DRRI 65 'Fritz' mod - report - now with added hemp!

noisepolluter

This involves routing the darker 'normal'  channel through the reverb/trem circuit, and putting both channels in phase for easier jumpering/blending.

Since hearing about the 68 custom deluxe I'd been toying with getting this mod done for a while, and as my amp was going in for a service anyway and is well out of warranty (second hand, and dates back to before they put the digital circuit trem in there - more on that later), I figured it was worth a try. I could have just had the bright cap clipped, but I wanted to compare the two and have the option of blending, using an A/B switch etc.

I'm extremely happy with the result - at volume 3-4 with pedals it sounds amazing now, especially for higher gain - just the right balance of warmth and clarity. I'd definitely say that running through the vib/verb circuit has brightened the normal channel very slightly, which I'm pleased with as previously I thought the two channels were a bit "too much/not enough" on that score.

 At very low volumes (i.e. late night home practice) I still use the vib channel with OD pedals or for very bright stratty cleans, so it's good to have kept that option.

I've not gotten round to blending/jumpering yet as I was having too much fun with the normal channel!

As it's an older reissue with the opto trem and the attendant loud ticking noise, I also had the mod done to reduce the tick (adding some kind of cap or resistor to one side of the "bug" - can't remember the exact details). I'm happy to say this was also a success! Ticking now barely perceptible.

I left the tonestack and negative feedback circuit alone rather than copy the 68, figured this is something I could get done another time if I really wanted. Given how good it sounds now I very much doubt I'll bother.

hoping this is of interest to any 65DRRI owners also considering the mods. Goes without saying that I took it to a trusted tech to get the work done!

colourofsound

As a '68 owner - this is interesting. Given the noise issues with the '68 knowing that there is a path to get the same sound with the (assumedly lower noise floor) '65 DRRI is good to hear.

If I ever decide I can't handle the noise on my '68 I could always flog it, buy an out of warranty '65 and mod away!

noisepolluter

Or once the 68 is out of warranty get the negative feedback resistor changed. Apparently you can even put it on a switch: 65/68/bonkers. I steered well clear! I find the 65 to be pretty quiet - by the time the volume (and treble, reverb) is cranked high enough for noise to be noticeable you're already pretty much at gig volume so it just disappears amid general cacophony. Whisper quiet at home levels.

colourofsound

@RiftAmps Tells me that the negative feedback resistor really isn't the issue, and won't fix the noise that is inherently part of the circuit.

I've manage to tame it by putting lower gain valves in the Reverb and Trem stages of the amp - it's certainly much more usable now. Not ideal though.

A real shame; it sounds awesome otherwise.

noisepolluter

I suppose neither the 65 nor 68 are intended to be played in situations where the noise floor is much of an issue - that's where the Princeton comes in - and it's just fluke that the 65 circuit has a low noise floor. 
It still puzzles me why they didn't put a bright switch on the reissue in the first place - the originals had them for a few years and it makes the amp so much easier to use.

RiftAmps

noisepolluter said:

It still puzzles me why they didn't put a bright switch on the reissue in the first place - the originals had them for a few years and it makes the amp so much easier to use.

I'm not aware of any DR ever having a bright switch (although I agree, they should have one). The bright switches were fitted to the bigger 6L6 amps, where have you seen one?

noisepolluter

I'm certain I saw one on an official fender video a couple of years back. It was a blackface but after '65.

keir

colourofsound said:

As a '68 owner - this is interesting. Given the noise issues with the '68 knowing that there is a path to get the same sound with the (assumedly lower noise floor) '65 DRRI is good to hear.

If I ever decide I can't handle the noise on my '68 I could always flog it, buy an out of warranty '65 and mod away!

