Want Pre500 tone? Here's how to get it!

[Shemham]

By all means try it and let us know how it sounds.

However, I highly doubt the early Rectifiers used 250Kohm Bass pots. 1Mohm bass pot is in alignment with traditional Fender Bassman tonestack design which both Soldano SLO and later Rectifier models build upon. The pot values taken by LesPaul70 also support this view even if the pots were attached to the circuit. Red Channel's presence pot value seems to be the only one that has changed significantly since the early models and all the other values have remained the same, including the gain pot value.

 

[JCDenton6]

Yeah, his readings do suggest that the pot is the same, He might have mixed up the number from another pot perhaps. Figured it was worth a shot anyways, I tinker with stuff too much haha :lol:

Got home from work and did the pot swap, damn it sounds like boosting a Rev C... it's super tight... interesting if you still think the amp is a little boomy but not ideal if you are using tight sounding pickups.

I'm going to swap the 1MA back in and swap the gain pot back to a 250k, this clip below was done at a moderate volume with the 250k bass pot. Tone controls at noon except gain at 9 o'clock.

https://dl.dropboxusercontent.com/u/47381724/250k%20bass%20pot.mp3

 

[JCDenton6]

I like the 1 meg pot better for my needs, I dig that it puts out more high frequencies than the 250k, it's tighter as well.

It was cool to experiment though with the 250k pots for gain and bass, probably my last update for quite a while.

250k gain pot clip: https://dl.dropboxusercontent.com/u/47381724/red%20gain%20250k.mp3

1 meg gain pot clip: https://dl.dropboxusercontent.com/u/47381724/red%20gain%201ma.mp3

 

[LesPaul70]

Yeah, his readings do suggest that the pot is the same, He might have mixed up the number from another pot perhaps.

Entirely possible. I could have - more likely that my son did, though. He's very young. (He read the part codes aloud for me, my eyes are already too old to accurately see those tiny numbers in a cramped space without a magnifying glass.) In any case, trust my meter readings more than the codes.

Interesting sound samples. But based on them alone, I would be hard pressed to say which combination sounds the most similar to my C. They are pretty different from the kind of music I play. :lol: Was your modded amp a Triple?

 

[JCDenton6]

Thanks again for your help and the contributions to the thread, very much appreciated!

Indeed my modded amp is a 2 ch Triple (Rev G)

I still have yet to play around with a few values but believe my amp is 99% there. Just wish I would've been able to play/look over an actual pre 500

 

[LesPaul70]

You're welcome.

If there still is something specific you want to know, just ask. I'll see if I can dig up the answer.

 

[Jorn218]

I am coming back to this thread since the previous foray into modding my amp didn't work out so well due to band schedule as well as an annoying ground loop problem with my pedalboard that has since been rectified(pun intended)

I went through all 29 pages of the thread and copied the modding information dealing specifically with a 3 channel Rectifier, or mods that will work with both 2 and 3 channel amps. I will list them below. I did this so I can keep a list of what mods I try and what my ears hear as I progress in modding my amp. When I mention "GAIN" in a mod, I am talking electrical amplitude, not "distortion"


- Change gain pots of Orange(2) and Red(3) channels 500K and 1M respectively
Effect- increased gain to preamp, allows higher frequencies past bright cap filter, what else?

- Preamp tube charging time - One of the more intriguing mod possibilities. Watch this video for
explanation why this is important on a different amp series, but probably pertains to the Pre-500/Post-500
discussion : http://www.youtube.com/watch?v=10mVhB-eMBs
Effect- "Unknown" Changes feel of 3 channel to older revision style? Apparently unused cap areas on pcb to change
this. No further mention in thread on if this was ever persued/documented. Also no values given to what cap
values could be.

- V1-3 cathode resistors pulled and jumpered. 100 ohm resistors are used here to simulate older revision LDRs
Effect - Not ever explained, nor was why would jumping a 100ohm resistor simulate the resistance of an LDR in
cathode position be better than using same value LDR as older revisions, or finding proper resistance the LDR is
contributing in the cathode and using "that" value. The discussion led me to believe that M.E. used the 100ohm
resistors as a compromise. More explanation would be beneficial on this isssue. For myself and others less amp circuit
savvy as others contributing to the thread.

