C34V love

ron-c · Dec 22, 2007

Another preamp tune up project. A C34V was mentioned the other day so lets see what it looks like, inside and out.
This sample had a fair ampunt of use and the trim piece around the push buttons was worn so the gold trim was off the right side. I painted the worn section with gold Testor's model paint but it did not look as new. Luckily McIntosh parts had replacements for the worn parts.
All the light bulbs were changed even though they were not burnt out as they were very dull and dim. New bulbs brought the original faceplate back to life.
The first batch of parts replacements were the power supply caps and 4 new high speed diodes. Someone had changed one in the past and not done the best job doing it. Another one of the original diodes fell apart when I touched it.
The C34 V now was looking better and working well.

to be continued,
Ron-C

ron-c · Dec 22, 2007

The C34 has many features which are shared by few other preamps. C32 and C33 preceded the 34. 33 and 34 are very similar where the 33 has two phonos and the 34 one. The 34 also can switch an external video switcher as well as the SCR2 speaker relay switch device which also works with other preamps C32, 28, 29, 33, 30, that preceded C34.
The on board 'Monitor" amp in the 33 and 34 is 20 watts per channel into 8 ohms and has Power Guard. It is the picture where the four transistors are mounted to a heat sink that is attached to the side panel in front of the very large and heavy power transformer.
The original C34vs had silver rear panel RCA jacks, the middle production a mix of silver and gold and the final version which this is one of, had all gold plated jacks.
The gold is more for marketing and is a thin coating. If you have the odd middle model with mixed rear panel jacks just use metal polish on them and they will all be a shinny silver.

Cont.

ron-c · Dec 22, 2007

The monitor amp has stereo speaker terminals on the rear panel. It also powers the twin, front panel headphone jacks. Gain controls which set sensitivity and the monitor amp input selector are mounted on the top right front of the preamp. Input choices are External, Listen or Record.
As you can see on the rear panel there are a lot of connection options. The main output is always on but the one and two are switched from the front panel. This allows the main amp to be muted while headphones are used or another amp for a remote area.
Processor loops are for EQs or Dolby/DBX devices. That said this series of preamps, starting with the C32 have a built in compressor/ expander or 'Compander". Controls on the top panel behind the faceplate set gain, speed, slow, normal or fast. The gain control should be adjusted so the volume is the same as the compander is switched in and out.

Con't.

ron-c · Dec 22, 2007

I see many who complain about the poor switch quality on the earlier model preamps. The basic problem is they are worn out. The switch quality on the C and C34 is very high with a top of the line Alps volume control that has excellent feel. These are a big step up from the earlier models and maintain excellent channel balance in operation. On board switching is performed by FET transistors which is very good although not at the level of the newer models sealed relays mounted next to the in-out jacks.
The front panel 5 band Eq. and the Compander can be bypassed or assigned to the other buss, record, while you listen to a source. This makes it possible to bypass these if you want purist sound. You can also doctor recordings using these. The compander is very handy for compressed sources like many FM stations or Rock/pop CDs. You can also compress for late night listening.
All in all a very cool preamp but...no REMOTE CONTROL...
All of the signal caps were replaced using Nichicon, Rubycon, Black Gate, Muse, and 105 degree long life caps in the power supplies. The sound is very full and modern with high signal to noise and low hiss. 10 op amps were swapped out for the low noise version. These are ON semi which are a good choice. Avoid US made versions for best noise response.
This C34 is now ready to control an elaborate system with many sources and much flexibility. Probably someone will be writing about it in another 30 years or so..
Thanks again,
Ron-C

Gregory · Dec 22, 2007

Ron.. the C33 is a fine instrument indeed!! Here's a brochure that Mc produced:

http://www.berners.ch/McIntosh/Downloads/C33_bro.pdf

My C33 is working flawlessly and there's nothing cosmetically that needs attention. It's really a remarkable product and sold new for $2495 back in the early '80s.

http://www.roger-russell.com/preamps.htm#c33

I picked one up for $1200 in the late '80s from EZ [Teletronics] which was intermittent. You've already heard the story of repairing a shielded cable crimp pin, and that was it. :music:

If possible, please expand more on the replacement ICs.. and if there are any panel illumination (i.e. lamp) tricks for the unit. BTW.. a large flat hex-nut was loose inside the C33 after the vanlines move this summer. What could that be from?

