Tracing The PeeCeeBee

[shaan]

Just saw the post. My GRR speaker build is over, finally. I was driving past Bangalore on my way from Trivandrum to my new place Kurnool and thought of hand delivering the X-LS & X-LS of forum member Sethu_nr who had requested me to help him out with the build. So, the speakers were in my Car's boot when I visited Manniraj, essentially to pick up the Ovation SX kit which I bought off him.

Coming to the point, I was skeptical of the DIY amp builders who used to document their design and builds on the forum.

We had FLAC files on his Laptop going through a Soekris DAC, NA BA-3, Peeceebee driving the Frugel Horns having Alpair 7.3P drivers. They were sounding nice but I thought the highs were a wee bit rolled off. I was wondering (probably stemming from my prejudice) how they would've sounded if driven by the SX. We then shifted to Continuums of Kartikey. Though highs were better, being small speakers, their limitation to reproduce the lows was clearly evident. They sounded marginally better when Kartikey played the source through his Mojo DAC bypassing the BA-3.

I wanted to see how the X-LS would sound in the same setting. We took out the pair from the boot, unpacked and plugged them in. I was completely taken by surprise at how good the setup sounded. The synergy of the whole chain was amazing. We played several tracks across the genre. All that came out was wonderfully balanced sound that was very pleasing to our ears. Kudos to Shaan for designing such a wonderful sounding amp.

Thanks for the review Rajesh. Much appreciated.

 

[Aniket]

A subwoofer amplifier yes. However, a BJT output amplifier will not be a PeeCeeBee.

Ok, so does it mean that with a BJT output this amp will be degraded sonically, and will only suit for subwoofer duty.

I don't think that's true. D

Is there a BJT version also on the cards ?
will try one.

Also, if output devices dictated THD then what on earth is GNFB doing in the damn circuit?

yes, of course output devices too dictate THD performance not as much as the preceding stages, but still they do. I think you misunderstood my statement mate. I said:

according to the datasheets Lateral FETs have much higher input and output capacitance, specially P-channel compared to BJT's,
and Lat FETs require much more idle current comparatively for similar THD performance.

regarding GNFB, that's a pretty obvious thing to be implemented in any Class AB amp. The above statement was said keeping GNFB into account.
So, keeping the GNFB same, FETs will need more idle current than BJT's for similar THD performance. of course there are other ways than heat sinks.

Respectfully disagree. There are multiple ways other than heatsinks to work around such a problem. As for example, PeeCeeBee V4 has 0.0005% 100Hz THD and 0.001% 1KHz THD with 30mA MOSFET bias i.e. deep into Class-AB.

The THD performance is very good:thumbsup: considering the simplicity of the design. the above figures are at rated power or 1W,5W or 10W.?

On the other hand, same or better THD performance can be achieved with a BJT output stage, at half of bias, i.e 30/2=15mA in this case, keeping the preceding stages identical. So, is there a BJT version you will design in future ?

Congrats for PeeCeeBee V4

Regards,
Aniket

 

[shaan]

Ok, so does it mean that with a BJT output this amp will be degraded sonically, and will only suit for subwoofer duty.

It may or may not. BJTs are not a drop-in replacement for Lateral MOSFETs so changes in the drive circuitry is a must. Apples to apples comparison is hardly a possibility here.

Is there a BJT version also on the cards?

I think so. Check diyA.

Yes, of course output devices too dictate THD performance not as much as the preceding stages, but still they do.

The fact is that they Always do, no matter what you do, the laws of Physics demand it!

My point is that if their effect is audible then the application procedure of GNFB is at fault, and tweaking GNFB means tweaking all the preceding stages. But the question is that whether it is sensible to tweak -100dB harmonics.

Regarding GNFB, that's a pretty obvious thing to be implemented in any Class AB amp. The above statement was said keeping GNFB into account.
So, keeping the GNFB same, FETs will need more idle current than BJT's for similar THD performance. of course there are other ways than heat sinks.

More idle current = more heatsink.

Anyways, the notion that Lateral MOSFETs need more idle current than BJTs to achieve similar performance is simply not true (I'm not pointing to FETs as a whole, your statement is true for Vertical FETs.).

The THD performance is very good:thumbsup: considering the simplicity of the design. the above figures are at rated power or 1W,5W or 10W.?

