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Old 9th April 2013, 07:14 PM   #13061
bcmbob is offline bcmbob  United States
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Progress!

The F5 test rig build sounds great with the addition of a preamp. I used a JC-2 clone built from an ebay kit that has a tendency to slightly sweeten anything it pushes without adding any distortion. I have a Carver C-1 to try but I don't think it will perform any better.

Bias at 0.59V and DC offset at 0.0-1 are stable with ~ 12 hours of use. Not sure about burn-in on an amp without caps but it seems to sound a little warmer with use.

Next step - the box.
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Old 10th April 2013, 12:38 PM   #13062
Rixsta is offline Rixsta  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
I suspect Pass determined the lowest gain the F5 could be used at, without needing separate compensation components when built using his recommendations.

Increasing the stability margins by increasing the gain can lead to a "flat" sounding amplifier. But since this is a PASS design I suspect there are a range of acceptable gain settings that all sound good.
Thanks, yes I plan to have a variable feedback possibly but within acceptable parameters

Another newbie question, i would like to add VU meters to my F5 well F5T
do you think theres any way the ones here would make the F5 sound worse ?
and is there any compatibility problem ive missed?

2xPanel VU Meter DB Meter+Driver DIY Assembled fr T AMP | eBay
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Old 10th April 2013, 07:17 PM   #13063
Floric is offline Floric  Europe
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Quote:
Originally Posted by Rixsta View Post
Thanks, yes I plan to have a variable feedback possibly but within acceptable parameters
Be careful if you are planning to use potentiometers, you need wattage that is defined in the schematic (at least).

I would recommend to use swappable power resitors and check the parameters (bias, DC offset) after swapping you could ruin your speakers in the case of a fault.

Regards

Floric
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Old 12th April 2013, 03:13 PM   #13064
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Got 2 F5 amplifiers running now. one with a shared toroid in a Hifi2000 case, very neat and tidy and that one has been sold. Another one for myself with dual E-core built on de back of an old JBL 6290 heatsink including transformers. Used my own PCB design because i thought it could be smaller (this is 76x34mm) and only needed one layer. Dual layer is too much for such a simple design. Keeping traces short (enough) helps a lot.

The NTCs and FETS are on underside of the PCB, rest is on top.

The 2 holes in the middle are there to hold the PCB tightly down, pressing the NTCs to the FETs. By using nylon bushes around these screws as spacers the same thickness as the NTCs+FETS together I get the best thermal coupling without bending the PCB.

The sound? I think the F5 has the best sound i've ever heard. It's musicality while keeping detail and definition at the highest levels is simply unbeatable.

I've got a Sony N77ES, some Accuphase beast, Moon, Rega and a borrowed Lyngdorf TDAI2200 and a whole list of other amplifiers to compare it with. Some are better in terms of absolute control. Most of them.. have flaws. But

None are better at music. With the F5, it just sounds right.
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Old 12th May 2013, 07:32 AM   #13065
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Helping my friend power up his F5 today, we ran into an immediate problem.

He has Peter Daniels tiny boards, that I meticulously populated myself, with the full circuit, and the original resistor values from the earliest schematic publication.


The power supply was tested prior to power up, and was reading 26.2v & -26.1v, but once connected to the amp board, for power up, was reading 19.2v & -19.2v.


The Problem:

On power up, across R11 & R12 values were reading 1.8v DC on both channels. Both P1s and P2s were set until clicking fully anti-clockwise. We did not test the speaker outputs yet, as we only have 2 multimeters, and we already had a power down problem. Searching the boards etc, yielded nothing but scratched heads. Can anybody help?

Many thanks
Lucas
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Old 12th May 2013, 07:42 AM   #13066
Marra is online now Marra  United Kingdom
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Lucas you need to set P1 & P2 so that you have the lowest possible resistance across R5 & R6 then adjust each trimmer by half a turn alternately until you start getting readings across the source resistors.You think that nothing is registering then they suddenly show a reading so slowly does it.Good luck.
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Old 12th May 2013, 07:49 AM   #13067
tinitus is online now tinitus  Europe
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Quote:
Originally Posted by LucasAdamson View Post
Both P1s and P2s were set until clicking fully anti-clockwise.
try measure on paralel resistor (R3/R4)....(no power on)
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Old 12th May 2013, 07:57 AM   #13068
sangram is offline sangram  India
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On the Peter Daniel boards the pot orientation is different from the cViller boards, IINM. One pot rotates in the opposite direction, don't remember which. If you want both to be rotated in the same direction the wipers have to be mirror-imaged.

Ideally you want to measure the resistance after the pot is in circuit, and check that the pot shows zero reading in power off mode.
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Old 12th May 2013, 09:33 AM   #13069
AndrewT is offline AndrewT  Scotland
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I always query the standard multi-turn pot orientation in a pre-made PCB.
I try to determine which direction of rotation is required to make the parameter increase. I then orient the pot such that "clockwise" = increase in parameter.

I never accept that the PCB designer's criteria are the same as mine.
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Old 12th May 2013, 12:26 PM   #13070
6L6 is offline 6L6  United States
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Quote:
Originally Posted by LucasAdamson View Post
The power supply was tested prior to power up, and was reading 26.2v & -26.1v,
Good.

Quote:
but once connected to the amp board, for power up, was reading 19.2v & -19.2v.
The PSU is sagging under a large load. (That's actually normal...)

Quote:
On power up, across R11 & R12 values were reading 1.8v DC on both channels.
That is three times the recommended bias current!

And also why the PSU is measuring so low...


Quote:
Both P1s and P2s were set until clicking fully anti-clockwise.
Nobody said anti-clockwise on the trimmer pots was 'down' --

Quite simply, you have the bias turned all the way up.

As Marra suggested, with the power off measure resistance across R3 and R4, and turn the pot until it reads the minimum amount. Then the pots should be all the way 'down'

You could also mark (with a small arrow) the pot face with the 'up' direction of rotation.
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