In that case maybe keep your eye on the swap meet, you might get lucky with a bargain.
https://www.diyaudio.com/forums/swap-meet/
https://www.diyaudio.com/forums/swap-meet/
In looking over the forum topics, I noticed the BA3 and remembered that the front end provides gain for an F4 output stage (and can also be used as a simple preamp). $14 in the store for the stereo board: Burning Amplifier Gain Stage for BA-3 – diyAudio Store
A natural pairing that's literally made to go together. I'm going to build a pair for my subwoofer channels.
I just finished my F4. Or should I say, I got my bias stable at temp and got to listen to the amp for a few hours.
It's unbelievable how good it sounds. I've been using a pair of ACAs and thought it might be hard to improve on their sound. The F4 seems to be in a different league. I guess it's time to build the BA3 Preamp.
Thanks to 6L6, Zen, Pico, Dennis, Ben, Cal and all the other frequent F4 thread or Diyaudio posters that I have been reading.
And most of all, thanks to Papa for his skill and generosity!
It's unbelievable how good it sounds. I've been using a pair of ACAs and thought it might be hard to improve on their sound. The F4 seems to be in a different league. I guess it's time to build the BA3 Preamp.
Thanks to 6L6, Zen, Pico, Dennis, Ben, Cal and all the other frequent F4 thread or Diyaudio posters that I have been reading.
And most of all, thanks to Papa for his skill and generosity!
Originally Posted by pelvez View Post
This is my first post in diyaudio.com so please forgive me if I'm posting a wrong thread.
I've the opportunity to buy a F4 at a reasonable price, I don't think my source will have adequate voltage swing so I need some gain. I'm wondering if a Lundahl LL7906 trafo at the input of the F4 could be a feasible solution? Has anyone used a transformer this way?
Or should I rather go for a little line stage with Burton Audio discrete op-amps Supreme Sound Opamp V6 – Burson Audio?
I guess both solutions can be implemented for around $300,- Other suggestions in that price range?
Pelvez
You might want to see:
Introducing the MAGMA front end for BA-2 and F4
as it gives an example of a transformer VAS for a BA-3/F4 type of current
amplification stage.
I have not heard the LL7906, but I have (and am currently using) a
buffer->LL7905->buffer->BA-3. I think it sounds fantastic. If your
rails are much over 25V, the buf between the transformer and output
stage needs to be re-designed from what the magma project did. I
used a DN2530 based buffer (self biasing, very simple). I use +/-33V
rails. The LL7905 can go to 20Hz with (relatively) low distortion at
28V peak. That drives the amp to 98W peak, or not quite 50W rms
at about 1% distortion with 0 feedback (aside from source resistor
degeneration). As an autoformer, it has about 6x voltage increase.
The short answer is that I think very highly of the LL7905. The LL7906
is supposed to be an update, so maybe it is even better. If you try
it, please let us know!
This is my first post in diyaudio.com so please forgive me if I'm posting a wrong thread.
I've the opportunity to buy a F4 at a reasonable price, I don't think my source will have adequate voltage swing so I need some gain. I'm wondering if a Lundahl LL7906 trafo at the input of the F4 could be a feasible solution? Has anyone used a transformer this way?
Or should I rather go for a little line stage with Burton Audio discrete op-amps Supreme Sound Opamp V6 – Burson Audio?
I guess both solutions can be implemented for around $300,- Other suggestions in that price range?
Pelvez
You might want to see:
Introducing the MAGMA front end for BA-2 and F4
as it gives an example of a transformer VAS for a BA-3/F4 type of current
amplification stage.
I have not heard the LL7906, but I have (and am currently using) a
buffer->LL7905->buffer->BA-3. I think it sounds fantastic. If your
rails are much over 25V, the buf between the transformer and output
stage needs to be re-designed from what the magma project did. I
used a DN2530 based buffer (self biasing, very simple). I use +/-33V
rails. The LL7905 can go to 20Hz with (relatively) low distortion at
28V peak. That drives the amp to 98W peak, or not quite 50W rms
at about 1% distortion with 0 feedback (aside from source resistor
degeneration). As an autoformer, it has about 6x voltage increase.
