Chris - Problem solved. Thanks for your help.
I finally tracked down the problem to old flux/dirt between tracks on the main circuit board (i.e., the track between the 681 ohm resistor and the phono coupling cap, and the PSU bias track next to it). I realised last night that I'd set out the wrong resistance measurements above and so set out to re-measure them again to double-check my notes. Although the 681 ohm resistor measures at 680 ohms, the resistance to ground as measured between it and the phono coupling cap was only measuring at about 380 ohms, which told me where to look. There was nothing to see - no apparent bridges - but a quick 'scrape' between the tracks solved everything. I'm really surprised that this has surfaced now, but glad that it wasn't anything else - I was really tearing my hair out!
Lesson: when you buy second-hand equipment which looks as though it's been accumulating dust for most of its life and has never been cleaned, clean it carefully ...
Back to the capacitors - having checked out the cost of decent 3mF and 8mF capacitors, I'd rather change them for something smaller where I can. What would you suggest? Looking at the circuit, I think that I can leave the phono input and first stage coupling caps at 3mF, but change the phono output cap to 0.047mF as the 5.1 circuit has it. I think the input cap to the line stage could then be 1mF as could the final output coupling cap - this would still give me a -3dB point at 2hz (although my maths is probably wrong).
Stephen
I finally tracked down the problem to old flux/dirt between tracks on the main circuit board (i.e., the track between the 681 ohm resistor and the phono coupling cap, and the PSU bias track next to it). I realised last night that I'd set out the wrong resistance measurements above and so set out to re-measure them again to double-check my notes. Although the 681 ohm resistor measures at 680 ohms, the resistance to ground as measured between it and the phono coupling cap was only measuring at about 380 ohms, which told me where to look. There was nothing to see - no apparent bridges - but a quick 'scrape' between the tracks solved everything. I'm really surprised that this has surfaced now, but glad that it wasn't anything else - I was really tearing my hair out!
Lesson: when you buy second-hand equipment which looks as though it's been accumulating dust for most of its life and has never been cleaned, clean it carefully ...
Back to the capacitors - having checked out the cost of decent 3mF and 8mF capacitors, I'd rather change them for something smaller where I can. What would you suggest? Looking at the circuit, I think that I can leave the phono input and first stage coupling caps at 3mF, but change the phono output cap to 0.047mF as the 5.1 circuit has it. I think the input cap to the line stage could then be 1mF as could the final output coupling cap - this would still give me a -3dB point at 2hz (although my maths is probably wrong).
Stephen
This proves my motto in science investigations, problems in life and in fixing or modding audio equipment, most clearly:
"The more difficult the problem to solve, the more basic the mistake."
Meaning, if you can't solve a problem then there is definitely someting missing in your data or information. And that missing part is a VERY basic component. A 'root' issue.
For example, as you may recall, your very own eyeballs have a blind spot, and your brain creates data for it, that isn't actually there, at all. It is interesting to note, that no matter how intensely we may look at a thing to discern it, our very own brain/eye combination lies to us, fabricates for us - within that very moment-every waking moment.
In similar consideration, mistakes are made or issues missed. Microcosms and Macrocosms of -and in- life...
"The more difficult the problem to solve, the more basic the mistake."
Meaning, if you can't solve a problem then there is definitely someting missing in your data or information. And that missing part is a VERY basic component. A 'root' issue.
For example, as you may recall, your very own eyeballs have a blind spot, and your brain creates data for it, that isn't actually there, at all. It is interesting to note, that no matter how intensely we may look at a thing to discern it, our very own brain/eye combination lies to us, fabricates for us - within that very moment-every waking moment.
In similar consideration, mistakes are made or issues missed. Microcosms and Macrocosms of -and in- life...
Hi smf,
Great troubleshooting job! Way to go! About caps. You can get really good film type caps up to say 4u7 from Solen. 1 uF are common. Golden brand names are a complete waste of money.
Hi Ken,
A careful cleaning is always your first step. I just fixed a tuner with an intermittent. It turned out to be a solder ball between smt pins in the flux. A good tech always cleans up the board after working on it.
-Chris
Great troubleshooting job! Way to go! About caps. You can get really good film type caps up to say 4u7 from Solen. 1 uF are common. Golden brand names are a complete waste of money.