-Gregory

Pappas3278 · Dec 22, 2007

ron-c said:
Controls on the top panel behind the faceplate set gain, speed, slow, normal or fast. The gain control should be adjusted so the volume is the same as the compander is switched in and out.

Great write-up Ron.
I'm just a little confused about what you stated above. I have a C32 and listen with head-phones quite a bit and wasn't aware of "proper" settings for the gain controls. Wouldn't this be directly effected by the Volume setting, which has no absolute setting? Can you elaborate a bit?

Thanks Ron.

-Mike

forzaroma · Dec 22, 2007

C34V love at first sight

A used (but mint) c34V was my intro to McIntosh (and the beginning of a slippery slope which resulted in my current MC201/C220/MC252 system). At first I was disappointed by the sound (too warm) but the I realized that I was listening a heck of a lot more than my previous set-up, and some of the recordings I had labeled as unlistenable (e.g. CDs made in the 80s) sounded good of all a sudden.

The C34V now is in my living room driving a pair of Tannoy Autograph Minis.

My favorite features in the C34V are the 5-band EQ and the continous loudness (wish more pre-amps had that)...

ForzaRoma

ron-c · Dec 22, 2007

The gain level control on the compandor should be adjusted so the perceived volume is similar when the compandor is switched in and out. This will assure the best tracking and least pumping.
The replacement ICs are On semi 5534AN. AN is the low noise version which are typically only used in the phono section. The Signetics that were used in the C34 are the normal 5534A version. There may not be any difference where the AN-low noise versions are often the ones tested for noise. At a buck something each it was no big deal to roll new ones in. Mouser is the source and can also supply power supply and hard to find non-polarized caps. Nichicon is preferred.

Thanks,
Ron-C

Gregory · Dec 24, 2007

ron-c said:
The gain level control on the compandor should be adjusted so the perceived volume is similar when the compandor is switched in and out. This will assure the best tracking and least pumping.

The replacement ICs are On semi 5534AN. AN is the low noise version which are typically only used in the phono section. The Signetics that were used in the C34 are the normal 5534A version. There may not be any difference where the AN-low noise versions are often the ones tested for noise. At a buck something each it was no big deal to roll new ones in.

Mouser is the source and can also supply power supply and hard to find non-polarized caps. Nichicon is preferred.

Thanks,
Ron-C

Thanks for the C34 tech notes Ron. Will have to go through the schematic and translate what you have here. Speaking of which, it might be a good idea to acquire a service manual for all my [your] Mc stuff. The C33 is working fine and sounding wonderful now, so a tune-up will be somewhat of a lower priority.

How about doing a `MC2205 love´ series next? :banana:

That's needed most!!

While the 2205 is on the bench, the C33 can handle the amp duties for a while. The 2505 can go to Terry, but the 2205 is just too heavy, precious and spotless to ship!!

Roma.. have read your posts and saved your photos in the past.

Ron.. what do you think about the SCR1 Relay? I have one with control cable in storage. It could use all-new screws and relays. Might as well install new barrier strips too. Is it useful and worth the effort?

-Gregory

Little Nellie · May 5, 2008

I wonder if there are any advantage to replace the old carbon comp resistors with metal film 1%?

I recall someone mention that carbon comp sounds better vs the carbon film for the tube set. How about these s/s ones?

LN

ron-c · May 5, 2008

I doubt you would hear much of a difference.

Thanks,
Ron-C

Mack · May 5, 2008

Love the tech tips :thmbsp: I have a mint C34V in my system.

Gregory · May 11, 2008

Mack said:
Love the tech tips :thmbsp: I have a mint C34V in my system.

