Carvin B2000 bass amp won't power on, need schematic.

[David Farber]

This Carvin B2000 bass amplifier was brought to me with the problem that
it wouldn't turn on. The user said it was working fine until there was a
bright flash that could be seen through the front grill. Then it went
dead. I opened it up and found a very fried and crispy looking disc
which I think is an MOV. It's labeled TR1 on the "main board close up"
as seen in these pictures. You can see by the photo it parallels the
(removed) relay's normally open contact (AC out?) and the common, AC in
contact.
Photos are here, https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

The other photos are to give you a general idea of what the board looks
like. The reason I took photos of the entire board is that Carvin's own
website, https://carvinaudio.com/pages/bass-amp-schematics shows
different versions of the B2000 schematic but none of them matches what
I see in the version I'm trying to troubleshoot. There is one vacuum
tube in the unit, a 12AX7.

After cutting out the MOV, and then powering it up, the power relays
would not engage. The other issue is that when I pulled out one of the
two power relays for inspection of its discolored contacts after it
failed to power up, one of the pins came out of its coil. There is no
writing on the relay and its physical construction doesn't look at all
familiar to any relays I've ever seen. I need to replace it assuming the
unit is worth fixing.

Does anyone have a schematic for this amp? There is a description of the
amp here:
https://carvinaudio.com/pages/archive-carvin-b2000-lightweight-mono-block-2050w-bass-amp-head

The owner said it was purchased around 2000. It looks in good shape for
being 20 years old. According to this report,
https://www.thetonerooms.com/threads/carvin-amps-out-of-business.3035/
Carvin went of business in 2017.

Thanks for your replies.
--
David Farber
Los Osos, CA

[Phil Allison]

David Farber wrote:

===================

** No schem from me- but it looks like you may only have a bad relay.

The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.

You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.

If the resistor smokes, you have a blown PSU.


.... Phil

[David Farber]

Hi Phil. I think I'll try using one of my audio, 8 ohm, 25 watt dummy
load resistors to test it. I'll also put a 200 watt light bulb in series
with the Variac just in case. If there's no overload, then I may as well
pull out the other identical inrush relay and see if I can figure out
what voltage and current it takes to close the contacts. Any idea what
voltage and current rating those contacts need to be?

Thanks for your reply.

[Phil Allison]

David Farber wrote:

==================

>>
> >
> > ** No schem from me- but it looks like you may only have a bad relay.
> >
> > The blown device is a PTC thermistor not a MOV - they are fitted to reduce excessive inrush surges at switch on. The relay bridges the PTC out of circuit to stop it overheating and exploding if made to pass the full load current.
> >
> > You can try using a 5 to 10 ohms, 5 watt or more WW resistor in place as a test and then bring the amp up with a Variac.
> >
> > If the resistor smokes, you have a blown PSU.
> >
>
> >
> >

> Hi Phil. I think I'll try using one of my audio, 8 ohm, 25 watt dummy
> load resistors to test it. I'll also put a 200 watt light bulb in series
> with the Variac just in case.

** That's fine.

> If there's no overload, then I may as well
> pull out the other identical inrush relay

* Are there 2 PSUs involved?

> and see if I can figure out
> what voltage and current it takes to close the contacts. Any idea what
> voltage and current rating those contacts need to be?
>

** 20A at 120VAC at least.


.... Phil

[legg]

It's a fairly common form used in HVAC switching, but more easily
obtained with a plastic dust cap. The open air parts are seldom
used outside of self enclosed fan-free environments, for obvious
reasons.

You may have a relay on both input (inrush limiting) and output
(click and pop supression).

You'll need to establish what the supply voltage is for the coils.

Check for Panasonic JTV or TEconnect T9AS1D series SPST NO.

RL

[legg]

On Sun, 20 Sep 2020 22:17:29 -0700, David Farber
<farberbe...@aol.com> wrote:

Actuslly, the second relay looks more like a line voltage
selector. It will close for line voltages below 180VAC.