Hi Ken,
I have never seen a good technician stuck on a complex problem. It's aways the simple ones and normally not from a normal failure.
A careful cleaning is always your first step. I just fixed a tuner with an intermittent. It turned out to be a solder ball between smt pins in the flux. A good tech always cleans up the board after working on it.
-Chris
Chris,anatech said:
Any particular Solen series you recommend? I was looking at Auricap (just a single 1uf to replace C56 (currently the stock 8uf 200V Wonder cap in my pre). I can get a 1uf 425V Auricap for ~$9. These are metalised polypropylene. I note that I could also get a Solen SM 1uf 630V polypropylene film and tin foil cap for around the same price, which I would think would be a superior construction to the Auricap?
Thanks,
Chris (Pars)
Hi Chris,
Once you get to film / foil caps it's pretty much personal preference. I would think the Solen "fast" series would be good. I would tend to purchase Siemens or any brand like that. Going for a "name" like wondercap makes me think you are paying too much. Just my opinion and I could be wrong.
-Chris
Once you get to film / foil caps it's pretty much personal preference. I would think the Solen "fast" series would be good. I would tend to purchase Siemens or any brand like that. Going for a "name" like wondercap makes me think you are paying too much. Just my opinion and I could be wrong.
-Chris
Good film caps are actually important. After mucho testing, I have concluded that: although solen caps are far, far, far better than any electrolytic, they are like the 'heinz' (means: common, average, ordinary, regular, not special, etc) of film caps. Ie, nothing special. There are far better standard film caps out there, but their quality is partially reflected in the pricing. For example, Multicaps have fallen out of favor, but are notably better sounding than solen 'standard' film caps. The solen film and foil types are notably better than their standard variety. Hovland is good, etc. But pricey.
When it comes to squeezing your money for it's best value, the multicaps are actually, decently priced. However, a small bypass cap, specifically of very high current capacity or very low internal impedance, can work wonders. It's the high impedance bypass caps that cause issues. So, bypass caps on film caps should be of film and foil type, as the high frequency or, conversely, transient current capacity is unimpeded, which is the essence of what you look for in a 'bypass' capacitor. The uf value of that bypass capacitor, compared to the uf value of a given cap (that is being bypassed-this, as the two are expressed as a 'formula rule') being bypassed becomes less of an issue if this fundamental issue is adressed.
Smearing transients is the root issue, and the lower impedance bypass cap cuts that issue down in it's tracks, thus making for a 'actual effective bypass cap'. Wiring counts too, so only use the original leads of a bypass cap, if at all possible, and no extra wire and solder which could and is likely to notably compromise it's effectiveness. Make sure the wire leads are actually touching with a solid connection too, as solder as the primary electrical transfer point is a bad thing. ie, like cheap metal binding posts, they just plain sound bad. Very low electrical conductivity (a primary point of solder itself), and this point of understanding (not properly connected) can easily lower the effectiveness of your bypass cap by 50% or so. We use solder in our circuits, a better sounding circuit by far, would be a flash welded one. Hugely so. I don't think anyone has ever attempted such, due to potential damage to components. It would likely fail, unless the component choices were specifically chosen for their immunity to such problems. Then we'd hear something we've never heard before. Zero solder. That would be a good thing.
Capacitors, if analysed by the WHOLE signal being passed, have vanishingly low distortion, and it is therefore concluded by engineers looking solely at their instruments, that capacitors matter little in a circuit. Do not listen to their basic ignorance. They are not aware of the psychoacoustic reality of how the ear works. Any audiophile with a set of ears attached to an actual working brain 🙄, will realize something FAR different. Read on:
The whole idea is to not smear, delay, or tear the transients being passed by the capacitor combination. The human ear works by decoding transients, over time, in comparison to one another; this statement should make it suddenly and abundantly clear why the above considerations are important in film cap and bypass cap choices. Hidden within the specifications of given capacitors is the information that tells the sad tale of how their primary distortion factors are issues invoving the smearing and dislocation of transients. Just Like almost any item or component used in audio design, overall. The same rules or concerns involving transient control and quality can be applied to the entire circuit as a whole or in part, for a notable improvement in fidelity.