Ok!! well Ron has given the nod to post the following link, which is a reformat of the C34v Love app-note. It makes good on my suggestion to publish some of these useful technical or how-to docs.

http://home.comcast.net/~mc_audio/C34V_Love.htm

I also have a C33 that is starting to seem overly warm, and has developed a low-level "static crackle" in the REC Program track, REC Ext Processor jacks, REC Monitor circuit. IOW, a speaker equalizer box connected to the REC Ext Processor jacks results in a low-level static in the right tweeter with REC MONITOR button pushed.

Please do comment on the formatted tech note. :thmbsp:

Have added some updated system pics.. hope you'all don't mind. :banana:

-Gregory

MR80, MCD7007, C33, MC2205, Thiel CS3.5

forzaroma · May 11, 2008

Gregory said:
Ok!! well Ron has given the nod to post the following link, which is a reformat of the C34v Love app-note. It makes good on my suggestion to publish some of these useful technical or how-to docs.

http://home.comcast.net/~mc_audio/C34V_Love.htm

I also have a C33 that is starting to seem overly warm, and has developed a low-level "static crackle" in the REC Program track, REC Ext Processor jacks, REC Monitor circuit. IOW, a speaker equalizer box connected to the REC Ext Processor jacks results in a low-level static in the right tweeter with REC MONITOR button pushed.

Please do comment on the formatted tech note. :thmbsp:

Have added some updated system pics.. hope you'all don't mind.

-Gregory

MR80, MCD7007, C33, MC2205, Thiel CS3.5

Great job Gregory. I love my C34V. No as fast or resolving as the more modern McIntosh pre-amps, but when I want some warmth, or some loudness for low-level listening, it's a champ.

I like it so much that I put it in the tape loop of my C220. Now, when the recordings, or the listening situation calls for it, all I have to do is press "Tape Mon" and I have access to its sound and controls. Hardly a purist approach, but listening time and pleasure is my ultimate metric and I've been using the C34V a lot.

Alberto

RobertBauer · Nov 5, 2008

Hi Ron,

very interesting thread, the C34V seems to a preamp that is misliked by some folks, because it's based on opamps. It's warm and full sound is made through lots of capacitors in the signal path (about 7 along the path for phono...) :scratch2:

When I got my C34V, I sweared to leave it unchanged, but then I started replacing the caps... then I did go two or three steps further and ...:

1. Replaced the (imho dull sounding) NE5534's in the "main listening path" (phono amp, loudness amp, filter amps) with BB OPA267's: big improvement.

2. Added a 22µF decoupling cap to each Opamp's positive and negative rail (the power C34V power design is quite inadequate ...)

3. Found that the OPA627 has a really close to zero DC offset and removed all coupling caps between the opamps in the main signal path. Mesured about 0,2 mv at the Main Out.

5. For perfection, i soldered in a 100k trim pot at the first opamp stage (loudness amp) and got a 0,0 mV reading at the output (as described in the OPA627 data sheet)

6. Over this, the decoupling cap in the phono box and the DC input blocking cap in the phono box are obsolete, too, if you use "zero" DC offset opamps, I removed them and left only ONE cap after the input selection FETs (they give about 300mV DC into the signal); OPA627 have no "reverse" DC output in their inputs as the NE5534's have.

7. Changed the remaining coupling caps to Black Gates 10µF/50V

RESULT: the C34V now delieveres a level of detail and precision that is amazing for this old guy; with the Burr Brown OPA627, the sound is still somehow "lush", but with plenty of detail and even bass. With my MC275 Mk1 it's nothing more than pleasure listing to records.

Yesterday I played around with the new BB OPA827 and they give even better results (if I can trust my hearing), especially in the phono section.

What do You think about this?

Robert.

ron-c · Nov 5, 2008

New coupling caps make a big difference after all these years. Using low noise versions of the NE5534 ICs is all you need. ON Semi for a buck or so each is all you need. Any IC change that results in dc or high frequency oscillation should be avoided.
Retouching the solders is a good idea also.

