classd4sure said:
I totaly agree regarding your discription of the FC's!
It seems you can't live without the extra bass clout and I can't live with that midrange🙂
I've got some more caps on order so I'll let you know how they sound when they arrive
t and Chris,
I'm getting near to doing a mod of the supply bypass caps on my very new version UcD400's.
I've got on hand:
FC 470uF 100V
FC 470uF 63V
FC 680uF 100V
Panasonic M series (someone commented they thought these were best some time back.)
470uF 100V
1000uF 100V
I guess I gapped and didn't get the 1000uF FC's. Chris's opinion earlier might have turned me off of these.
The 63V FC 470 is half the size, so I suspect lower inductance.
I'm thinking this might be a good try.
I am rather un-impressed with the low end. Its musical and all that, but with 4 sensitive 15 inch woofers... Its not the most authoritive low end I've heard.
Any comment on what to try first?
How long is break in take?
I also got some high power 100mohm resistors to try negative output impedance which I'm looking forward to also.
Should be quite simple with the IA front end.
I'm going to get a couple more UcD400's ultamately for some lab amps at work, but in the mean time... ;>)
Does anyone have experience or heard good or bad on the Avel Y23 family of toriods?
Thanks,
Mike
I'm getting near to doing a mod of the supply bypass caps on my very new version UcD400's.
I've got on hand:
FC 470uF 100V
FC 470uF 63V
FC 680uF 100V
Panasonic M series (someone commented they thought these were best some time back.)
470uF 100V
1000uF 100V
I guess I gapped and didn't get the 1000uF FC's. Chris's opinion earlier might have turned me off of these.
The 63V FC 470 is half the size, so I suspect lower inductance.
I'm thinking this might be a good try.
I am rather un-impressed with the low end. Its musical and all that, but with 4 sensitive 15 inch woofers... Its not the most authoritive low end I've heard.
Any comment on what to try first?
How long is break in take?
I also got some high power 100mohm resistors to try negative output impedance which I'm looking forward to also.
Should be quite simple with the IA front end.
I'm going to get a couple more UcD400's ultamately for some lab amps at work, but in the mean time... ;>)
Does anyone have experience or heard good or bad on the Avel Y23 family of toriods?
Thanks,
Mike
Dear Chris:
Not yet. I was planning to.
See, the small caps that I'm talking about may well be "signal coupling caps " instead. I'm not sure. They are located after the signal input connector at UCD180ST PCB. If they are coupling caps I will make super E-caps with 2* 4.7 or 2*10uF BG N type.
The small decoupling caps on UCD400 are located to the right side of the PCB as per a recently posted photo (Matjans I think)
We need some photos or diagrams to better communicate 🙁
I don't have a camera (better spend money on caps )
I don't think so. The HF noise was present before the mod (and was one of the reason for trying it). The HF noise from my UCD400 was worse than that of UCD180 and was cured with the change in PS wiring. The noise on UCD180 is some ringing on extreme HF. Quite annoying. 😡
Fortunatelly, I learn more from mistakes than from success 😉
This week I expect to build a "technical balanced isolation transfomer". If I succed, maybe I could try to float de PS and ground the signal again.
Wish me luck as I do over you 😉
Best regards
Mauricio
Not yet. I was planning to.
See, the small caps that I'm talking about may well be "signal coupling caps " instead. I'm not sure. They are located after the signal input connector at UCD180ST PCB. If they are coupling caps I will make super E-caps with 2* 4.7 or 2*10uF BG N type.
The small decoupling caps on UCD400 are located to the right side of the PCB as per a recently posted photo (Matjans I think)
Maybe you talk about the small caps that flank the T piece. Yes, I'm aware that one pair of them, the nearest one to the T piece(?) , has a critical role in damping resonance. I wouldn't touch them. (at least before I get a scope and learn to use it)
We need some photos or diagrams to better communicate 🙁
I don't have a camera (better spend money on caps )
I don't think so. The HF noise was present before the mod (and was one of the reason for trying it). The HF noise from my UCD400 was worse than that of UCD180 and was cured with the change in PS wiring. The noise on UCD180 is some ringing on extreme HF. Quite annoying. 😡
Fortunatelly, I learn more from mistakes than from success 😉
This week I expect to build a "technical balanced isolation transfomer". If I succed, maybe I could try to float de PS and ground the signal again.
Wish me luck as I do over you 😉
Best regards
Mauricio
I really hope we can come up with something.
If I'm totally honest my AvondaleNCC200 bass is far better than my UCD180 although the detail of the UCD180 is better.