It looks like this unit isn't power factor corrected.

RL

[legg]

If that's the case, then you could do a quick fix by
relocating the voltage select relay to the inrush
position, short out the old voltage select relay
contact position, then place a large sticker on
the back indicating "100-130VAC INPUT ONLY".

RL

[David Farber]

Hi Phil,

I've found what I think is a partial schematic for this model which I've
added to my Carvin folder here:
https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

[David Farber]

What an ingenious workaround! I'll definitely check out that relay swap
option.

By the way, the user informed me the model was not purchased in 2000. It
was purchased in 2009. There is a schematic for that year but it looks
incomplete to me. I've uploaded it to:
https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre

[legg]

On Mon, 21 Sep 2020 09:57:39 -0700, David Farber

<farberbe...@aol.com> wrote:

>On 9/21/2020 8:34 AM, legg wrote:
>> On Mon, 21 Sep 2020 09:59:22 -0400, legg <le...@nospam.magma.ca> wrote:
>>
>>> On Sun, 20 Sep 2020 22:17:29 -0700, David Farber
>>> <farberbe...@aol.com> wrote:
>>>
>>> Actuslly, the second relay looks more like a line voltage
>>> selector. It will close for line voltages below 180VAC.
>>>
>>> It looks like this unit isn't power factor corrected.
>>>
>>
>> If that's the case, then you could do a quick fix by
>> relocating the voltage select relay to the inrush
>> position, short out the old voltage select relay
>> contact position, then place a large sticker on
>> the back indicating "100-130VAC INPUT ONLY".
>>
>> RL
>>
>What an ingenious workaround! I'll definitely check out that relay swap
>option.
>
>By the way, the user informed me the model was not purchased in 2000. It
>was purchased in 2009. There is a schematic for that year but it looks
>incomplete to me. I've uploaded it to:
>https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre
>
>Thanks for your reply.

Unfortunately, this doesn't cover the power section.

RL

[legg]

On Mon, 21 Sep 2020 09:57:39 -0700, David Farber

<farberbe...@aol.com> wrote:

>On 9/21/2020 8:34 AM, legg wrote:
>> On Mon, 21 Sep 2020 09:59:22 -0400, legg <le...@nospam.magma.ca> wrote:
>>
>>> On Sun, 20 Sep 2020 22:17:29 -0700, David Farber
>>> <farberbe...@aol.com> wrote:
>>>
>>> Actuslly, the second relay looks more like a line voltage
>>> selector. It will close for line voltages below 180VAC.
>>>
>>> It looks like this unit isn't power factor corrected.
>>>
>>
>> If that's the case, then you could do a quick fix by
>> relocating the voltage select relay to the inrush
>> position, short out the old voltage select relay
>> contact position, then place a large sticker on
>> the back indicating "100-130VAC INPUT ONLY".
>>
>> RL
>>
>What an ingenious workaround! I'll definitely check out that relay swap
>option.
>
>By the way, the user informed me the model was not purchased in 2000. It
>was purchased in 2009. There is a schematic for that year but it looks
>incomplete to me. I've uploaded it to:
>https://app.box.com/s/ch670hnsrtoswqhebtrye95n2vw5ktre
>
>Thanks for your reply.

The following schematic covers models:
DCM1540L
DCM2000L
DCM3000L
DCM3800L
B2000 Rev J

https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645

It has a line input and power stage looks similar to the
one you're fooling with, but I don't see a tube section
inserted anywhere.

You can wade through other Carvin docs:

https://carvinaudio.com/pages/power-amplifier-schematic

The older B2000 had a 60Hz transformer power supply, unlike
your unit.

RL

[Phil Allison]

Phil Allison wrote:

===================

>
>
> The blown device is a PTC thermistor
>
>

** Of course that should be an * NTC thermistor*.

https://passive-components.eu/how-to-use-ntc-thermistors-for-inrush-current-limiting/


..... Phil

[David Farber]

I found this NTC-5D11 on eBay.
https://www.ebay.com/itm/141513042814
The datasheet says it's 5 ohms, continuous current 4 amps, and 0.0156
ohms at max current.

