hoffy
New Member
Posts: 35
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Post by hoffy on Jan 26, 2022 2:33:05 GMT -7
Hi guys, I have just bought a used Z28 head (export version made in 2012) and the amp just has way too much bass. Even with the bass knob all the way down, there is some low bass frequency which is more pronounced then on my 75 Vibrolux - I compared them through the same cabinet. When listening to some demos on YouTube, there is balanced frequency response even with the bass knob at noon. Most guys, however turn the bass knob around 10-11 o'clock. With my Z28, I am still getting was too much bass in this position and I need to get the bass knob down to 9 o'clock or even lower. I have several cabinets and speakers and the bass is too much on all of them, but my main reference cab is a 1x12 Zilla open back with Celestion Creamback 65 and it is just unusable with the amp. I feel like the bass is coming from the power section, because it stays there even with the bass knob all the way down.
I AM IN EUROPE and we have 230-240V in the wall here. At home with 240V in the wall I am reading 357V on the 6V6 plates, at another place where the socket voltage is 230V, the plate voltage is 344V. From what I have read on this forum, it should be around 370-380V (supposedly?). Is there anything wrong with the amp? Are the power tubes old? They were changed about 3 years ago and the bias was set at around 23mA when I got the amp.
I tried to set up the bias at the recommended 70% which is around 27,5 mA for my 240V wall voltage and the bass is even more pronounced (which I expected). Even with the bias at around 22-23 mA which is about 60% dissipation the overpowering bass is still there.
So I actually have 2 questions:
- Is my plate voltage 344-357 normal or is there something wrong with the amp? The amp sounds really loud so I do not feel like there is lack of power.
- Could it be the preamp tube? I do not have a spare EF86 yet. There is some Russian NOS in there. All tubes are to the Z28 specs and there is 12AX7 in the PI position.
- Do you also find the 28mA bias recommendation too hot or, again, is there something wrong with my amp because it has too much bass and low mids with the 70% dissipation bias?
Thanks a lot! Peter
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Post by Ridgeback on Jan 26, 2022 9:16:19 GMT -7
In a used amp, I'd be inclined to suspect the power or PI tubes rather than bias but I'm not familiar with biasing issues related to European voltages. Good luck.
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Post by Mark (Basement Enthusiast) on Jan 26, 2022 11:13:43 GMT -7
With 2 x 6V6 tubes between about 344 and 357 V, your 28 mA bias current seems pretty much spot-on at 70%. (28 mA is also Doc's recommended bias point.) I would not say that your bias is abnormal at all.
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Post by ME on Jan 26, 2022 16:55:00 GMT -7
I’m no expert, but it’s possible that there was either a mod to or a component failure in the tone stack. Maybe not, but a potential source of your issue. ME
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Post by bubs42 on Jan 29, 2022 20:53:16 GMT -7
hoffy, two questions. 1. What years is the amp, 2. What Cab/Speaker are you using?
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hoffy
New Member
Posts: 35
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Post by hoffy on Jan 30, 2022 2:19:40 GMT -7
hoffy , two questions. 1. What years is the amp, 2. What Cab/Speaker are you using? Hi bubs42, it is a 2012. I have tried it with a bunch of different cabs and speakers - Zilla 1x12 with Creamback 65, Vintage 30, Greenback, Eminence Legend, some custom made pine cabs, cab and speakers from my Vibrolux Reverb (old Fender labeled AlNiCo from 70s). It sounds different with each one, but the bass is overpowering on all of them. The Zilla cab is actually very close in size to the Dr.Z 1x12 - www.zillacabs.com/compact What strikes me the most is that through the same cabinet it has more bass than my 70s Vibrolux, which is very bassy already. I took it to a an experienced amp tech yesterday and he measured all the components and said there was nothing wrong with any of them. There are Orange drop caps labeled Dr.Z. Blue pen marks on each solder point so the amp has obviously not been touched. We tried swapping some tubes. Changing the original Russian EF86 for the current production EHX helped a bit, but these are subtle changes. What also helped a bit was lower the bias to around 23-24 mA, but then the amp does not sound as Doctor intended, I think. It loses mids and the breakup is later and not as smooth. And even with the bias set low, the bass is still too much. We actually found some schematics of this amp on the net with the amp tech. I do not know the schematics is original, but the component values fit the actual values in the amp. Thanks!
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Post by daddyelmis (Greg) on Jan 30, 2022 5:43:39 GMT -7
What guitars and style of music are you using with the Z28? With mine, I found humbuckers were not it’s favorite as it got bassy. The Z28 loves strats and other single coils. It’s also a more bluesy amp, I would not think it to be a metal amp in case that’s where you’re at.
I’ve played mine through a Dr Z 2x10 cab that it came with, and a TRM vertical 2x12 with the Z Best combination of a V30 and G12H30. Both sounded great with the 2x10 more punchy. There’s a number of folks that play the Z-28 with strats and the knobs at 3-3-3 and it’s wonderful, but can be bassy on neck pickup (I tended to use 3-3-12 … based on “clock face” orientation).