- Change Presence pots to 250K in channels 2 & 3 Deemed not necessary unless one is usually diming the Presence knob
Effect - Amp overall brighter (250K may make amp too bright, try other values here)

- Cap/Resistor removal - 33K resistor directly after Orange channel tone stack. Can also remove .003uf cap right next to it
instead. One or other should do same thing. Did not say remove both. Can be used in conjunction with Presence pot
swap if amp is still deemed too dark after that mod.

- Dullness cap removal on Channel 3. Located on 3 channel amp on the pcb right after the gain pot Value is 10pf. Is this
cap here for what, parasitic oscillation prevention?
Effect - Unknown.

- Preamp power supply cap values. In relation to? This may tie back in to the preamp tube "charging" that was discussed
via the Randall Smith video and alluded to within the thread (my personal understanding).

- Pre-gain filter modifications. Lots of back and forth on this throughout the thread I won't post these except that the
82pf/2.2M filter works in conjunction with the .0022uf/680K network to produce a close approximation to the
.0022uf/475K network of a Pre 500 revision. It was stated to leave this alone and just place a 5M5(or as close as
possible resistor to 5M5) in parallel with the 680K to acheive the "Exact" Pre 500 value needed here.
Reading back, removing the 82pf/2.2M filter I think kills Channel 1?
Effect- Unknown need clarification on this.

- Add a 5nf cap in between the 100k resistors that are tied to pins 1 and 6 on V2 and the D power rail (In other words,
NOT the tube side of the 100K resistors). This is done after changing the Channel 3 gain pot to 1M.
Effect - Unknown, need clarification as to why you want to do this, and not even sure this applies to a 3 Channel amp.

- Removal of the 20pf cap that is on V2a's grid. Perform this when using 1M gain pot as Tremoverbs did not include this
cap.
Effect - Unknown, more clarification needed.

- Cap removal 2m/20pf circuit that's in parallel with the 680k/.002uf right before V1
Effect - Adds tightness, clear gain/mid boost

- (Optional mod when all others have been tried)Cap removal of 120pf caps that jump the two plate resistors of
V5 (Phase Inverter)
Effect - Brightens amp. May make Channel 3 way too bright.

Mod idea Not yet discussed on this thread. What about matching voltages of the 3 Channel amps to what the 2 Channels
used where appropriate? Are the two amps running at very different voltages? Is the B+ of the two amps within the same region of tolerance? I do not have a M.E. version of the two channel Rectifier amps like I do the 3 channel, so I can only theorize.

If you decide to explain any of the "unknowns" above, please copy/paste the mod to your post before your answer. I will try to edit my post to fill in the un-answered gaps to try and keep it in one place to avoid getting lost by page count.

 

[Shemham]

- V1-3 cathode resistors pulled and jumpered. 100 ohm resistors are used here to simulate older revision LDRs
Effect - Not ever explained, nor was why would jumping a 100ohm resistor simulate the resistance of an LDR in
cathode position be better than using same value LDR as older revisions, or finding proper resistance the LDR is
contributing in the cathode and using "that" value. The discussion led me to believe that M.E. used the 100ohm
resistors as a compromise. More explanation would be beneficial on this isssue. For myself and others less amp circuit
savvy as others contributing to the thread.

Actually Rev C/D did not use LDRs at all on cathode positions. LDRs were added starting from Rev E in order to switch few 47Kohm resistors to drop the gain levels for the clean mode. LDRs added some resistance even when they were open, thus they incidentally altered the lead mode tone. 100ohm resistors on the 3-channel models were added simply to simulate the LDRs. They alter the frequency response of the stage and if removed, you will end up with more mids, less bottom-end and faster attack/response.

So if you wanted to get your 3-channel head closer to the original Dual Rectifier, IMO jumping the 100ohm resistors would be the way to go.