The short answer is that I think very highly of the LL7905. The LL7906
is supposed to be an update, so maybe it is even better. If you try
it, please let us know!
Congratulations! What are you driving the F4 with?
Thanks! Last night I ran it with an H2 that I use as a preamp. Tonight I'll try it with the ACP+ that I built at Burning Amp.
Or upgrade - Sony VFET front end
Yes, that would be great. I'm sure it would sound superb.
Thanks, Cal. And thanks for the N and P devices.
I really can't believe it will sound better than it already does.
You could try a few things with Aleph J. The improvement is quite dramatic... I have Dynaudios that are 86dB efficient and have pretty even 4 ohms impedance. The bottom control, definition and extension are exceptional (as is the overall sound).
1. Remove the 1uF cap from the input. This is by far the most important mod. This will make Aleph J a nice DC amp, so be careful as well....
2. Organise the PCB placement inside the amp in such way, to minimise the AC wiring length, and the power rails/speakers wiring lengths.
3. Use a VERY short & think wires for DC rails and speakers
4. Tune the power supply - there are provisions for the snubber capacitors and resistors on the PCB - do not use the resistors, but only the capacitors. I used 100uF / 50V caps in parallel with the capacitors bank (+ some other smaller values caps... this will fine-tune the sound). Do not underestimate the importance of this fine-tuning.
5.Remove the short circuit/overload protection
6. Use low impedance speaker wires... I use silver alloy ribbons
7. Play with IEC filter... I use it and like the result, but the amp may sound better without the RF IEC mains filter.... highly debatable.
1. Remove the 1uF cap from the input. This is by far the most important mod. This will make Aleph J a nice DC amp, so be careful as well....
2. Organise the PCB placement inside the amp in such way, to minimise the AC wiring length, and the power rails/speakers wiring lengths.
3. Use a VERY short & think wires for DC rails and speakers
4. Tune the power supply - there are provisions for the snubber capacitors and resistors on the PCB - do not use the resistors, but only the capacitors. I used 100uF / 50V caps in parallel with the capacitors bank (+ some other smaller values caps... this will fine-tune the sound). Do not underestimate the importance of this fine-tuning.
5.Remove the short circuit/overload protection
6. Use low impedance speaker wires... I use silver alloy ribbons
7. Play with IEC filter... I use it and like the result, but the amp may sound better without the RF IEC mains filter.... highly debatable.
Attachments
I've tried the F4 with the ACP+ as well. The gain was a bit on the low side
but it sounded great anyway.
Adding the BA3 preamp will give you essentially the BA3 push-pull amp.
It will be great.
Cheers,
Dennis
Originally Posted by pelvez View Post
I have not heard the LL7906, but I have (and am currently using) a
buffer->LL7905->buffer->BA-3. I think it sounds fantastic.
Tell us more
How about a schematic? 
I have this power supply. +/-20V about 800VA
53.000uf/rail.
What do you think, is it suitable for a stereo F4?
This one belongs to Bonsai SX class A,but i can live with 2 amplifiers & 1 power supply (Interchangeable)
At the same time this will be the chassis bottom.
53.000uf/rail.
What do you think, is it suitable for a stereo F4?
This one belongs to Bonsai SX class A,but i can live with 2 amplifiers & 1 power supply (Interchangeable)
At the same time this will be the chassis bottom.
Attachments
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Never thought of it, but AJ->F4 might be a nice thing to do. AJ is one of my favorite amps, but it doesnt do very well in low/"difficult" impedance speakers.
p.s. As you can tell this pandemic made me start thinking about building amps again hehe
BA2 is virtually the same thing.