I still need to check the circuit first to make sure there is no overload.

Thanks for your reply.

[David Farber]

That's a great find. I wonder if the schematic I found earlier in my
research,
https://cdn.shopify.com/s/files/1/0476/5297/files/80-42000revd25feb10.pdf?2161
interconnects with this new one you found.

[Phil Allison]

David Farber wrote:

=================

>
> > ** Of course that should be an * NTC thermistor*.
> >
> > https://passive-components.eu/how-to-use-ntc-thermistors-for-inrush-current-limiting/
> >

> I found this NTC-5D11 on eBay.
> https://www.ebay.com/itm/141513042814
> The datasheet says it's 5 ohms, continuous current 4 amps, and 0.0156
> ohms at max current.

** Way to much to pay for shipping.

Newark has the same for 50 cents each.

>
> I still need to check the circuit first to make sure there is no overload.
>

** The original NTC may be way higher in value than 5 ohms - up to 50 ohms maybe.

I gave that number for tests using a Variac only.


.... Phil

[David Farber]

On 9/20/2020 10:40 PM, Phil Allison wrote:

Before I went to the trouble of dismantling my audio dummy load resistor
setup, I found two, 3.3 ohm, 1 watt resistors, put them in series, and
soldered them in place of the thermistor. (My supply of resistors in the
low ohm, high power range is almost nil.) I know you said to use at
least a 5 watt resistor but I wanted to get some idea of what kind of
current the amp would draw on power up. I did put a 200 watt lamp in
series. By the time the line voltage was up to 50 ACV, the lamp was
glowing at about half strength and the AC current was about 1 amp. The
voltage across the resistors was over 3 volts so they were already
overloading. At that point I aborted the test. If I do repeat this test
with the 8 ohm, audio, 25 watt dummy load resistor, should I leave the
light bulb in series? Would it take more than 2 amps of continuous AC
power even when bringing up the voltage slowly? What if I bypass the
relay contacts and eliminate the resistors? There shouldn't be any
inrush surge while bringing the voltage up slowly, right?

I should also mention that the power amp has a 25 amp line fuse inside.
Does that sound reasonable? Neither the schematic nor the PC board
indicate what the fuse rating should be.

[Phil Allison]

David Farber wrote
==================:

>
> Before I went to the trouble of dismantling my audio dummy load resistor
> setup, I found two, 3.3 ohm, 1 watt resistors, put them in series, and
> soldered them in place of the thermistor. (My supply of resistors in the
> low ohm, high power range is almost nil.) I know you said to use at
> least a 5 watt resistor but I wanted to get some idea of what kind of
> current the amp would draw on power up. I did put a 200 watt lamp in
> series.

** Completely spoils the test.

> By the time the line voltage was up to 50 ACV, the lamp was
> glowing at about half strength and the AC current was about 1 amp.

** So nearly 50V AC was across the 200W lamp.

Odds are very high the PSU is a dead short to the AC supply - though the bridge rectifier may be OK. Check that and some FETs with a multimeter on diode tests.



.... Phil

[David Farber]

I will recheck for shorts in the PSU.

[David Farber]

Schematic is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645

I finally was able to figure out where all the power supply components
were hiding. They were obscured by the heat sinks. The culprits were
Q800 and Q802. Their part numbers are STGW30NC60W and they were both
shorted across all three terminals.

I still have one issue that needs resolving. I performed an in circuit
diode test across D809 and D810. They both read 105 ohms (regardless of
the polarity of the probes). In essence, connecting either one of those
diode's terminal with one probe and then connecting the other to ground
yields that same 105 ohm reading. On the other side of that bridge diode
circuit, D811 and D812 yield normal front to back in circuit diode
readings. Desoldering any of the components is quite a chore because of
the double-layered board. I am stumped trying to figure out the
troubleshooting path of least resistance here. I haven't ruled out that
the 105 ohm reading may just be normal but my gut feeling says it's not.