Yes it's really simple. 10Watt.

On the other hand, same or better THD performance can be achieved with a BJT output stage, at half of bias, i.e 30/2=15mA in this case, keeping the preceding stages identical.

And that would mean a practically better performing amplifier?

I think you didn't notice but I did not design the PeeCeeBee V4 with ultra low THD throughout the audible frequency range in mind. I experimented with three compensation schemes, three VAS stage configs and two input stage configs in combinations with one another, among which one combination gave me 0.0002% THD at 10KHz 10W while MOSFETs still being driven directly from the VAS. But I was displeased with its horrendous audible performance, especially at HF. Yes those combos were simultaneously simulated and assembled as well.

So, is there a BJT version you will design in future?

I can't say yes or no. There are so many BJT implementations of similar designs in diyAudio that it seems rather pointless. However, who knows when something suddenly starts sounding very good? So stay tuned.

Congrats for PeeCeeBee V4

Thanks a lot.

 

[jls001]

@Shaan: do we need to match the BC546Bs (and BC556Bs)?

Thanks for sending many extra components.

My kit contains the MJEs instead of the BDs so I assume I can push rail voltage to +/-42V? Can you please explain the limitation you mentioned for 4 Ohm speakers in the v4 GB thread?

Assuming I use +/-42V rails, what kind of power would it produce into 4 and 8 Ohms? I'm just trying to gauge if it's worth buying a transformer with higher secondaries for the extra power output.

For a quick build I plan to plonk the v4 into my MyRef Rev C amp since the rail is already ~+/-35V.

BTW, the boards are awesome. Never seen such thick PCBs :thumbsup:

 

[shaan]

@Shaan: do we need to match the BC546Bs (and BC556Bs)?

Thanks for sending many extra components.

My kit contains the MJEs instead of the BDs so I assume I can push rail voltage to +/-42V? Can you please explain the limitation you mentioned for 4 Ohm speakers in the v4 GB thread?

Assuming I use +/-42V rails, what kind of power would it produce into 4 and 8 Ohms? I'm just trying to gauge if it's worth buying a transformer with higher secondaries for the extra power output.

For a quick build I plan to plonk the v4 into my MyRef Rev C amp since the rail is already ~+/-35V.

BTW, the boards are awesome. Never seen such thick PCBs :thumbsup:

Hello Joshua.

Matching not essential. The BJTs I send are not manually matched but are not far apart regarding hFE. I measure them between 275 - 325.

Extra components? Well, that's no problem I hope I didn't miss anything.

The PSU rail voltage limitation comes from the MOSFETs' SOA. Current supplied into a 4R load with 42V rails causes the FETs to work on the boundary of their safe operating area which is not very safe.

With 42V rails you can expect ~75W into 8R load, and ~140W into 4R load(not recommended!).

Happy to know you like the boards. They are sturdy yes, also the plated holes aren't as brittle as some PCBs. I have ran a couple of them through 4-5 resoldering sessions and nothing.

 

[manniraj]

I think 50W is more than powerful and I am experiencing it first hand with V4. At just 9 o'clock position the volume is very high on my full rangers

 

[jls001]

I think 50W is more than powerful and I am experiencing it first hand with V4. At just 9 o'clock position the volume is very high on my full rangers

Yes, 50W is more than enough. I was just being greedy

Also, no point pushing the MOSFETs to the boundary of the SOA. The gain in power is is not even 3 dB.

Update: all resistors populated in the two boards. Will continue tomorrow. Bending so many resistor leads is such a tedious task. I think I'll design a rig to bend leads

 

[thekingstallion]

Yes, 50W is more than enough. I was just being greedy

Also, no point pushing the MOSFETs to the boundary of the SOA. The gain in power is is not even 3 dB.

Update: all resistors populated in the two boards. Will continue tomorrow. Bending so many resistor leads is such a tedious task. I think I'll design a rig to bend leads

You can try something like this:
https://m.indiamart.com/proddetail.php?i=8507327891

Or diy something like this:

Sent from my GT-N7100 using Tapatalk

 

[shaan]

Or diy something like this:

Thanks for the idea! :cheers:

 

[shaan]

Getting a pair sealed bookshelves done in this week. Plan to pair them with a couple sealed subs in a 2.2 active crossed system. Testing in a rough setup.

