Everything seems fine. The VAS bias measuring resistors are R29/30 in V4 (rev1 or 2) and R25/26 in V4H.
If you are reading proper voltages at R29/30 then all is well. The 47R resistors near output terminal are part of the zobel and are indeed in parallel, in both rev1 and 2.
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There are a few other things that change from v4; e.g. 220R, 22k, 1n4148, gate resistors, decoupling capacitor value and physical place on board, different zobel configuration and physical orientation, feedback resistors and FET source resistors.
Hi Shaan,
Thanks for the update, glad to know everything is ok.
Regarding the VAS bias measuring resistors, I got the information that they should be R25/26 for the V4 rev2 from the August 2018 PeeCeeBee Rev2. amplifier setup guide. I gather this was a mistake in the text and was rectified later?
Anyway, looking forward to getting this assembled into its case next week. Thank you very much for your help Shaan, it's been much appreciated by this novice!
Cheers
Neal
Thanks for the update, glad to know everything is ok.
Regarding the VAS bias measuring resistors, I got the information that they should be R25/26 for the V4 rev2 from the August 2018 PeeCeeBee Rev2. amplifier setup guide. I gather this was a mistake in the text and was rectified later?
Anyway, looking forward to getting this assembled into its case next week. Thank you very much for your help Shaan, it's been much appreciated by this novice!
Cheers
Neal
I upgraded the compensation network according to Rev2 #704 and i didn't expected so much difference after this.
I would really appreciate if someone else would like to share their perception in sound change after Rev2 mod.
My subjective impression is that the sound became more energetic, more lively, bass is much stronger (sometimes a bit too strong, need more listening), voices more proeminent and more details in the treble area. I use a SMPS power supply.
Great little amp Shaan! Thanks!
I would really appreciate if someone else would like to share their perception in sound change after Rev2 mod.
My subjective impression is that the sound became more energetic, more lively, bass is much stronger (sometimes a bit too strong, need more listening), voices more proeminent and more details in the treble area. I use a SMPS power supply.
Great little amp Shaan! Thanks!
Hi Adrian.
The Rev2 mod attenuates higher order harmonics at upper mid and high frequencies to minuscule levels. This simulates the behavior of a class a amplifier that uses high bias to linearize its output stage. In v4's case however the linearization is performed by utilizing available negative feedback across the VAS and output stage. The VAS is of emitter follower type so has a very large gain, and trading some of the gain to linearize the output stage before global feedback is taken from the output is an excellent and practical idea (thanks again to Mr. Baxandall (RIP) and Mr. Self). I feel the cost to performance ratio of the mod is such low that it is ridiculous, works almost like magic!
The first time I listened to the rev2, it felt like I was listening to a monster class-a amplifier, but without all the waste heat. I have always been impressed by the effect of high bias, almost a thumbnail trick to reduce high order distortion in nearly every push-pull amplifier as long as you buy sufficient aluminium and electricity i.e. there are tradeoffs. Likewise, while similar performance is achieved by negative feedback, I learned that in order for NFB to work the way you want, you must treat it like your woman and give it what is demands - attention, respect, proper treatment and a very stable window of operation, and V4 Rev2 gives her all the above! Result - happy family.
While it took some brain cells and some sleep, in the long run it saved lots of aluminium and electricity.
The cost of using this technique is a couple dB of less feedback i.e. a couple dB more THD and some reduction in damping factor, at LF. But hey, even after that, we measured 0.0005% at LF and as members report, the bass is top class!
Cheers and Happy Listening!
shaan
The Rev2 mod attenuates higher order harmonics at upper mid and high frequencies to minuscule levels. This simulates the behavior of a class a amplifier that uses high bias to linearize its output stage. In v4's case however the linearization is performed by utilizing available negative feedback across the VAS and output stage. The VAS is of emitter follower type so has a very large gain, and trading some of the gain to linearize the output stage before global feedback is taken from the output is an excellent and practical idea (thanks again to Mr. Baxandall (RIP) and Mr. Self). I feel the cost to performance ratio of the mod is such low that it is ridiculous, works almost like magic!
The first time I listened to the rev2, it felt like I was listening to a monster class-a amplifier, but without all the waste heat. I have always been impressed by the effect of high bias, almost a thumbnail trick to reduce high order distortion in nearly every push-pull amplifier as long as you buy sufficient aluminium and electricity i.e. there are tradeoffs. Likewise, while similar performance is achieved by negative feedback, I learned that in order for NFB to work the way you want, you must treat it like your woman and give it what is demands - attention, respect, proper treatment and a very stable window of operation, and V4 Rev2 gives her all the above! Result - happy family.
While it took some brain cells and some sleep, in the long run it saved lots of aluminium and electricity.
