f5 feedback mod per NP
Just thought I'd post my initial impressions of having modified the feedback network relative to Nelson's suggestion( R11 & 12 to 1 ohm/
R5 & R8 to 100 ohms and R1 & R2 to 22ohms-pass site)
Yep,Yep amp runs a little cooler(perhaps 8-10 degree farenheit) and the "tight fist" now has a velvet glove!
I found the original spec a bit dry and etched in sound relative to my dynaco st70- accurate and detailed but lacking a bit of body or warmth. The new feedback seems to be a definite step in the right direction. This am I'm listening to Joni Mitchell "Court and Spark"(DCC issue) and on "Twisted" the trumpet is nicely placed behind Joni, edgy but not etched. I clearly hear her pushing the air from her sinuses, from her throat, from her chest depending on the note or the intended emphasis. Cheech and Chong sound like Cheech and Chong and perhaps they have been consuming some controled substances? Judge for yourselves, point is the sound is more relaxed. I have even turned my REL Strata sub down from a x-over point in the mid 40's to the high 30's- I don't need the extra warm. This is subtle but very indicative of the change from the feedback modification. Thanks for the suggestion Nelson. N.P. you won't have any measurement or o-scope shots of this feedback level relative to the original spec would you?
Thanks for your help in this.
Probably dumb question but here goes- two identical transformers wired in parallel(ac input joined together4 wires to 2/ ac output 8 wires to 4) gives me the same voltage and twice the amperage(VA)-yes,yes?
have a great weekend, you-all
rob
Just thought I'd post my initial impressions of having modified the feedback network relative to Nelson's suggestion( R11 & 12 to 1 ohm/
R5 & R8 to 100 ohms and R1 & R2 to 22ohms-pass site)
Yep,Yep amp runs a little cooler(perhaps 8-10 degree farenheit) and the "tight fist" now has a velvet glove!
I found the original spec a bit dry and etched in sound relative to my dynaco st70- accurate and detailed but lacking a bit of body or warmth. The new feedback seems to be a definite step in the right direction. This am I'm listening to Joni Mitchell "Court and Spark"(DCC issue) and on "Twisted" the trumpet is nicely placed behind Joni, edgy but not etched. I clearly hear her pushing the air from her sinuses, from her throat, from her chest depending on the note or the intended emphasis. Cheech and Chong sound like Cheech and Chong and perhaps they have been consuming some controled substances? Judge for yourselves, point is the sound is more relaxed. I have even turned my REL Strata sub down from a x-over point in the mid 40's to the high 30's- I don't need the extra warm. This is subtle but very indicative of the change from the feedback modification. Thanks for the suggestion Nelson. N.P. you won't have any measurement or o-scope shots of this feedback level relative to the original spec would you?
Thanks for your help in this.
Probably dumb question but here goes- two identical transformers wired in parallel(ac input joined together4 wires to 2/ ac output 8 wires to 4) gives me the same voltage and twice the amperage(VA)-yes,yes?
have a great weekend, you-all
rob
Hi dear Babo,
You got me.
Early in my DIYer career I discovered that I cannot stick strictly to offered schematics and always build with mods (even if my very limited knowledge would counsel against) and then cannot help but continue modding...I think this is a common feeling around here...
I would say without false modesty that I recognize a good idea when I see it, he, he...
In this case I will proceed as with my B1. The power supply will feature ECdesigns- charge transfer circuit and will then regulate with Teddy Pardo-s PowerReg. I will try to post picks of the power rails.
The box will be completely DIY . Ugly but I think it will ran cool as I am using it for the Zero Component Amp, ZCA, which is a little Class A amp with around 1,5A current at idle.
Regards,
M
You got me.
Early in my DIYer career I discovered that I cannot stick strictly to offered schematics and always build with mods (even if my very limited knowledge would counsel against) and then cannot help but continue modding...I think this is a common feeling around here...
I would say without false modesty that I recognize a good idea when I see it, he, he...
In this case I will proceed as with my B1. The power supply will feature ECdesigns- charge transfer circuit and will then regulate with Teddy Pardo-s PowerReg. I will try to post picks of the power rails.
The box will be completely DIY
. Ugly but I think it will ran cool as I am using it for the Zero Component Amp, ZCA, which is a little Class A amp with around 1,5A current at idle.Regards,
M
I suppose its not two transformers in paralel, but double windings on each transformer in paralel
One transformer on each rail
Problem is then whether transformers are matched closely to get excact same voltage on each rail?
btw, if in EU
Just seen that BMM now sell Amplimo toroids with the hard to get low voltage/high wattage
As I recall theres 2x 18V with both 6A and 10A
One transformer on each rail
Problem is then whether transformers are matched closely to get excact same voltage on each rail?
