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Glass resistor mod and pairing amps in monoblock (Read 2099 times)
mk60
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Glass resistor mod and pairing amps in monoblock
03/17/23 at 16:19:09
 
I'm currently looking for a second SE84UFO25 to pair with my current one so that I can run them as monoblocks. My current unit has "glass" written on the label on the bottom of the unit, and it's also serial no. 35, so I assume that this means that it has the glass resistor upgrade that Steve used to offer with these.

Question: Would it be a bad idea to buy a second one that *doesn't* have the glass resistor upgrade if I'm going to run them together in mono? Will there be a mismatch in sonic signature?

(also if you have one and are thinking of selling soon, please do reach out!)
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Main System: Lumin U2 Mini->Denafrips Pontus II->ZTPRE->[2x SE84UFO25 in Differential Balanced Mono]->Klipsch La Scala AL5 + 2x REL 212/SX
Office System: Naim Uniti Atom->SE34I.5->Zu Dirty Weekend 6 Supreme
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bramar
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Re: Glass resistor mod and pairing amps in monoblock
Reply #1 - 03/17/23 at 17:59:47
 
This is very anectdotal, it’s my loose understanding that Steve said the glass resistor is a barely audible mod.

If it were me, I wouldn’t sweat it.

Brad
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mperdue63
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Posts: 139
Re: Glass resistor mod and pairing amps in monoblock
Reply #2 - 03/18/23 at 11:11:59
 
I have a pair of Anniversary amps configured in mono, one with glass mod, one without. There is not a noticeable difference that I can hear. Other differences between the amps are likely to be more apparent such as caps , volume control, etc. One of my amps has stepped volume and the other has smooth volume control and my CSP325 has dual volume control as well. Getting the volume or gain set is similar to operating a nuclear reactor control room during a meltdown! Extremely rewarding setup once you get it dialed in. I have a zrock in front of the CSP325 and I use it for volume changes.
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JBzen
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Re: Glass resistor mod and pairing amps in monoblock
Reply #3 - 03/18/23 at 12:51:59
 
Interesting mperdue63 on your comment of the task of gain riding. Using the Zrock as a volume control after setting the pre and amps seems like a good move.

In my case, the amp has no volume control. The Zbox and Csp2+ are the means of setting gain riding in the system. Been using the Cps2 main dual gang pot control to adjust volume. Have to give using the Zrock as a volume control after setting the others for general optimum performance a try.

Thanks Wink

John
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mperdue63
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Re: Glass resistor mod and pairing amps in monoblock
Reply #4 - 03/18/23 at 12:58:58
 
John,
I meant to say I use a ZBit to control volume, not a ZRock
Posting to early in the morning, lol
Malcolm
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LHY SW10}HiFi Rose 130RS}Holo Audio May KTE}Decware Sarah #003}Spatial Audio X5's
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mk60
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Re: Glass resistor mod and pairing amps in monoblock
Reply #5 - 03/18/23 at 22:49:02
 
Oof good point. The UFO25 I have is stepped, and it would be super convenient if the one I got to pair was also stepped volume. If not, I'd be tempted to just put both on max gain and attenuate with a pre, or the "lossless" digital vol control on my streamer.
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Main System: Lumin U2 Mini->Denafrips Pontus II->ZTPRE->[2x SE84UFO25 in Differential Balanced Mono]->Klipsch La Scala AL5 + 2x REL 212/SX
Office System: Naim Uniti Atom->SE34I.5->Zu Dirty Weekend 6 Supreme
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mk60
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Posts: 91
Re: Glass resistor mod and pairing amps in monoblock
Reply #6 - 04/03/23 at 01:18:58
 
I have a similar question (and suspect a similar answer, but I'll ask anyway): I've landed myself a second UFO25 to make a pair. I e-mailed Steve to ask if there are any component differences between my two amps (serials no 35 and 156) that would make any meaningful difference in sound. He mentioned that the early models (like my no 35) were built with "beeswax copper foil caps" and later models (like my no 156) were built with "Miflex caps, also copper foil".

Number 156 hasn't arrived yet, but I took a peek inside no 35, and saw a pair of Jupiter caps -- are these the beeswax caps that Steve was talking about, or are they maybe some of the less conspicuous looking caps? It's not completely obvious to me which caps are the ones in the signal path.

If it's the Jupiters, I'm curious why the Jupiters were changed to Miflex in later builds? Surely the Jupiters still have wide availability, so, is it that the Miflex are "better"? Curious to see if I'll be able to hear the difference once no 156 arrives! Even if not, my OCD may force me to swap out the caps in one to match the other..
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Main System: Lumin U2 Mini->Denafrips Pontus II->ZTPRE->[2x SE84UFO25 in Differential Balanced Mono]->Klipsch La Scala AL5 + 2x REL 212/SX
Office System: Naim Uniti Atom->SE34I.5->Zu Dirty Weekend 6 Supreme
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Lon
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Re: Glass resistor mod and pairing amps in monoblock
Reply #7 - 04/03/23 at 01:22:31
 
It is in fact the Jupiters that are the "beeswax" caps.

I think Steve cited unavailability in the quantities he needs as the reason for the move to Miflex but I'm not certain--I do remember him mentioning the move in the past on the forum. Perhaps a search of the forum may bring up his mention.

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HR-1,ZBIT,ZROCK2,SEWE300B,CSP3-25mod; Rega RP3 all GrooveTracer mods;PSAudio:PST+DSD, DAC Mk II, P15,NPC,PowerBases,AC-12 pwr cbls, Reference spkrcbls; Mapleshade SamsonV3; VooDoo:Cremona+Amati interconnects, IsoPods; headphones: Sennheiser HD800S,ZMF Ori,Oppo PM1
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