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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Tue Sep 11, 2012 5:21 pm
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Aspiring Musician
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Location: Houston Texas
:D

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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Tue Sep 11, 2012 5:32 pm
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Rock Star
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Location: Natural Bridge, Virginia
Hou-Tex wrote:
:D


Thanks. That says it all. 8)

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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Tue Sep 11, 2012 5:56 pm
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Rock Star
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Bluesy! Very, very cool. I swear solving these things is the next best thing to the best thing. And we ain't talking photos of amplifier head units still covered.

Dang, I wasn't going to mention that! Bad boy! But, in the excitement, I made boo-boo.

Enjoy that beast. Where you live? I've have the VLR no lower than "8" tonight. How 'bout some old fashion "beck-&-call?"


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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Tue Sep 11, 2012 6:34 pm
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Aspiring Musician
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Joined: Sat Mar 31, 2012 6:38 am
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Tenacious B. showing how it's done. Play hard. Sleep well.

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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Tue Sep 11, 2012 7:36 pm
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Rock Star
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Location: Natural Bridge, Virginia
Thanks, guys. It was a fun exercise.

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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Wed Sep 26, 2012 4:44 pm
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Rock Star
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Location: Natural Bridge, Virginia
Made a few more mods to my BDRI.

Going back to the BDRI schematic:

http://support.fender.com/schematics/gu ... _Rev-A.pdf

I decided to remove the 1.5K ohm grid swamper resistors (R64 and R65). I decided to leave the two flyback diodes (D4 and D5) as they don't have any affect on the tone of the amp. With this change, the power amp stage is now virtually identical to my 5F6A Bassman clone. There are some minor differences in the phase inverter feedback loop due to the fact that the BDRI takes the feedback from the 8 ohm OT tap and the 5F6A takes it from the 2 ohm OT tap. I may run through the math and see if there are any differences between the two, but I don't really hear any difference in performance.

I also decided to mod the tonestack. The tonestack of the BDRI is the same as the tonestack in the 1959 Bassman LTD reissue which is a little different from that in the 5F6A clone. The 5F6A clone uses a 250 pf cap and 250K ohm linear taper pot for treble, a 0.022 mf cap and 1M ohm audio taper pot for bass, and a 0.022 mf cap and 25K ohm linear taper pot for midrange. It also uses a s l o p e resistor of 56K ohm. The BDRI uses 250 pf cap and 250K ohm audio taper pot for treble, a 0.1 mf cap and 1M ohm audio taper pot for bass, and a 0.022 mf cap and 25K ohm linear taper pot for midrange. It also uses a s l o p e resistor of 100K ohm.

I replaced the 250 pf ceramic cap with a 250 pf silver mica cap. I also replaced the 0.1 mf cap with a 0.022 mf Orange Drop cap for bass. I was going to replace the stock midrange cap with an Orange Drop, but the space is a little tighter and decided to leave it be. I decided not to change the s l o p e resistor or the pots.

The result of these changes are shown in the graph of the tonestack response:

Image

The picture quality is not great, sorry. My original tone settings were Treble = 4, Bass = 2, and Midrange = 6, bright switch on, and presence = 6 for use with my humbucker equipped guitars. It sounded good, but with the Cannibis Rex speaker, the low bass could be a little bloated. If you look at the bass part of the curve, the upper, green curve is the low bass response for the stock configuration. If you look at the lower red curve, you will see that the bass rolls off faster below about 60 Hz. Treble and midrange settings are the same, but bass is now set to 4. Notice how nicely the curves overlap.

The net result is that the low bass is tighter with less boom and the highs seem a little bit smoother. Midrange did not really change. I have to say that the amp sounds better now than it ever did. The changes I made were pretty simple and except for partly removing the tube PCB to get to the plate resistors for V3A, no real disassembly was required.

Note: for some reason I have to type it s l o p e. Otherwise I get $@!&#. :lol: :lol: :lol:

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Last edited by bluesky636 on Sat Nov 03, 2012 5:08 pm, edited 1 time in total.

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Post subject: Re: Strange Problem With My Fender BDRI
Posted: Wed Sep 26, 2012 9:32 pm
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Rock Star
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Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Thinking now about how to make the effects loop driver side switchable to keep it from loading the signal path when it is not is use. :idea:

I've seen a mod to add a cathode follower too. I'll have to dig it up. 8)

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