FDP Forum / Formula for one mean sounding DRRI/ 14 messages in thread.

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Fritz_D_Cat

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Nov 13th, 2010 09:48 PM        

Announcing an ODS style front end voicing mod for the DRRI Normal channel !!<br /> <br /> This one is not for beginners. The control pots' daughter board needs to come out and the mainboard must be unfastened and then picked up to stand vertical from the front side. No need to disconnect any wires, though, other than the push-ons that you undo for the control pot board. Undo the nut for the bias control so that can ride up when you tilt the main board.<br /> <br /> The amp can't do it without the right back bone installed. Get an aftermarket output transformer. I like Allen TO26, but MM oversize replacement works great, too. You *have* to do Fritz mods 1 and 2, on my profile. Put in some JJ 6V6S's and bias to 20 to 24 mA each. Select a copper cap (solid state) rectifier so that you have at least 405 volts on the plates when idling at 20 mA.<br /> <br /> All resistors are 1/2 W metal oxide 2%. Electrolytic caps are 50V or greater.<br /> <br /> <br /> On the daughterboard...<br /> <br /> Remove C10 if you like your regular tone to be more like the normal channel.<br /> <br /> R-09 > 10 K<br /> C-02 > 470 pF silver mica<br /> <br /> While you are here it's a good time to replace the reverb control with a 250 K audio pot - same part number as bass control.<br /> <br /> <br /> On the mainboard...<br /> <br /> C-01 > 5 uF @ >50V<br /> R-05 > 3.3 K<br /> R-04 > 220 K for sweet mild OD voice about same volume as normal channel, keeps more of the DRRI character. 270K for rawkin' out. 330K is too hot and brings in some noise on this critical first stage.<br /> R-06 > 150 K<br /> R-24 > 1.1 K<br /> C-11 > 1 uF @ >50V<br /> R-11 > 220 K<br /> R-30 > 1.0 K<br /> <br /> If you have a ticky trem, you can fix that with an 0.01 uF ceramic cap @ 1000V (see my profile for that).<br /> <br /> 220 K on R-04 makes this channel sweet. It sounds just like my Fuchs ODS 30 in Jazz setting but with just a little more authority on the bottom. Unbelievable at taking pedals, and NO fizz. 270K puts it about 1/2 way between Jazz and Rock mode. More versatile.<br /> <br /> Have fun !<br /> <br /> <br /> Edit to add: a decent tech with DRRI experience should charge between 2 to 2 1/2 hours for the work.



pdf64



UK

Nov 15th, 2010 03:32 AM        

I'd love to see what you've done with this, but am too lazy to go through the schematic noting the mods. Have you got a amended schematic that you could post?



Fritz_D_Cat

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Nov 15th, 2010 09:22 AM        

Nah, at least not yet. - I'm too lazy to draw it up. 8^)<br /> <br /> There is some voicing in the tone stack for more throat.<br /> <br /> 10K R-09 up from 6.8 raises the midrange scoop about 5 dB.<br /> <br /> 470 pf in C-02 shifts the scoop down some in the frequency band. So it scoops more lower mids than upper mids.<br /> <br /> 150K in R-06 lowers the throughput to bass and mid dumps so the flat of the bass curve comes down a bit. But that is needed because the power side mods including stiffening and OT increase the bass punch, which is not quite where you need the accent on a 'lead' voice. The mods below also accentuate bass and lower mids, so this tone stack adjustment accommodates and re-voices just a bit.<br /> <br /> 1st stage 270K plate increases gain, cathode is 5uF and 3.3K so you get tons of even harmonics from being far to the right on the load line.<br /> <br /> 2nd stage a bit more moderate, 220K plate, and 1uf and 2.2K (actually 1.1K shared over two triodes) on the cathode.<br /> <br /> R30 is adjusted to center bias reverb recovery stage - gets a tiny more headroom and uber small 2nd order harmonics add.<br /> <br /> Still just summing the outputs of the preamp stages prior to R-25 for the rev on both channels - the basic 'Fritz' mod.



jesse1d

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canada

Nov 15th, 2010 04:00 PM        

This sounds great Fritz...any chance we could get a sound clip?



Fritz_D_Cat

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Nov 15th, 2010 06:47 PM        

8^)<br /> <br /> Sure, get right on it, right after I get the schematic done for Peter.<br /> <br /> I'm taking this little dude to CO for a couple shows and jams next week.



Fritz_D_Cat

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Nov 15th, 2010 06:49 PM        

All kidding aside, clips likely some time after my vacation next week.



Mike62Jazz

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Mike
Nov 17th, 2010 07:27 AM        

Fritz, Where you going to be in Colo.?



Fritz_D_Cat

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Nov 17th, 2010 01:35 PM        

Coming through your way and will have this amp with me. Got your email.



Fritz_D_Cat

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Nov 18th, 2010 11:19 AM        

For Peter, and all interested, here's a link to the DRRI schematic.



Fritz_D_Cat

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Nov 19th, 2010 11:58 AM        

This is pretty stellar the way it is, bootstrapped together with A/B switch in both #1 inputs.<br /> <br /> Normal (ODS) vol 5.5 tre 5 bas 3<br /> <br /> Vibrato vol 4 tre 4 bas 3<br /> <br />



WillieBoy



USE

Nov 26th, 2010 06:59 PM        

Recommendations for Resitor and Cap values if you have a Super Reverb type where R24 and C11 are separate on V1 and V2 (I have a Hoffman version that is PTP).



jesse1d

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canada

Nov 30th, 2010 08:36 PM        

Would love to know more about the tone of this ODS style mod. I have done your other Fritz mods and found them to be excellent. I usually bridge the 2 channels on the DRRI but this ODS mod sounds intriguing.



Fritz_D_Cat

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Dec 1st, 2010 12:00 PM        

@ WillieBoy<br /> <br /> C11 = 1 uF > 25V<br /> R24 = 2.2K 1/2 watt<br /> <br /> @jesse1d<br /> <br /> This is not 4 stages of gain like a Fuchs ODS. When you crank it up it sounds like the Fuchs clean channel cranked (which is amazing without any OD channel). It's a lot like a BJr with my voicing mod (see profile) but a tad beefier.<br /> <br /> The 2 channels bridge together wonderfully. They sound very rich together due to the differences in voicings.<br /> <br /> I used a a-b-y pedal rather than a simple jumper. When you jumper you engage a bit of the front end rolloff on one channel. The pedal allows both at full gain.



Fritz_D_Cat

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Dec 1st, 2010 09:33 PM        

I plugged the mods into Duncan's tonestack calculator.



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