When I fitted the higher capacitance FC's the bass of my UCD180 had more clout but it lost out on speed and realism compared to the AvondaleNCC200 and still not as deep
Its only my opinion of course🙂
If I'm totally honest my AvondaleNCC200 bass is far better than my UCD180 although the detail of the UCD180 is better.
When I fitted the higher capacitance FC's the bass of my UCD180 had more clout but it lost out on speed and realism compared to the AvondaleNCC200 and still not as deep
Its only my opinion of course🙂
Portlandmike said:
Hi Mike,
Can't tell you w which to try first. Might be an idea to change them in one module at a time so you can compare to a control if you will. Also perhaps you can test the self resonance of the two FC's, to determine inductance. I think it's determined mostly by lead spacing but understand it can vary with winding technique. Overall height may play no other factor than bigger=slower. Very much lookin forward to your results. It might be an idea to change filter caps first in order to better hear the decoupling caps, but again I don't know what kind of cap is used on the 400 these days. Just don't think much of the stacked film (white/yellow).
maxlorenz said:
Ah, those are perhaps better called coupling caps, since they AC couple the signal. What version module do you have? There was some problem awhile back with EMI on them, from a bad connection to the decoupling cap which connects to the T-sink, makes it more of a transmitter. You could be suffering heterodyn issues, but then you have monoblocks.. or maybe your source isn't decoupled very well and noise is feeding through that way.. maybe try a different one.
classd4sure said:
Chris,
You ask me awhile back what the new UcD400's ship with.
I couldn't see anything very well without taking the module out.
I can say its red. That's about it for now. I have no idea what it is. I guess I could ask Hypex.
Any recommendations on where to buy a filter cap that is shown to work good. I'd be up for the experiement.
Thanks Chris 🙂
It must be heterodyning then !!! (now that I know what this is 😀 )
It sounds like a ringing tone 😡
Maybe I can re-solder the caps while I wait for the BG's.
Any other easy to implement remedy? (like dividing panels)
Is Jan Peter around? 😉
Actually my UCD180 are stereo and my UCD400 are mono...sorry for the confusion
I think UCD180ST V2.2. I'll check.
Many thanks for your kind interest and help.
Mauricio
It must be heterodyning then !!! (now that I know what this is 😀 )
It sounds like a ringing tone 😡
Maybe I can re-solder the caps while I wait for the BG's.
Any other easy to implement remedy? (like dividing panels)
Is Jan Peter around? 😉
Actually my UCD180 are stereo and my UCD400 are mono...sorry for the confusion
I think UCD180ST V2.2. I'll check.
Many thanks for your kind interest and help.
Mauricio
maxlorenz said:Thanks Chris 🙂
It must be heterodyning then !!! (now that I know what this is 😀 )
It sounds like a ringing tone 😡
Maybe I can re-solder the caps while I wait for the BG's.
Any other easy to implement remedy? (like dividing panels)
Is Jan Peter around? 😉
Actually my UCD180 are stereo and my UCD400 are mono...sorry for the confusion
I think UCD180ST V2.2. I'll check.
Many thanks for your kind interest and help.
Mauricio
Hi,
I can't say if that's the affected version but it sounds like about that era anyway. Usually heterodyne effect is described as a whistle, but as you looked it up it's just the difference in switching frequencies falling into the audio band, brought on by EMI, I can see that described as a HF ring.
Unless it's been changed you can see the SMT cap in question right next, and connected to, the screws which fasten the T-sink to the board. Make sure the screws are snug (don't crack your board) have a low resistance to the T-sink, check resistance from the screw to the nearest side of the cap and from the opposite side of the cap to ground. Check for bad solder joints or just touch them up easily enough.
Makes alot more sense this would be the problem knowing it's stereo now. Get that fixed and I doubt you'll have the need for panels/extra shielding or anything like it, because normally they're extremely low EMI modules.
If that doesn't help perhaps email JP about it he might have the exact fix for you.
BTW it's been said that a good film cap can be better for coupling than even BG's... something worth experimenting with I think.
Hi Mike,
Break in period for the FC's as I experienced was next to none.
I was very suprised by this. Certainly their sound changed some over the course of about a day, but very subtle and they didn't have the usual harshness I've come to know with a new electrolytic.
They'll break in faster if you drive them harder too.
I too have highly sensitive (102dB) 15" woofers (just two though) and you can see why I prefer feeling the bass with the FC's, anything less just doesn't seem right.
