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Post by Magic Dragon on Feb 3, 2024 9:17:29 GMT -7
My 2014 Racing Stripe has not been modded and doesn't have it.
The photos I've seen of the new PPIMV Ghia's don't have it.
Anyone know when it was removed from the circuit and why?
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wally
Junior Member
Posts: 53
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Post by wally on Feb 3, 2024 11:54:54 GMT -7
My 2013 racing stripe Carmen Ghia does not have the conjunctive filter. It also has the 2.2m NFB resistor.
I might have to change that???
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Post by bubs42 on Feb 4, 2024 8:39:52 GMT -7
So just an interjection. I have 3 Gold Plate Z28’s and have owned 3 early route 66’s. I take gut shots of most of my old amps just as reference to see that when I bring another amp in I can tell if anything has been messed with. Well not one of the 6 amps is exactly the same, but I can’t say that without putting them right next to each other they sound any different. If they do it’s very minor or subtle.
If it sounds good, it sounds good.
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Post by Magic Dragon on Feb 4, 2024 12:10:43 GMT -7
So just an interjection. I have 3 Gold Plate Z28’s and have owned 3 early route 66’s. I take gut shots of most of my old amps just as reference to see that when I bring another amp in I can tell if anything has been messed with. Well not one of the 6 amps is exactly the same, but I can’t say that without putting them right next to each other they sound any different. If they do it’s very minor or subtle. If it sounds good, it sounds good. I am an engineer who has built, modded, repaired tube amps as a hobby since the late 1980s. While I appreciate that layouts and minor component adjustments occur, that is not the case here. For example: I own 2 Maz 18s, both factory updated to MKII spec. They each have different plate to cathode (dull/snubber) cap values on V1. I believe the updates and voicing are tailored to some degree to the desires of the owner paying for the update. In the case of the Ghia, and the Hammond AO-35 on which it is based, there is a conjunctive filer across the output transformer's primary winding. The purpose of this corrective network has been explained by Dr. Z himself in interviews and on this forum. I began looking into this because my 2014 Ghia sounds very different than a friend's 2000 Ghia. Mine is much brighter and becomes increasingly so as the amp is overdriven. In reviewing both amps, I discovered that mine is missing the conjunctive filter circled in the picture of the 2011 Ghia in my first post. This is not a minor component adjustment. This is a removal of a complete circuit from the amplifier that Doc has stated in a Tonequest interview: "affects the primary impedance of the transformer and allows frequencies to be very flat, or balanced. From say, 100Hz to 3K,". It appears, from the photos I can find, and Wally's post here, that the conjunctive filter circuit was removed from the amp sometime between 2012-2013. As has been documented, the amp had been revised 4 times previously to this latest revision, which appears to be an intentional revoicing of the amp. I suspect it may have been removed because more and more players wanted that "Vox chime" and this modification gives that in spades. I have also read of issues related to capacitor failure in the circuit associated with power tube failure. Thus, it may have been removed to enable the ETL certification of the amps. It is a straightforward modification to add it back into the circuit. I just thought I'd ask here to see if anyone knew of when (now established by Wally's post) and why the change was made. |
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Post by DRZ on Feb 4, 2024 15:37:17 GMT -7
As I recall it was in mid 2011.
My amps were going through ETL Certification , and it was removed on request of the examiners .
Even though it was safe , the possibility of failure could have been serious , and considered a safety issue.
Z
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Post by Magic Dragon on Feb 4, 2024 19:20:01 GMT -7
As I recall it was in mid 2011. My amps were going through ETL Certification , and it was removed on request of the examiners . Even though it was safe , the possibility of failure could have been serious , and considered a safety issue. Z Thank you. I think I'm going to clip it back in and see how I like the sound. The Ghia is one of my favorite amps clean but I don't much get on with it overdriven. |
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Post by prefsnider on Jul 5, 2024 10:47:25 GMT -7
Interesting. I just got an '08 Ghia in for repair and the CF resistor is open and appears to have been very overheated. What is the correct value of this resistor and a recommended wattage? Thx! Pete / Dutchman Ampworks Llc
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wally
Junior Member
Posts: 53
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Post by wally on Jul 5, 2024 13:20:53 GMT -7
The Phoenix schematic for the Carmen Ghia calls for a 10K/5watt resistor and a .0022mfd cap. The Hammond AO-35 schematic calls for a 10k and a .0022mfd.