[legg]

On Thu, 1 Oct 2020 15:21:36 -0700, David Farber
<farberbe...@aol.com> wrote:

<snip>

>Schematic is here:
> https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645
>
>I finally was able to figure out where all the power supply components
>were hiding. They were obscured by the heat sinks. The culprits were
>Q800 and Q802. Their part numbers are STGW30NC60W and they were both
>shorted across all three terminals.
>
>I still have one issue that needs resolving. I performed an in circuit
>diode test across D809 and D810. They both read 105 ohms (regardless of
>the polarity of the probes). In essence, connecting either one of those
>diode's terminal with one probe and then connecting the other to ground
>yields that same 105 ohm reading. On the other side of that bridge diode
>circuit, D811 and D812 yield normal front to back in circuit diode
>readings. Desoldering any of the components is quite a chore because of
>the double-layered board. I am stumped trying to figure out the
>troubleshooting path of least resistance here. I haven't ruled out that
>the 105 ohm reading may just be normal but my gut feeling says it's not.

The anodes of D809 and D810 are DC-shorted through the transformer
winding. The 105R reading is likely between LORAIL+ and ground.

RL

RL

[legg]

On Thu, 1 Oct 2020 15:21:36 -0700, David Farber

Check the gate components, if the fets fail. They don't always
survive.

The primary housekeeper around Q803 should run independently, with big
fets out of circuit, so you can check basic control and drive circuits
without a lot of risk (taking in mind it's still a primary-connected
circuit.

RL

[Phil Allison]

David Farber wrote:

------------------
>.

> Schematic is here:
> https://cdn.shopify.com/s/files/1/0476/5297/files/30-02050revj.pdf?2645
>
> I finally was able to figure out where all the power supply components
> were hiding. They were obscured by the heat sinks. The culprits were
> Q800 and Q802. Their part numbers are STGW30NC60W and they were both
> shorted across all three terminals.
>

** That is bad sign of other problems in the amp.

Those are high power IGBTs and they do not blow without a reason.



..... Phil

[David Farber]

Thank you Phil and RL. After much poking and prodding trying to reverse
engineer which circuit was going where, the previous 105 ohm low
readings across D809 and D810 are now normal. Maybe a spec of solder
took up residence in the area when I was desoldering the adjacent
transistors, Q800 and Q802?

Next (but still without a new set of IGBT's installed) I slowly powered
the unit on with the Variac. Relay K1 now energizes right after power up
and the internal green LED glows normally. I will now place an order for
the IGBT's and NTC thermistor. Phil brought up the point, what would
cause them to blow in the first place? After much checking, I could not
find any other faults in the circuitry. I'll update you after the new
parts arrive and are installed.

I do have one other question regarding the 25A line fuse. What the heck
is that supposed to protect? If the power supply fails/shorts, the
thermistor bypass relay de-energizes and then the line voltage is sent
through the thermistor. I think the 25A fuse will win that battle and
not protect anything. The specs on the back of the amp say, 2050W into 2
ohms so I guess a large fuse is necessary however wouldn't a smaller
fuse, maybe a slo-blo type, make more sense?

One last comment about the schematic. This B2000 model is a mono amp so
anything in the schematic that says CH2, does not exist though about
one-third of the circuit board has empty spots for those components.

Thanks for your replies.

[Phil Allison]

David Farber wrote:

------------------

> >
> > ** That is bad sign of other problems in the amp.
> >
> > Those are high power IGBTs and they do not blow without a reason.
> >
>

> Next (but still without a new set of IGBT's installed) I slowly powered
> the unit on with the Variac. Relay K1 now energizes right after power up
> and the internal green LED glows normally. I will now place an order for
> the IGBT's and NTC thermistor. Phil brought up the point, what would
> cause them to blow in the first place? After much checking, I could not
> find any other faults in the circuitry. I'll update you after the new
> parts arrive and are installed.