When it comes to squeezing your money for it's best value, the multicaps are actually, decently priced. However, a small bypass cap, specifically of very high current capacity or very low internal impedance, can work wonders. It's the high impedance bypass caps that cause issues. So, bypass caps on film caps should be of film and foil type, as the high frequency or, conversely, transient current capacity is unimpeded, which is the essence of what you look for in a 'bypass' capacitor. The uf value of that bypass capacitor, compared to the uf value of a given cap (that is being bypassed-this, as the two are expressed as a 'formula rule') being bypassed becomes less of an issue if this fundamental issue is adressed.
Smearing transients is the root issue, and the lower impedance bypass cap cuts that issue down in it's tracks, thus making for a 'actual effective bypass cap'. Wiring counts too, so only use the original leads of a bypass cap, if at all possible, and no extra wire and solder which could and is likely to notably compromise it's effectiveness. Make sure the wire leads are actually touching with a solid connection too, as solder as the primary electrical transfer point is a bad thing. ie, like cheap metal binding posts, they just plain sound bad. Very low electrical conductivity (a primary point of solder itself), and this point of understanding (not properly connected) can easily lower the effectiveness of your bypass cap by 50% or so. We use solder in our circuits, a better sounding circuit by far, would be a flash welded one. Hugely so. I don't think anyone has ever attempted such, due to potential damage to components. It would likely fail, unless the component choices were specifically chosen for their immunity to such problems. Then we'd hear something we've never heard before. Zero solder. That would be a good thing.
Capacitors, if analysed by the WHOLE signal being passed, have vanishingly low distortion, and it is therefore concluded by engineers looking solely at their instruments, that capacitors matter little in a circuit. Do not listen to their basic ignorance. They are not aware of the psychoacoustic reality of how the ear works. Any audiophile with a set of ears attached to an actual working brain 🙄, will realize something FAR different. Read on:
The whole idea is to not smear, delay, or tear the transients being passed by the capacitor combination. The human ear works by decoding transients, over time, in comparison to one another; this statement should make it suddenly and abundantly clear why the above considerations are important in film cap and bypass cap choices. Hidden within the specifications of given capacitors is the information that tells the sad tale of how their primary distortion factors are issues invoving the smearing and dislocation of transients. Just Like almost any item or component used in audio design, overall. The same rules or concerns involving transient control and quality can be applied to the entire circuit as a whole or in part, for a notable improvement in fidelity.
KBK - Thanks. I think I'll order a selection from Partsconnexion and experiment. There isn't a huge amount of space in the preamp and so I'm going to be pretty limited as to what I can get anyway.
Two further questions on caps:
- the PSU caps in the preamp are all the original pieces (Spragues bypassed by Wondercaps). The B+ voltages, etc. are all within spec. I'm tempted to leave these for now - sensible? (I'd eventually like to replace them with BGs or Jensens, but this is getting expensive.)
- I can't find replacement cap sizes in Hong Kong (or online) for the RIAA section of the phono section (20.6 nF and 7nF). Any ideas?
Chris - Some posts ago we talked about tube rolling being a waste of time if you can't measure distortion. After getting my preamp working again, I hooked it up to my PC to see whether I could use RMAA 5.5 to do this. Success (sort of as it was very difficult to get the volume/gain at the right level that RMAA wanted, such that I couldn't get to the right level for the phono section on its own). It was very, very interesting - the preamp was way out of alignment, with large amounts of 2nd, 3rd, 4th and 5th order distortion. After a couple of hours of tweaking, I've managed to reduce THD to c.0.3%. I could get the total a bit lower (c.0.2%) but at the cost of slightly increased 3rd and 4th order, whereas the higher amount had a bit more 2nd order but with lower 3rd and 4th order distortion (and lower total IMD). I'm now ready to try the EH6922s to see how I can improve on the old tubes. Do you have any tips as to the best compromises? Do I need to adjust both trimmers in the phono section or just the second one (as the manual suggests)?
I had thought that the preamp sounded good before I'd started adjusting for lower distortion, I was pleasantly surprised as to how much 'cleaner' and quieter it now sounds.
Stephen
Two further questions on caps:
- the PSU caps in the preamp are all the original pieces (Spragues bypassed by Wondercaps). The B+ voltages, etc. are all within spec. I'm tempted to leave these for now - sensible? (I'd eventually like to replace them with BGs or Jensens, but this is getting expensive.)
- I can't find replacement cap sizes in Hong Kong (or online) for the RIAA section of the phono section (20.6 nF and 7nF). Any ideas?
