I built an ACA and was quite blown away, then did an F5.
The F5 isn't housed in a chassis yet, but wires are fairly well separated.
Its got maybe 15hrs on it. It seems to be missing something in the upper bass, the acoustic bass in Tears in Heaven by Clapton (live) has almost disappeared, its very faint.
The ACA presents the same song bewdifully!
Checked all phasing which was fine, yet the lower bass registers are also fine. I noticed the upper bass missing in quite a few other CD's but never really nailed exactly what was missing until I played Tears in Heaven.
F5 bias is set at 0.59vDC, DC offset 10~15mV.
I have P1 mounted, set mid range (30 turn pots) so set at 15 turns
Heatsinks are static at 39degC
Rails are +/- 22.8vDC
It's using the following;
Antek 5218
Monolithic 35A Rectifiers
16 gauge wire for DC power
Twisted CAT5 for inputs
16 gauge output wire
120,000uF Caps total (+ and -)
When I changed the ACA v1.8 out for the F5, I changed nothing else.. just the amps.
The F5 isn't housed in a chassis yet, but wires are fairly well separated.
Its got maybe 15hrs on it. It seems to be missing something in the upper bass, the acoustic bass in Tears in Heaven by Clapton (live) has almost disappeared, its very faint.
The ACA presents the same song bewdifully!
Checked all phasing which was fine, yet the lower bass registers are also fine. I noticed the upper bass missing in quite a few other CD's but never really nailed exactly what was missing until I played Tears in Heaven.
F5 bias is set at 0.59vDC, DC offset 10~15mV.
I have P1 mounted, set mid range (30 turn pots) so set at 15 turns
Heatsinks are static at 39degC
Rails are +/- 22.8vDC
It's using the following;
Antek 5218
Monolithic 35A Rectifiers
16 gauge wire for DC power
Twisted CAT5 for inputs
16 gauge output wire
120,000uF Caps total (+ and -)
When I changed the ACA v1.8 out for the F5, I changed nothing else.. just the amps.
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You try fully reversing the speakers' connection?
Which preamp are you using? Is it a single-ended that reverses phase?
Which preamp are you using? Is it a single-ended that reverses phase?
Those monolithic 35A rectifiers are dropping an awful lot of voltage. A beefy 500VA transformer should be able to give you more than just +/– 22.8V DC on the rails. That won't affect the bass performance, but it does suggest overall power improvement is possible.
The suggestion to confirm the phase of the amp & system is a good one. Dynamic impulse content requires correct phase alignment to sound right. This may also suggest some experimentation with the bias current is in order.
The suggestion to confirm the phase of the amp & system is a good one. Dynamic impulse content requires correct phase alignment to sound right. This may also suggest some experimentation with the bias current is in order.
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Maybe just a typo but P3 is the one to leave alone. P1 and P2 do bias and offset. Maybe the pots are in the wrong place?
S-Lost... your correct, sorry typo, P3 is set at mid point (15 turns).
I'm using a Krell Showcase Pre, I dont believe it reverses phase. I haven't had this problem with other amps I've used in this system.. like Rotel, Krell, Parasound, Luxman & the ACA.
I tried reversing the rectifier inputs, that made no difference.
Have double checked all other phasing on this F5, it all looks good.
Will try taking the bias up while watching temps. I understand I can increase bias to just below the point of current draw taking off. Does anyone know roughly what bias voltage this usually starts to occur on an F5?
Unfortunately I cant find my DMM Clamp so dont have a means to monitor current draw at the moment
I'm using a Krell Showcase Pre, I dont believe it reverses phase. I haven't had this problem with other amps I've used in this system.. like Rotel, Krell, Parasound, Luxman & the ACA.
I tried reversing the rectifier inputs, that made no difference.
Have double checked all other phasing on this F5, it all looks good.
Will try taking the bias up while watching temps. I understand I can increase bias to just below the point of current draw taking off. Does anyone know roughly what bias voltage this usually starts to occur on an F5?
Unfortunately I cant find my DMM Clamp so dont have a means to monitor current draw at the moment
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Assuming the amp is biased correctly (should be 1.4A or whatever temp the heatsink reaches about 50c) you may be hearing the lack of 2nd harmonic in the f5. Basically, you might be hearing what's actually on the record instead of a juicier version like w/the ACA. The single ended, low wattage ACA w/high 2nd harmonic will make the bass more bloated and appear bigger. It's a possibility.
