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Amp for mono reproduction (bridging?)

 

Clogartist
Unregistered guest
I am looking for an amp that can play mono. I currently have a Marantz PM32 which is old but not old enough to have a mono switch. I picked up somewhere that it is important to play back 78s and mono LPs in mono mode as playing them in stereo has an adverse effect on background hiss.

In relation to this, I wonder if a 'bridgeable' amp such as the NAD C370 could be the answer, but I would appreciate a little explanation that anyone could give about what precisely is involved in bridging (also whether it is then easy to switch between stereo and mono) - and whether this would have the desired effect.

The speakers I am using are B&W DM601 S3s.

Any advice greatly appreciated.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3361
Registered: May-04


Until the 45/45 method of stereo reproduction in LP's was accepted in the 1950's, the playback of mono recordings on disc involved only horizontal deflection of the stylus. When stereo became the accepted norm, the vertical movement of the stylus also reproduced the turntable rumble from the drive system. Most tables at that time were rim drive tables which gave a direct connection, and hence path for transmission, of motor to platter and then to cartridge and tonearm. Playing a mono recording in mono at the outset of the reproduction chain is going to eliminate much of the phase related low frequency noise from the turntable motor but will do little to nothing to remove record hiss. Steady state hiss is related to the physical action of dragging the stylus through the record groove, both when the master disc is cut and during playback. To reduce hiss, the approach is first to have very clean records. Secondly, the better the playback system mechanically, the lower the noise floor as random motion between parts of the system is reduced giving the actual information in the groove a better opportunity to escape unharmed. Finally, if you are playing original recordings and not remastered discs, remember there was no noise reduction system utilized by the recording companies until Dolby A was adopted in the early 1970's.

A mono switch on the pre amp is effective in reducing the noise floor of mono recordings. A "rumble filter" is also useful. Look for these features on older components (pre 1985 and especially 1950 through 1975) when phono systems were still a major playback source. After the signal has left the pre amp, using an amplifier in mono mode, bridged or otherwise, is like putting a BandAid on the wound. It will help but the problem is best addressed at the first part of the playback system.







 

Clogartist
Unregistered guest
Jan, very many thanks for your detailed explanation.

It looks like hunting for some older equipment may be the way to go. (I did look at preamps on the market today that have a mono switch, but they seem to be in the thousands of dollars bracket, way out of my reach).

I've found some NAD machines pre-1986 available used: the 1155 (preamp) and the 3150 (int amp). Both have mono switches. Just one question: would the preamp be preferable, or does the mono switch on the integrated do more or less the same? I confess I have no experience with anything other than integrated amps.
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3369
Registered: May-04


It doesn't matter. If the switch is on the front panel, it is switching the pre amp section and not the power amp into mono. The power amp operates as a two channel amplifier being fed a mono signal. Power amps are bridged, most commonly, by an internal switch and then hooking the output terminals together in a parallel or series connection on a "bridgeable" amplifier. While any amplifier with common grounds "can usually" be bridged, it is normally not an option on most equipment.


 

Clogartist
Unregistered guest
Thanks again: this is very clear.

Another used option has just popped up while I was searching on Ebay: someone in Germany offering a NAD 1130 preamp and 2155 power amp as a pair. Again, the 1130 has a mono switch. This sounds an attractive option - perhaps more so than the 3150 integrated?

The prime consideration now is how this equipment measures up to what is available today and what kind of difference the mono will make. As I understand it, mono cartridges are also an option, used with a stereo amp. I have been without a functioning turntable for a while, so the possibilities are open - without wanting to be extravagant. I was attracted by the idea of the Pro-ject Debut III Phono Speedbox, as this can play 78s and is very manual, but it's hardly top-of-the-range equipment. (This should perhaps go to a phono thread!)
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3375
Registered: May-04


The German unit is likely to be a 220v/50Hz unit. Make certain it will operate on your voltage.