Chris - Some posts ago we talked about tube rolling being a waste of time if you can't measure distortion. After getting my preamp working again, I hooked it up to my PC to see whether I could use RMAA 5.5 to do this. Success (sort of as it was very difficult to get the volume/gain at the right level that RMAA wanted, such that I couldn't get to the right level for the phono section on its own). It was very, very interesting - the preamp was way out of alignment, with large amounts of 2nd, 3rd, 4th and 5th order distortion. After a couple of hours of tweaking, I've managed to reduce THD to c.0.3%. I could get the total a bit lower (c.0.2%) but at the cost of slightly increased 3rd and 4th order, whereas the higher amount had a bit more 2nd order but with lower 3rd and 4th order distortion (and lower total IMD). I'm now ready to try the EH6922s to see how I can improve on the old tubes. Do you have any tips as to the best compromises? Do I need to adjust both trimmers in the phono section or just the second one (as the manual suggests)?
I had thought that the preamp sounded good before I'd started adjusting for lower distortion, I was pleasantly surprised as to how much 'cleaner' and quieter it now sounds.
Stephen
Hi Stephen,
I have found the 6922EH a positive step for most gear that use 6DJ8's. I do recommend that you do a complete setup even when replacing the tube with the same type number and make. You have to look at tubes as being individuals.
Now you know how much a pain in the "keester" the alignment can be. RMAA does make the job easier. I'll venture a guess that most shops do not align these as required.
Also, you have correlated what I've been saying about "tube rolling". Counterpoint is capable of good performance if set up properly. Do yourself a favour and recheck your alignment periodically to make sure it's still on the mark.
I'm looking forward to your test results.
-Chris
I have found the 6922EH a positive step for most gear that use 6DJ8's. I do recommend that you do a complete setup even when replacing the tube with the same type number and make. You have to look at tubes as being individuals.
Now you know how much a pain in the "keester" the alignment can be. RMAA does make the job easier. I'll venture a guess that most shops do not align these as required.
Also, you have correlated what I've been saying about "tube rolling". Counterpoint is capable of good performance if set up properly. Do yourself a favour and recheck your alignment periodically to make sure it's still on the mark.
I'm looking forward to your test results.
-Chris
Ebay seems to have the requisite Rifa brand (or other brands) polystyrene capacitors for the phono section. I'm not sure 630V caps are needed, either. Look at the circuit and see what would work best.
I would personally leave the main caps alone at this point, but just about any newer low impedance cap will sound better than 20-25 year old Sprauge Atom caps. They were great bargains when new, though. I've been stuck with the same dillema myself on my 3.1 Preamp. I don't think that making the caps larger in terms of uf value is of any use. M. Elliot make them oversized in the first place. I'd look at complex Z of the cap and transient current flow at high frequencies. Long foil, and maybe higher Voltage rating. The higher voltage rating tends to give a cap with better z at higher frequencies. These days, a cap of the same uf rating (or a hair higher) and nearly twice the Voltage rating can be put in the same spot.
Local capacitor buffers, right at the plate resistor is the way to go. This keeps transients as clean as possible, it cuts out some bits of 'micro-smear' of transients due to long supply lines for the power. What I did, in my 3.1 unit, is I placed ~ 30uf of 350V polypropylene film capacitance on EACH point just above each plate resistor 'set' for each tube.
Now this little 3.1 blows away any 'small signal' (9-pin) tube preamp I've ever heard.
Chris:
Are the original plate resistors 2 watt metal oxide? I bought some 3 watt metal film resistors, looking for some sonic improvement. I just shut the unit down and am replacing them now. I guess I'll find out soonest.
I would personally leave the main caps alone at this point, but just about any newer low impedance cap will sound better than 20-25 year old Sprauge Atom caps. They were great bargains when new, though. I've been stuck with the same dillema myself on my 3.1 Preamp. I don't think that making the caps larger in terms of uf value is of any use. M. Elliot make them oversized in the first place. I'd look at complex Z of the cap and transient current flow at high frequencies. Long foil, and maybe higher Voltage rating. The higher voltage rating tends to give a cap with better z at higher frequencies. These days, a cap of the same uf rating (or a hair higher) and nearly twice the Voltage rating can be put in the same spot.