 

[Jorn218]

@Shemham
Any chance that you have one of the two channel Rectifier schematics you could email me? I am at a loss comparing the two circuits without one.

I swapped the gain knobs of channels 2 & 3 today, as well as jumpered the 100ohm resistors on v1-3. I will probably swap the 1M pot for a 500K one though as 1M turns to un-usable white noise after about 2:00, I noticed a nice amount of compression around 10:00 that continued til about 1:30 then blended with the whitenoise after that. Sounded ugly and not in a good way.

The 500K on channel 2 is perfect for that channel. Usable amount of distortion gain starts about 9:30 and continues until maxed out. I didn't play around to find a sweet spot on either channel.

For the cathode resistor swapping. The Channels are both now more aggressive and immediate and I did notice a nice mid frequency shift as lead tones sounded more pleasing. My normal eq settings did not work and starting from scratch I noticed I had to use some more treble and presence than normal and bass quite a bit less. Mids actually needed to be bumped up a tad. Again I didn't really sit down and hammer out sweet spots.

Both channels opened up quite a bit. Chords chime better as well as blooming. The over-bearing brightness of Channel 3 was tamed, but it is missing some sizzle it had previously. May be a good thing in the long run as I need to re-eq the amp in a band setting to really see how these mods affect the amp in that situation. Channel 2 still has the wool blanket over it, but it has improved. An analogy would be, before channel 2 it would be like listening to the amp through a brand new wool army blanket. Now, the same army blanket has been around for 50 years and is well worn in, washed until it no longer scratches and lets light through it in spots. I want to be rid of it. I like the tonal differences between the two channels, but the volume differences is still unsat, as well as the woofiness.

Will changing the presence pot in channel 2 change the volume output to match channel 3 or are there other circuit mods needed?

I know this thread is how to emulate the earlier revisions of the rectifier amps, but also seems to be merging into a tailoring the amp for the player in a few places as well.

 

[Jorn218]

GAH!!!! I am loving this amp now.... A Dual rec that Kerrangs if that makes sense. I really want to hear this recorded now.

 

[JCDenton6]

Hell yeah man!! :twisted:

 

[xiwiwix]

- Removal of the 20pf cap that is on V2a's grid. Perform this when using 1M gain pot as Tremoverbs did not include this
cap.
Effect - Unknown, more clarification needed

- Change gain pots of Orange(2) and Red(3) channels 500K and 1M respectively
Effect- increased gain to preamp, allows higher frequencies past bright cap filter, what else?


^I've got a TOV and want to know if I need to do both mods or if changing the gain pots (500k on the orange and 1M on the red) is all I need to do inorder for the amp to get a little brighter and have more gain.

 

[Shemham]

- Removal of the 20pf cap that is on V2a's grid. Perform this when using 1M gain pot as Tremoverbs did not include this
cap.
Effect - Unknown, more clarification needed

- Change gain pots of Orange(2) and Red(3) channels 500K and 1M respectively
Effect- increased gain to preamp, allows higher frequencies past bright cap filter, what else?


^I've got a TOV and want to know if I need to do both mods or if changing the gain pots (500k on the orange and 1M on the red) is all I need to do inorder for the amp to get a little brighter and have more gain.

Changing the pot for greater value will make the amp brighter/tighter. The downside is that the lower gain tones suffer a bit. 500k will be more reasonable for general purposes. 1M can be nice if you want to make the amp feel like you had boost pedal with maximum output on all the time.

BTW, has anyone tried to clip the 2M2 resistor going to ground between the first filter network and the first coupling cap (R321 on the schematic below)? While this is not early Recto related, with the 500k ohm pot this change would be one step closer to SLO.

EDIT: Nevermind, I just tried it myself. It practically just muddied the amp a bit while providing some more gain and slightly more liquid feel. Not that useful change really.

 

[JCDenton6]

^ Ah you did it before I could warn you about it. I tried this in the past and didn't like the change either at all.

 

[Big_Al]

Does this mod work for a Roadster and if so, what location for the PCB component(s)?