** I have you have an isolation transformer or a scope that can be safety floated above earth. You need to inspect the drive waves to each IGBT.

As you Variac up, the wave should snap on staring with a very low duty cycle, then fill out to a perfectly symmetrical square wave.

> I do have one other question regarding the 25A line fuse. What the heck
> is that supposed to protect? If the power supply fails/shorts, the
> thermistor bypass relay de-energizes and then the line voltage is sent
> through the thermistor. I think the 25A fuse will win that battle and
> not protect anything. The specs on the back of the amp say, 2050W into 2
> ohms so I guess a large fuse is necessary however wouldn't a smaller
> fuse, maybe a slo-blo type, make more sense?
>

** At full power with 2ohms load, the AC will be 25amps RMS.

( 2100 /120 = 17.5 with a PF of about 0.7 = 25. )

If you know the speaker being used is 4 or 8 ohms and the player does not thrash the heck out of it - then a 15amp slo-blo will do OK.


.... Phil

[David Farber]

Thanks for the tips. I'll check out the drive to each IGBT while
powering it up slowly.

[David Farber]

On 10/3/2020 4:33 PM, Phil Allison wrote:
>

> David Farber wrote:
>
> ------------------
>
>>>
>>> ** That is bad sign of other problems in the amp.
>>>
>>> Those are high power IGBTs and they do not blow without a reason.
>>>
>>
>> Next (but still without a new set of IGBT's installed) I slowly powered
>> the unit on with the Variac. Relay K1 now energizes right after power up
>> and the internal green LED glows normally. I will now place an order for
>> the IGBT's and NTC thermistor. Phil brought up the point, what would
>> cause them to blow in the first place? After much checking, I could not
>> find any other faults in the circuitry. I'll update you after the new
>> parts arrive and are installed.
>
> ** I have you have an isolation transformer or a scope that can be safety floated above earth. You need to inspect the drive waves to each IGBT.

The parts finally arrived. I'm a bit confused as to how the schematic of
the IGBT in the datasheet compares to the resistance readings on the
component itself.
http://datasheet.octopart.com/STGW30NC60WD-STMicroelectronics-datasheet-10835944.pdf

Placing the positive probe on pin 2 and the negative probe on pin 3
reads open circuit. If I then put the positive probe on pin 1 and the
negative probe on pin 3 it reads open circuit. Then going back to my
original test of positive on pin 2 and negative on pin 3, I get a
reading of a good diode check around 475 ohms. Subsequently reversing
the probes from pins 1 and 3 and then going back to pins 2 and 3, that
will revert to an open circuit. These readings are what I expect when
testing an FET. According to the datasheet, there is a diode across pins
2 and 3. That would mean if I put positive on pin 3 and negative on pin
2, I should get a good diode check reading but I get an open circuit.
Can you make sense out of these tests?

Thanks for your reply.

[Phil Allison]

David Farber wrote:

----------------
>
> The parts finally arrived.

** From where ????



> http://datasheet.octopart.com/STGW30NC60WD-STMicroelectronics-datasheet-10835944.pdf


** Shows a a reverse diode HAS been added to the device.

If it is genuine, you should see diode conduction ( 0.8 to 1V) with a DMM set to "diode check" range.



.... Phil

[David Farber]

Parts were from Digi-Key. I took another look at the original, shorted
parts. They are, STGB30NC60WD. I somehow managed to omit the "D" at the
end of the part number when I ordered the replacements (and also omitted
it when I reported to the group what the part number was). That would
explain why the reverse diode is absent. I guess it's a very good thing
I checked all of this out before powering it up again. I will order the
correct parts and check back with you in a week or so.

