I am getting to the nitty gritty of my winter amp project and all that is left before building is deciding on and ordering the iron. My budget is sufficient for either Hammond 1628SE or James 6123HS.
There was a thread here a while back about frequency response issues with the Hammonds (a big drop out at 15K IIRC and another anomaly lower down, 3K?). I haven't seen any actual data on the James, nor do I know anyone who is using them.
My feeling is that if the Hammonds have a systemic issue that hasn't been resolved I would probably go with James. But if the Hammond thing was a temporary production glitch or something that has been fixed I'd go with Hammond since the other iron, PTX and choke will be Hammond and it would be nice to have everything match.
Any input on either the Hammond issue or any real-world measurements and use of James?
There was a thread here a while back about frequency response issues with the Hammonds (a big drop out at 15K IIRC and another anomaly lower down, 3K?). I haven't seen any actual data on the James, nor do I know anyone who is using them.
My feeling is that if the Hammonds have a systemic issue that hasn't been resolved I would probably go with James. But if the Hammond thing was a temporary production glitch or something that has been fixed I'd go with Hammond since the other iron, PTX and choke will be Hammond and it would be nice to have everything match.
Any input on either the Hammond issue or any real-world measurements and use of James?
I use the 1628Se and don't recommend it. My samples have severe issues in the 13 kHz range. For more info see:
http://www.sacthailand.com/transformerTest1.html
Edit: For what it's worth, the amp in my avatar uses them. It makes 3 watts and the problem is still evident. The PS iron is also Hammond and it appears to be wound 10% over on the primary. Both the HV and filaments read high, the latter at 7 volts which I discovered late and after cooking a few EL84's. I might consider a 125se for benching, but I'll never build another serious amp with Hammond iron again.
http://www.sacthailand.com/transformerTest1.html
Edit: For what it's worth, the amp in my avatar uses them. It makes 3 watts and the problem is still evident. The PS iron is also Hammond and it appears to be wound 10% over on the primary. Both the HV and filaments read high, the latter at 7 volts which I discovered late and after cooking a few EL84's. I might consider a 125se for benching, but I'll never build another serious amp with Hammond iron again.
Approaching 50 and, as of yesterday, hearing still good to 15 kHz.
Measurement-wise the TX problem - in my amp - manifests itself as a short, quick 2 dB rise at 13 kHz under rather large amounts of purely resistive feedback, significant ringing on square waves and rapidly rising distortion with frequency. Ironically I spent the night before Sherman's post on the bench tuning the feedback capacitor trying to minimize just these issues. The best I could achieve was dead flat response to 14 kHz, a 1 - 1.5 db downward knee to 16 kHz, relatively flat to ~ 18 kHz, followed by a rapid rolloff (~ -3 dB @ 20 kHz) and then an ultrasonic rise in the 40-50 kHz range. A very odd frequency response. It wasn't possible to eliminate a large spike on the rising edge of square waves or the rising distortion with frequency. This is at 1 watt output.
The problem is suprisingly audible as a 'dirty' high end, to my ear similar to speakers with high freuqency issues, for example the Tang Band W4-657s with its very narrrow 4-6 dB rise centred at 8 kHz. It's not as obvious but very similar in character. Carefully tuning the feedback cap reduces it significantly but the highs never really sound clean and extended. Cymbals suffer the most.
Check the SAC Thailand test results. That's nasty stuff.
Measurement-wise the TX problem - in my amp - manifests itself as a short, quick 2 dB rise at 13 kHz under rather large amounts of purely resistive feedback, significant ringing on square waves and rapidly rising distortion with frequency. Ironically I spent the night before Sherman's post on the bench tuning the feedback capacitor trying to minimize just these issues. The best I could achieve was dead flat response to 14 kHz, a 1 - 1.5 db downward knee to 16 kHz, relatively flat to ~ 18 kHz, followed by a rapid rolloff (~ -3 dB @ 20 kHz) and then an ultrasonic rise in the 40-50 kHz range. A very odd frequency response. It wasn't possible to eliminate a large spike on the rising edge of square waves or the rising distortion with frequency. This is at 1 watt output.
The problem is suprisingly audible as a 'dirty' high end, to my ear similar to speakers with high freuqency issues, for example the Tang Band W4-657s with its very narrrow 4-6 dB rise centred at 8 kHz. It's not as obvious but very similar in character. Carefully tuning the feedback cap reduces it significantly but the highs never really sound clean and extended. Cymbals suffer the most.
Check the SAC Thailand test results. That's nasty stuff.
planet10 said:
Dave,
That is interesting since they are the same price at ~ $90US each. I'm not discounting what you are saying but all I seem to find on James is "they used to be with xyz and build top notch trafos" etc. I have yet to find someone that has said "I have used them and they sound great" or "I use them and have measured a flat FR from 20-20K Hz +/- 1dB" or something like that.
However I doubt I could hear a -3dB dip at 15K Hz (or even a 9dB dip
). But it would be nice to know the TX is making noise where it is supposed to be!If I decide to go with James do you have any idea where I might find covers for a Hammond PTX and choke that will help them match the James OTX? (The equivalent James PTX is US $190 vs. $51 for Hammond, and the equivalent James choke is $90 vs. $25 for Hammond. I'm building monoblocs to I need 2X
.)
Sherman said:
There was a recent joelist thread on James OPTs... quite a few stepped up and said good things about them... no one had anything to say against them.
A local fellow built a monster PSE 300B amp with James with excellent results.
