I took a look inside my units to verify speaker polarity for BTL. The red Right post is connected to the red wire, which goes to pin 1 (amp channel 2 out) on the Speaker header of the 125ASX2. So based on Fig 17 page 25, the RIGHT red post is positive speaker polarity and the LEFT red post is negative for BTL. I am assuming the preamp is noninverting. This corresponds with the Vocopro manual page 14, except that the right and left are reversed, adding to the confusion. I sent an email to Vocopro tech support. No response yet.
Also, there is one NJM4580 on a powered PCB between the two PCB mount TRS jacks, so the balanced input is converted to unbalanced, with a shielded two conductor wire running from the TRS PCB header to the preamp board. As best as I could estimate the package size of the 4580, I think they are about 3mm square, so the package appears to be MSOP8. I was unable to directly measure, because it's sitting between the two TRS jacks.
The potentiometers on the preamp board are 100k.
Also, there is one NJM4580 on a powered PCB between the two PCB mount TRS jacks, so the balanced input is converted to unbalanced, with a shielded two conductor wire running from the TRS PCB header to the preamp board. As best as I could estimate the package size of the 4580, I think they are about 3mm square, so the package appears to be MSOP8. I was unable to directly measure, because it's sitting between the two TRS jacks.
The potentiometers on the preamp board are 100k.
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So it seems the preamp stage is not top notch?
I will take it out and drive it with 3e ADAU 1701 DSP
The FA-500 sounded good on some music and not others. Had me fooled. Just making the assumption at this point that it's the preamp board. I've read that the 125 should sound better than the 500.
Still a good deal considering I have a project case, some decent binding posts and cable set for the 125.
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The other thing about the FA-500 is the bad layout. The SMPS is at the end of the box with input jacks and binding posts. From the TRS inputs, there is a 4850 based balanced receiver, and the shielded single-ended input cable crosses over the SMPS to get to the preamp board at the amp end of the module. Also, the untwisted speaker output wires cross over the SMPS. I think the first thing to try is have the inputs and outputs on the amp end of the module. Easy first step.
Or just cut off the leads soldered in, and a dual pot to the leads hanging out. SafeIf we knew the value
On mine there is about a 1K difference between the two channels on the pot. I wondered why they used dual gang pots for mono volume controls, must have gotten a good deal.
On mine they did. Both were off by about the same amount. I had a 50K pot that I put in it for now.
They cut the pins off the top gang on both pots. At first I removed one pot and ran wires to connect to what was left of the top connectors on the other. I immediately noticed the volume was higher on one side. When I measured the resistance on the pot that I had remove it was about 1K higher on one gang and when I removed the other pot it was the same.
I also twisted the power cord inside the case and plan to unsolder the speaker wires inside and twist them too. I haven't looked at twisting the input wires, it gets pretty tight inside the case.
These amps are designed as Karaoke amps but according to the instructions I don't see a reason why they went with separate controls and on top of that don't have detentes. They call them 'gain controls' but then go on to say to use them to adjust the volume and not the volume on your source.
http://vocopro.com/products/pdf_manuals/featheramp.pdf
I have a B1 buffer that I may try with mine at some point, but I've been running it today with the built in buffer and a single 50K stereo pot replacing their original ones.
For the subjective part:
I'm really impressed so far. For critical listening I still prefer my tube amp but I've had this one on most all of the day today and it is plenty enjoyable to listen to while I do other things. The lower power usage and less heat is ideal in those situations. I'm half tempted to use a switch box and have the option of using either amp.
For me I like it better at lower volumes, it doesn't have any harshness at that level but seems to get a bit much at higher volume. But that may just be that I'm used to an 8 watt tube amp and a 25 watt M2 amp for most of my listening prior to this. It does better at jazz and classical than I thought it might.
I also twisted the power cord inside the case and plan to unsolder the speaker wires inside and twist them too. I haven't looked at twisting the input wires, it gets pretty tight inside the case.
These amps are designed as Karaoke amps but according to the instructions I don't see a reason why they went with separate controls and on top of that don't have detentes. They call them 'gain controls' but then go on to say to use them to adjust the volume and not the volume on your source.
http://vocopro.com/products/pdf_manuals/featheramp.pdf
I have a B1 buffer that I may try with mine at some point, but I've been running it today with the built in buffer and a single 50K stereo pot replacing their original ones.
For the subjective part:
I'm really impressed so far. For critical listening I still prefer my tube amp but I've had this one on most all of the day today and it is plenty enjoyable to listen to while I do other things. The lower power usage and less heat is ideal in those situations. I'm half tempted to use a switch box and have the option of using either amp.
For me I like it better at lower volumes, it doesn't have any harshness at that level but seems to get a bit much at higher volume. But that may just be that I'm used to an 8 watt tube amp and a 25 watt M2 amp for most of my listening prior to this. It does better at jazz and classical than I thought it might.
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Thanks for valuable info. Are the potentiometers linear or logaritmic ?
I got two of the FA-500. I think they will do better in a standard amplifier chassis where space for more convenient wiring and locations of sockets and pots can be done.
The pots are log. Before investing in expensive pots, consider dumping the preamp board. Like you, I now plan to get the modules out of the FA-500 cases. Rerouting the speaker and input cables helped the sound quality significantly, but still the preamps are not up to the audiophile standard of the icepower modules. The modules are very powerful, but there is some distortion I'm sure is from the preamp board. It makes no sense to have a substandard preamp for an audiophile grade power amp. For BTL mode, I need a balanced line driver. I'm first trying an input transformer, then plan to make a 5532 based balanced line drivers.
Be sure to check designer's manual for proper cable routing and other mounting considerations. The cable lengths are very good except for the power cable, that looks like it is short. The binding posts are pretty good quality and can be reused.
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Another messed up thing with the FA-500 is that the output of the preamp board looks like it goes through the 8 lead rainbow cable going to the signal header of the 125 (P102). But there are no shielded audio grade wires for signal in that cable. It's hard to see back there, but if that is in fact the case, that is not right. The preamp may not be the problem. Again, it could be wiring.
I took the bottom cover off and yes the P102 has only unshielded hookup wire.
I took the bottom cover off and yes the P102 has only unshielded hookup wire.
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