By the way, I noticed a potential problem with checking the input
waveforms to the gates of Q800 and Q802. If I put one scope probe across
one transisor, from G to E, that should be OK however if I want to see
both waveforms together while powering up the unit and then connect a
second probe to the scope on the other transistor, the common ground of
the probe will short out Q802. Should I just float the ground on one of
the probes? Will that work? The amp will be powered by my Sencore
isolation transformer/Variac.

[Phil Allison]

David Farber wrote:

====================

>
> By the way, I noticed a potential problem with checking the input
> waveforms to the gates of Q800 and Q802. If I put one scope probe across
> one transisor, from G to E, that should be OK however if I want to see
> both waveforms together while powering up the unit and then connect a
> second probe to the scope on the other transistor, the common ground of
> the probe will short out Q802. Should I just float the ground on one of
> the probes? Will that work?
>
>

** Both signals come from the same transformer - out of phase.

You can monitor the outputs of the 3525 IC or the primary side of the tranny without the iso in use.

Plus check continuity of secondary windings and their connections to the IGBTS.

.... Phil

[David Farber]

Thanks for following up with the details Phil.

[David Farber]

Note: The tests I performed below were without the control board
connected. The control board is responsible for connecting the earth
ground to the audio ground. The schematic of the control board is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/80-42000revd25feb10.pdf?2161

The schematic of the main board is here:
https://cdn.shopify.com/s/files/1/0476/5297/files/80-42000revd25feb10.pdf?2161

I received the correct parts and installed them. I checked the waveform
at the primary side of T2. As I powered it up slowly with the Variac,
there was no gradual change in the duty cycle. It was either flat line
or full on. I checked the signal across Q802 from drain to source and it
was a very clean square wave and measured approximately 400 Vpp. At this
point I could reassemble everything and see if it actually will perform
properly. But before I do that, I would like to figure out the operation
of the power supply circuit that is rectified by diodes D805-D808. It's
easy to see that when pin 20 of T3 goes positive, D805 conducts and
becomes the V+ line. From that point, it feeds the load and then I
imagine it ends up going through ground via the terminal marked HI RAIL
on T3 and also through the other ground circuit which is in series with
the array of capacitors, C811-812, C849-850, and C34, C36, and C51.
Apparently there is also a connection to the bridge circuit, D809-D812.
Is there some voltage adding going on there with the secondary
transformer windings interacting with the two bridge circuits? This is
not a configuration that I have come across before. At the very least
I'd like to know where ground is for the V+ supply coming from the
cathodes of D805 and D806. I am measuring 90 volts individually across
capacitors C850 C852.

Thanks for your reply.

[Phil Allison]

David Farber wrote:

==================

>
> As I powered it up slowly with the Variac,
> there was no gradual change in the duty cycle. It was either flat line
> or full on.
>

** Very bad.

Check the 22uF on pin 8 of the PWM IC.

This cap enables the Soft Start circuitry.

https://www.ti.com/lit/ds/symlink/uc3525a.pdf?ts=1604980536419&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUC3525A

Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.


.... Phil

[David Farber]

I hadn't realized that the ramp up occurred within 1 second. I powered
it on without the Variac and sure enough, the waveform made a gradual
change within that 1 second timeframe. Everything seems to powering up
OK. Checking the audio will be next.

I'm still curious about the power supply question I asked in my previous
post (see below) regarding how the two bridge diode circuits seem to be
adding voltage in a series circuit.
============================================

[Phil Allison]

David Farber wrote:

==================

>
> >
> > Using a Variac slowly may be an issue, but nothing will happen until the +/- 15V rails appear, then it should ramp up the PWM in about 1 second.
> > >
> >

> I hadn't realized that the ramp up occurred within 1 second. I powered
> it on without the Variac and sure enough, the waveform made a gradual
> change within that 1 second timeframe. Everything seems to powering up
> OK. Checking the audio will be next.