Woody -- a member here -- has gotten at least a couple pairs. The latest for a 6C45pi spud amp.
dave
If you want "dirt" on James transformers, do a search. Someone here posted a link with measurments showing that the James universal output transformer performance was clearly inferior to some of the Tango universal units. The link was a sight showing the measured performance of many transformers.
Of course, the Tango are much more expensive.
Of course, the Tango are much more expensive.
First of all, I believe it is not fair to take only the Hammond 1628 for comparison with others. My friend built a 2A3 power amplifier with Hammond 1627 OPT. He measured the frequency and square wave response and the result was excellent. The frequency response is very flat from a few hertz to almost 100kHz. The square wave at 10kHz has a very little spike at the edges. The important thing is, his amplifier sounds much better than the Audio Note Kit One using 300B output tube.
I built myself a 45 tube amplifier with 1628 OPT. I measured the frequency response at both 8-ohm and 4-ohm output taps. The result for 8-ohm looks a bit urgly but at 4-ohm it is reasonaly good. The frequency response at low end frequency is extremely good. I believe it is because of the big inductance it has. By the way, I having measure the response for 16-ohm tap because I am rather lazy to rewire the wires at the primary of the OPT.
My measurements for 1628 is attached in Excel file.
Johnny
I built myself a 45 tube amplifier with 1628 OPT. I measured the frequency response at both 8-ohm and 4-ohm output taps. The result for 8-ohm looks a bit urgly but at 4-ohm it is reasonaly good. The frequency response at low end frequency is extremely good. I believe it is because of the big inductance it has. By the way, I having measure the response for 16-ohm tap because I am rather lazy to rewire the wires at the primary of the OPT.
My measurements for 1628 is attached in Excel file.
Johnny
planet10 said:
Well, after all these replies and a little more research (there really is surprisingly little "real" info out there on James considering the apparent value and low price) I've decided I'll go with James for the OTXs. They have the right primary impedance, can handle the current and they look awfully nice.
Now I just have to figure out the best way to "match" the Hammond PTX and Hammond choke to the look of the James. Maybe just some paint but a cover would be nice.
Once this project is complete maybe I can get started on the DIY Reference Full-Range speaker project (gotta finalize that design!). The way that is developing it might make a pretty nice match for a 4-5W SE amp.
kmtang said:
Johnny,
Thanks for the info. My understanding is that the 1627 has a completely different construction from the 1628 and is in fact an excellent performer. Unfortunately the primary impedance is too low for my current project or I would go that route.
A wider search (more than just this forum) turned up quite a few pages on the 1628 and its less than stellar performance. To be quite honest though, I doubt I could actually hear any anomalies above 13 KHz if they were less than 6dB, so the 1628 might work fine for my ears. But as long as the cost is within reason I might as well go with James if the performance is better.
Hi Sherman, I think you'll be much happier avoiding the 1628se in this application. If my reaction to Hammond seems a bit extreme, the PS transformer from them was also bad in every way - voltages 10% over, mismatched isolation washers, screws of different types cut to length with side cutters (!) and a finish which flaked off with a thumbnail. Neccessity drove me to strip and repaint the TX housings on my amp, not aesthetics. I've worked with Hammond product, mostly line-level and PS transformers but racks as well, for almost 25 years and never saw anything this shoddy.
Attached is a jpg of the measured results with the 1628se. The FR is resistive feedback only. That rising distortion with frequency response is audible, most bandwidth limited gear I've measure in the past shows falling distortion with increased frequency, as would be expected since the depressed high frequencies of the device under test is suppressing harmonics.
Attached is a jpg of the measured results with the 1628se. The FR is resistive feedback only. That rising distortion with frequency response is audible, most bandwidth limited gear I've measure in the past shows falling distortion with increased frequency, as would be expected since the depressed high frequencies of the device under test is suppressing harmonics.
Attachments
rdf said:
Well, all the responses here convinced me and I placed an order for James OTXs yesterday. If they sound as good as they look I'm sure I'll be more than satisfied with them.
I still haven't ordered the PTXs or chokes but know that my budget on this won't support James products for those items. They are 4x the price of similarly rated Hammonds. Everything else is either here or on order so the last piece of the puzzle is the PS iron. I hope to place an order this week sometime.
One can agonize forever over components and end up not building. Since my budget is not unlimited compromises are inevitable (heck they'd be inevitable even if my budget was unlimited).
I would say Hammond transformers are not the best transformers in the market but they have extremely good value/quality for the price.
Regarding the overvoltage issue, surely you need to provide it with sufficient loading. The voltage specification is based on full output rating. Of course, if you use it with very low loading, the voltage will rise to a small percentage.
Therefore, we need to bare in mind that if we choose the transformer that is overrated, we need to either picking transformer with lower output voltage or using extra regulators.
Just my 2 cents.
Johnny
Regarding the overvoltage issue, surely you need to provide it with sufficient loading. The voltage specification is based on full output rating. Of course, if you use it with very low loading, the voltage will rise to a small percentage.
Therefore, we need to bare in mind that if we choose the transformer that is overrated, we need to either picking transformer with lower output voltage or using extra regulators.
Just my 2 cents.
Johnny
rdf said:Mind if I ask where you're getting the James from? I want to start project two.
I ordered mine late Saturday night from Euphonia Audio (www.EuphoniaAudio.com). $189/pair, shipping was $12 I think. I just got an email from them saying they shipped and providing a FedEx tracking number so they may show up this week!
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