I was discussing the 68 deluxe reverb with an amp tech and apparently the excessive noise comes from the reverb tank being the wrong way round, meaning the end that amplifies the reverb signal is at the same end as the amp's power transformer. 

noisepolluter

keir said:

colourofsound said:

As a '68 owner - this is interesting. Given the noise issues with the '68 knowing that there is a path to get the same sound with the (assumedly lower noise floor) '65 DRRI is good to hear.

If I ever decide I can't handle the noise on my '68 I could always flog it, buy an out of warranty '65 and mod away!

I was discussing the 68 deluxe reverb with an amp tech and apparently the excessive noise comes from the reverb tank being the wrong way round, meaning the end that amplifies the reverb signal is at the same end as the amp's power transformer. 

How odd. Presumably that's just an irregularity and easily fixable rather than a conscious design thing. 

jpfamps

noisepolluter said:

keir said:

colourofsound said:

As a '68 owner - this is interesting. Given the noise issues with the '68 knowing that there is a path to get the same sound with the (assumedly lower noise floor) '65 DRRI is good to hear.

If I ever decide I can't handle the noise on my '68 I could always flog it, buy an out of warranty '65 and mod away!

I was discussing the 68 deluxe reverb with an amp tech and apparently the excessive noise comes from the reverb tank being the wrong way round, meaning the end that amplifies the reverb signal is at the same end as the amp's power transformer. 

How odd. Presumably that's just an irregularity and easily fixable rather than a conscious design thing. 

That would be a construction error re the reverb tank. I've seen this a few times.

The tremolo ticking can almost always be cured by altering the lead dress around the tremolo oscillator valve; if the wires on the anodes of this valve are too close to the phase inverter then noise can be coupled into the power amp.

The phase inverted input impedance is very high, a few M ohm, so it doesn't take much capacitance to couple noise into the power amp.

noisepolluter

Brief addition in that I've since swapped the stock Jensen C12K speaker for an Eminence Cannabis Rex which I got in a great deal from @strat84
I'm very pleased with it - if I were to sum up in a couple of words my impressions after a few weeks of use, I'd say 'clear' and 'balanced'.

I'd read some reviews that the CRex could be dark sounding, but actually found it to have better overall definition than the stock C12K, albeit without the upper-mid spike the Jensen seemed to have which I found a bit harsh at higher volumes. The CRex certainly doesn't make the amp sound less 'fendery' to my ears.

The CRex has also unexpectedly improved the amp's low volume response, whereas the Jensen tended to muffle things until it had some volume behind it. 

The CRex definitely complements the wiring mods I described earlier in the thread, and as a further bonus it's shaved nearly 2lbs off the amp weight!  

Mickeyji

noisepolluter said:

Brief addition in that I've since swapped the stock Jensen C12K speaker for an Eminence Cannabis Rex which I got in a great deal from @strat84
I'm very pleased with it - if I were to sum up in a couple of words my impressions after a few weeks of use, I'd say 'clear' and 'balanced'.

I'd read some reviews that the CRex could be dark sounding, but actually found it to have better overall definition than the stock C12K, albeit without the upper-mid spike the Jensen seemed to have which I found a bit harsh at higher volumes. The CRex certainly doesn't make the amp sound less 'fendery' to my ears.

The CRex has also unexpectedly improved the amp's low volume response, whereas the Jensen tended to muffle things until it had some volume behind it. 

The CRex definitely complements the wiring mods I described earlier in the thread, and as a further bonus it's shaved nearly 2lbs off the amp weight!  

I also did the speaker swap and came to the very same conclusions as you did. The C-Rex  is a great alternative for taming the sometimes - to my ears at least - brittle "clanginess" of some of the stock Deluxes. It's interesting how DRRI's definitely don't all sound the same out of the box. Don't know if this is due to cold/hot biasing, speaker break-in or different tubes used, but to me the best ones  have a woody, slightly "smokey" quality to them. (Don't know if that makes any sense, but it's hard to describe subtle tonal differences..) Often the old, original blackface and silverface had that sound - and the C-Rex adds some of that timbre, IMO