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.
Mezmerize B1 Preamp:
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!
My plan is to build a B1 preamp and a stock F5.
Design Features
Mezmerize B1 Preamp:
- 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? - 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? - Shunt voltage reg (granted, since it's the Mezmerize DCB1)
. - 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?
- 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? - 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.
- 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? - 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!
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/cviller/191-gb-f5-guide-pcb-version-2-page5.html#comments
the Jfets are very critical. you can get those from a member here, spencer.
3. i have not used those boards.
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/cviller/191-gb-f5-guide-pcb-version-2-page5.html#comments
the Jfets are very critical. you can get those from a member here, spencer.
3. i have not used those boards.
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
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
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.
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.
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.
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.
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.
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.
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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
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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.
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'
I believe the F5 has an input impedance of 100k? if so this makes it ideal for a Lightspeed Attenuator inclusion.
Cheers George
Rotini: The B1 is highly likely to be fine with 97db speaks as the experts are mentioning, you just won't be driving an F5 to clipping with the volume maxed, which you really can't sanely do with 97db sens speakers anyway. (See ZM's post above)
As far as keeping DC off of the speakers, one solution is to install two outputs on the B1; one direct coupled and one cap coupled, then you have a choice.
I just built a hypnotize DCB1 (PCB from Tea-Bag here on the forum) and it was a straightforward, fun build, and it sounds like well, nothing,... as it should.
In my experience, the most important thing you can do to help your DIY project is to buy (or make) your chassis. Do this first. Everything else is easy compared to that.
The F5 is a small amp that needs big heatsinks, so everything will fit in a box that has sufficient heat sinking.
The Mesmerize is going to require a bit more thought, as you need to fit the PCB as well as switches, knobs, attenuation, jacks, etc... And decide between an internal or external powersupply.
You mention that you are new to this, I would suggest a chassis that is a bit bigger than 'ideal' instead of one that's a bit smaller...
Concerning gain - Changing the feedback resistors (R5, 6, 7, 8) from the stock 100ohm to a slightly higher value, say 150-220ohm will increase the gain of the amp. I have built two F5's, one of them was with 150ohm resistors in those positions to help better integrate into a bi-amped system. It made a nice difference. There have also been reports of people having very good luck with 220ohm, who need more gain.
That said, with Heresy speakers, you will probably never need it. It's very easy to change later, if you want/need.
The F5 is a small amp that needs big heatsinks, so everything will fit in a box that has sufficient heat sinking.
The Mesmerize is going to require a bit more thought, as you need to fit the PCB as well as switches, knobs, attenuation, jacks, etc... And decide between an internal or external powersupply.
You mention that you are new to this, I would suggest a chassis that is a bit bigger than 'ideal' instead of one that's a bit smaller...
Concerning gain - Changing the feedback resistors (R5, 6, 7, 8) from the stock 100ohm to a slightly higher value, say 150-220ohm will increase the gain of the amp. I have built two F5's, one of them was with 150ohm resistors in those positions to help better integrate into a bi-amped system. It made a nice difference. There have also been reports of people having very good luck with 220ohm, who need more gain.
That said, with Heresy speakers, you will probably never need it. It's very easy to change later, if you want/need.
AudioSan, is there any modification required for a F5C board to be built as a stock F5? Or is it just a matter of populating only the stock F5 components and leaving the rest as-is?
The B1 is not DC coupled. It has a great big capacitor in the output feed.
The F5 is DC coupled.
But just like any AC or DC coupled amplifier, if the output stage shorts to one supply rail then the speakers are likely to be damaged. The amp does not need to be DC coupled for this unfortunate eventuality.
Single polarity Power supply fed amplifiers must have a DC blocking cap on the output to allow them to operate. This DC blocking cap also happens to be the speaker protection cap. Isn't that just fortuitous. A dual purpose output cap and only half as many capacitors in the PSU, Another saving.
The F5 is DC coupled.
But just like any AC or DC coupled amplifier, if the output stage shorts to one supply rail then the speakers are likely to be damaged. The amp does not need to be DC coupled for this unfortunate eventuality.
Single polarity Power supply fed amplifiers must have a DC blocking cap on the output to allow them to operate. This DC blocking cap also happens to be the speaker protection cap. Isn't that just fortuitous. A dual purpose output cap and only half as many capacitors in the PSU, Another saving.
110 or 120r resistors in lieu of the standard 110r resistors will increase the gain of the F5 if you really do need to be able to clip the F5 output when driven by a CDP.
110r, resistors will allow clipping with 2.3Vac output CDPs and 120r resistors will allow clipping with 2.1Vac output CDPs.
And you have the option to use 100r (gain=6), or 110r (gain=6.5), or 120r (gain=7), each can be retro fitted fairly cheaply to let you hear the difference that clipping makes.
You may decide that an unclipable output is a good thing.
110r, resistors will allow clipping with 2.3Vac output CDPs and 120r resistors will allow clipping with 2.1Vac output CDPs.
And you have the option to use 100r (gain=6), or 110r (gain=6.5), or 120r (gain=7), each can be retro fitted fairly cheaply to let you hear the difference that clipping makes.
You may decide that an unclipable output is a good thing.
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Yes, certainly true for a 'normal' B1.
However, in this case the OP is talking about a Mesmerize DCB1.
And in my experience with my first F5, it is actually quite nice.
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When I was at Uni my lecturers use to say, "rescale that y-axis, your throwing away information" (we didn't have Excel by the way, just graph paper). Fortunately, I was dumb enough to understand what they meant. Based on that principle I design amps in a similar manner for the same reason.
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