 

[Amitkg]

Looks stunning. Only gripe is the driver frame's colour. Are you going to keep it as same as it appears? If possible please make it black.

 

[shaan]

Thanks.

I have just finished stuffing and lining of the internal walls and will spray the frames black before final assembly. Eager to see how they pair up with my V4s.

Heard each of them in mono and seems I won't need tweeter at all! Had to tweak the stuffing a lot. There happened to be a sweet-spot, more polyfill and it sounded thin, less and it sounded "boxy". Took almost two days to find the right amount and density.

 

[shaan]

Farewell Renesas.

We have moved to UK! Now PeeCeeBee will sing with Exicon! :yahoo:

I'm going to miss the 2SK/J pair! They have been with me for the last 10 years in all sorts of experiments from amplifiers to solid state tesla coils, and have repeatedly proven their extreme ruggedness and simple drive requirements. It is such a shame that instead of replacing the old TO-3P package with TO247, they just decided to not produce it at all!

I really hope they hand over the design/manufacture of this pair (and a few other audio pairs) to some other company, like Hitachi handed it over to them.

 

[sadik]

Do share the Comparison between both the Mosfets.

Sadik

 

[shaan]

Hi Sadik.

Will do. I use 3 channels of V4 with Renesas FETs on a daily basis and they are always naked and ready to be played with.

There seems to be a "universal" agreement of better sonics with the Exicon FETs around the net. Time to check it out (however, I am expecting zero difference ).

 

[Manoranjan]

Farewell Renesas.

We have moved to UK! Now PeeCeeBee will sing with Exicon!

Good news, the replacement FET's have arrived.

 

[musiclovr]

Hi
Am new here..need some suggestions from you..Can someone suggest a preamp for the V4.. ill be using the amp mostly for music.. indian music to be precise

Sent from my XT1706 using Tapatalk

 

[avesbilal]

Hi
Am new here..need some suggestions from you..Can someone suggest a preamp for the V4.. ill be using the amp mostly for music.. indian music to be precise

Sent from my XT1706 using Tapatalk

@musiclovr: what is your source, I use V3 and I believe it is better to go directly from source to power amplifier if you can control volume at source.

My chain is laptop-->DAC-->PeeCeeBee power amplifier.

I control the volume at laptop.

I have built K-buffer and another preamp, tested these in between the DAC and PeeCeeBee but didn't like the end result when compared to direct from DAC.

I'm also planning to check out a tube buffer/preamp in the setup in future, hope it might be an improvement.

This is just my experience, others might think otherwise.

Regards
Bilal

 

[musiclovr]

@musiclovr: what is your source, I use V3 and I believe it is better to go directly from source to power amplifier if you can control volume at source.

My chain is laptop-->DAC-->PeeCeeBee power amplifier.

I control the volume at laptop.

I have built K-buffer and another preamp, tested these in between the DAC and PeeCeeBee but didn't like the end result when compared to direct from DAC.

I'm also planning to check out a tube buffer/preamp in the setup in future, hope it might be an improvement.

This is just my experience, others might think otherwise.

Regards
Bilal

I mainly play music from my phone.. it is a moto budget phone.. nothing fancy in the output and occasionally from my desktop there also i use the onboard sound card...Someone earlier had mentioned that if u are playing music from a phone its better to hav a preamp to get the desired output.. any diy preamp/eq which is popular?

Sent from my XT1706 using Tapatalk

 

[avesbilal]

I mainly play music from my phone.. it is a moto budget phone.. nothing fancy in the output and occasionally from my desktop there also i use the onboard sound card...Someone earlier had mentioned that if u are playing music from a phone its better to hav a preamp to get the desired output.. any diy preamp/eq which is popular?

Sent from my XT1706 using Tapatalk

Yes, in both cases of phone and computer as a source you would need a preamp. I would say you can try barrow a preamp from FM's in your city before building one.

It will be a huge improvement if could add a dedicated DAC. If you add a DAC then preamp is not required to match the input sensitivity of PeeCeeBee. (Better go for 2 VRMS output DAC)


You can get preamp kits from below websites.
AliExpress/Diyaudiocart/eightaudio.

Regards
Bilal