The cost of using this technique is a couple dB of less feedback i.e. a couple dB more THD and some reduction in damping factor, at LF. But hey, even after that, we measured 0.0005% at LF and as members report, the bass is top class!
Cheers and Happy Listening!
shaan
Finally got my V4 finished!
I had hums and buzz for a while, but now it's at the stage where I have to have my ear next to the speaker to hear a faint buzz when no music is playing.
I've only had it through my office and kitchen setups, where the speakers aren't that great, but the sound is fantastic. I've tried it with reggae, electronic and classical music so far and it really does handle a wide variety of music well.
I found this build quite challenging, but it has taught me patience and I've learned along the way, which is important to me.
I would like to express my gratitude and admiration to Shaan for making this amp and PSU available to us, and especially for his help and advice. Similarly to the other forum members who chipped in with suggestions, thank you, it is much appreciated.
I had hums and buzz for a while, but now it's at the stage where I have to have my ear next to the speaker to hear a faint buzz when no music is playing.
I've only had it through my office and kitchen setups, where the speakers aren't that great, but the sound is fantastic. I've tried it with reggae, electronic and classical music so far and it really does handle a wide variety of music well.
I found this build quite challenging, but it has taught me patience and I've learned along the way, which is important to me.
I would like to express my gratitude and admiration to Shaan for making this amp and PSU available to us, and especially for his help and advice. Similarly to the other forum members who chipped in with suggestions, thank you, it is much appreciated.
Attachments
Hi Neal.
It's great to know you finished the V4 amp build. The enclosure is awesome.
Thanks for the kind words, and happy listening.
Hi Greg,
Thank you very much.
Two extra circuits were used. The ground loop breaker is indeed based on the ESP circuit. The website circuitbasics has a link to a PCB you can order for fabrication yourself. I ordered 10 for £6 inc p&p.
There is also a Hypex softstart module, and this also incorporates some additions, such as the ability to have status LEDs, temperature monitoring and a push button switch.
Cheers
Neal
Thank you very much.
Two extra circuits were used. The ground loop breaker is indeed based on the ESP circuit. The website circuitbasics has a link to a PCB you can order for fabrication yourself. I ordered 10 for £6 inc p&p.
There is also a Hypex softstart module, and this also incorporates some additions, such as the ability to have status LEDs, temperature monitoring and a push button switch.
Cheers
Neal
I've had a week with the PeeCeeBee V4 now and just thought I would share some observations.
After moving the amp into its final home -the office/shed in my garden - the hum/buzz increased to a level that was unacceptable. I did lots more reading and experimenting and finally got to the point where for all intents and purposes (bearing in mind I'm 51 years old with some tinnitus) the amp is silent when no music is playing. I have the ground/shield from the RCA inputs tied together at their tabs, but the shield goes to V-- at the amp rather than the PSU ground. This cable (signal and shield) was always close to the AC input and soft start but routing it away from these worked, even though it's now longer and right next to the transformer!
I have it connected to a Schiit Modi Uber DAC and Magni 3 headphone amp which I'm using as a preamp for the moment (I'm planning on building a Rod Elliott ESP preamp next to go with the PeeCeeBee). I think the sound is just superb. I swapped between the PeeCeeBee and a Cambridge Audio amplifier that I've been using previously and for me there are two noticable differences. I am useless at describing sound, but the bass certainly feels tighter and punchier, it seems to have less of a bloom than the Cambridge. The mids seem to have a little more clarity, almost sharp, but not in a harsh way, but this is less obvious than the difference in the bass.
Once again, I'm really happy with this, it's a superb amplifier.
After moving the amp into its final home -the office/shed in my garden - the hum/buzz increased to a level that was unacceptable. I did lots more reading and experimenting and finally got to the point where for all intents and purposes (bearing in mind I'm 51 years old with some tinnitus) the amp is silent when no music is playing. I have the ground/shield from the RCA inputs tied together at their tabs, but the shield goes to V-- at the amp rather than the PSU ground. This cable (signal and shield) was always close to the AC input and soft start but routing it away from these worked, even though it's now longer and right next to the transformer!
I have it connected to a Schiit Modi Uber DAC and Magni 3 headphone amp which I'm using as a preamp for the moment (I'm planning on building a Rod Elliott ESP preamp next to go with the PeeCeeBee). I think the sound is just superb. I swapped between the PeeCeeBee and a Cambridge Audio amplifier that I've been using previously and for me there are two noticable differences. I am useless at describing sound, but the bass certainly feels tighter and punchier, it seems to have less of a bloom than the Cambridge. The mids seem to have a little more clarity, almost sharp, but not in a harsh way, but this is less obvious than the difference in the bass.
Once again, I'm really happy with this, it's a superb amplifier.