The bass is now as tight and controlled as before, only with some real grunt /thunder behind it, I like it!
As far as output cap any polypropylene is a good contender. I opted for film/foil instead of metallized, but whatever you can find that looks right for the job. Try to keep it less than 10mm lead pitch to keep loop inductance down, mine is 12.5 and I can live with it.
See what digikey has for you. I'm very happy with my selection of cap but it's only 50V so I don't think it's a great choice for the 400.
Break in period for the FC's as I experienced was next to none.
I was very suprised by this. Certainly their sound changed some over the course of about a day, but very subtle and they didn't have the usual harshness I've come to know with a new electrolytic.
They'll break in faster if you drive them harder too.
I too have highly sensitive (102dB) 15" woofers (just two though) and you can see why I prefer feeling the bass with the FC's, anything less just doesn't seem right.
The bass is now as tight and controlled as before, only with some real grunt /thunder behind it, I like it!
As far as output cap any polypropylene is a good contender. I opted for film/foil instead of metallized, but whatever you can find that looks right for the job. Try to keep it less than 10mm lead pitch to keep loop inductance down, mine is 12.5 and I can live with it.
See what digikey has for you. I'm very happy with my selection of cap but it's only 50V so I don't think it's a great choice for the 400.
image, harmonic richness ????
Hi dears,
First a question: I got two 35-0-35V 650VA high grade adio toroidals from Avondal Audio. I would like to test what happens with UCD180st. Do I am forced to use fuses or some other current protection? Which one would be the best solution?
I stopped to make experiments with UcD180 but I want to stat again. I play mainly records and I don't fell very happy with ucd (and class D/T in general) when I play my analgue sources. If I listen to the UCD for some reason when I go from the CD to the LP I fell something is missing. It is like the sound becomes "more digital". My impression is that there is some loss in harminic richness. So this is a bad point for me. It would be interesting to hear from you about that.
The other point is that these amps are extremely able to give an incredible sound stage. All musicians are placed in a well defined place of the room, the position of the instruments is quite stable at least in the song. For example I was listening to Nirvana (Never Mind, LP), in all songs all the cymbals were playing in the same point of the space, the voice is always there, the guitar takes all the stage, and this is constant accross the traks.
Third point: I think our discussion is not very productive if we do not mention the system we are using. For example I have read about lack of basses, mids etc. But which speaker are you using? If we are playing a couple of wonderful Rogers LS... there is no way to reach 20Hz flat, isn't it? So we should be a little bit more precise when we judge frequency response.
Bye
KEPha
Hi dears,
First a question: I got two 35-0-35V 650VA high grade adio toroidals from Avondal Audio. I would like to test what happens with UCD180st. Do I am forced to use fuses or some other current protection? Which one would be the best solution?
I stopped to make experiments with UcD180 but I want to stat again. I play mainly records and I don't fell very happy with ucd (and class D/T in general) when I play my analgue sources. If I listen to the UCD for some reason when I go from the CD to the LP I fell something is missing. It is like the sound becomes "more digital". My impression is that there is some loss in harminic richness. So this is a bad point for me. It would be interesting to hear from you about that.
The other point is that these amps are extremely able to give an incredible sound stage. All musicians are placed in a well defined place of the room, the position of the instruments is quite stable at least in the song. For example I was listening to Nirvana (Never Mind, LP), in all songs all the cymbals were playing in the same point of the space, the voice is always there, the guitar takes all the stage, and this is constant accross the traks.
Third point: I think our discussion is not very productive if we do not mention the system we are using. For example I have read about lack of basses, mids etc. But which speaker are you using? If we are playing a couple of wonderful Rogers LS... there is no way to reach 20Hz flat, isn't it? So we should be a little bit more precise when we judge frequency response.
Bye
KEPha
perspective
Kepha,
This sometimes, in fact most of the time, happens when we change out a component in our systems for a more revealing one. The UcD amps just let through a lot more information and sometimes they are uncovering flaws somewhere else that you weren’t aware of. If you are addicted to the “tube” sound there is no hope as you will not get this with the UcD’s. Some have used tube preamps to help recreate this sound but all this is just getting further away from the musical truth! It is true that almost all of the available recorded material is crap and we can’t do much about that. Once in a while we will uncover a gem and this will make it all worthwhile. I personally do not want my equipment to edit the material in any way, I just want to hear what is on the disk and nothing else. The UcD’s do get me closer to this goal than any other amp I have ever worked with.
