I apologize for the long post but there’s a lot to cover for this wonderful amp. I want to give a good write up for anyone considering this amp who visits the site.
I finally picked up a Z-Plus. I’ve been eyeing one for quite a while. I wanted a lower powered amp with a nice clean sound with some headroom if needed. I don’t gig anymore and just wanted it for my studio. I could never seem to find one in a shop to try, so I just went on Reverb and took a shot from a local guy. I picked up a Z-Plus from 2021 with a Z12 speaker.
I first heard the Z-Plus in the seller's garage with the doors open, so basically an outside audition. He had it on half power. I brought my Tele with Fralin Vintage Hot pups to test it. The clean sound was wonderful. I knew I wanted it.
I took it back to my studio and plugged it in. I tested the Master Volume and half/full positions. I ran the volume up and MV down and visa versa. Checked the tone stack and bypass pedal switch. Everything worked as advertised.
Dr Z meet Dr Evil. The only amp I have on hand to compare with is one I built I call Dr Evil. (I sent my Ghia to Dr Z for the PPIMV mod). It is basically a Tweed Bassman preamp with Brown Deluxe power amp section with 6V6 tubes in fixed bias. Building amps is fun but one issue you have is the transformers you can get are just off the shelf. PT and OTs make a huge difference in sound and feel. Dr Evil has a Princeton Reverb PT and OT and is push/pull with selectable negative feedback. It also has other selectable mods I put in to hear and learn about, but I ran it with no negative feedback for the comparison. It has a Scumback M75 65W speaker which is basically a Celestion Creamback and is housed in a Princeton Reverb size combo cab. This amp doesn’t really get very clean and is almost always on the edge of breakup because of the design. It’s a nice sound don’t get me wrong, but doesn’t do clean unless you turn the volume way down below where the mojo is.
Z-Plus Sound.
Overall this is a wonderful amp. On the Dr Z site, the descriptions and videos refer to even order harmonics that only singed-ended amps have. You have to hear it to understand. There is a sweet harmonic that hangs in the air when you hold a note. With a bit of delay, it just keeps going! It’s hard to hear on videos but it is definitely there and not in any push/pull type amp I’ve played.
The Z-Plus doesn’t have a lot of gain like a Plexi, but it still crunches pretty good with the volume pot up and hotter pickups. My Tele definitely can push the amp. I don’t have a humbucker guitar at the moment, but I’m sure it would drive the Z-Plus pretty well. The videos on the Dr Z site show this. The amp has a nice feel to it due to the PT/OT combination. Pick attack can drive the amp as can power chords, but if you ease up, it cleans up.
Because the amp has Master volume and a half/full operation, you get a lot of options. You really need to take time and try them all.
Volume. The amp starts to open up with the volume pot around 9:00. At this level and the Master full, I get a very nice clean sound with both my Strat and Tele. Around 11:00, it’s on the edge of breakup and is driving the 6V6s. Dialing back the Master at this point cleans things up a bit. At 2:00, it’s into a nice overdrive that cleans up well with the guitar’s volume pot. Full on has a nice crunch and the amp has a punch to it with pick attack.
Half power. The half power sound is nice. The bass drops out a bit on half power as does the volume, but not as much as you would think. At half power the amp has more chime to my ear. You can dial in gain with the volume knob and then pull the master back to taste.
Full powerhas a bit more volume but also more warmth. It seems to have more width to the sound too if that makes sense. You see this effect in amps where you’ve bridged the inputs like a tweed deluxe or Marshall Plexi. Parallel signals have a touch more gain but it is more of a fullness you hear. My Dr Evil amp has parallel inputs, so it does this in the preamp section. I think I prefer the Full power mode more for this reason on the Z-Plus.
Master Volume. MV works by dropping some of the preamp signal to ground. Because of this, you don’t drive the next stage as hard as you turn the MV down. The Z-Plus MV is after the gain stages and before the power tubes. What I noticed is you can hear the 6V6 tubes go from clean into overdrive as you dial the MV up at a fixed volume pot position. 6V6 tubes have a lovely OD sound. With the 5Y3 rectifier, you get a nice sag too and a bit of compression. After a point, the amp doesn’t get louder but compresses more and has that 6V6 overdrive feel. The volume pot on your guitar can clean this up which is nice. Some amps can’t do this. This is an excellent master volume as the tone doesn’t change.The Z-Plus is single-ended, so this is not a PPIMV but a well tuned master volume.
