Help on new #40 build

[martin manning]

Personally, I have a 124-type ODS and an outboard D'lator. With that set-up this is the result:

Preamp out -> MV -> SendBuffer -> Send Level -> FX -> Return Level -> RecoverStage -> Recover Out Level -> Power Amp.

The front panel MV becomes a redundant send level control at the send buffer input, and the Recover Out Level becomes the MV. Most people put the amp's MV around noon and leave it there, and use the send level control to set the send level. This is a waste of a front panel control, IMO.

With an inboard loop, you could replace the amp's MV with a fixed divider, and return the MV function to the front panel:

Preamp out -> SendBuffer -> Send Level -> FX -> Return Level -> RecoverStage -> MV -> Power Amp.

This is what you have now, I believe, except there is no divider between the preamp output and the send buffer. The MV function is returned to the front panel, and the send level is controlled by the send level control only. That is fine as long as the signal going into the send buffer doesn't exceed about 60V p-p, where the send buffer will begin to clip.

What I'm proposing above is moving the send level control to the input side of the send buffer, controlling the send buffer output level by limiting its input level:

Preamp out -> Send Level -> SendBuffer -> FX -> Return Level -> RecoverStage -> MV -> Power Amp.

Are you planning to have a bypass switch for the loop?

[andresound]

"are you planning to have a bypass switch for the loop"

I was under the impression, the buffered loop, improved the sound and was part of the "mojo"?

[martin manning]

I was under the impression, the buffered loop, improved the sound and was part of the "mojo"?

Maybe. It certainly adds the buffered loop capability for line-level as well as "guitar level" FX, and it provides more options with another gain stage that can be overdriven if desired. A bypass is just another option for a built-in loop.

[Smokebreak]

Are you planning to have a bypass switch for the loop?

Thanks Martin, looks there's there are a lot of ways to skin this thing. I'm definitely gonna put the loop on a switch, as well as make it switchable for parallel operation. I want the loop to be available as a boost, too.

The way I drew it the other day is kinda the antiquated way of going about it, I think, but I will not have a global master anywhere other than on the front panel. I know that much.
I need to examine all this further, but at first glance it looks like the only problem I'll have with the recover (MV) out of the loop is that I may lose boost functionality. Having never built one, I'm guessing at this point.

Sorry to hijack this thread fellas, I'll start a new one when the time comes for that amp.

[andresound]

Great! That narrows it down to the recover stage.

Yes, you can kill all the volume anywhere there is a control pot with it's CCW lug grounded. Turning down the treble means more mids, so I think more perceived volume is expected behavior.

Here's an updated schematic showing where the OD entrance trimmer and ratio controls are on later amps. If you want to add a trimmer, a 430k resistor and a 50k trimmer would replace what's there.

On the lower-right is my proposed mod to the send buffer.

Can I use a 100k trimmer at the OD entrance? Have many on hand.

[martin manning]

Sure, 100k will work; just keep to the same total resistance that is there now which is about 500k. A 390k resistor and a 100k trimmer would be fine.

[andresound]

Will install tonight.

[ayan]

I don't have an internal D-lator loop, but I think I would have a hard time deciding where to have level controls if I did implement one.

One of the biggest considerations for me would be on the send side. On the one hand, to me everything seems to sound better when you hit the cathode follower as hard as possible but without clipping it. But to get to that point one would need something like the amp's inherent MV. If the preamp gain level is kept low, the amps' MV would have to be turned up to hit the CF hard. Conversely, if the preamp gain is set hight, the MV would have to be turned down. In any case, when the CF is hit hard, the signal present at the output of it will be way higher than +4dBu and most FX units inputs could experience clipping, especially pedals since they don't usually include an "input level" control. So we would need a "send" control from the loop to pad that down.

On the return side, however and as I understand it, what we have come to call the "return level" was only was only added on to a couple of Dumbleators because their owners had very hot FX without an output level and undesired distortion would occur unless the signal was padded down at the inout of the recovery stage. I have seen many pictures of D-lator clones that include that return level control, and it is almost always turned up all the way. That would be an easy way to delete one pot in my view.

Cheers,

Gil

Personally, I have a 124-type ODS and an outboard D'lator. With that set-up this is the result:

Preamp out -> MV -> SendBuffer -> Send Level -> FX -> Return Level -> RecoverStage -> Recover Out Level -> Power Amp.

The front panel MV becomes a redundant send level control at the send buffer input, and the Recover Out Level becomes the MV. Most people put the amp's MV around noon and leave it there, and use the send level control to set the send level. This is a waste of a front panel control, IMO.

With an inboard loop, you could replace the amp's MV with a fixed divider, and return the MV function to the front panel:

Preamp out -> SendBuffer -> Send Level -> FX -> Return Level -> RecoverStage -> MV -> Power Amp.

This is what you have now, I believe, except there is no divider between the preamp output and the send buffer. The MV function is returned to the front panel, and the send level is controlled by the send level control only. That is fine as long as the signal going into the send buffer doesn't exceed about 60V p-p, where the send buffer will begin to clip.

What I'm proposing above is moving the send level control to the input side of the send buffer, controlling the send buffer output level by limiting its input level:

Preamp out -> Send Level -> SendBuffer -> FX -> Return Level -> RecoverStage -> MV -> Power Amp.

Are you planning to have a bypass switch for the loop?

[norburybrook]

I like having level and the extra tone controls with the 2 extra bright switches on my external Dumbleator.

It really is a useful device especially when you need to keep levels under control.



Marcus

[martin manning]

Thanks Jeremy, Gil, and Marcus for the added inputs on this subject. I like the flexibility of the external loop too, but for some it's just too many knobs. Some of the loop's tonal contribution may indeed be lost if the CF input is throttled.

Andre, below is an update to the schematic above showing the OD entrance values from Tony's Second Gen layout, which I believe you are using. Re your high OD volume, make sure you have the under-board ground connected as shown there and in the schematic, or you won't get the required input signal attenuation. If you want to install a 100k trimmer there, I'd put the outer legs of the trimmer where the 33k is, and take the output from the wiper to the V2a grid. The 1M2 can stay, or you could replace it with a 1M or a 1M1. Sorry for the confusion.

[andresound]

Many thanks Martin,
I will install this weekend and report. Have a great weekend.
Regards

[Smokebreak]

Another worthwhile spot for a trimmer is in the 1M2 spot. You put a 1M trimmer in series with a 680K pot, so at half rotation on a lin pot, you have the stock 1M2. Different pickups like different values there. That's a tweak courtesy of ToneMerc.

[andresound]

Smokebreak
Thank you for that. But, I am a newbie (first dumble build), so will try Martin's mod first and then get the voltages right. No disrespect. Once amp is up and running, I will start to tweak.
Regards

[ToneMerc]

Another worthwhile spot for a trimmer is in the 1M2 spot. You put a 1M trimmer in series with a 680K pot, so at half rotation on a lin pot, you have the stock 1M2. Different pickups like different values there. That's a tweak courtesy of ToneMerc.

Yes, I have used either a 560k or 680k resistor in series with a 1M trimmer as a substitute for the 1.2M resistor. That is my my preferred method for deploying that "funky OD entrance".

TM

[Smokebreak]

Smokebreak
Thank you for that. But, I am a newbie (first dumble build), so will try Martin's mod first and then get the voltages right. No disrespect. Once amp is up and running, I will start to tweak.
Regards

It's all good buddy! I think we've collectively furthered the tweak for the funky entrance. The 680K(or560K) series with 1M trimmer, then 100K trimmer as a divider to ground. BTW 100K to ground there sounds wicked mean.