Since it's new run it in for 40 to 50 hours with a burn-in track or FM static from a tuner or receiver with pre outs. Also don't downplay the importance of a solid chassis.
In general, the f5 is not a “fat” amp I think. I think that’s what you are hearing. For simple acoustic music an amp like the aca will sound more romantic. Especially if you are not listening loud.
When things get complicated and loud is where you will come to appreciate the F5 and it’s lack of bloat and overhang. If you still don’t like it play with p3. If that’s not enough then it would be best to pair it with a preamp with some flavor like the korg b1.
If your bias is good and phase is correct you are listening to the way the amp sounds. Your bias (.6v) is correct but if your heatsinks are only 39c I would think they would be hotter than that. Hard to tell because they aren’t enclosed in a chassis. Also, they need air from the bottom to cool correctly. You can take the bias up higher to 1.8a or so…this will give the f5 more weight and body. Your heatsinks should be under 55c though…so watch the temps.
When things get complicated and loud is where you will come to appreciate the F5 and it’s lack of bloat and overhang. If you still don’t like it play with p3. If that’s not enough then it would be best to pair it with a preamp with some flavor like the korg b1.
If your bias is good and phase is correct you are listening to the way the amp sounds. Your bias (.6v) is correct but if your heatsinks are only 39c I would think they would be hotter than that. Hard to tell because they aren’t enclosed in a chassis. Also, they need air from the bottom to cool correctly. You can take the bias up higher to 1.8a or so…this will give the f5 more weight and body. Your heatsinks should be under 55c though…so watch the temps.
Also, I’d try something other than cat5 or the input. It’s probably not your issue but my experience has been that sometimes cat5, although should be technically fine, can sound odd. I used to wire every signal in a chassis with cat5 and sometimes it just sounds etched and bad. Now I just just use regular interconnect wire, even if I have to strip down an interconnect of its shielding.
The input impedance is 47k, so if your source has a coupling capacitor of at least 2uF,
that won't be a problem. The F5 is direct coupled from input to output, so the bass should
be better than other amps which are not. That may take a while to get used to, though.
that won't be a problem. The F5 is direct coupled from input to output, so the bass should
be better than other amps which are not. That may take a while to get used to, though.
ACA has much higher output impedance and distortion so interacting with your speaker impedance is different and can be heard, I guess that is "the problem".
I remember the F5 being sensitive to temperature.
It's been a while since I built them.
Just waving my hand over the circuit would alter the bias.
Maybe once you get a case together, the amp will settle.
The F5 might have a critical sound, but it's not a dud.
It's been a while since I built them.
Just waving my hand over the circuit would alter the bias.
Maybe once you get a case together, the amp will settle.
The F5 might have a critical sound, but it's not a dud.
Yes, different speakers will interact less (or more), depending on their impedance.
Try something else and see.
thanks fella's, some good pointers there. Well I decided to tidy things up a bit and check the bias & offset again. Following is what I did before another listening test:
Temporally mounted RCA and Speaker posts to sinks to shorten and tidy up CAT5 in and speaker out cables
Rearranged the DC wires from PSU, twisted together a little now. Still room for improvement on left channel - will do this today
Flip sinks so Mosfets are sitting below PCBs.. runs a tad hotter now ~41degC (was around 39degC with Mosfets above PCB)
Re-bias amp. 0.59v with ~0 DC offset (offsets were around +20mV)
Did a listen test... WOW, the improvement is massive! I've now got all the upper bass that was missing, everything has fallen into place, its very well balanced across the spectrum, nothing is missing or bloated. The noise floor has dropped a little too. The improvement in dynamics was unbelievable, this amp now sings, I'm pretty chuffed.. I love it!!! So that means the ACA can now go up in the workshop 😀
I think the main problem was 2 things...
EMI getting into the CAT5, beforehand they were pretty long and dangling in the vicinity of AC
This time when biasing I shorted the inputs... I didnt realise this had to be done too prevent stray signal ingestion
Today I also plan to set P3 using FFT. Is there any preference for what resistance load to use, ie 4 or 8 ohm? I understand P3 should be set with 1KHz @ 1W into the load.
