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Old 30th August 2012, 02:07 AM   #1
rotini is offline rotini  United States
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Default New to DIY - F5 Questions

Hi. I'm a couple years late to the party, but I've decided to build a stock F5. As a DIY newbie, I'm faced with a number of challenges and I was wondering if you guys could help me out. In addition, it appears that most groupbuys pertaining to the F5 are now over, which makes some components difficult to source.

My plan is to build a B1 preamp and a stock F5.


Design Features




Mezmerize B1 Preamp:
  1. Remote-controlled as much as practical without compromising sound quality: Input selection, motorized volume pot, ON/OFF that can be tethered to the F5
    - Does an RC circuit introduce noise/other design complications?
    - The BOM asks for a 50VA - 2X12V transformer. Will this need to be increased to accomodate an additional circuit board?
  2. Lightspeed Attenuator for volume control
    - Is the Lightspeed still recommended as an attenuator? Secondly, is it possible to implement this with the motorized pot proposed above?
  3. Shunt voltage reg (granted, since it's the Mezmerize DCB1)
    .
  4. High quality components
    - It appears I need four matched and six unmatched 2SK170-BL JFET's, according to the BOM. Is anyone still supplying matched JFETs, and are there certain JFET's that are more preferable to others? (Toshiba, IRF, etc.) I know Pass is still selling these on his website, but I'd like to use the diyaudio B1 board and so would have to buy an extra board if I went with Pass' JFETs
    - The same question applies to B1 MOSFETs. It does not appear that any need to be matched, therefore sourcing these should not be as difficult. Is anyone still supplying these, and are there any types that are preferred?
F5 Amp:
  1. Stock design as cascoded/increased outputs/turbo seems too ambitious for a beginner (unless you think that it's worth it to for the hotrodded versions)
    DIYaudio sells the F5-c and F5 PCB's. Is it feasible to get the F-5c version with the intent of leaving the "upgrade" option available, or is it more practical to just get the F5 version?
  2. High quality critical components
    - Best matched output MOSFETs. Are these of the Toshiba variety, and are there any sources currently available?
    - Now that TechDiy no longer sells F5 parts kits, does anyone have a BOM that shows what parts were used in that kit? Improved alternatives are also welcome. For the JFETs and transistors, are these as critical as getting "high quality" MOSFETs (e.g. well-regarded Toshiba), or should I stick with whatever is readily available? Is the N JFET 2K170 the same as getting the B1 JFETs (2SK170-BL)?
    - Should the transformer be isolated/shielded away from the signal path?
    - I live in a RF prone area so shielding is important. Would constructing a case out of aluminum be enough? I plan to use Heatsinks USA (or Conrads MF35's if I can find them) that would be 6-7" tall and with a length of 10-12". Tops would be perforated metal, and at a minimum bottom would be reinforced.
  3. Soft start/DC protection board from diyaudio store (in lieu of thermistors)
    - Is this advised and is there any potential that a board such as this would degrade sound quality/introduce noise?
  4. On/off control using B1 signal, if practical
    - I am envisioning a separate cable that goes from the B1 to the F5 which can remotely shut the F5 off. I would still like to be able to turn the F5 off manually with a switch.



Whew, sorry for that wall of text. I'm stoked with beginning this build, and while I'm willing to pay for the features/best possible sound quality, I'm not exactly eager to drop $1000 for my first diy project.

Thank you to everyone in advance!
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Old 30th August 2012, 09:26 AM   #2
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first of. B1 is not optimal for F5. the F5 only has 15db gain. so a pre amp with 10+db gain is a must if you want to use all the power.

regarding F5:
1. stock F5 with one pair of outputs is not somting you want to cascode and drive with high voltage/bias. then you need the dual outputs.
and yes, the F5c boards can well be build as a stock F5 and upgraded at a later point.

2. i have not just the toshiba parts. maybe some forum members are selling matched sets. if not. h_a is selling matched irf parts.
here is a BOM for all 3 variations of the F5c: http://www.diyaudio.com/forums/blogs....html#comments
the Jfets are very critical. you can get those from a member here, spencer.

3. i have not used those boards.
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Old 30th August 2012, 12:23 PM   #3
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Regarding gain: You can easily increase the gain of the amp from 6 to 8 which is high enough to clip the amp. I am not sure you need more than that unless you like the sound of a clipped amp.
Another point, is it really is going to come down to how sensitive your speakers are (I don't exceed 1 W), in regard to how much gain you need, so the B1 may still be fine.