 

[afu]

Regarding the 100 ohm resistors under the cathode bypass cap:

The resistor alters the gain of the stage. The DC voltage "sees" 1.8k and 100 in parallel = 94 ohms. Gain boost is reduced from a circuit with 1.8k and 1uf to ground.

The resistor also alters the corner frequency for the gain boost. AC voltage "sees" 1.8k and 100 in series to the cap. The gain boost affects frequencies over 83.8 Hz (vs 88.4 without it).

It's called a cathode boost limiting resistor, IIRC. In this case, removing the 100 ohms would alter the gain boost much more than the corner frequency.

My personal opinion would be to leave the one on stage 1 alone if you want a clean sound that's clean. Since the tone stack follows it, the treble, presence, and gain controls for CH1 should cause breakup and overtones much earlier than the stock setting, were it removed.

 

[Jorn218]

I cannot believe I was such a slacker I never got around to uploading a recording.

This is a scratch track I made for my drummer to lay his tracks down to. Forgive the beep as It is hard coded in the mp3 for him.

https://soundcloud.com/lasanche/hell-correct

We did this a few weeks back. Running my Ibanez DT-250 into my Dual with mods I made from this thread. No changes to the amp since I last posted. I think I was actually running the Orange channel for this recording.

Amp settings Pres: 11:00, Master: 1:30, Gain: 11:30
Bass: 12:00, Mid: 1:00, Treble: 4:00

Guitar has single volume, no tone control, Dimarzio Megadrive pickup.

In September I had decided to stop down tuning to B which we had been using since 2013. I had grown tired of trying to figure out how the guitars and bass can play nice with each other at that tuning. After listening to all the stuff I loved when I was growing up. the music that really moved me and made me want to play this style and after listening to my holy grail heavy tune Slowly We Rot and finding out it is in standard tuning, I tuned back up to standard tuning. That doesn't fit my voice so we dropped it down a half step, now all guitars have their space. My bassist has even started using distortion on his bass, which I had always hated before, but it actually compliments the guitars right now.

 

[Shemham]

I finally got around to make some clips of my modified Multi-Watt DR.

nearly two years ago I made the following changes: 1) jumped the 100 ohm resistors 2) added 5M5ohm Resistor in parallel to the 680k resistor in the first filter section to drop the total resistance to Rev C/D values.

Here you can find link to the clips:

http://www.tonefinder.com/index.php?section=user&value=shemham

Basically I recorded two clips in Vintage and Modern modes practically everything set towards noon. Then I made one fine tuning to Modern settings and used my standard settings for another Vintage clip. I tried to make the clips very plain to demonstrate the actual tone and texture of the modified amp. I use a clean boost to bring my guitar signal to moderate levels as I'm using fairly low output pickups. Anyway, you can find most of my settings and gear used behind the link.

 

[kramerxxx]

I finally got around to make some clips of my modified Multi-Watt DR.

2) added 5M5ohm Resistor in parallel to the 680k resistor in the first filter section to drop the total resistance to Rev C/D values.

Hi,
What does this do to the sound/feel of the amp?

I've done the 100 ohm resister jumpers, that made the amp more present.

 

[afu]

I finally got around to make some clips of my modified Multi-Watt DR.

nearly two years ago I made the following changes: 1) jumped the 100 ohm resistors 2) added 5M5ohm Resistor in parallel to the 680k resistor in the first filter section to drop the total resistance to Rev C/D values.

Here you can find link to the clips:

http://www.tonefinder.com/index.php?section=user&value=shemham

Basically I recorded two clips in Vintage and Modern modes practically everything set towards noon. Then I made one fine tuning to Modern settings and used my standard settings for another Vintage clip. I tried to make the clips very plain to demonstrate the actual tone and texture of the modified amp. I use a clean boost to bring my guitar signal to moderate levels as I'm using fairly low output pickups. Anyway, you can find most of my settings and gear used behind the link.

I really like the tube/modern one. The other one is really good, too. All of the dirt channel recordings sound good.