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Post by prefsnider on Jul 5, 2024 16:45:42 GMT -7
Thanks. I found the Phoenix schematic. I'll probably go with the 10k as the cap is an 0.0022 mfd OD. The resistor in this Ghia is a much smaller wattage, like a 2W. Maybe that's why it overheated over the years. I believe the Ghia is from 2008. Thx again!
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wally
Junior Member
Posts: 53
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Post by wally on Jul 5, 2024 19:05:41 GMT -7
It would be a good time to compare the ‘before and after’. My 2013 does not have the filter. I am curious
As to the difference. Maybe something in the high end when the amp is pushed? The filter keeps that in check?
I have not experienced that difference…if it is there, but Inhave read people assert that the filter stabilizes the high end.
Curious, I am.
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Zed
Full Member
Posts: 236
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Post by Zed on Jul 7, 2024 9:53:34 GMT -7
As I recall it was in mid 2011. My amps were going through ETL Certification , and it was removed on request of the examiners . Even though it was safe , the possibility of failure could have been serious , and considered a safety issue. Z Thank you. I think I'm going to clip it back in and see how I like the sound. The Ghia is one of my favorite amps clean but I don't much get on with it overdriven. when I clipped mine out of the circuit, it opened up the tone a bit. Major difference to my ears. Less compression maybe? Let us know how you like it! |
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Post by Magic Dragon on Jul 8, 2024 16:35:40 GMT -7
Thanks. I found the Phoenix schematic. I'll probably go with the 10k as the cap is an 0.0022 mfd OD. The resistor in this Ghia is a much smaller wattage, like a 2W. Maybe that's why it overheated over the years. I believe the Ghia is from 2008. Thx again! These are the correct values. From the amps I've seen, the resistor was increased to a 5 watt ceramic in later amps with a 0.0022uf 2kV ceramic cap. |
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Post by Magic Dragon on Jul 8, 2024 16:39:43 GMT -7
Thank you. I think I'm going to clip it back in and see how I like the sound. The Ghia is one of my favorite amps clean but I don't much get on with it overdriven. when I clipped mine out of the circuit, it opened up the tone a bit. Major difference to my ears. Less compression maybe? Let us know how you like it! I like the amp more when overdriven with the filter. It does cut some of the chime but I dont really miss it. Before the filter the Ghia was the brightest amp I own - brighter than my AC15. It sounded great, never harsh, but it had more than enough treble to last a lifetime. I play a Tele so I can afford to dial back the top end and not miss it. |
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Post by DRZ on Jul 10, 2024 11:56:51 GMT -7
Just for a little clarification on the Conjunctive Filter on the Ghia.
As you know the Ghia was based on a Hammond Organ reverb amp mounted in a B 100 console organ.
Now it drove a spring reverb unit which has limited frequency bandwidth, hence the filter cut highs and lows giving a somewhat flat mid centric drive signal. This was actually nice for overdriven tones on the Ghia, but limited the clean frequency response .
Removing the filter opened up the Ghia's response displaying its gorgeous rich clean tones.
In engineering you never get anything for nothing , gain one way lose other always a trade off.
Z
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Post by Magic Dragon on Jul 10, 2024 16:56:44 GMT -7
I just want to chime in here and second what Dr. Z has said: everything has a trade off. I'm not advocating for modding these (or any other) amps. Too many people do that because of something they read online, without knowledge of what they are doing to the circuit. I deleted the photo post of my modded amp so as not to encourage others. I'm an engineer in the electrical power generation industry. I was taught tube electronics in the 80s by a retired NASA telecommunications engineer. I have a fundamental understanding of what this corrective network does in this circuit from an engineering perspective. You will lose some of the very unique and amazingly beautiful high-end in the Ghia with this network installed. In my specific use case, I play a Telecaster 90% of the time, I found the amp to work better, to my ears, for mild overdrive, with this filter installed. The trade off is the clean isn't as brilliant. I can live with that trade off knowing that I have the skills to revert the amp to its original condition at any time should my needs change. There are other non-sonic trade offs of this filter that Doc has already mentioned in this thread. So, don't mod your Ghia. Love it for what it is. It is a very special amp. Frankly, I am amazed at how gracious Doc has been with this discussion and I am grateful for his input here and on other forums over the years. It's one of the reasons I buy and play Dr. Z amps. I'm also that one guy who was bummed when colored cabs were discontinued -although I must admit I prefer my Z-28 and Jetta in black.     |
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Post by detuned on Jul 10, 2024 17:50:24 GMT -7
I miss the colors too.