Roger
Kepha,
This sometimes, in fact most of the time, happens when we change out a component in our systems for a more revealing one. The UcD amps just let through a lot more information and sometimes they are uncovering flaws somewhere else that you weren’t aware of. If you are addicted to the “tube” sound there is no hope as you will not get this with the UcD’s. Some have used tube preamps to help recreate this sound but all this is just getting further away from the musical truth! It is true that almost all of the available recorded material is crap and we can’t do much about that. Once in a while we will uncover a gem and this will make it all worthwhile. I personally do not want my equipment to edit the material in any way, I just want to hear what is on the disk and nothing else. The UcD’s do get me closer to this goal than any other amp I have ever worked with.
Roger
KEPha,
I have found a similar issue with the UcD400's.
I find them very good at stage presentation with CD's. They work well for that, and I like them.
what rather suprises me is that I don't notice the big improvement I use to get in SACD's. They sound rather the same as CD's. The other day, I actually bothered to listen to a disk with both formats, and there wasn't much difference. In the past, with a wideband solid stage amp, it was much more significant.
So, perhaps its not that records suck, but something else.
I've also noted that although the UcD's really stage wonderfully, and perhaps deeper than I've experienced, they seem to lack the live dynamic element. (any recommended mod's would be appreciated.)
That all said, to the defence of the UcD's, I'm about to place an order for 5~7 more amps this week, so I guess i'm not to disapointed. Bottom line is I mostly listen to red book, and hey, the amps are very entertaining.
Best Regards,
Mike
I have found a similar issue with the UcD400's.
I find them very good at stage presentation with CD's. They work well for that, and I like them.
what rather suprises me is that I don't notice the big improvement I use to get in SACD's. They sound rather the same as CD's. The other day, I actually bothered to listen to a disk with both formats, and there wasn't much difference. In the past, with a wideband solid stage amp, it was much more significant.
So, perhaps its not that records suck, but something else.
I've also noted that although the UcD's really stage wonderfully, and perhaps deeper than I've experienced, they seem to lack the live dynamic element. (any recommended mod's would be appreciated.)
That all said, to the defence of the UcD's, I'm about to place an order for 5~7 more amps this week, so I guess i'm not to disapointed. Bottom line is I mostly listen to red book, and hey, the amps are very entertaining.
Best Regards,
Mike
Hi KEPha 🙂
And...
Very good point. In my view, UCD's are so inexpensive 🙂cool: 😀 )
that we can and must enter the "active speaker system" world.
In my secondary system I use: a very cheap Behringer active crossover; two stereo UCD180 amps; cheap Paradigm M3 for midrange and HF plus DIY 15'' Eminence woofers.
I can't blame it for lack of bass of "live sound". On the contrary, even studio recordings sound "live". Of course I want now upgrade every step of it to increase refinement also.
My primary system uses:
CDPRO->DIP upsampler->superregualted M-audio superDAC->TVC->UCD400 mono's->Tannoy Definition 500.
I mention the source because there is where the bass is retrieved 😀
I don't feel lack of bass but dynamic contrast are not as powerful as in my active system, yet the sound is on another level for transparency, detail and definition. I am comparing a speaker that used to cost +/- USD 2500 v/s a USD 300 active speaker system 😎
When warranty expires I will convert my beloved Tannoy to active speakers! 😀 😀 That is IF I still have them.
That said, I think the opinions about subjective change of sound with caps or R and even wire are valid, at least on a relative manner. You willl have to adapt this new "knowledge" to your own system in order to predict behaviour.
For example, I don't like Panasonic FC in DAC's so I won't use them here (and I'm waiting for other mates that find a better solution 😀 ).
In contrast, I'm using OCC copper wire for hook up signal and I'm quite happy with it 🙂
Best wishes.
Mauricio
And...
Very good point. In my view, UCD's are so inexpensive 🙂cool: 😀 )
that we can and must enter the "active speaker system" world.
In my secondary system I use: a very cheap Behringer active crossover; two stereo UCD180 amps; cheap Paradigm M3 for midrange and HF plus DIY 15'' Eminence woofers.
I can't blame it for lack of bass of "live sound". On the contrary, even studio recordings sound "live". Of course I want now upgrade every step of it to increase refinement also.
My primary system uses:
CDPRO->DIP upsampler->superregualted M-audio superDAC->TVC->UCD400 mono's->Tannoy Definition 500.
I mention the source because there is where the bass is retrieved 😀
I don't feel lack of bass but dynamic contrast are not as powerful as in my active system, yet the sound is on another level for transparency, detail and definition. I am comparing a speaker that used to cost +/- USD 2500 v/s a USD 300 active speaker system 😎
When warranty expires I will convert my beloved Tannoy to active speakers! 😀 😀 That is IF I still have them.