Temporally mounted RCA and Speaker posts to sinks to shorten and tidy up CAT5 in and speaker out cables
Rearranged the DC wires from PSU, twisted together a little now. Still room for improvement on left channel - will do this today
Flip sinks so Mosfets are sitting below PCBs.. runs a tad hotter now ~41degC (was around 39degC with Mosfets above PCB)
Re-bias amp. 0.59v with ~0 DC offset (offsets were around +20mV)
Did a listen test... WOW, the improvement is massive! I've now got all the upper bass that was missing, everything has fallen into place, its very well balanced across the spectrum, nothing is missing or bloated. The noise floor has dropped a little too. The improvement in dynamics was unbelievable, this amp now sings, I'm pretty chuffed.. I love it!!! So that means the ACA can now go up in the workshop 😀
I think the main problem was 2 things...
EMI getting into the CAT5, beforehand they were pretty long and dangling in the vicinity of AC
This time when biasing I shorted the inputs... I didnt realise this had to be done too prevent stray signal ingestion
Today I also plan to set P3 using FFT. Is there any preference for what resistance load to use, ie 4 or 8 ohm? I understand P3 should be set with 1KHz @ 1W into the load.
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Good work.
Monitor the bias when adjusting P3.
Work slowly, in gradual changes.
Make sure the bias doesn't run up on you.
Monitor the bias when adjusting P3.
Work slowly, in gradual changes.
Make sure the bias doesn't run up on you.
I know people will say “wire is wire” but I’ve replaced cat 5 in a preamp with regular interconnect wire (unshielded) and experienced similar changes. So, no more cat5 for me.
.. will do vdi_nenna, thanks heaps for the input.
Tidying up has made the world of difference - but I also wasn't shorting the inputs and the CAT5 dangled around AC... there's no doubt that didnt help matters.
Thats interesting Hikari1, I do plan to try different input wire at some stage, be interesting to see how it goes.
For now I'm a Happy Chappy - thank yo'll
Tidying up has made the world of difference - but I also wasn't shorting the inputs and the CAT5 dangled around AC... there's no doubt that didnt help matters.
Thats interesting Hikari1, I do plan to try different input wire at some stage, be interesting to see how it goes.
For now I'm a Happy Chappy - thank yo'll
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Is shorting of inputs for biasing something that should be done as a matter of course for any amp (not just the FWs)?
yesterday I put the F5 on FFT to set P3, 1KHz sinewave @ 1W, tried with both 4 and 8 ohm loads.
The 3rd harmonic was higher than the 2nd. My preference is to have the 3rd lower than the 2nd and maybe even knock the 3rd out completely as reports suggest 3rd harmonics bring listening fatigue.
I went about 4 turns clockwise and also anticlockwise but could see any change in the harmonic levels.
Also the 4 ohm load seems to emphasise harmonics more than an 8 ohm load, why?
I didnt want to go to far with P3 as I've read reports where people have cooked components from having P3 incorrectly set
Am I doing something wrong??
My setup was as follows;
~750mV 1KHz sinewave signal = 1W at the 8 ohm load
FFT was AC coupled
No scope earth wire used to prevent grounding F5 outputs, only (+) probe used
FFT signal was more prominant with scope probe on (-) speaker side of either load
As mentioned I went about 4 turns in both directions with P3 but the F5 didnt appear to respond ?!?
The 3rd harmonic was higher than the 2nd. My preference is to have the 3rd lower than the 2nd and maybe even knock the 3rd out completely as reports suggest 3rd harmonics bring listening fatigue.
I went about 4 turns clockwise and also anticlockwise but could see any change in the harmonic levels.
Also the 4 ohm load seems to emphasise harmonics more than an 8 ohm load, why?
I didnt want to go to far with P3 as I've read reports where people have cooked components from having P3 incorrectly set
Am I doing something wrong??
My setup was as follows;
~750mV 1KHz sinewave signal = 1W at the 8 ohm load
FFT was AC coupled
No scope earth wire used to prevent grounding F5 outputs, only (+) probe used
FFT signal was more prominant with scope probe on (-) speaker side of either load
As mentioned I went about 4 turns in both directions with P3 but the F5 didnt appear to respond ?!?