual function.

[Ten Over]

A bypass switch is usually handy.

[Mark]

Thanks for your interest Miles. The insertion point will be after the master volume.

http://guiguijones.free.fr/Electronique ... e/mk1b.gif

http://guiguijones.free.fr/Electronique ... irga_1.jpg

Hi Stephen, thanks for your reply, The power transformer is the 100 watt version I suspect and I’m thinking the filament current won’t be a problem. The amp can run reverb which is an additional 12AX7.

My amp doesn’t have reverb.

A Dumbleator will work fine in there. You can take a look over at my schematic for my 183 to see how I implemented it. Same insertion point, between master and PI. Depends what you're after though. The DL is not a transparent circuit. Some like it, some don't. Also, Tube Town do a solid state FX loop as well, about 30 Euros.

I actually like the colouration from the Dumbleator when it encounters a large signal, I don’t think it works as well with the HRM amps for some reason.

For this reason I like the idea of using the master volume to determine drive, though the master volume would equally work well after the effects loop.

I would like to be able to switch it in and out of circuit.

[Mark]

I want to put an effects loop into my Mesa Boogie SOB and was wondering what people have had good results with.

Thanks for your assistance.

After trying several I've settled on this for my builds.
The 12DW7 "AU"half is the cathode follower send. The "AX " half is the common cathode return gain stage. It has send and return level controls and a series/parallel switch and sounds great.
20220216_123421.jpg
Here is a sketchy sketch of the PtP layout.

Thanks for providing your circuit diagram to me, much appreciated.

The 12DW7 is an underrated valve, I’m surprised that they haven’t made their way into Fender Tweed amps, Marshall and Vox amps.

[Stephen1966]

Thanks for your interest Miles. The insertion point will be after the master volume.

http://guiguijones.free.fr/Electronique ... e/mk1b.gif

http://guiguijones.free.fr/Electronique ... irga_1.jpg

Hi Stephen, thanks for your reply, The power transformer is the 100 watt version I suspect and I’m thinking the filament current won’t be a problem. The amp can run reverb which is an additional 12AX7.

My amp doesn’t have reverb.

A Dumbleator will work fine in there. You can take a look over at my schematic for my 183 to see how I implemented it. Same insertion point, between master and PI. Depends what you're after though. The DL is not a transparent circuit. Some like it, some don't. Also, Tube Town do a solid state FX loop as well, about 30 Euros.

I actually like the colouration from the Dumbleator when it encounters a large signal, I don’t think it works as well with the HRM amps for some reason.

For this reason I like the idea of using the master volume to determine drive, though the master volume would equally work well after the effects loop.

I would like to be able to switch it in and out of circuit.

There's been a debate about the Master being usurped by the DL but personally, I don't find it a problem. I look for unity gain with the loop bypass and unless I am just messing around, I don't have any reason to go altering the Master in play. The Return level on the tail of the loop (post Master) doubles up usefully/occasionally as an attenuator. For bypass if you don't want to hang loads of switches off the chassis (ruining it's aesthetic ) jacks can be used as switches as well. [Edit: sorry! that's a pretty dumb statement - the jacks should bypass the signal when unplugged. My head is in the clouds but this is the way I used them in my amp for switching between passive and buffered lines in and out.]

Thumbs up for the 12DW7 as well. Not sure you will find this useful, but did you know JJ also do a version with the triodes on the opposite pins?

[Stephen1966]

Here's an idea of what you might be able to do with DL style loop in this chassis.

I'm assuming you don't want to drill any more holes in the backplate and you want a bypass switch. I think it's useful to have a send level as not all pedals will be able to balance the gain so if you only have three holes (one for the send jack, one for the return), the third could be fitted with a push-pull pot for your send level. The DPDT portion of the pot could be used for bypass switching - I'm also assuming you want the FX to be in series. The signal could be routed through the switch to the Master which proxies as a Return level (as well) when the loop is engaged. [like Ten-Over's "bypass" topology, above.]

What's the space like inside? Do you have much to play with?

I've toyed with the idea of using these push-pull pots and if they are CTS (I'm suspecting) the phenolic wafer with the trace can be swapped out for any other (same diameter) taper/value you want. The CTS pots are pretty servicable like that and the wafers seem to be a generic design - easily swapped out.