F5 Turbo Builders Thread

[rubofdagreen]

I had a very similar situation with my F% when I built it. The FETs were fine but I had 2 resistors next to each other in the wrong holes. Took an awful lot of staring to find that.

[AudioSan]

as i always say. build it right the first time

[anilva]

Originally Posted by AudioSan

as i always say. build it right the first time

I don't think anyone starts building an amp with an objective not to build it right ;-) Errors do creep up in different forms including component failures and spurious copies.

[AudioSan]

anilva. ofcource. component falilure is out of our control
as for the rest. it has been done before. and working
so i stick with do it right the first time

[rubofdagreen]

Audiosan,
Thank you so much. Your observations are always so astute. I on the other hand have screwed up on construction projects everyway possible. It has helped me learn how to fix things. Try this, unhook the board from the heatsink, using a variac bring the power up slowly and carefully, to around 8 or 10 volts output on the power supply. Feel the output transistors. If only one side +/-, gets warm, you can test the transistors on the other side. If they test fine start looking at the resistors.

[anilva]

Originally Posted by anilva

OK, got the board that was giving problems (left channel), wired up again after fixing few dry solders and a loose connection at middle leg of P3.


Board biased nicely. Took it up to 200mV bias and let it settle. Then connected the speaker and played music. Seems to play well and without any gain issues, previously encountered, but I could hear distortion a little bit, compared to the other channel (right channel) which is playing music brilliantly like with any Pass amp, no distortion and full dynamics.

Tried taking the problem channel (left) to bias around 350 mV. That's when I realized there is a problem. The trimmer P1 maxed out and could not push the bias anymore than 320 mA. Then twiddled around with P3 and there seems to be a big impact on output null and the bias levels. Altered a little bit of P3 and managed to set the bias to 350mA. Connected music and played - same problem as earlier case. No gain. Very feeble. Then turned the P3 the other way and connected, while monitoring the bias. Music played back normally (with little bit of distortion) and in a short while, smoke came out from 2SK170. Quickly disconnected the power and removed the board to examine. 2SK170 split open near the base of it's legs. I suspect the P channel MOSFETs are also gone. Luckily the speaker is a test one and nothing happened to it.

Any insights what could have happened? May be it's a bad P3 component. Rest of the components are checked. Seem OK.

I will park this board for a while to debug in leisure. I cannot afford blown MOSFETs. I have a spare PCB. Will stuff it up, double checking this time with presets and everything else.

Cheers.

Wired up a new PCB and component set for the bad channel. Works perfectly well now. Biases nicely and stable. Took it upto 350mV bias. The heatsinks are massive and very effective. Originally over engineered for Turbo V3. They get to be mildly hot.

Checked the audio. Works perfectly. Did not listen enough to find the differences between my existing F5 builds and this. Looks like I have completed the build of F5 Turbo V2. Will post pictures once I tidy up the wiring in a day or so.

Thanks to everyone for their help.

Cheers.

[buzzforb]

Awesome. I would like a impression based on direct comparison with regular F5. You may be one of few that has both on hand to compare.

[anilva]

Originally Posted by buzzforb

Awesome. I would like a impression based on direct comparison with regular F5. You may be one of few that has both on hand to compare.

Thanks. I will compare both and post my impressions. BTW the mosfets and the diodes are from you ;-) Thanks for the help to the DIY community. My next one in a identical chassis is the V3. But for the screw-up w.r.t to mounting holes on the heatsink for the mosfets, I would have gone into the testing phase of V3 as well.

[anilva]

As mentioned in an earlier post, completed the build including setting up the biases, monitoring heat and stability etc.

Also did few hours of sound testing with my Fostex back loaded horns, which are currently used with a standard F5.

As far as impressions of the sound are concerned, the amp is simply outstanding. It has F5 like detail and clarity and has very strong dynamics and a solid bass support. Each and every instrument can be felt and heard. The amp does not attract attention and one instantly starts enjoying the music rather than hearing the amp. There is no fatigue. The difference between a regular F5 and F5 Turbo V2 as far as my build comparison is concerned, is that the Turbo is bit more warmer and more in control. It has stronger dynamics and support for stronger bass. These needs to be taken as a relative comparison and in no way a comment on standard F5's sound. While the sound signatures are almost similar, I should be able to tell a Turbo in a blind test due to stronger dynamics and bass.

Definitely a keep in my collection. Have a minor non-instrusive hum problem to be resolved in terms of double ground from my preamp. Also have a suspicion that 8 x 10000 uF per power supply rail is not sufficient enough. It probably needs to be 8 x 22000 uF. With higher bias, the capacitors are adding leakage current.

The heatsinks are warm and not hot enough. The Toroid is a 1KVA model. Both these are a overkill for a V2. Will use the trafo for V3 soon and swap it with a 600VA model.

Here are the pictures:

[dazed2]

Anivila, great job!
Thank you for the review of your impressions against the F5. What you said is exactly the reason I am about to embark on building the V3

BTW how did you go about tuning harmonics using P3?