** So far - so good.

>
> I'm still curious about the power supply question I asked in my previous
> post (see below) regarding how the two bridge diode circuits seem to be
> adding voltage in a series circuit.
> ============================================

** Yep- it sure is complicated !!.

The DC supply is *series stacked* with a low an high voltage components.

Then a pair of IGBTs for each channel is used to *regulate* the voltage to the main BJT amplifiers so it TRACKS the incoming audio. Maybe not perfectly but reasonably close to demand and just a lite more volts than needed by the load at any moment. The low voltage DC supply sets a fixed lower limit.

Look up "class H" on Wiki.

I only know of one other amp maker doing this, Lab Gruppen.

Crazy complicated - why not go Class D an keep it simple ??


..... Phil

[Phil Allison]

David Farber wrote:

==================

** FYI Dave,

The marketing for this model (B2000) is totally wrong.

1. It is not a "mono block"- it has two distinct power channels that must drive two different speakers.

2. It sure as HELL ain't "class D" Either.

The PSU tracks so it is "clearly class H"

WTF ???



.... Phil

[David Farber]

Hi Phil,

My experience with commercial(?), high powered audio gear with switching
power supplies is almost nil. I'll check out class H on Wiki and while
I'm there, I'll check out any other classes that I haven't come across.

Yesterday, I installed the PC board into the chassis and connected the
front panel connectors. The result was the earth ground became tied to
the power supply ground which should have made voltage testing much
easier except for the fact that I could no longer access the bottom of
the PC board. It's next to impossible to accurately put a probe on
anything from the component side. Many parts are covered in epoxy(?) or
hot glue(?) and the power transistors are totally obscured by the heat
sinks that surround them.

[David Farber]

Hi Phil,

When I was still trying to figure out if the schematic matched the pc
board, I mentioned in passing that the second channel audio amplifier
components were not installed. There are however marked out spaces for
them. In summary, any components that refer to CH2 do not exist. As to
whether it is class D or class H (I don't think my electronics training
from the 1970's went past class C), I'll leave that up to you and in the
meantime, I'll turn to the internet to update my knowledge about the
alphabet soup of amplifier classes.

[Phil Allison]

David Farber wrote:
===================

>
> > ** FYI Dave,
> >
> > The marketing for this model (B2000) is totally wrong.
> >
> > 1. It is not a "mono block"- it has two distinct power channels that must drive two different speakers.
> >
> > 2. It sure as HELL ain't "class D" Either.
> >
> > The PSU tracks so it is "clearly class H"
> >
> > WTF ???
> >

> >
> >
> >

> Hi Phil,
>
> When I was still trying to figure out if the schematic matched the pc
> board, I mentioned in passing that the second channel audio amplifier
> components were not installed. There are however marked out spaces for
> them. In summary, any components that refer to CH2 do not exist.
>

** So you posted the wrong schematic.

Bound to be many differences when the PSU only has to power 1 channel instead of 2.

> As to
> whether it is class D or class H (I don't think my electronics training
> from the 1970's went past class C),

** No, classes G and H are more recent inventions.

If you have not kept up with the literature (ie electronics magazines) since the early 70s you are living in the dark ages. Before the internet ruined everything, I used to buy 4 magazines each month. Only one of them is still published.

Wireless World from the UK was the best, but it folded years ago.

> I'll leave that up to you and in the
> meantime, I'll turn to the internet to update my knowledge about the
> alphabet soup of amplifier classes.
>

** Be sure not to confuse the topic with "alphabet people".



..... Phil

[David Farber]

I finally reassembled, tested, and returned the amp to the customer. It
works just fine now. I've watched several video explanations of the
class D and H amps. I don't want to take this thread too off topic but
those new classes really seem to help the efficiency of an amp. This
Carvin amp weighs in at 14 lbs (5.2kg). That would be unheard of 50
years ago.

Thanks for your support (and RL too) throughout this adventure!
--
David Farber
Los Osos CA

[Phil Allison]

** Wow - a happy customer.

" Should have him stuffed... "


..... Phil