Local capacitor buffers, right at the plate resistor is the way to go. This keeps transients as clean as possible, it cuts out some bits of 'micro-smear' of transients due to long supply lines for the power. What I did, in my 3.1 unit, is I placed ~ 30uf of 350V polypropylene film capacitance on EACH point just above each plate resistor 'set' for each tube.
Now this little 3.1 blows away any 'small signal' (9-pin) tube preamp I've ever heard.
Chris:
Are the original plate resistors 2 watt metal oxide? I bought some 3 watt metal film resistors, looking for some sonic improvement. I just shut the unit down and am replacing them now. I guess I'll find out soonest.
Hi Ken,
Yes, the sometimes overheated resistors are 2W metal oxide. I use 3W metal oxides as well when replacing those. do this so that the unit works properly, longer after I've done a repair. I don't change them unless they have been overheated.
Bypassing the supplies more locally can be good, but you have to return those caps on a noisy ground or you will pollute your clean ground possibly. 😀
When is a ground, not a ground? In audio, there are no grounds to speak of.
-Chris
Yes, the sometimes overheated resistors are 2W metal oxide. I use 3W metal oxides as well when replacing those. do this so that the unit works properly, longer after I've done a repair. I don't change them unless they have been overheated.
Bypassing the supplies more locally can be good, but you have to return those caps on a noisy ground or you will pollute your clean ground possibly. 😀
When is a ground, not a ground? In audio, there are no grounds to speak of.
-Chris
Thread hijack!
Chris: on the Precision fidelity M-8 Amp, there are 4 pots per channel. Are we talking offset and bias, per pair?
Can you direct me to a nice clean schematic of a similar nature so I can 'get it' when I try to tune this puppy?
I changed every single diode in the unit (16 per channel!!) to ultra fast soft recovery vishay units, and ended up with low level distortion in the one channel, and the one channel aways ran far too cool for my liking. That's the one (channel) with what sounds like crossover distortion. A little more A on the B, please....
It's a fabulous sounding amp, which is why some dude is asking for one on Audiogon, dead or alive.
Chris: on the Precision fidelity M-8 Amp, there are 4 pots per channel. Are we talking offset and bias, per pair?
Can you direct me to a nice clean schematic of a similar nature so I can 'get it' when I try to tune this puppy?
I changed every single diode in the unit (16 per channel!!) to ultra fast soft recovery vishay units, and ended up with low level distortion in the one channel, and the one channel aways ran far too cool for my liking. That's the one (channel) with what sounds like crossover distortion. A little more A on the B, please....
It's a fabulous sounding amp, which is why some dude is asking for one on Audiogon, dead or alive.
Hi Ken,
I'd have to look at it again to tell you. I did set up the bias, so it should still have been okay. If not, something is wrong. I believe there are four DC offset controls but could be mistaken. Remember, it's four amps, each pair is bridged. Supplies were 25 VDC I think.
I don't believe I had a schematic. Once I figured it out, the service was pretty straight forward.
-Chris
You're so funny. Memory problems, remember?
I'd have to look at it again to tell you. I did set up the bias, so it should still have been okay. If not, something is wrong. I believe there are four DC offset controls but could be mistaken. Remember, it's four amps, each pair is bridged. Supplies were 25 VDC I think.
I don't believe I had a schematic. Once I figured it out, the service was pretty straight forward.
-Chris
That's enough info for me to go on Chris, and start twidlling those pots. I think the cut-off on the vishay diodes is not identical to the standard diodes (4001), and there may be a cummulative effect, with so many per channel. Also, the thing ran quite cool from the get-go, so I would suspect the bias is far lower than it needs to be or was originally intended. All I have to do, is actually break down and pull a board, and actually trace the circuit from the pots. Then I'll know.
Hi Ken,
I would have measured the bias and set them all to what seemed like the proper value. If no common bias I tend to go for 20 ~ 25 mA for bipolars and 50 ~ 100 mA (up to 125 mA) for mosfet designs. Certain brands either run hot or not, so I adjust for that too.
At the end of it all, I run THD measurements and look for crossover distortion in the residuals.
I don't know how to get any closer than that. 😉
-Chris
Edit: Ken, you didn't change any bias diodes, did you?? If so, put the old ones back. Bias diodes are always forward biased (or should be).