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Post by bubs42 on Jan 30, 2022 6:20:59 GMT -7
hoffy , two questions. 1. What years is the amp, 2. What Cab/Speaker are you using? Hi bubs42, it is a 2012. I have tried it with a bunch of different cabs and speakers - Zilla 1x12 with Creamback 65, Vintage 30, Greenback, Eminence Legend, some custom made pine cabs, cab and speakers from my Vibrolux Reverb (old Fender labeled AlNiCo from 70s). It sounds different with each one, but the bass is overpowering on all of them. The Zilla cab is actually very close in size to the Dr.Z 1x12 - www.zillacabs.com/compact What strikes me the most is that through the same cabinet it has more bass than my 70s Vibrolux, which is very bassy already. I took it to a an experienced amp tech yesterday and he measured all the components and said there was nothing wrong with any of them. There are Orange drop caps labeled Dr.Z. Blue pen marks on each solder point so the amp has obviously not been touched. We tried swapping some tubes. Changing the original Russian EF86 for the current production EHX helped a bit, but these are subtle changes. What also helped a bit was lower the bias to around 23-24 mA, but then the amp does not sound as Doctor intended, I think. It loses mids and the breakup is later and not as smooth. And even with the bias set low, the bass is still too much. We actually found some schematics of this amp on the net with the amp tech. I do not know the schematics is original, but the component values fit the actual values in the amp. Thanks! The depth of the cabs IMHO is important, Doc's Cabs sound fantastic and even though I like the little small cabs, Doc's modern 1x12 sound amazing and I have been super impressed. The Z28 has a lot of bass, I hardly ever bring it above 9 O'clock, the Treble around 12:30/1:00. Sometimes I don't belong here, because I don't like the 333 setting and I don't like Celestion Gold.
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hoffy
New Member
Posts: 35
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Post by hoffy on Jan 30, 2022 7:42:16 GMT -7
What guitars and style of music are you using with the Z28? With mine, I found humbuckers were not it’s favorite as it got bassy. The Z28 loves strats and other single coils. It’s also a more bluesy amp, I would not think it to be a metal amp in case that’s where you’re at. I’ve played mine through a Dr Z 2x10 cab that it came with, and a TRM vertical 2x12 with the Z Best combination of a V30 and G12H30. Both sounded great with the 2x10 more punchy. There’s a number of folks that play the Z-28 with strats and the knobs at 3-3-3 and it’s wonderful, but can be bassy on neck pickup (I tended to use 3-3-12 … based on “clock face” orientation). Greg, I mainly use single coils. Strat and telecaster. Humbuckers are almost unusable with this amp, even with the bass way down. In any case, when I turn the bass below 9 o'clock, I am loosing the fatness in midrange. I cannot imagine using the amp with the bass on 3 o'clock. I can't even use it with the bass at noon with single coils. I should point out that I am a fingerpicker, so my tone is already quite round.
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Post by goodez on Jan 30, 2022 22:14:49 GMT -7
For what it’s worth I also keep my Z28 bass setting at around 9 o-clock. I run it through a Dr.Z 2x10 with 2 Celestion Golds. The amp by nature just has a lot of bass. I was hoping for some minor changes to the amp rather than any major dna alterations on the mkii but I’m not the surgeon. Some subtle tweaks such as bass reduction and just a hair more treble would’ve been perfect in my opinion.
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hoffy
New Member
Posts: 35
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Post by hoffy on Jan 31, 2022 4:18:06 GMT -7
For what it’s worth I also keep my Z28 bass setting at around 9 o-clock. I run it through a Dr.Z 2x10 with 2 Celestion Golds. The amp by nature just has a lot of bass. I was hoping for some minor changes to the amp rather than any major dna alterations on the mkii but I’m not the surgeon. Some subtle tweaks such as bass reduction and just a hair more treble would’ve been perfect in my opinion. Yeah, bass at around 9 maximum and even then too much bass there. But aren't you losing the fat mids when you turn the bass knob down? How is your bias set? What strikes me the most is that the amp sounds quite different than in this official Dr Z demo. Either the sound was EQued with a highpass filter in the demo or it is some newer model with different caps or tweaked circuit. Mine has more bass with the bass knob at 9 than the amp in the video with the bass above noon.
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Post by loucardguitar (Johnathan) on Jan 31, 2022 9:44:42 GMT -7
Another question to ask, just mainly because I haven't seen it asked is where do you have the Volume set? I had a Z28 at one time, but it's been a while since I've played it. I can't remember if the Z28 liked to be opened up a bit, but I do know that it is loud as all get out. You're not really going to get usable "bedroom levels" without some sort of attenuation. I know I used an attenuator. And I do know some amps will emphasize the bass when the volume is down at quieter levels. May not be the issue but just throwing a thought out there.
Hope you get it figured out. The Z28 excellent amp.
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Post by bubs42 on Feb 5, 2022 6:58:36 GMT -7
I have another 19x19 cab coming in and I will put a couple of "American" speakers in and see how it sounds. I think Dave's video sounds really great with that Z Speaker. I'd like to try that with my Z28.
Cold as all get out this weekend, I'll get the OP a couple of short clips so he can compare.
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