Tell us what speakers you have and it might be easier to give advice
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Old 30th August 2012, 12:35 PM   #4
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increasing gain do not come without a cost.
i for one often use very much of the power
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Old 30th August 2012, 12:41 PM   #5
AndrewT is online now AndrewT  Scotland
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The B1 is a buffer and has a gain of 1times.
The F5 has a gain of 6times.
The clipping voltage of the F5 is ~ 21Vpk, or 14.7Vac

The B1 would need 2.45Vac to clip the output of the F5.
Most CDP put out around 2.1Vac to 2.3Vac.
These will not quite run the F5 via a B1 into clipping.
You would need a little bit of extra gain to clip the F5 from a CDP. Maybe just 1.2Times, or increase the gain of the F5 to 7times.

You certainly don't need 10dB of extra gain (about 3.1Times) to replay from CDP and DVD and similar.
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Old 30th August 2012, 12:52 PM   #6
rotini is offline rotini  United States
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Thanks for everyone's input.

Quote:
Originally Posted by Melon Head View Post
Tell us what speakers you have and it might be easier to give advice
I plan to use a pair of Klipsch Heresy II's for the time being, which have an efficiency of roughly 97db I believe. I have also a pair of Spica TC-50's (very inefficient and low impedance) that I think would be out of the question. Also laying around are some Advent 5002's, Infinity Qe (4 ohm), and Klipsch RB-62 bookshelves.
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Old 30th August 2012, 02:16 PM   #7
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Rotini: Your plan looks quite reasonable, although it sounds like you may be slightly low on gain. One other thing; mating the B1 and the F5 means no caps in the signal path, which is subjectively great for sound quality but you run the risk of DC getting to your speakers which can be a bad thing.

Do you know what the max output voltage of your sources are? If the voltages are a bit higher than average, then you may have enough overall gain. If they are a little lower than average, well......Easy enough to measure if you can play a sine wave through them.

In addition to h_a and spencer for matched parts, Mouser presently has 2SK170-BL's, and Digikey has IRFP240's and 9240's. You need 6 unmatched 2SK17's for the mez, as well as 4 matched ones, and you need a few for the F5, as well as 2SJ74's. They are easy enough to match with a power supply and a voltmeter. Same for the outputs if you want to spend the time and buy a few extra parts.

Last edited by boywonder; 30th August 2012 at 02:19 PM.
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Old 30th August 2012, 02:51 PM   #8
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Quote:
Originally Posted by rotini View Post
Thanks for everyone's input.



I plan to use a pair of Klipsch Heresy II's for the time being, which have an efficiency of roughly 97db I believe. I have also a pair of Spica TC-50's (very inefficient and low impedance) that I think would be out of the question. Also laying around are some Advent 5002's, Infinity Qe (4 ohm), and Klipsch RB-62 bookshelves.
If your speakers are that efficient (97dB) then the B1 will be fine. You don't need the extra gain.

EDIT: Just checked your speakers here http://www.klipsch.com/heresy-ii-floorstanding-speaker . You will be fine

Last edited by Melon Head; 30th August 2012 at 03:00 PM.
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Old 30th August 2012, 05:05 PM   #9
rotini is offline rotini  United States
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Quote:
Originally Posted by boywonder View Post
Rotini: Your plan looks quite reasonable, although it sounds like you may be slightly low on gain. One other thing; mating the B1 and the F5 means no caps in the signal path, which is subjectively great for sound quality but you run the risk of DC getting to your speakers which can be a bad thing.

Do you know what the max output voltage of your sources are? If the voltages are a bit higher than average, then you may have enough overall gain. If they are a little lower than average, well......Easy enough to measure if you can play a sine wave through them.
Boywonder, thanks for those points. Honestly, my decision to go with the B1 might be a bit premature. I'm new to DIY so it was natural after seeing the B1 mentioned so often on the Pass forums. I'll dig up some more threads on preamp matching with the F5, but I'd be interested in hearing any other opinions as well.

I never thought of the doubled risk of DC getting to my speakers. I guess I'll have to evaluate further the tradeoffs between DC protection vs capacitors in signal path vs sound quality.
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Old 30th August 2012, 05:26 PM   #10
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by Melon Head View Post
If your speakers are that efficient (97dB) then the B1 will be fine. You don't need the extra gain.

EDIT: Just checked your speakers here Heresy II Floorstanding Speaker | Klipsch . You will be fine
if you need checkin' Heresy's , then you need to see a Doc , for more checkin'

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