I would have measured the bias and set them all to what seemed like the proper value. If no common bias I tend to go for 20 ~ 25 mA for bipolars and 50 ~ 100 mA (up to 125 mA) for mosfet designs. Certain brands either run hot or not, so I adjust for that too.
At the end of it all, I run THD measurements and look for crossover distortion in the residuals.
I don't know how to get any closer than that. 😉
-Chris
Edit: Ken, you didn't change any bias diodes, did you?? If so, put the old ones back. Bias diodes are always forward biased (or should be).
-all- diodes in the circuit were swapped.and oh.. many a resistor too, now that I remember, so a complete retune will be nessessary.
OH! that reminds me, I 'left the stove on'. I am adjusting the idle bias on a NPS 200 I just finished modding, and have to go back and check the idle temp. the 'warm as toast' hand method.
Just checked it. Turned down the bias on the one channel just a hair...and the OTHER gets hotter??
.
oh yeah...it's a counterpoint.....
(I do have the tech book for it)
OH! that reminds me, I 'left the stove on'. I am adjusting the idle bias on a NPS 200 I just finished modding, and have to go back and check the idle temp. the 'warm as toast' hand method.
Just checked it. Turned down the bias on the one channel just a hair...and the OTHER gets hotter??
.oh yeah...it's a counterpoint.....
(I do have the tech book for it)
continuing the punishment, I'm putting a pair of toroidals in there first, on the M-8 Precision fidelity unit. I think the amp is good enough to do the work and recieve rewards that are commensurate to the effort.
The question is: The DC rail voltage is, according to the info on the boards....25VDC. It is actually measuring 22VDC. seems to be fine. In many an amp, the voltage is not that critical on the power section.
I have two choices, a 115VAC:2x20VAC transformer, or a 115VAC:2x23VAC transformer.
So....20x1.414-1.4V eagles:26.88VDC (No load) or...31.1VDC on the second (23VAC) transformer, each rated at 400VA.
These are the toroids from the Ebayer, 'antek'
Any opinions on punching that VDC up a few volts?
The question is: The DC rail voltage is, according to the info on the boards....25VDC. It is actually measuring 22VDC. seems to be fine. In many an amp, the voltage is not that critical on the power section.
I have two choices, a 115VAC:2x20VAC transformer, or a 115VAC:2x23VAC transformer.
So....20x1.414-1.4V eagles:26.88VDC (No load) or...31.1VDC on the second (23VAC) transformer, each rated at 400VA.
These are the toroids from the Ebayer, 'antek'
Any opinions on punching that VDC up a few volts?
Hi Ken,
We are talking about the Precision fidelity M-8 Amp right? What are your filter caps rated for, or will you be replacing them as well?
I might go for the first option. It depends on any supplies to op amps if they exist. I can't remember. If it's a straight amp, then I might go higher with the supplies. As I recall, your amp didn't really run too warm. Just keep an eye on other circuits as your 31 V option is actually almost 10 V higher than the circuit is running on right now.
What outputs are used? It's a bridge design so your currents will be higher than expected.
-Chris
We are talking about the Precision fidelity M-8 Amp right? What are your filter caps rated for, or will you be replacing them as well?
I might go for the first option. It depends on any supplies to op amps if they exist. I can't remember. If it's a straight amp, then I might go higher with the supplies. As I recall, your amp didn't really run too warm. Just keep an eye on other circuits as your 31 V option is actually almost 10 V higher than the circuit is running on right now.
What outputs are used? It's a bridge design so your currents will be higher than expected.
-Chris
It's bipolar toshiba, IIRC. wait, I have my camera at work and it has some photos in it. I believe they are a well known 200 or 250V rated 12-15 amp 'pair'. De-rigeur for late 70's early 80's amps.
The amp is fully discrete, no op-amps.
darn, I erased the images. but, the above coment still stands. They are 200+V rated 12-15 amp toshibas.
The beefy 'over the top' guy in me wants to go with the 30+DC on the rails..but I also rememeber that the primaries are rated at 115AC on these antek transformers, not 120AC. Not a big difference, but it's still there!
The amp is fully discrete, no op-amps.
darn, I erased the images. but, the above coment still stands. They are 200+V rated 12-15 amp toshibas.
The beefy 'over the top' guy in me wants to go with the 30+DC on the rails..but I also rememeber that the primaries are rated at 115AC on these antek transformers, not 120AC. Not a big difference, but it's still there!