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*umbleator ?

1/14/2006 6:49 AM
Pete C *umbleator ?
has anyone with an ODS clone or similar sucessfully incorporated the *umbleator style send and return loop shown at Schematic Heaven/Blue Guitar ?  
I have plenty of heater curent headroom and space for the extra circuit in my ODS clone and was wondering if the schematic in circulation is correct / good.  
Many thanks  
Pete C
1/16/2006 10:55 AM
Pete C
sorry - for bumping my own question here  
anyone tried ?  
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1/16/2006 11:29 AM
Tommy Dale

E-mail me.  
1/16/2006 12:12 PM
Ray Ivers
I've never compared a real Dumbleator with that circuit; in fact, I've only seen pictures of real Dumbleators, although I have had close encounters with three actual Dumble amps.  
I have heard a Dumbleator circuit built from the Blue Guitar schematic incorporated into a fairly high-gain MV amp using a Dumble-esque early mid boost, though. It had quite a bit of gain available, seemed a bit noisy to me, and was also pretty bright, even without either 'bright' cap engaged. The loop-send and output impedances are pretty high IMO - roughly 60K worst-case - which could make a real difference with some effects (my buddy recently got a rack-mount 31-band EQ with a 10K input impedance, which this loop would definitely not like) and also proved to be a problem in this amp, as the 'Return Level' control was directly driving the tone stack (this was changed, and all was well).  
I found out this morning that a real Dumbleator apparently inserts in the signal path directly before the phase inverter. My own feeling is that this loop is designed and voiced specifically for Dumble amps, for insertion at one specific point in their gain structure - so perhaps it will work fine in your ODS clone, provided no super-low-input-Z FX are used with it.  
1/17/2006 1:42 PM
I've tried that circuit but it is in a 2-channel amp and the loop is after the tone stack but before the PI. It's always in circuit and the Return Level control is my Master Volume.  
The Send circuit seemed to lack headroom and just sounded anemic. I changed it to something more like the Send circuit in a Mesa Dual Rectifier. Basically a cathode follower with a split-load cathode resistor (82k/22k), then a .47uF cap, then the Send Level control. I used a .47uF cap on the grid and used fixed-bias (2M2/1M). This sounded much better to me.  
I left the Dumbleator Return circuit in but I've been wanting to change it too. It seems to change the tone through the sweep of the Return Level control but that might not be due to the Dumbleator Return circuit. For some reason, that treble peaking circuit bothers me and I want to try something even more simple. But it sounds really good within the MV range that I use it so I'm not compelled to change it unless I'm in there for some other reason. And my amps never break so that may never happen.:D
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