Schoeps CMC4 Upgrade

 
 

We modify the Schoeps CMC4 “T-power” microphone amplifiers

into the exact amplifier circuit that is contained in the CMC5,

allowing 48 volt phantom power operation.


The Schoeps CMC4 amplifiers use the obsolete 12 volt “T-Power” (Tonader or A-B power) standard. CMC4s have fallen into disuse, or they require an external power supply or barrel adaptor.  This upgrade will allow the CMC4 to use 48 volt phantom power, without the need for an adaptor. Circuit design and performance of the

the upgraded CMC4 is identical to a Schoeps CMC5, 48 volt amplifier.

 

Upgrades are performed by Pete Verrando, a location sound recordist with over

30 years experience in component-level electronic construction.

Upgrade cost: US $154 plus return shipping.  

Payable with credit card via Paypal upon completion of service.

 

Email pete@cmc4upgrade.com to request an order form.   Tracked, insured shipping is recommended.  Turnaround time is about a week. Do not send Schoeps mic capsules. 

After receiving your CMC4, we:

  1. 1.Take a photo of the unit with serial number and order form.

  2. 2.Test your amplifier and check for correct circuit voltage points.

  3. 3.Record a reference “before” file, documenting functionality and self-noise.

 

If any deficiencies or other issues are encountered with these preliminary tests, you will be contacted for consultation of repair options or the return of your CMC4. 

 

Assuming your CMC4 is fully functional, the amplifier will then be upgraded to a schematically correct CMC-5. 

New Feature: RF immunity modification for plug-on transmitters, Lectrosonics HM and Zaxcom TRX (@ 75mw or lower)is included as part of upgrade.

New Feature: Circuit and component surfaces meticulously cleaned to remove any high impedance “shorts” that contribute to higher noise floor.   Some amps we have upgraded have shown up to -4 db noise floor reduction as a result.

New Feature: On about 20% of amplifiers upgraded, C10 (220uf 10V) is found to have failed. This electrolytic is now checked for value, ESR and leakage in every amp. Out-of-spec C10’s are replaced with a high quality Philips unit.


“Blue Dot” (+5 db) modification can be added or removed as requested on the order form.  


After modification, the amplifier:

1. Is tested with 48 volt phantom power, then powered for 24 hours and tested again.
2. Check for correct internal voltages & current draw. CMC4 ID ring is stamped with "PH48". 
3. Record an “after” reference file and review before/after files.

4. You are emailed an invoice for service, parts of $154 plus return shipping. Paypal accepted.
5. When payment is received, the unit is packed, and shipped back to you.

1. What exactly are you doing in the upgrade?  

The existing circuit is rebuilt to the original Schoeps CMC5 circuit, using the existing board, parts, and several new components. The upgrade requires removing some parts, and adding new parts. The new part values must be carefully matched before installation.

2. Can you just send me the information/parts so I can do it myself?

DIY mods are not advised. Experience with the circuit topology, test equipment and excellent soldering/electronic skills are required.

3. Won’t the Schoeps factory upgrade my CMC4?

We’ve asked, and they will not.  

4. Do you offer a warranty?

We offer warranty service for issues specific to our amplifier modifications for a period of 1 year. See order form for warranty specifics.

5. I have other microphones that are T-powered. Will you upgrade them?

We upgrade Sennhesier 416T shotgun microphones. www.416Tupgrade.com.

6. What’s wrong with T-Power barrel adaptors?

Left unknowingly in-line, T-power supplies can cause electronic damage to other microphones. They may magnetize microphone parts and transformer cores, possibly causing distortion.  Plugging dynamic, ribbon or phantom powered microphones into a T-powered outlet is an invitation to disaster. A T-Power adaptor puts DC blocking capacitors in line with your signal.  An “organic” CMC5 has a much higher street value than a CMC4, even if the T-power adaptor is included. For location sound mixers, T-power adaptors are cumbersome. They add unnecessary XLR and barrel length to the mixer’s input connector, or to the microphone itself.  Adaptor barrels create dangerous leverage. A cable yanked from a barrel can cause damage at the mixer input panel.

7. What’s the deal with the “blue dot?”

A “blue dot,” which Schoeps painted on the mic after the CMC4 moniker, indicated the amplifier was internally wired to be +5 db hotter than a “non” blue dot amplifier.  The tradeoff, however, is a slightly higher noise floor and less available headroom.  Blue dot amplifiers are popular for recording low-level sources like narrative dialogue.

8. How does the CMC5 compare to the CMC6?

In addition to the Schoeps circuit,  CMC6 amplifiers include comparators and voltage regulators. Some people claim this adds noise to the amplifier. (inaudible, but observable on a scope) The response of the CMC6 is flat to 20 Hz.  The CMC5 rolls off at 30Hz. In fact, Schoeps does not recommend mixing CMC5’s and CMC6’s in stereo pairs.  It’s been said that Schoeps would love to retire the CMC5 model completely, but too many recordists prefer them over the CMC6. Many people prefer to have only either all CMC5 or all CMC6 in their mic lockers.  Having a CMC4 modified to a CMC5 is an economical way to achieve this, or to get any CMC4 "back in action."  

9. Is the upgrade cost effective as opposed to buying new or used CMC5s?

A new CMC5 sells for over $1000. If you can find them, a used CMC5 averages about $800. A used CMC4 can often be found for much less. Location guys often have a couple of CMC4s  “set out to pasture.” Our upgrade can yield a genuine CMC5 for substantially lower cost.    

10. Aren't you just stuffing a T-Power adaptor into the body of the microphone?

No. Using the Schoeps original CMC5 schematic, we install the exact components to create the "Schoeps Circuit," a Class A symmetrical amplifier with no coupling capacitors or transformers. And besides, a T-power adaptor circuit won't fit inside the amplifier shell. (see above photo)

11. How did T-power originate?

Before the advent of DC-DC converters, the 12 volts of T-power was much easier to generate from Nagras and other portable battery-powered equipment,  than the 48 volts required by early phantom systems. This explains its previous ubiquity in film work. 

  1. 12.Where are you located?

Dallas, Texas USA. Your CMC4’s are sent to a secure mail facility.

  1. 13.Will the upgrade resolve all RF interference issues?

Mostly. Some CMC4, CMC5, and early CMC6 amplifiers are known for RF “noise-up” issues from plug-on transmitters, remote-focus transmitters, walkie-talkies, etc. The upgrade resolves RF interference issues with the exception of Zaxcom Plug-on transmitters running at the highest power, i.e 125mw.

Frequently Asked Questions

To upgrade your CMC4, email pete@cmc4upgrade.com

and request an order form. Then ship your unit & form to the provided address. Turn-around time is about 2-3 days from receipt of your amplifier.

(If a backlog exists, we’ll let you know before sending your unit.)

To request an order form and receive shipping information:

email pete@cmc4upgrade.com