Thanks,
Ron-C

Gregory · Nov 5, 2008

RobertBauer said:
Hi Ron,

very interesting thread, the C34V seems to a preamp that is misliked by some folks, because it's based on opamps. It's warm and full sound is made through lots of capacitors in the signal path (about 7 along the path for phono...) :scratch2:

When I got my C34V, I sweared to leave it unchanged, but then I started replacing the caps... then I did go two or three steps further and... RESULT: the C34V now delieveres a level of detail and precision that is amazing for this old guy; with the Burr Brown OPA627, the sound is still somehow "lush", but with plenty of detail and even bass. With my MC275 Mk1 it's nothing more than pleasure listing to records.

Yesterday I played around with the new BB OPA827 and they give even better results (if I can trust my hearing), especially in the phono section. What do You think about this?

Robert

LoL ... leave it to the Germans to come up with this stuff..

The C34V Love webpage was revised on Oct 25th: (best to go 1020 pix wide with browser)
http://home.comcast.net/~mc_audio/C34V_Love.htm

Soon there will be a C29 Love webpage too!!
http://www.audiokarma.org/forums/showthread.php?t=102687

And we're even working on a MC2205 Love 'howto.' :banana:

-Gregory

bg3009 · Nov 5, 2008

ron-c said:
The C34 has many features which are shared by few other preamps. C32 and C33 preceded the 34. 33 and 34 are very similar where the 33 has two phonos and the 34 one. The 34 also can switch an external video switcher as well as the SCR2 speaker relay switch device which also works with other preamps C32, 28, 29, 33, 30, that preceded C34.
The on board 'Monitor" amp in the 33 and 34 is 20 watts per channel into 8 ohms and has Power Guard. It is the picture where the four transistors are mounted to a heat sink that is attached to the side panel in front of the very large and heavy power transformer.

Cont.

Hi Ron,

I remember reading an article from Audio magazine that pegged the monitor amp at about 30 watts. I have driven a pair of XR7s using that amp, and it was very sweet sounding, although slightly lacking in bass. I can certainly give the seperate listen and record busses a miss, but the 5 band EQs, continous loudness control and compandor features are what I miss most on the C2200.

Cheers

Gregory · Nov 6, 2008

ron-c said:
New coupling caps make a big difference after all these years. Using low noise versions of the NE5534 ICs is all you need. ON Semi for a buck or so each is all you need. Any IC change that results in dc or high frequency oscillation should be avoided. Retouching the solders is a good idea also.

Ron-C

Ron.. would this be the Op Amp you describe?
http://www.onsemi.com/PowerSolutions/product.do?id=NE5534

The case would need to be a 626-05? PDIP yes?
http://www.onsemi.com/pub_link/Collateral/626-05.PDF

Posts in other forums like diyaudio talk about compensation caps, and that would change the design, wouldn't it?

-Gregory

RobertBauer · Nov 11, 2008

LoL ... leave it to the Germans to come up with this stuff..

anyway, imho the old Signetics NE5534's should be perfectly ok, the "A" spec has slighty besser noise rating, which really depends on the source impedance and application mode given in a circuit. It is not a "rule of thump" that a lower noise rating will lead to lower noise in the given circuit design... Some people evern prefer the "Old" Signetics 553X over the Philips/TI remakes.

If You're going to change the OpAmps, You should go to something more state-of-the-art like OPA627, perhaps AD797 - or leave the old ones in as long as they're doing their job. With OPA627, You won't need several decoupling caps anymore because there is virtually (<0,1mV) DC that needs to be decoupled.

However, the change of working decoupling caps to new ones may only lead to a sonic difference because the new caps need to settle / "burn in". A technican told me he had several caps older than fifty years which still met their specs.

Nevertheless, I felt a big improvement using the Black Gate NX caps - they are not build anymore and cost a little fortune.

Just my opinion. Robert.

C34V love

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