Mono cartidges are the best way to play mono records since the sylus tip will fit the mono groove better than a stereo stylus tip.


 

New member
Username: Only_mike

Seattle, Wa Usa

Post Number: 5
Registered: Mar-05
What source are you listening to? Are you playing records on a turntable?
mz
 

Clogartist
Unregistered guest
I should explain I am in the UK, so the voltage shouldn't be a problem.

One thing intrigues me: if I am to use a mono cartridge (and for 78s a special 78 cartridge), is there still any benefit in having a mono switch on the preamp?
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3377
Registered: May-04

First, a 78 RPM stylus is essential in playing those discs. A modern stylus is too small and will damage the much wider groove of the 78.

At that point the mono switch becomes a convenience for other issues. A rumble filter is still beneficial or else you are likley to see the woofers of your speakers moving large excursions at very low frequencies. Neither switch is essential if you have a dedicated mono cartridge that will be used strictly for old records.

A consideration you might want to make is the EQ of 78's. If you will look at many of the pre amps/integrated amps with phono sections from the late 1940's to the early 1960's you will see many of the better units included a selection of EQ's for different record companies. There were no set RIAA EQ levels until the mid 1950's. Even at that time, the European manufacturers allowed the individual companies to set their own EQ for several years before standards were adopted. This meant that a record played back with a fixed EQ might sound very thin or very thick depending on how the manufacturer's EQ varied from the levels set in the pre amp. A standard RIAA EQ will not give the best results with older discs. For those serious about hearing the performance as close to the intent of the original production as possible, the availability of the various EQ levels is an enormous improvement.

If there is a shop which will serve as your source for these discs, I would ask about anyone or any group locally that you might contact who can give you more information.



 

Clogartist
Unregistered guest
Appreciate the sound advice, which I have already taken up. As it turns out I'm not sure there is even such a thing as a shop that sells 78s in this country now (i.e. a place you can walk into). Those I have spoken to were very reticent about giving advice, as they "sell records, not hifi". But time will tell.

My plan will probably be as follows: to get a 1980s preamp with a mono switch and a Pro-Ject Debut turntable. That way I can at least play mono LPs (and as a listener of exclusively classical music that is very important, as the 1950s were a golden age: Toscanini etc.). The Pro-Ject could in theory be equipped with a Speedbox to play 78s, but in light of what you say it sounds like that would be pretty hit-and-miss without dealing with the issues of EQ... I think quite a process of education will be required before I really get playing 78s sorted out. And this is not easy given the limited interest in these things.

Thanks again for the explanations, which are a great basis for further exploration.

Btw, please let me know if acquiring an old NAD preamp/amp + the Pro-Ject Debut sounds like a terrible blunder -- before I commit said blunder. (+ I have a NAD C541i CD player, which I hope will come out of it well.)
 

Gold Member
Username: John_a

LondonU.K.

Post Number: 2973
Registered: Dec-03
Clogartist,

Your question seems to be spread around on different threads and I am sure anyone reading the others will be interested in J.V.'s responses on this one.

All you will need to do with a German NAD is change the plug or get an adaptor.

There are indeed record shops in UK. "Gramophone" probably has listings and advertisements.
 

Unregistered guest
I have a NAD 3150 amplifier which is now 23 years old. So far the only problem I have experienced with this equipment is the protection circuit that is always inssisting in not disarming. It has gone three times for repairement but the failure reapeared.
I am wondering some one could give any clue on how can I buy this specific circuit to refurbish this piece of equipment. Is it still worth to keep on spending money on it or it is better to acquire something newer, such as another NAD amplifier
By the way I live in Brazil..
 

Gold Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 3833
Registered: May-04


You can call NAD and ask for the address of a NAD regional service center. This shop will have the best trained technicians who can evaluate your equipment. However, after this amount of time, there is every likelyhood you will spend as much shipping and repairing the unit as you would buying a newer unit.




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