JC951t said:
btw, if in EU
Just seen that BMM now sell Amplimo toroids with the hard to get low voltage/high wattage
As I recall theres 2x 18V with both 6A and 10A
nigelwright7557 said:
Stateside, I think that if the WalMart, Costco, Walgreen and Radio Shack's were required to certify compliance with FCC Part 15 fo things they sell the problems would go away. In fact, the problem would disappear world-wide as the big retailers would force the stuff back up the pipeline.
I am straying a bit, but we have traffic signals and monitors which emit radiation that you can measure hundreds of feet away. My DAC power supply went into the waste-basket almost immediately upon receipt.
The best test is an a.m. radio detuned from a broadcast station.
The problem is bad, and getting worse -- compact fluorescents emit all sorts of EMI and RFI.
F5 is completed. The attached pic may be of interest to some who are considering a point-to-point wiring approach as opposed to using a printed circuit board. It was fun and challenging to build, but not too complex. The amp parts come from TECH-DIY, where I selected the Vishay/IRF hexfet kit. The power supply is based on the schematic shown on the last page of the F5 Operations Manual (with its included F5 construction article). Power supply parts and fans were ordered from Farnell-Newark Singapore. The fans’ power supply parts are locally sourced. The transformer is only 250VA – I could not find a 300VA unit through Farnell; it gets just slightly warm, but otherwise OK. The chassis and heat sinks were bought here in Jakarta at the famous Glodok electronics parts market – a dark, hot, crowded network of tiny shops that is actually a fun place to explore. The heat sinks were slightly under spec, therefore the fans.
The sound of the F5? It has a magical see-through quality! I’ve never really heard reproduced music with such ‘pure clarity’. My mainstay amp for many years has been an Audio Research VT-100 Mk II that I keep well trimmed. The VT-100 sounds beautiful, with a full-bodied and textured sound, and although the sound is wonderfully clear, the prime attribute would not be what one would call ‘clarity’, if you know what I mean. In contrast, excellent solid state amps that I’ve listened to over the years do have clarity as their prime attribute, but with very subtle shades of coldness, dryness, or a hard-edgedness. Not so with the F5. ‘Pure clarity’ is the best phrase I can offer at the moment to describe the wonderful sound of this amp.
If you are contemplating building the F5, then DO SO! You WILL be rewarded. Much help can be gained from this thread. Overall, careful planning of the physical layout was the key for me. The 6moons Audio review photos of Nelson’s F5 boards gave me permission to consider separating the input stage from the output stage on separate boards, connected to each other via the jfet drains and the output rail. It worked!
The attached pic was taken prior to my construction of the little fans’ power supply which works fine. Anyway, I am happy to provide pics showing details if people are interested. Thanks to Nelson and the thread participants for a wonderful construction adventure!
-Steve
The sound of the F5? It has a magical see-through quality! I’ve never really heard reproduced music with such ‘pure clarity’. My mainstay amp for many years has been an Audio Research VT-100 Mk II that I keep well trimmed. The VT-100 sounds beautiful, with a full-bodied and textured sound, and although the sound is wonderfully clear, the prime attribute would not be what one would call ‘clarity’, if you know what I mean. In contrast, excellent solid state amps that I’ve listened to over the years do have clarity as their prime attribute, but with very subtle shades of coldness, dryness, or a hard-edgedness. Not so with the F5. ‘Pure clarity’ is the best phrase I can offer at the moment to describe the wonderful sound of this amp.
If you are contemplating building the F5, then DO SO! You WILL be rewarded. Much help can be gained from this thread. Overall, careful planning of the physical layout was the key for me. The 6moons Audio review photos of Nelson’s F5 boards gave me permission to consider separating the input stage from the output stage on separate boards, connected to each other via the jfet drains and the output rail. It worked!
The attached pic was taken prior to my construction of the little fans’ power supply which works fine. Anyway, I am happy to provide pics showing details if people are interested. Thanks to Nelson and the thread participants for a wonderful construction adventure!
-Steve
Attachments
best part sources for F5?
I've managed to gather Conrad heatsinks, and a set of cvillier's F5 boards (power supply, rectifier, and output).
Next steps are buying a transformer and components. Any recommendations?
Is TECH-DIY still the preferred place to get all the components in one place (I see they're warning that "due to current limited availability of 2SJ74 JFET's -- the N and P Channel devices are no longer matched").
What's a good place to get a reasonable price on a transformer for the F5? People find differences between Plitron, Antek, others?
Thanks for any help -- this will be my first DIY build project. You guys are an inspiration.
I've managed to gather Conrad heatsinks, and a set of cvillier's F5 boards (power supply, rectifier, and output).
Next steps are buying a transformer and components. Any recommendations?
Is TECH-DIY still the preferred place to get all the components in one place (I see they're warning that "due to current limited availability of 2SJ74 JFET's -- the N and P Channel devices are no longer matched").
What's a good place to get a reasonable price on a transformer for the F5? People find differences between Plitron, Antek, others?
Thanks for any help -- this will be my first DIY build project. You guys are an inspiration.