Okay, really just the red - really made the line stand out, IMO. But I get why the Doc did it. Gotta stay solvent!
Another appreciation from me for the Doc - he's always been generous with the knowledge and the insights.
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Post by darwinh on Jul 11, 2024 6:31:55 GMT -7
Just for a little clarification on the Conjunctive Filter on the Ghia. As you know the Ghia was based on a Hammond Organ reverb amp mounted in a B 100 console organ. Now it drove a spring reverb unit which has limited frequency bandwidth, hence the filter cut highs and lows giving a somewhat flat mid centric drive signal. This was actually nice for overdriven tones on the Ghia, but limited the clean frequency response . Removing the filter opened up the Ghia's response displaying its gorgeous rich clean tones. In engineering you never get anything for nothing , gain one way lose other always a trade off. Z . Could a mod be offered to add a switch to bring it in or out of the circuit? |
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Post by Don A on Jul 11, 2024 7:16:50 GMT -7
Just for a little clarification on the Conjunctive Filter on the Ghia. As you know the Ghia was based on a Hammond Organ reverb amp mounted in a B 100 console organ. Now it drove a spring reverb unit which has limited frequency bandwidth, hence the filter cut highs and lows giving a somewhat flat mid centric drive signal. This was actually nice for overdriven tones on the Ghia, but limited the clean frequency response . Removing the filter opened up the Ghia's response displaying its gorgeous rich clean tones. In engineering you never get anything for nothing , gain one way lose other always a trade off. Z . Could a mod be offered to add a switch to bring it in or out of the circuit? I was thinking the same thing! |
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Post by premiumplus (Dave) on Jul 11, 2024 7:30:10 GMT -7
Could a mod be offered to add a switch to bring it in or out of the circuit? I was thinking the same thing! It could be done, but it's probably not a great idea because you're switching high voltage. |
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Post by Don A on Jul 11, 2024 11:36:29 GMT -7
I was thinking the same thing! It could be done, but it's probably not a great idea because you're switching high voltage. I looked it up and see that now. Thanks! |
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Post by darwinh on Jul 13, 2024 6:51:50 GMT -7
The Zwreck switches high voltage on the speed and comfort switch. 300v and 330v plate voltage.
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Post by KeithA on Jul 13, 2024 6:58:21 GMT -7
Just to sidetrack a bit……
I know I’m in the minority, but the racing stripe Ghia looks the best of all Ghias 😉
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Post by DRZ on Jul 13, 2024 8:19:34 GMT -7
The Zwreck switches high voltage on the speed and comfort switch. 300v and 330v plate voltage. Not the same circuits or application. Z Wreck switches between two different voltage supplies to the rectifier/power supply circuit via a toggle switch. If applied to the conductive filter it would attempt to switch a RC network to the high voltage plates of the output tubes , not easily or safely done. Z |
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Post by Magic Dragon on Jul 13, 2024 10:24:38 GMT -7
Just to sidetrack a bit…… I know I’m in the minority, but the racing stripe Ghia looks the best of all Ghias 😉 Agreed. |
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Post by Mark (Basement Enthusiast) on Jul 13, 2024 14:40:59 GMT -7
Just to sidetrack a bit…… I know I’m in the minority, but the racing stripe Ghia looks the best of all Ghias 😉 Yes, but any of the red-tolex ones SOUND the best.  |
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Post by GuitarZ on Jul 13, 2024 15:42:39 GMT -7
Just to sidetrack a bit…… I know I’m in the minority, but the racing stripe Ghia looks the best of all Ghias 😉 Well, maybe standard dress. But, if we're talking about custom work, I'm partial to my Ghia's look with Harvey's woodwork and my wife's Z logo placement.  |
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wally
Junior Member
Posts: 53
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Post by wally on Jul 14, 2024 17:01:43 GMT -7
Just to sidetrack a bit…… I know I’m in the minority, but the racing stripe Ghia looks the best of all Ghias 😉 Agreed. |
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