That said, I think the opinions about subjective change of sound with caps or R and even wire are valid, at least on a relative manner. You willl have to adapt this new "knowledge" to your own system in order to predict behaviour.
For example, I don't like Panasonic FC in DAC's so I won't use them here (and I'm waiting for other mates that find a better solution
😀 ). In contrast, I'm using OCC copper wire for hook up signal and I'm quite happy with it 🙂
Best wishes.
Mauricio
When I talk about "lack of bass" it isn't the speakers, its a relitive thing, and one I'd guess you'd even hear on a 6 inch two way if you were use to it.
My only system hooked up right now is:
Sony SACD 777
Gold Point passive stepped attenuator.
UcD400AD
JBL4435.
Chris,
A couple of questions for you.
What toriod did you use in your UcD400 that you posted pics on lately?
Have you heard anything bad about the Avel Y23 series?
Did you use OCC for your UcD400 too?
How do the UcD180 sound in comparison, pretty much the same?
Thanks
Mike
My only system hooked up right now is:
Sony SACD 777
Gold Point passive stepped attenuator.
UcD400AD
JBL4435.
Chris,
A couple of questions for you.
What toriod did you use in your UcD400 that you posted pics on lately?
Have you heard anything bad about the Avel Y23 series?
Did you use OCC for your UcD400 too?
How do the UcD180 sound in comparison, pretty much the same?
Thanks
Mike
Wow, Mike, what a speaker! 😀
I will build in the next few months my beloved Tannoy Autograph for replacing my present "active speakers".
In fact I opened a thread for this:
http://www.diyaudio.com/forums/showthread.php?threadid=74241&highlight=
😀
Very pretty the Goldpoint.
Did you ever considered a transformer based passive? With the right source (high Vout) they are a perfect match for UCD's, IMHO.
Sorry, is this question for me? If yes, the answer is yes.
I find it "sounds" quite transparent, punchy and colourfull, not as transparent as silver but much enjoyable at last (compared in other circuit).
Kind regards.
Mauricio
I will build in the next few months my beloved Tannoy Autograph for replacing my present "active speakers".
In fact I opened a thread for this:
http://www.diyaudio.com/forums/showthread.php?threadid=74241&highlight=
😀
Of course, the speaker only does what it is ordered to do 😉
Very pretty the Goldpoint.
Did you ever considered a transformer based passive?
With the right source (high Vout) they are a perfect match for UCD's, IMHO.Sorry, is this question for me? If yes, the answer is yes.
I find it "sounds" quite transparent, punchy and colourfull, not as transparent as silver but much enjoyable at last (compared in other circuit).
Kind regards.
Mauricio
maxlorenz said:Very pretty the Goldpoint.
Did you ever considered a transformer based passive?
Kind regards.
Mauricio
Mauricio,
I like the JBL 4435 speakers. They seem to do it all w/o effort.
Someday I"d like to try to biamp them and my own active crossover to shape the horn, but then after my experience with caps, yuk. Then again, I guess the crossover has them too. 😉
I've also got some JBL 4343's and 4315's. I went a bit nuts on JBL for awhile.
Haven't really heard of transformer based passive before.
Is it like a wiper on an auto transformer or something?
I got the version that has only two resistors in the path at any time. I upgraded the resistors from the dales to, but I can't recall what they are. Roderstiens maybe? I actually don't like passive preamps I've decided. The problem is the UcD is kind of a bitch to AC couple with no offset. I haven't been as happy with my two transistor buffer since I AC coupled it. In the past, I prefered it.
I have a plan to do a simple AD8620 single ended preamps. A thought is, if I do that, and add some gain, then I could bypass the AD8620 in the UcD. More gain, earlier and away from the big power.
Mike
Help with offset
Hi guys,
Perhaps not the right thread, but I didn't want to start a new one.
One of My rev 5 UcD400's is showing an offset of 16~20mV DC.
The other one reads dead zero mV. I recall they actually were both really low, like .1mV.
I have shorted the ac coupling caps. And the offset doesn't change when I short the inputs.
Any ideas?
I also swear its off too, that's actually why I checked it.
All else I could think of looks sound, the rails measure 60V no load, the ripple is pretty much the same at 35mV both rails, Don't know what else to check without snooping on the board.
Thanks
Mike
Hi guys,
Perhaps not the right thread, but I didn't want to start a new one.