My Dr Evil amp doesn’t have PPIMV because it is fixed bias. So I have to use the Z-Brake attenuator to lower volume. Dr Z explained this in an AMA. PPIMV with fixed bias doesn’t sound good because there is dc current running through the pots because the circuit is connected to the bias voltage supply. I tried it and the good Doc is correct. It sounds grainy and unpleasant to my ear.
Tone Stack. The tone stack sounds to me like the popular TMB stack (treble, mid, bass) that Fender then Marshall popularized. These types of tone stacks filter highs, mid and bass by sending some signal to ground through high and low pass filters. It works really well for dialing in the sound you want. A few factors in the design can give you either a Fender feel or Marshall feel depending on the resistor/capacitor combination. This sounds closer to a Fender, which I prefer and is tuned for the Z-Plus circuit. The pots have plenty of range so don’t be afraid to go low or high depending on your guitar.
Tone Stack (EQ) Bypass switch. The switch most likely works at the end of the TMB tone stack by adding resistance after the Mid pot (I’m guessing here). More resistance to ground allows more signal to go to the next stage and less through the tone stack. It’s like turning up your Mid pot to 11! This increases gain and drives the next stage and levels out the tone response. If you turn up the switch full, there is a lot more gain but the mids come way up and you lose a bit of treble. The treble is still there but the mids take over. I think this switch works best dialed back so it just gives your sound more thickness. Around 9 on the dial works for me. My Dr Evil amp has this.
CUT. The Cut pot works as a power amp tone control by acting as a high pass filter. The advantage to this is you can keep the treble and mid pots up through the gain stages and enhance the overdrive sound then tweak the high end just before the power tubes. It is more effective than a presence pot I feel. Dr Evil has this cut circuit in it. I tried a Presence pot like the Bassman, but preferred the cut to it. Presence works differently in that it feeds back certain frequencies to the input of a stage and they cancel out and is more subtle than the Cut circuit.
Reverb. This is a nice reverb similar to the Fender Princeton. I tend to like a bit of it for ambience and don’t ever go full **** Dale. I did play Pipeline with the reverb up and I did sound nice though. One thing to remember is when you drive the amp more in the preamp section, even with pedals, the reverb will increase. It’s the nature of the circuit. This can happen with reverb pedals too.
Z12 Speaker. I would put the Z12 somewhere between a Celestion Creamback or Blue and a Fender Jensen type speaker like the Weber 12A150 or 12F150. The treble is well balanced as are the upper mids. The bottom end is tight and it doesn’t woof out at higher volume. It is more in the mid scooped range than the Scumback, but sounds nice when dialed in. It is not as mid-scooped at the Webers.
I tried the Z-Plus with the Scumback while it was still in my other combo cab. It’s a smaller cab 19” wide. The speaker sounded good but definitely more mid range than the Z12. The smaller cab can also make it sound a little boxy.
Pedals. I like to use pedals for different sounds. I like to get my base sound with the amp near or at the edge of breakup and use pedals to boost or add some crunch. I tested my J. Rocket Lenny Boost, Maxon OD-9 with Analogman mods, Keeley D&M drive and Wampler Tumnus and Tumnus Deluxe. They all sounded very good after some gain and tone tweaks. I tend to run them at lower gain and stack them if I want more gain or a different kind of overdrive.
Delay and Chorus. I have a Wampler Faux Echo and it sounded glorious in the Z-Plus. The repeats carry the amp harmonics on held notes and they just ring. My Analogman Chorus also sounded excellent.
Effects Loop. I tested the loop with a Catalinbread Talisman, which is a plate reverb emulator, and the Faux Echo and they sounded lovely. The loop is very transparent. I think a tremolo would work wonders in the loop.
All in all I am very pleased with this amp. What sets this apart from other Fender Champ type amps is the OT. It sounds much more full range than a Champ OT or even a Princeton Reverb OT. I’ve played the Victoria Vicky Verb, which is basically a Tweed Champ with reverb. It’s a nice amp but Z-Plus sounds more full and is much more versatile with the Master and parallel output. The Z-Plus OT is partly responsible for this as is the circuit design. I’m not sure how many hours the previous owner had on it, but the Z12 doesn’t sound like it needs much more breaking in. I’ve put about 15 hours on it so far.
It’s also not an overly loud amp. With the volume at 10 and MV full it wasn’t painful. I measured around 90 dB on my iPhone. My studio room has wood paneling so there is some deadening.
Lastly, I have Dr Evil on top of the Z-Plus and the feet match exactly to the chassis bolts on the Z-Plus. Not sure why, but this made me happy because I don’t want to blemish the Z-Plus tolex.
Scott
