HRM in a Tweedle Dee?

[professormudd]

Title pretty much sums it up. I'm wondering if an HRM board could be inserted into a Tweedle Dee and produce good results. If so, where would you insert it?

Has this been done already?

Thanks in advance for tolerating my stupid question.

[ijedouglas]

I haven't but I'm wondering why you would want to do that? The HRM was intended to better balance the clean and OD tonally by inserting a post-OD tonestack. Not sure how a Tweedle-Dee would benefit from this?

[professormudd]

I thought of it as a way to add a TMB eq that would still fit inside of the 5e3 chassis.

[pompeiisneaks]

I guess you could, but having to take the amp out of the chassis every time you want to tweak it? Seems like it might just be easier to drill a few more holes and replace the Tone with a TMB instead.

I know space is tight already, but...

~Phil

[ijedouglas]

Not sure about the insertion loss but a bigger issue would be trying to change your TMB settings

[professormudd]

The HRM is inconvenient to adjust in an ODS just the same but people keep including them in their builds as small boards with trimmers tucked inside the chassis. The narrow panel tweed seems a bit more convenient to access since you can just take the back panel off.

General discouragement aside, I have a couple of HRM boards and I would like to try to stick one in my Tweedle Dee.

Does anyone have any recommendations as to where to place it? Should it replace the coupling cap V1B? be placed inline between the "normal" volume and V2 Grid? Somewhere else?

[ChopSauce]

Using it for the "normal" channel, which normally has no tone stack attached to it is the first thing that comes to my mind.

[fred.violleau]

Heu guys,

Interesting idea... I have been playing with cascading the two channels while trying to keep the original bright channel. So I guess you could add the HRM board to the normal channel in order to voice it differently and tweak for the cascade setting so that the EQ would be switch d only on the cascade mod?

May try this... I am completing my tweedle cab so it is out of the box... May try to add an HRM boad after the first V1A. The only thing is the new EQ would add loss on the signal. Good news is, if you plan on removing the interaction of the 2 EQs on the bright and normal channels, then adding loss may not be an issue since you would have to add a 220k resistor at the vol output in order to balance the signals as the original design.

Will try to get a board together next weekend and report, I am now intrigued

Cheers,

Fred.

[donvan]

The HRM is inconvenient to adjust in an ODS just the same but people keep including them in their builds as small boards with trimmers tucked inside the chassis. The narrow panel tweed seems a bit more convenient to access since you can just take the back panel off.

General discouragement aside, I have a couple of HRM boards and I would like to try to stick one in my Tweedle Dee.

Just trying to see what you are attempting to accomplish. What is your goal?
Here is the reason that I ask this:
On an ODS without the HRM circuit, you can set the regular tone controls and those settings affect both clean and Overdrive mode. So lets say you are on a gig using the clean setting on a song and you want to switch to Overdrive for the solo. Unfortunately, the Overdrive changes the tone. In other words, the tone settings that were made for clean may not be the best settings in Overdrive mode. I believe (and I may be wrong) it was for this reason that Dumble came up with the HRM board that only affects the Overdrive circuitry and has no affect on clean mode. So with the HRM board, the player can modify tone settings that ONLY affect the overdrive mode and can therefore have different tone settings when switching between Clean and Overdrive.

I don't know the exact topology of a Tweedle Dee but if you can't switch it between Clean and OD with a footswitch then adding an HRM will do nothing for you in my humble opinion.

[mojotom]

The easiest would be to insert the HRM board between V1 and V2, take a look at Divided by 13 CJ11, just like a BF Fender with a volume control after the stack but it does only work with one channel, not 2 like the 5E3 amp (more like a 5F11 Vibrolux for exemple). Maybe with a higher value slope resistor like 56k or 100k.

[professormudd]

The HRM is inconvenient to adjust in an ODS just the same but people keep including them in their builds as small boards with trimmers tucked inside the chassis. The narrow panel tweed seems a bit more convenient to access since you can just take the back panel off.

General discouragement aside, I have a couple of HRM boards and I would like to try to stick one in my Tweedle Dee.

Just trying to see what you are attempting to accomplish. What is your goal?

To put a small EQ inside of a small amp chassis that does not otherwise have room for a full TMB on the face.

[professormudd]

The easiest would be to insert the HRM board between V1 and V2, take a look at Divided by 13 CJ11, just like a BF Fender with a volume control after the stack but it does only work with one channel, not 2 like the 5E3 amp (more like a 5F11 Vibrolux for exemple). Maybe with a higher value slope resistor like 56k or 100k.

Thanks for that. I did the high-gain/cascade mod to this amp as found on the Robinette site. That being the case, I am expecting that applying this to the "bright" channel still makes a difference on the formerly-normal channel.

[professormudd]

Interesting idea... I have been playing with cascading the two channels while trying to keep the original bright channel..

I also have the high-gain mod on mine, and I really like it. I was originally just expecting the HRM to be "universal" by putting it on the bright channel since normal now feeds into it. But you got me thinking. Maybe it would be better on the formerly normal channel as a way to make it even more distinct.

[fred.violleau]

@professormudd if you did Rob's cascade high gain / cacsade mod, you have the following:
1- interactive EQ between normal and bright channels
2- norm chan cascading into bright chan when cascade mod engaged
3-high gain mod on the normal channel

You could add the HRM EQ on one channel, but would probably not want the HRM to interact with both channels. In order to do this, you need to disconnect the EQ interaction (described on Rob Robinette's website).

So you will have to add a 220k mixer resistor on the output of each vol pot in order to keep impedance the same as the original. Otherwise the sound will be affected.

I was thinking that adding one HRM tonestack would replace one of the 220k resistors but I am no pro at designing amps, so I will leave that to the guys who know.

Will try it anyway, just to test !

Fred.

[fred.violleau]

I tested it, I remembered I had an old HRM board sitting somewhere from a build I rescued. So I plugged it into the normal channel and it worked fine. There is a little signal loss compared to the bright channel but nothing to worry about.

I would like that settings to shape the sound when in cascade mode.
It would probably work better if this HRM board was coming later in the preamp circuit ala Marshall, after the two cascading gain stage. But then you are trying to reinvent a Marshall or a fender or a little dumble

All this too say, have fun and try it. If you use often the same instrument with an amp, might as well tune the amp for the guitar! A cool way would be to have a relay engaging the HRM board only when cascading!

Here is a pic of my ugly setup:

PXL_20220215_025234200.jpg

Fred