One of My rev 5 UcD400's is showing an offset of 16~20mV DC.
The other one reads dead zero mV. I recall they actually were both really low, like .1mV.
I have shorted the ac coupling caps. And the offset doesn't change when I short the inputs.
Any ideas?
I also swear its off too, that's actually why I checked it.
All else I could think of looks sound, the rails measure 60V no load, the ripple is pretty much the same at 35mV both rails, Don't know what else to check without snooping on the board.
Thanks
Mike
trafos
Hi folks,
I asked a question about a new trafo I am going to try... no one answerd. They are two Avondale 35-0-35 with 650VA, they are supposed to be top stuffs. Now my question is, can I use that trafo in a monoblock without current protections?
Let me know,
K
Hi folks,
I asked a question about a new trafo I am going to try... no one answerd. They are two Avondale 35-0-35 with 650VA, they are supposed to be top stuffs. Now my question is, can I use that trafo in a monoblock without current protections?
Let me know,
K
Hi Mike:
That's OK, man. Nobody will blame you 😉
It happens to me with Tannoy.
I've heard an old JBL (don't remember the model). Impressive with 6W SE tube amp, but I did not like the lack of integration between horn and woofer (of that one). Kind of different sound presentation.
Yours must be way better
Ahemm...😀 Maybe it's my time of paying back your efforts.
Volume control step down Transformers have multiple secondaries each with a different volume attenuation:
*They are not so sensitive to interconnect lenght.
*they can be configured to be totally balanced or totally unbalanced or change from one format to the other.
*compared to R attenuators they convert V to I with minimum heat (energy) loss so the lower the seting the better the bass sounds, IMHO, retaining good performance at low volumes.
*mine are Sevens&Billingtons with OCC copper windings, from Bentaudio.com where you can have more info.
http://www.bentaudio.com/index2.html
*You can DC couple the UCD's for more transparency. My UCD400 are DC coupled and I read 14mV offset. Do you find it high? 🙁
Unfortunatelly, they are not cheap (I bought mine before price increased 😉 ) . USD 550 plus selectors, connectors, wire and case.
Now they have many reviews if you like to read them. I don't have the guts to read the last 6moons review.
http://www.6moons.com/audioreviews/musicfirst/passive.html
Once heard the transparency of TVC I can go back to actives.
Sorry Kephaudio 🙁
Yes you will need a "soft start" for that big TX (and fuse(s) of course). I believe more than 250VA deserves one.
To save big money I use a simple 2 step power-on with a resistor (220R-20W) in parallel with the power cable: I power-on the R path, count to 8, ten power-on the real power path and power-down R path. Never fails (safe if children or spouse powers-on 😀 ).
I guess is 3 step, because then I power-on the amp module.
Cheers
Mauricio
That's OK, man. Nobody will blame you 😉
It happens to me with Tannoy.
I've heard an old JBL (don't remember the model). Impressive with 6W SE tube amp, but I did not like the lack of integration between horn and woofer (of that one). Kind of different sound presentation.
Yours must be way better
Ahemm...😀 Maybe it's my time of paying back your efforts.
Volume control step down Transformers have multiple secondaries each with a different volume attenuation:
*They are not so sensitive to interconnect lenght.
*they can be configured to be totally balanced or totally unbalanced or change from one format to the other.
*compared to R attenuators they convert V to I with minimum heat (energy) loss so the lower the seting the better the bass sounds, IMHO, retaining good performance at low volumes.
*mine are Sevens&Billingtons with OCC copper windings, from Bentaudio.com where you can have more info.
http://www.bentaudio.com/index2.html
*You can DC couple the UCD's for more transparency. My UCD400 are DC coupled and I read 14mV offset. Do you find it high? 🙁
Unfortunatelly, they are not cheap (I bought mine before price increased 😉 ) . USD 550 plus selectors, connectors, wire and case.
Now they have many reviews if you like to read them. I don't have the guts to read the last 6moons review.
http://www.6moons.com/audioreviews/musicfirst/passive.html
Once heard the transparency of TVC I can go back to actives.
Sorry Kephaudio 🙁
Yes you will need a "soft start" for that big TX (and fuse(s) of course). I believe more than 250VA deserves one.
To save big money I use a simple 2 step power-on with a resistor (220R-20W) in parallel with the power cable: I power-on the R path, count to 8, ten power-on the real power path and power-down R path. Never fails (safe if children or spouse powers-on 😀 ).
I guess is 3 step, because then I power-on the amp module.
Cheers
Mauricio
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