100W Ultimate Fidelity Amplifier

sonal kunal · 2016-02-08 9:37 pm

SoundsGreat said:
2) For the life of me Am not able to measure the bias (voltage across the .33Ohm),It just sits @ 0V or 0.1.Have a autorange DMM and it refuses to... Not sure whether it's the DMM fault or (cause was able to measure the V drop across the Power resistor),So have kept the 1K bias preset to the middle at 500 Ohm.Also tried to see if varying it has any effect but unless I bring it to zero no other value has any effect,If I bring to zero the Relay trips and switches off.

Increase resistor R16 from 1k to 2.2k (it's near BD139) then you can adjust bias. I have encounter similar problem both in AX14 and AX20.

still4given · 2016-02-09 3:15 am

The FX8 is singing. I set the bias to 128mA at the rails. Clipping looks perfect and square waves look nice and square. Sound is lovely as you would expect.

ammel68 · 2016-02-09 5:40 am

still4given said:
The FX8 is singing. I set the bias to 128mA at the rails. Clipping looks perfect and square waves look nice and square. Sound is lovely as you would expect.

Terry, how much power does the FX8 output into 8 and 4 ohms before clipping?

Also, how does the FX8 compare to the AX11 in sound quality?

Thanks...

still4given · 2016-02-09 6:17 am

I will hook them up tomorrow and give a listen. I will be surprised if there is any difference in sound. when you get this low in THD they pretty much all sound the same. So far I have only played them through my test speakers. A pair of JBL 4311B. Very good bass response and clear highs. I'm only running them at +-31V right now. I measured 19V AC into 8ohms at clipping. I'll do some better testing tomorrow and take some pics of the scope. So far it is a really nice little amp. I didn't have any BD139's so I used KSC3503E, KSA1381E. No sign of oscillation, very stable.

thimios · 2016-02-09 7:02 am

still4given said:
I will hook them up tomorrow and give a listen. I will be surprised if there is any difference in sound. when you get this low in THD they pretty much all sound the same. So far I have only played them through my test speakers. A pair of JBL 4311B. Very good bass response and clear highs. I'm only running them at +-31V right now. I measured 19V AC into 8ohms at clipping. I'll do some better testing tomorrow and take some pics of the scope. So far it is a really nice little amp. I didn't have any BD139's so I used KSC3503E, KSA1381E. No sign of oscillation, very stable.

How is the sound in the bass range?

still4given · 2016-02-09 7:52 am

Hi Thimios,

I'll let you know tomorrow. It's midnight here right now.

thimios · 2016-02-09 7:57 am

still4given said:
Hi Thimios,

I'll let you know tomorrow. It's midnight here right now.

Oh sorry Terry,good night!

apexaudio · 2016-02-09 9:03 am

still4given said:
The FX8 is singing. I set the bias to 128mA at the rails. Clipping looks perfect and square waves look nice and square. Sound is lovely as you would expect.

Nice work,
Regards

sonal kunal · 2016-02-09 12:35 pm

Sprint file of AX-20.

prasi · 2016-02-09 1:17 pm

still4given said:
The FX8 is singing. I set the bias to 128mA at the rails. Clipping looks perfect and square waves look nice and square. Sound is lovely as you would expect.

Very Very Nice Terry!. Is it a winner? Can you post the scope shots, if already photographed?

reg
Prasi

us1070 · 2016-02-09 2:19 pm

What are the supplementary for Transistor BC640

still4given · 2016-02-09 2:38 pm

us1070 said:
What are the supplementary for Transistor BC640

I used KSA1845.

SoundsGreat · 2016-02-09 2:45 pm

Hi,

Increase resistor R16 from 1k to 2.2k (it's near BD139) then you can adjust bias. I have encounter similar problem both in AX14 and AX20

Thanks for the input Sonal,Will try that,What about the relay issues ??

Also Sonal if its not too much to ask,Can you please add the protection circuit to the AX20 layout that you just shared ??

Dragon and Juan where are you guys ??? Not a single comment !!

Regards.

ammel68 · 2016-02-09 6:25 pm

sonal kunal said:
Sprint file of AX-20.

Very nice! Thank you for sharing your Sprint file.

Do you plan on doing a Sprint PCB for the FX8 like Terry shows in post 6202?

still4given · 2016-02-09 6:26 pm

prasi said:
Very Very Nice Terry!. Is it a winner? Can you post the scope shots, if already photographed?

reg
Prasi

I got a chance to hook it up to my A/B setup. I don't have an AX14 hooked up right now so I compared it to some other amps. Held its own against the Honey Badger, DX MKIII, and a Peeceebee. To answer Thimios' question, the bass is very good. Strong and solid. These little Latfets never cease to amaze me. Attached are some scope shots. Forgive the lighting.
The voltages shown are at clipping. Negative rail on the left and AC RMS output on the right. This into 8ohm resistive load.

Blessings, Terry

ammel68 · 2016-02-09 6:41 pm

Thank you for the comparisons and scope shots.

What transformer and power supply are you using?

Do the Latfets need to be matched?

still4given · 2016-02-09 6:44 pm

ammel68 said:
Very nice! Thank you for sharing your Sprint file.

Do you plan on doing a Sprint PCB for the FX8 like Terry shows in post 6202?

Here is my Sprint file. It has slight changes to the one I posted. I just moved things a little to improve it.

EDIT; BTW the trimmer ends up about 200R so a 500R trimmer would probably be better.

ammel68 · 2016-02-09 6:50 pm

still4given said:
Here is my Sprint file. It has slight changes to the one I posted. I just moved things a little to improve it.

EDIT; BTW the trimmer ends up about 200R so a 500R trimmer would probably be better.

Thank you!

still4given · 2016-02-09 6:58 pm

ammel68 said:
Thank you for the comparisons and scope shots.

What transformer and power supply are you using?

Do the Latfets need to be matched?

Right now I am just using a small test PSU. 160VA 30-0-30vac and using a variac to set the rails. They sag quite a bit when testing to clipping. I have the rails set to +-36V and as you can see it sags to almost +-32V at full clip. However, during even loud listening it barely drops at all. If I built this into a complete amp I would of course us a stiffer supply.

There is only one pair of Latfets so no matching is required. I did hFE match the input pair. I have <14mV offset on both channels.

apexaudio · 2016-02-09 7:01 pm

still4given said:
I got a chance to hook it up to my A/B setup. I don't have an AX14 hooked up right now so I compared it to some other amps. Held its own against the Honey Badger, DX MKIII, and a Peeceebee. To answer Thimios' question, the bass is very good. Strong and solid. These little Latfets never cease to amaze me. Attached are some scope shots. Forgive the lighting.
The voltages shown are at clipping. Negative rail on the left and AC RMS output on the right. This into 8ohm resistive load.

Blessings, Terry

Nice work... replace C7 with 1000uF/16V instead 100uF/63V to improve 50hz square.
Regards

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